GL4 and GL5 Oil - Transmission Lubrication Oils Explained

I discuss some of the new oils today for manual transmissions and take apart a Muncie 4 speed that welded up. There has been a great deal of misinformation about GL-5 based oils corroding synchronizer rings. I've never seen this happen in 1000's of tranmissions I've serviced. We have seen more GL-4 based oils come to the market within the past 3 years, but prior to that everyone was OK using GL-5 oil for the past 20 to 30 years. The new GL-4 oils are a plus because we now have better formulated oils for our muscle car transmissions.
I use Red Kap Shirts: red-kap.pxf.io/...
~~~~ Contact and Social Media ~~~~
WEBSITE ~ super661.com
EMAIL ~ [e-mail]
INSTAGRAM ~ / 5speeds
FACEBOOK ~ / gearboxvideo
SUPPORT THIS CHANNEL
~~~~ My Books and Store ~~~~
BUY ME COFFEE ~ www.buymeacoff...
MAIN STORE ~ www.5speeds.co...
BOOK #1 ~ amzn.to/3b7x6fT
BOOK #2 ~ amzn.to/3RUaK25
AMAZON STORE ~ a.co/ftlbr0s
disclaimer:
The content of this video is available for informational and educational purposes only. It is not intended to be a substitute for the professional advice of a mechanic who has personally inspected your vehicle, nor does it create a relationship of any kind between GearBoxVideo (Paul Cangialosi) and you. Every situation may be different, and GearBoxVideo does not make any warranties, whether express or implied, as to the accuracy, fitness, or applicability of the information or automotive parts portrayed in this video to any project and makes no guarantee of results. GearBoxVideo and any sponsors or manufacturers of parts that may appear in this video or any of the channel's content will not be liable for any damages related to personal injury, property damage or loss of any kind that may result from the use or reliance on this video and/or any automotive parts represented in this video. You are using the information and automotive parts portrayed in this video solely at your own risk.

[@drigney]

It's fun to watch the few videos done by knowledgeable people who are passionate about their work. This guy is clearly one of those people. Watching this makes me wish I had transmission problems just so I could have him fix it! Very well done Paul. Thank you taking the time to make this video.

[@Bathy650]

Hi from Australia, Truck mechanic here, Years ago my son had a Holden LD Astra, basically a re-badged N13 Nissan Pulsar, he decded to freshen up the gearbox with new oil, went down the local parts store, got the oil they recommended. 1 month later this box was stuffed, grinding every gear, luckily he had another box, so he decided to just swap the box, instead of re-building it. Anyways, i got home from work midway through his swap, and noticed a drain container full of black oil, "ohhhh, changing the engine oil too, i see" i commented, he replied, "nope, that's the old gearbox oil" I knew straight away exactly what had happened, asked for the old bottle of oil he used in it and the new oil he was going to put in his 2nd box, yep, both the same, both GL5. A quick search in the manual showed nissan specifies GL4, he went straight back and swapped the GL5 for some GL4, the parts store accepted no responsibilty for their error, they (incorrectly) argued that GL5 just supercedes GL4, long story short, we don't use that part store anymore. that 2nd box with the GL4 was still going strong years later. Another thing I've noticed in all my years twisting spanners, is the effect synthetic oils can have on old gearboxes. mainly if it's an old box designed back when only mineral oils were available, with most likely, larger tolerances, they tend to shift better with mineral oils and become notchy with the fancy synthetics. This is really noticable as well on the Eaton-Fuller road ranger non-synchro boxes too, factory specfies, DD50(sae 50) engine oil, shifts nice, put in a synthetic gear oil, notchy. new boxes on the other hand, designed with tighter tolerances tend to work better with the new synthetics. even with making sure the viscosity is as the manufacturer specifies, the synthethics just don't seem to shift right in old boxes, just what i've noticed anyways. Cheers.

[@GearBoxVideo]

Great comment. Thanks

[@georgedennison3338]

My Gawd, I haven't looked inside a Muncie in 30, no 40 years! I love it... I about 15, when the guy who owned the Esso station taught me how to rebuild transmissions. This was '68, so it was 3 & 4 speeds everywhere. The funny thing about Gary, the station owner was you would think he'd never be able to get a hand inside a Muncie,, let a lone rebuild one. The first strong memory I had during the vid, was the pain involved, the cuts and nicks, the smashed fingertips. LOL Gary was about 6'2-6'3" and had to weigh 300-350, easy..probably more, it was a long time ago. But that guy could tear apart and rebuild a transmission like he was playing piano, it was amazing. He did everything with his fingers. He was strong enough in his hands, and his fingers were long enough, it looked like he was washing his hands in a finger bowl, then bang, out pops the cluster, or "You can put the side cover back on, it's done.", and you're still cleanin' the damn side cover! Thanks, I haven't thought of that in 20-30 years easy, a lot of that I'd forgot since I saw it happen. Thanks, again. Oh, that Brad Pitt oil looked like the good ol' green, stinky tranny lube I recall. If it has a tendency to hang a bit more, that may be a big asset in heavy load situations, keep a better layer on the gears, themselves.

[@GearBoxVideo]

PLEASE READ: Wow this video is getting a great deal of hits lately. I'm noticing the same questions asked over and over so please take the time to read other comments I have responded to. First off this transmission locked up on a dyno because they forgot to put oil in it. In regards to what OIL I think is best for your transmission... There will always be debates from fans of various oil brands as to what they think works best. If it works best for you and you have exhibited better performance, less wear and are happy with the result, then that oil is best for you. With so many transmissions with different types of clearances and synchro types, understand that what may work great for you may not for someone else. OIL TEMPERATURE COMMENTS: There are some that will argue that unless I did these tests with the oils at operating temperature that they are meaningless. This is not true. Manual transmission oil when cold will greatly effect how the transmission will shift UNTIL it warms up. However that is not even the point of the comparison. The point of the comparison was to show how the different advertised grades of the oils compare when cold. In the future I will probably do a test with oils at an average operating temperature. THANK YOU ... for taking the time to watch my videos and subscribe.

[@calholli]

How am I just finding this channel? Keep it coming.

[@alext9067]

I just found this channel. To cut down on repeat questions, some people don't know about using f3 to do a word search. (I'm using a PC) For those that don't, hit the f3 button and put in a word like "viscosity" or "temperature". If you want to not have that word embedded into another word like the word "oil" will show up in the word "broil" and so on, put a space before and after your word. It will cut down on the irrelevant hits. This way you don't have to read hundreds of comments to search for your issue. Hope this helps.

[@nopenottalib4366]

Do you do anything with automatic transmissions? I've got a GM FWD 4T65e transmission in my car that I'd love to have overhauled at some point. It's running good now, but with almost 100k on the clock, I'd love an expert to tear into it and beef up anything that looks "iffy" or fix any potential design flaws it might have, etc. I'd rather have it rebuilt BEFORE it breaks than wait till after. That and I'm trying to keep the car as stock and original as possible, so I want to be extra sure the same tranny that came in it stays in it. Thanks and sorry if this is a common / repetitive question.

[@ctaggart1973]

You do some good vids. I just had my sag 4 spd with 255 1st from my 68 camaro rebuilt. Wish i had stumbled across this channel a year and a half ago. Keep the great work.

[@supermarketsweeps]

wow you tube keeps putting you in may recommended so i cracked great vid , yes learnt something power lose having thicker oil , but how this work with limited slip diffs in front wheel drives , i was recommend 80/140 for it but was having trouble with gear changes , so i change to 80/90 and the diff keeps locking on corners :( so im using half and half seems ok ish

[@ON743729]

Paul, a good take on the GL4/5 saga. Thanks for taking the time to publish these videos.

[@GearBoxVideo]

"Saga" is a good term. There have been more new GL4 oils released in the past 3 years to capture a market. However as mentioned, its a good thing that companies are formulating better oils to grab market share for classic manual transmissions.

[@kitecattestecke2303]

@@GearBoxVideo maybe people are cheap on fuel, and even manual needs oilchange...give even better milage as gearbox is very lossy

[@xblinkusedfinchx]

Your videos are the best gearbox videos on the internet!! You rock!

[@GearBoxVideo]

Thank you

[@jimyguitar3177]

Since 82 my Isuzu Pup has 400K miles with 10W-30 in the transmission, I think I won't touch or breath hard on it.

[@blake86303]

Finally!! A real explanation from the Muncie guru himself. I was going crazy with all the internet hype about the proper lube to use in Muncies. So much contradiction. I will use the Royal Purple 75W90 I had on my shelf in my M20. Thanks, man.

[@AD-xt9og]

My car calls for a 75-90 gear oil gl-4 or 5 . At 100,000 miles I put in RedLine gl-5. At about 150,000 I started having problems making a fast shift from 2nd to 3rd. It was harder to push into gear and some times would cluck into gear. So I avoided doing that shift. At 200,000 miles I put in RedLine gl-4 and the problem went away. I now have 255,000 on the car and it is shifting fine.

[@fogey50]

I have a 2008 Mazda MX-5, 6-speed, which the dealer replaced the fluids in. On the receipt I saw they used a GL-5 based gear lube in the trans. I could hardly get it to shift through the gears going home. I let it sit, ended up ordering the Redline MT90, GL-4 and replaced it myself. The car immediately shifted fine right from the git-go. Five years later and it's still performing great. Made a believer out of me.

[@AikidoTubeSock]

Thanks Mr. Gearbox for your info. I recently changed the gear oil in my 2000 Camry 5 speed. When I drained it there was only about 6 ounces of fluid out of 2.3 quarts. The Toyota manuals all agree that GL-4 or GL-5 gear oil is recommended so I put in Lucas (full) Synthetic 75W-90 which is supposed to exceed GL-4 or 5 oils. After looking around it looks like it's GL-5 oil. After the gear oil change I heard about "yellow metal compliant" gear oil and did some research. One review rated Lucas one of the top 5 but in the pro and con it claimed that it could damage the brass parts of the trans. I was considering draining and then using Redline MT 90 synthetic GL-4. Since your video I am comfortable with leaving the Lucas oil in place until my next scheduled gear oil change. Your explanation about marketing makes sense based on the evidence I have been able to acquire. Thanks for the input.

[@GearBoxVideo]

If you don't exhibit any shifting issues I'm sure it will be fine. However I think the new GL4 formulations are better than "classic" formulations.

[@jemcnair76]

If you close your eyes you can hear Harvey Keitel give a wonderful lesson on transmissions and oils.

[@GearBoxVideo]

People have said that.

[@robertmedina3982]

I believe, it is Harvey Keitel.

[@J_S209]

🤣

[@Tony-ib2vm]

Mr. White...

[@mildbill222]

@@Tony-ib2vm Your transmission’s gonna be okay Say it with me “your transmission’s gonna be okaaaaaay”

[@vegansynths7757]

THANK YOU SO MUCH for clarifying the debate. I would trust your decades of experience over internet opinions. This video is gold.

[@cscarter71]

I think the buildup on the syncro rings may effect the ability to grab the cone of the speed gear causing possible shifting issues. I was a Mitsu tech for years and the Evo six speeds required gl4 and a bulletin was released warning not to use gl5. There were no specifics given, just it would damage the syncros. Also, I would have liked to see the BG syncro max fluid tested as well. Nice video as always.

[@GearBoxVideo]

Scott_C. Never seen build up on rings

[@e-curb]

Scott, can you post pictures of this buildup on a Mitsubishi synchro ring?

[@rtaggs8178]

Thinking about getting an older Toyota Tacoma with a Manual Transmission. Glad I found out that a GL 4 rated gear oil needs to go in there with the brass syncros.

[@8wireracing694]

thankyou very much i run a 350 to 400hp ls1 thru a t56 tremec manual and 3 73 to 1 rear gear in my hsv senator this cleared up an issue i was so confused about and now feel confident that i have bought the correct oil for my transmission. as usual an excellent video i find your vids watch and then start wrenching in that order thanks paul.

[@GearBoxVideo]

Thanks for watching the videos. Much appreciated.

[@ketobeast8489]

Great job on Sons of Anarchy. I had no idea you were a mechanic too. Awesome job!

[@GearBoxVideo]

Tig thanks you for watching.

[@beingrealhere9480]

I love GL4 on manual gearbox but differentials/rear diff I use gl5

[@jaredmayer3960]

I love this dude! “I think I wanna take this one in, do a video on it…it’s gonna be pretty awesome!” So awesome

[@GearBoxVideo]

Thanks

[@vwvwso4176]

Right! Good stuff man!

[@sockmonkey3393]

Toyota manual transmissions especially calls for gl4 and if gl5 is used it will cause gear clash.

[@mr.m325]

my corolla manual says use either gl4 or gl5

[@owenjohns6301]

The best fluid I've found so far is multitriac tractor fluid. It made the shifting feel easier in both my toplader car and my WC t5 car. Most brands of it are GL4 rated as well.

[@georules]

thanks for this. I was recently really concerned about the yellow metal problem in my older vehicle from internet research. this has calmed my nerves.

[@rolonmascara]

I use Amzoil synthetic gear oil in my Tiger' T10 for 20 years without any problems. The improvement was spectacular.

[@oillease1881]

Used same in my NVG 4500, slicked it up more than the original synthetic.

[@Wheelsinthesky80]

I am so glad that I found this channel and I really enjoyed your video. I will watch your all video that I haven’t watch.

[@GearBoxVideo]

Thanks!

[@williamfoster4268]

Good video! People who use Motul Gear 300 usually don't realize it can be used in GL-4 or 5 applications. Same goes for your Royal Purple Gear Max Synthetic. Modern(Doesn't contain molybdenum disulphide in it's EP additive) GL-5 does not corrode brass or bronze. Most synchronizers are made out of brass. Internet guys will say GL-5 can attach itself to the metal and delaminate it but don't realize it's solid brass to begin with, not a plating, so there is nothing to delaminate. At most if you have copper being exposed to a modern GL-5 you will go from 1a(freshly polished copper coupons with slight discoloration, but barely noticeable) to 1b (slight tarnish) in the ATSM D130 test. People on the internet regurgitate the same bullshit that sounds good until it becomes a bro fact. One day of bad driving will do more damage to your synchros over it's lifetime than GL-5 based fluid would do in that same time frame.(provided were talking about copper here which would be worse case scenario for a transmission and GL-5) Oh and for GL-5 to be damaging beyond a tarnish your fluid has to reach over 250 degrees F.

[@superchuck3259]

What a beautiful flathead screwdriver. Awesome tool!

[@lizard944]

Most abused tool in the box

[@quailstudios]

Thank you. I was planning on putting Royal Purple 75W 90 in my Miata Trans and differential. It seems that It will work well.

[@ronanrogers4127]

Great video. It’s interesting that Castrol (BP) doesn’t seem to be so common or popular in the US, whereas it’s often the staple of European makes like VAG, MB etc. You’re right about people often using the same oil brand. I use Castrol Edge Titanium Long Life in my VAG turbo diesel because of its very low ash and high VI, and I also use Castrol in the transfer and differential even though there’s many other good GL-5 oils.

[@eliteman7685]

Fun fact/story from a few years back...Ford Toploader 4 speeds don't last long when rebuilt and you are recommended (By a parts store) Synchromesh GL-4 instead of actual gear oil. 4,000 miles on a full rebuild and my toploader locked up. Unlocked it and it growls in all 4 gears...after a full rebuild. One of those *2 hours before Hot Rod Powertour, stab the transmission in the car and go moments*

[@GearBoxVideo]

Synchromax not Synchromesh. Gear lubes come in different viscosities. That's up to you to chose the correct weight. Meaning a Gl4 gear lube can be specd out at many different viscosities. Also a rebuild with new gears may cause a seize up because most builders don't understand that the replacement gears need to be polished and the bores are too tight. Changing parts is not the same as having good skill levels. You can rebuild him correctly and they can last just as long as the original if you know what the hell you were doing

[@eliteman7685]

@@GearBoxVideo I’d agree, my issue was I had a local shop rebuild my toploader, and it had new main cluster gear, 3rd gear and a full kit from David Key. Reused the other gears, main shaft, input, and secondary shaft for first/reverse. It was actually silent and shifted amazing, but I was having fun and yes, I failed to make sure I had gear oil instead of the Syncromax fluid. It was just really abrupt, I was driving “normal” and went to shift and it locked between a 2-3 shift. I could not get it out of gear with clutch depressed. Let it sit for 20-30min and used a wrench on the nut on the shaft for one of the external shifter rods, and got it back into neutral. Fired back up, and sounded like all four gears were grinding. Again, my fault for incorrect gear oil. Just amazed it would do that.

[@eliteman7685]

@@GearBoxVideo also, had a typo on my original post. Didn’t mean you yourself recommended the SM fluid instead of gear oil. I was focused on GL4 oil only and that’s all I could find with a GL4, Valvoline Syncromax fluid instead of gear oil. Also…thanks for responding. Love the blunt non BS response!

[@GearBoxVideo]

The only gears available for the Toploader are made in Taiwan. They are of good quality but like anything you have to check bore fits. Sort of like checking rod or main bearing clearance. Its important to also check for bore taper. Thanks for taking the time to share your experience to others can learn.

[@MrJeep75]

I used gl5 for years with no problems

[@tylerkrug7719]

I like your wooden handle screw drivers, pretty nice. Interesting video

[@obiecanobie919]

The syncros in some units have plastic type coating on the friction area , gl5 oil can can be not so friendly to the plastics

[@frekkledipped]

Thanks really helps as I have my tran removed and it spilled a bit so I was wanting info of this very subject. I just ordered some shifter bushings due to your video on them. Thanks again DR

[@GearBoxVideo]

Thank you

[@lifeisgood070]

Redline I heard makes a solid GL4 75w-90. And amsoil and other's I think make a compatible GL-5. Though, I guess generic supertech gl-5 would work - though my temps were significantly higher with it (15-20F higher) @ 90-100mph for 200miles.

[@skylinefever]

5:40 Wouldn't it be easier if you used a slide hammer with claws, then centered it around that bolt? 12:00 Sometimes German car companies create their own specification. I'm not sure about other parts of Europe. I'm a water cooled VW fan, but I know that BMW and Benz do the same thing. However, an oil may also have API ratings and also say meets certain proprietary specifications for certain VW/Audi, BMW/Mini, and/or Benz numbers. You will see the exact same thing every time you pick up an engine oil that says something about use in European cars. Anyway, I give this video a thumbs up and a subscription.

[@GearBoxVideo]

Thanks for subscribing. Two things. Some Muncies have studs some have bolts. Most times you can pull it out with your hand, some people simply put pliers on the bolt or stud to pull it out. It's not that tight. Rigging a slide hammer will take more time for such a simple task. I am well aware of truck transmissions with multiple counter gears. If you are into that sort of thing check out my visit to Midwest Truck video. There is a Mac transmission on a Dyno with 3 counter gears and an auxiliary box.

[@skylinefever]

Excellent, thanks!

[@fiddlerpin]

Good info Paul on the gear lubes. I will go with what you recommend. Man those gears were wasted!

[@thegamermechanic2970]

Great video! Gear oils can be complicated. I did an oil change on the front differential of my 05 Grand Cherokee and forgot to put the friction modifier. Talk about chatter lol.

[@63mrl]

I've used and recommend SYCHROMESH or the likes in all street application TREMEC transmissions I've build for customers with very good results.

[@deanhemblade8683]

All good information, wanted to come see you when we were in FL but time got away from me, maybe next time, always enjoy your videos keep it up Thanks

[@Juarally]

Excellent video as always!!!!!!! Thanks so much Paul for share your knowledge

[@GearBoxVideo]

Your Welcome

[@andrewevanoff1192]

I've had best luck with Red Line MT-90, GL-4 oil in manual transmissions. Gears shifted better than with any other oil. For everything else I use Amsoil.

[@GearBoxVideo]

What kind of endurance road racing are you doing?

[@andrewevanoff1192]

Mostly to and from work. Sometimes in heavy "stop and go" traffic.

[@GearBoxVideo]

These oils seem to work great for applications such as yours. Unfortunately they never protected transmissions well when used in high speed endurance racing where heat levels can get extreme. Both Red Line and Amsoil showed signicant scuffing and heat checking on tear downs and inspections.

[@andrewevanoff1192]

Interesting. I always hear the opposite. I sold my Tacoma that had a 5 speed manual transmission (crappy transmission) and currently own a new 4Runner. Manual transmissions are a rarity these days. Perhaps there are better oils for manual transmissions but anything I tried was only making that 5 speed shift a lot worse. It would always grind 1st to 2nd and most of the time from 3rd to 4th. Engaging 1st gear was almost impossible unless the vehicle was completely stopped. I was not very impressed with that 2010 Tacoma. Lots of problems. The new 4Runner, on the other hand, has been a solid performer. Assembly quality is 10 fold better. The whole vehicle is 100% Japanese, including assembly. Actually I've been thinking of switching the factory filled Toyota WS transmission fluid with Amsoil Signature ATF. Everyone who switched ATF to Amsoil really praised it. I plan on doing a lot of towing with it. Amsoil also seems to do a lot better in the rear differentials. Once I switched, it seems to run much cooler and there are a lot less wear particles on the magnet when compared to other leading oils. Amsoil in the engine has also demonstrated a very noticeable positive difference. This is why I keep using their oils in everything, including lawn movers and generators.

[@GearBoxVideo]

I'm sure again for your application these have worked fine. When you run race transmissions that are seeing an average of 90 to over 100 mph for a 5 hour clip that is when wearablity and heat scuffing become a factor.

[@1MrErling]

The video start at 11:35

[@Ratlins9]

Enjoyed your video and thanks for showing the various gear oil comparison.

[@cstar2839]

I found this video very informative and fascinating. Well done

[@GearBoxVideo]

Thank you

[@Stomachbuzz]

Hey Paul, I watched your video and I enjoyed learning about some of the old school Muncie 4 speeds. Helps a lot since we've always got 3 or 4 of them sitting under the work bench. I'm only 23, but my best friend's dad (whose garage I'm always in) is a die hard Detroit muscle guy, and he's quite the knowledgable guy about all things automotive 'back in the day'. His fetish for the Borg-Warner Super T10s and Muncie 4 speeds is ridiculous. Anyway, I hear what you're saying, but I gotta disagree with you about the GL4/GL5 vs. yellow metals. I've literally called several oil companies (Valvoline, Amsoil, and 1 or 2 others) and talked to real techs or the 'science-y guys'. I love, love, love that these companies still have real guys answering the phone. I talked to a guy at Valvoline last week, about the "GL5 eats yellow metals?" and he said 'yep, that's pretty much the truth.' This has also been confirmed by a tech at Amsoil, and every other oil company tech I've talked to. Every few years (usually when I have to change M/T oil because GL4 is never sold in stores), I call them up again and ask "so...have y'all made GL5 play nice with synchros yet?" and they all say "nope." I've also seen a few pictures post on various forums of GL5 fluid literally dissolving the brass. I distinctly remember one person posted a picture of shifter taken off their mid-90s Nissan transmission. He took the picture of the stagnant M/T fluid. It was like when you pour oil on water - His gear oil had an iridescent film of milky yellow metallic on the top.

[@GearBoxVideo]

You have to understand a few things. I've also spoke to engineers at oil companies and have built 1000's of transmissions and have used GL4 and GL5 oils in the past with no issues. Never in the thousands of transmissions have we ever seen GL5 oil "eat" yellow metals. There are many causes of ring failure. Biggest is poor clutch release eating the rings and overheating them. It is very common to see metallic particulate in a manual transmission oil due to no filtration present. Also as mentioned, this GL4 craze has only happened in the past 5 years because of marketing. The new GL4 formulations however are better than the old standards and have several advantages over older "classic" formulations. By the way when you have a "milky" film or milky oil, its usually due to water contamination getting sucked down breathers which will eat your rings. So remember, GL4 only formulations were available with limited visibility pre-internet. You built a transmission you went to the auto parts store and purchased the proper gear lube for your transmission. Nothing happened. Its my 38th year in business. I've never seen more BS on the internet and banter on forums over a subject that was never a concern and again never in the thousands of transmissions built such a flogged issue. So the guy building that one transmission now doesn't go to the parts store and just get oil, he instead asks the advice from people on a forum, who "research" other stuff they see on the internet and so on and so on. Turns out the oil companies are well aware of this behavior as are other companies. Thus rebirth of the GL4. However again, new GL4 formulations by some manufacturers are better in terms of creating a smoother shifting and cooler running box.

[@Stomachbuzz]

Again, I hear ya, but you're not going to change my mind. It's one of those age old human psychology dilemmas where you're tempted, but too scared to try. (Anyone remember Lost and pressing the button every few hours??). I knew 'milky' was going to be a hot-spot word, but I didn't have anything better to use. It didn't seem like a water contamination issue. Are you familiar with hydro dipping? It looked like someone made a hydro-dipping sheet out of liquid brass and cloudy silver. As far as convincing me to make the leap of faith over to putting GL-5 in everything, I just can't. With all due respect (and I respect your credentials), it's the techs at the oil companies (who literally designed the stuff, and publish their ph# to answer precisely these questions) saying "yes, this will eat your brass synchros" vs. a KZbin guy saying otherwise. I don't think the GL-4 craze is new. I've personally known about it for over 7 years, and I've read forum posts about it dating back to the early 2000s. I think a key detail here may be a very specific characteristic of Japanese manual transmissions. They may use a certain type of synchro composition that became prevalent in the 90s, but that's just a guess. I know that sulfur is the bad actor at play here, and whenever I put some off-the-shelf GL-5 gear oil in my rear diff, it's always got me gagging at how strong the sulfur odor is. As long as it's a transmission I care about, and I can order some Redline MT90 online, that's what I'll do. I thought of a way to 'agree to disagree' for now. Someone - maybe you, or me if I can get my hands on a couple synchros, or anyone else - could get a hold of a couple of brass synchros and submerge one in GL-5 oil and another synchro in GL-4 oil. Maybe leave it sit for a while and check on it occasionally.

[@GearBoxVideo]

I've submerged rings in GL5 for months. You won't see a thing. I don't think it works like that. It's a temperature thing. I'm not saying to use GL5 at all, in fact I recommend the new GL4 formulations from Driven Racing as well as Royal Purple Max gear because of the positive results when used in severe use applications. I think you are missing my point. The point I am trying to make is that for years (if my experience matters) -- never seen an issue.Neither have any other builders. Yet now because of this hype, ( a positive thing ) we have actually have better choices available to us in terms of lubricants that offer more than just a GL4 API classification. We have seen cooler running transmissions as well as better shifting units. If transmissions run composite Synchros you should always use what the manufacturer recommends. Thanks for your great comments and input.

[@larryperry2094]

Cool little oil crash course. Thanks.

[@GearBoxVideo]

Thank you

[@Thunderstormworld]

Also oils is temperature dependant as ATF oils is pretty useless in hot climates above 35C, in such conditions go to a thicker oil.

[@GearBoxVideo]

Depends on the transmission and the composition of the synchro rings.

[@justinhale8595]

Beautiful video quality. What did you shoot it on? I'm also in the middle of a GL4/GL5 fact finding mission. After consultation with oil company techs, it appears there's two separate issues; yellow metal corrosion and yellow metal stripping. Yellow metal corrosion is what you described in the video. However the other issue is yellow metal stripping. The EP (extreme pressure) additives in modern oils are phosphorus and sulphur. These create a sacrificial layer between gear teeth when exposed to raised pressure and temperature. This sacrificial layer between the teeth peels away thus protecting the metal surfaces. However, in older syncromesh transmissions, this peeling process also takes some of the yellow metal surface with it (but is harmless to the steel gears). The theory is that over time this process eats away the brass syncro rings. I've been in contact with oil companies whose product says 'Non- corrosive to yellow metals' on the label, but who will admit that while their product is non-corrosive to yellow metals per se, it will strip away yellow metals in the course of shedding the sacrificial layer. It also largely depends on the individual car and what it's transmission setup is. I have a transaxle in which the differential and the syncromesh gearbox share the same oil. For my particular car most of the oil company tech departments lean towards recommending a dual rated GL4/GL5 (GL4 +/ plus) oil to provide just enough EP protecting sulphur and phosphorus to protect my high pressure hypoid bevel final drive while not too much sulphur and phosphorus that would eat away at my syncro rings over time. So I guess you'd call these oils a GL 4 and a half. I still haven't come to a decision on what to use though; I need to research the issue more before I'm 100% confident I'm not putting something in my car that is going to harm it.

[@GearBoxVideo]

As mentioned in the video.... never a concern for the past 20 to 30 years. Never seen yellow metal corrosion or stripping as they claim. However now it is. Why is that? Marketing.. probably. Yet there are better formulations now that work better than the older oils. Problem with people writing articles is that they may show you a picture of a worn ring, which may be worn due to a bad clutch release issue, having nothing to do corrosion or stripping, because that person has never seen hundreds of rings borken, flattened, or trashed from hard shifts. So it works like this. Most like yourself read this stuff but I'm guessing have never built easily over a 1000 race units. Neither has the oil engineer guy. So through race testing we can see what works and doesn't work. Although we don't like to see gears break, most units come back for case repairs ( track accidents ) and broken gears. So you get to see what's working and not. I specialize in synchronized race units unlike a Nascar trans for example that doesn't use rings. Most of my concern is with heat checking on gear teeth. People for years were running Valvoline GL5, never an issue, yet for endurance racing we saw a fair amount of tooth scuffing. My go to oils for the Muncie and T10 have been the Driven GL4 as well as the Royal Purple Max 75wt. No issues.

[@stevejette2329]

Wish I knew things so well that I could just take it apart without labeling everything. Experience !

[@joebrown9621]

Hyundai makes SAE 75W-85 GL-4 which is a blended oil for their manuals and dual clutch trannies.. seems it may have some boron in it than sulfur anyways price is good and the protection isn't bad especially for guys with classic boxes or who live more north wanting a oil that flows well.. part number 000HC-75W85 $48CA for a 4 Litre jug

[@stevew.6407]

I love your videos and after watching your Muncie videos, I want to head out to the garage and upgrade my M21! I didn't - too many things but not enough time. My question relates to a 2016 GMC Sierra Denali, which I recently bought used with about 50k miles on it, with I believe to be an 8L45 transmission. Once I brought it home I then discovered the shifting issues which I then found out are 'typical' for that transmission. GM's TSB 18-NA-355 is recommended as a fix, but will it be a permanent fix? In doing some research, I found that for the 4L60E transmissions, the 1-2 and 3-4 accumulators were originally plastic but an aftermarket Sonnax accumulator piston made of aluminium was a fix that eliminated those shift issues for that particular transmission. Based on that aftermarket solution for the 4L60E, is there a better solution for the 8L45 than what is suggested in the 18-NA-355 Service Bulletin? I would like to drive this truck to 300K miles but really don't want to fix the transmission even 50 to 75K. Thanks Steve

[@bobl78]

I am not so much concerned about syncronizers being dissolved... but whenever I put something else than GL4 in my transmission designed for GL4, shifting suffers....with GL5 you can hardly shift gears without grinding.. you have to shift veeery slowly... even with GL-4+, it does not feel good .. with GL4, everything is perfect

[@bobl78]

I forgot to say that GL5 oils reduce friction to a point where the syncronizers do not work anymore.. in the past I had a car who´s tranny called for a GL5 and was designed for that.. worked without problems...Conclusion for me. use type of oil recommended by manufacturer ... if you want to reduce wear, think about frequent oil changes and proper driving style

[@davidmiller1151]

There is too much knowledge all at once .thanks man

[@Rodney154]

My 1964 MGB manual specifies using engine oil in the gearbox. I've had some gear teeth failures likely due to my driving style of spinning the tires. I've switched to 75W-90 EP lubricant and the gearbox for sure is quieter. Any thoughts or concerns of using gear oil versus the engine oil?

[@pir869]

after the first 1:02 i thought about my triumph spitfire,it MUST use GL4(i think) the lower sulphur content oil,i'm an electronics technician not a chemist,but as i have read this about "yellow" metals,brass based bushes and thrusts etc. When the oil heats up it can emulsify with water,at any rate the oil mixes with water,maybe the heat creates the next reaction,the sulphur and water create sulphuric acid,this will dissolve the "yellow" metal parts bronze bushes too i think. I've read there are some synthetic oils that are formulated to have low sulphur,but the fact this vid is about bad maintainance and not chemical reactions of sulphur content,though the gearbox(yes i'm in the uk) has "yellow" metal syncros,or appear to be ,the "triumph" issue should be looked at also,just sayin'.

[@TheBlaert]

Gear oil is more critical than alot of people think. I know my older Peugeots must run on 75w80 (unsure what the US spec on that is) instead of 75w90 which is vastly more common. I put the wrong grade in my 405 Mi16 once. Shifted like crap and when I drained it out it had turned a weird colour and had thinned out alot

[@deusexaethera]

I once tried Group 5 gear oil in my Mazda RX-8. It was awful. I don't know exactly what was happening to the synchronizers, but they would develop some kind of super-slippery film on the surfaces that would cause them to engage before they had fully synchronized the selected gear to the midshaft, with all of the grinding noises you would expect in that scenario. I had to burnish the synchos on a regular basis by trying to shift the transmission with the engine idling and the clutch closed, and that kept things working properly. A few months later I saved up enough money to get another gear oil change done, and I "downgraded" to Group 4 oil and I never had prematurely-engaging synchros again.

[@deusexaethera]

@ShadowPBPBC: Why would you put ATF in an engine, even for a short time? ATF can't withstand combustion heat, _and_ it's formulated to become super-sticky when squeezed into a microscopic film. Both of those are terrible for engines. Just use a bottle of Seafoam if you want to loosen gunk in an old engine.

[@bhepburn7]

Atf in the engine does good to remove varnish/deposits... If adding just a quart and then changed after a few miles. Highly recommend. Better than seafoam. If youre worried about lubrication well what do u think seafoam will accomplish.

[@benny6712]

I can smell the gear oil just watching this 😂

[@marklowe7431]

Love this channel. I know shit about gearboxes but this helps heaps. Cheers.

[@joebrown9621]

Water / moisture mixes with sulfur in the oil change the PH to be more acidic.. higher the sulfur content.. the more acidic in the presence of water

[@GearBoxVideo]

Worrying about sulfur content in your oil and the rest of the PH properties associated with it will be the least of your problems if you have ANY moisture or water contamination in your oil.

[@turbofiat]

I've owned several Fiats (the ones sold before 1983) and about all of them have had some issue with the synchronizers. It's usually 2nd gear in the 124 Spider that goes out first. Sometimes it's 3rd gear. I've heard the same thing that GL-5 will rot the synchronizers. Fiat recommended GL-1 90 weight in their older models. Other than NAPA, you can't find this oil from most auto part stores. You have to find it from a place that sells tractor parts like Tractor Supply because this oil was used in allot of old tractors. I had mine rebuilt 20 years ago and it's still doing OK. I do run GL-1 90 weight in it and I pause a bit between shifts and don't rough house the transmission. So I've been curious to know if the reasons these synchronizers wear out is not from the oil but from abuse from the previous owner. And possibly lack of oil since these transmissions are prone to leaking oil. My Citroen 2CV calls for this GL-4 85W90 gear oil you talk about. That's why I watched your video! I had issues trying to find it here in the United States. I finally found it from some company on Amazon.com. It's made by Sta-Lube. That car had what smelled like GL-5 in it (sulfur). That transmission has a weak 3rd gear synchronizer. The weird thing is there is no gear clash when going from 2nd to 3rd. It's when going from 4th to 3rd. On that car no amount of double clutching will prevent gear clash when downshifting. The other weird thing is, when the gear oil is cold (for the first few miles), there doesn't seem to be any gear clash when downshifting but once the oil heats up it does. I'm wondering if there is some other oil than would remain more viscous that might help or buy me some time? I tried adding some Lucas oil stabilizer but it didn't seem to do any good.

[@GearBoxVideo]

we sell Driven GL4 oil or go to www.gl4oil.com The Fiat synchros were not that well engineered to begin with. Its hard to base what the life factor in theory should be. Meaning at what mileage do they fail or are they failing from poor clutch release. From what I remember the 124 synchros were very truck like, meaning the rings were the cone

[@supatipanno]

GL-1 oils have zero additive treat. Just straight base oils. If you cannot find that buy a 50 weight engine oil made for Roadranger truck transmissions (Delvac 1350) or something like Mobiltrans HD-50. It appears your Fiat box has plain straight cut gears.

[@turbofiat]

No, my Fiat has synchronizers. I can get GL-1 at Tractor Supply. It was my Citroen 2CV which uses the elusive 80/90 GL-4 gear oil. I was just looking for something a bit thicker to put in it to see if it would buy me some more time with my worn 3rd gear syncro which doesn't seem to grind when the oil is cold (thicker).

[@chooiseah1377]

Paul Simon? 🤣🤣🤭🤭🤭🤭

[@watershed44]

*It isn't just the sulfur but the extra extreme pressure additives along with sulfur, it doesn't corrode but actually peels back the brass coating on the rings and will damage the rings.* This has been proven in testing. Also GL-4 has been around in abundance in Europe for decades now.

[@GearBoxVideo]

There is no brass coating on a solid bronze ring. What exact test are you speaking of? Can you give us a link? From an actual oil manufacturer? You might be thinking of coated steel rings used by ZF and Getrag

[@watershed44]

@GearBoxVideo Actually there are often coatings of friction linings that can be on some rings these EP additives will peel them off. Also some rings use brass or bronze plating. GL-4 offers the correct additives and viscosity that allows for smooth engagement of the ring gears and long life too. GL-5 additives are meant for extreme pressure environments and they are too harsh on the softer brass and bronze rings.

[@GearBoxVideo]

Most of the newer boxes are running Carbon fiber linings and are using basically a Dexron type of ATF, for decreased power losses as well as keeping the linings absorbed with fluid. Synchromax, Mobil 1 ATF , GM synchromesh, Penzoil Synchromesh any many more are what we are seeing in newer gearboxes.

[@matteightytwo]

I saw this video when it came out, it popped up again today, and yesterday I happened to change gearbox and diff oil in a 2011 Audi TT. VW have specified GL4 in a pretty much every box I've had for years, the 80s stuff had it and current ones do. I've read all the yellow metal stuff on the net, I'm not a chemist, I just keep it simple and stay roughly with that's suggested.. just need to work out where the haldex is leaking from, bloody modern cars, give me 90s tech any day!

[@cew142]

I agree with the brad penn. I been using it for 2 years and have no issues other than.... In colder temps 40's and below, I noticed the transmission shifts hard- aka tight due to the fluid being thick. From 50 degF and above, you don't know the thicker fluid is in there. In florida year round, you would not notice any difference. Unfortunately there is more to oil than flow. Like carbon versus synthetic. Synthetic oils break down quicker at high temps than the traditional carbon oils. Just be careful which one you use depending on where you live.... Just a little note to share... The number one priority of oil is to not lubricate. Its main purpose is to remove heat from the bearings and gears. This is where thinner synthetic oils can get you into trouble.

[@GearBoxVideo]

Not necessarily true. Most of the endurance transmissions I build run wide open for 6 hours or run Bonneville. The Synthetics are very brand specific when it comes to seeing what oils produce more wear or heat checking. They vary a great deal. Until Driven came out we pretty much used RP max gear 75w -90 with extremely good results based on tear down and inspection and not white paper generalization. Parasitic drag can lead to heat build up and horsepower losses, that is why all endurance boxes have a high polish to the gears as well as a Teflon coat to the case. Thanks so much for your input and time watching the video.

[@cew142]

GearBoxVideo very good point about drag that costs HP and extra load on the gear train. I was assuming that no other variables were introduced. As soon as you design a case with teflon coated surfaces that are polished, the case is designed for a thinner synthetic gear lubricant. I was talking about factory gears with large tolerances that need a thicker lube to fill the void. So i apologize. Nevertheless...keep those vids coming!

[@GearBoxVideo]

There are some early videos here that show the "Spec-25" treatment. Most transmissions have extremely tight space between the gear's OD and the case wall. In working with gearbox design if we can "not' limit that space we'd have enough cooling from oil but reality is some clearances are less than 1/4" , so the drag of the oil trying to pull itself apart because it's clinging to the case wall and gear generates a fair amount of heat and frictional loss, not to mention the pumping effect of straight cut gears ( typically used in race only applications ). So we modify the older cases by getting them polished and coated. Heat reduction and horsepower gains on dynos have had proven results of 8 percent. All Nascar transmissions use this method and in fact use lighter weight oils for qualifying laps only.

[@cew142]

GearBoxVideo 8% increase? Thats impressive! I would not have guessed that much. Thanks for enlightening me!

[@GearBoxVideo]

cew142 The car was run on a chassis dyno. We also found that the semi helical m22 gears compared to straight cut spur gears also reduce pumping losses.

[@davidclay1362]

he should have added a banana skin. i heard it can at least reduce the noise

[@walrus4248]

Never saw gearbox videos before

[@carleynorthcoast1915]

If viscosity is the rate of flow then All oils of the same viscosity should flow roughly the same unless SAE uses something other than simple flow to determine grade

[@GearBoxVideo]

The point of the video is that stated viscosity is not necessarily a rate of flow but how oil flows or adheres to parts greatly affects heat generation, HP losses and shift quality with the same rating

[@rollmeister]

I add MBL8 to manual transmission oil. There are demo videos of it on KZbin.

[@GearBoxVideo]

You mean the ones with the lever machine showing the anti friction capabilities? Never use friction modifiers in a standard transmission which requires a certain level of friction for synchro rings to work.

[@rollmeister]

@@GearBoxVideo Yes, I should have mentioned that. The product brochure explains what applications the MBL8 can be used with.

[@GrandFunalleyMedia]

Smart man.

[@dominicfong6341]

It is mesmerizing just by looking at the oil dripping during the test. Do have a question: those oil with a clingier nature, is it possible to put in less of it, say 30% less to reduce fluid drag?

[@GearBoxVideo]

No, because oil also cools. So you have more of a chance of the transmission running hotter than it should. There is some people that are giving bad advice about putting low oil levels in muncie's for example to prevent oil from blowing out of vents. That will just create a heat problem rather than just fix the venting issue

[@dominicfong6341]

GearBoxVideo Thank you very much for your expert advice and prompt response sir!

[@joeclarke9782]

Thanks. Very informative

[@animalcorvair]

wow you know your shit good job

[@boilermaster]

Local rebuilder recommended Penziol Syncromesh trans fluid in my M20 when I picked it up. Oil seemed kind of thin but I put in in anyway. I'm hearing that may be a mistake. I have only driven the car (69 Camaro) maybe five miles since rebuild. Thoughts ??

[@GearBoxVideo]

boilermaster Pennzoil synchromesh was designed for later transmissions using composite rings and tighter clearances. Yet, I have had people use this with no issues. The biggest problem would be front retainer oil leaks due to the lower viscosity. So if you have no leaks then you should be fine.

[@boilermaster]

Thank you ........I will keep an eye out for leak. Seems to shift fine so far

[@ferfire9]

I ve put Synthetic liqui moly 75w90 on my 020 transmission (VW ) that required GL4 in the manual, 75w90 or 80w. I did the wrong choice, this oil was very expensive, at 14 euros a liter and made my shifting worse, especially when cold, its very hard to change gear, before that it was a lot easier (original oil 140.000 km 22years) , not even comparable. Because of that i am on my way to change oil again and this time for a 80W mineral oil. I believe they are better suited for these old transmissions from VW. Not sure what brand to use, i would like to have some feedback from anyone with experience on this transmission.

[@kitecattestecke2303]

Hello I am from Europe/Germany and had that issue with a mercedes manual box and liquimoly gearbox oil. Shifted harder, I went with a Kroon oil gerabox oil (instead of castle and the other know n brands over here) worked perfectly. The recommended one was specified a mercedes mb100 something and should have been GL3 bought liquimoly GL3+ something which supposedly works said their homepage. Old mercedes man recommend to buy the OEM stuff at the counter to sleep well or go with Kroon Oils recommendation (asked via mail) bought online and it is night and day better. Find someone locally who fixes cars or buy expensive oem oil to be safe for the next 20years. Manual gearbox is not cheap...

[@HoliSupps]

Can I use redline 75w90 in my e90 318ies

[@lordofbees9067]

i dont use so much thick oil i use atf, and then i put some molykote in it... never had any problem with my gearbx

[@snapdragogon69]

Very early GL5 formulations would corrode synchro rings but this was soon spotted by the industry and reformulated. I can't remember the details of the metal but I think it was alloys containing a copper element (it was yellow metals), I also can't remember the anti-wear additive responsible. it was probably over 20 years ago.

[@remogaggi82]

Brass. Sulphur.

[@watershed44]

@snapdragon69 Yes now it won't corrode the brass but the additives in GL-5 will eventually peel the brass layer right off the gear. Also the additives aren't correct for smooth shifting of the synchronizers. GL-4 is a very different spec than GL-5.

[@dezertraider]

1987 4Runner( in pic at Bonneville) what would you use to keep this Old Buggy going?Bonneville Land speed Steward,I dont run it the track...Thank you..Great lighting/Video/Audio,Fantastic!73

[@markk3652]

I have a 39 ford 3 speed trans, I'm pretty sure the 600w gear oil it calls for can be improved upon with a modern oil. Any suggestions for something this age?

[@awajiokichejames5641]

thank you sir please are the causes of the gear damage?

[@firebreathinggarage2117]

Great video on gearbox oil.

[@paulg444]

like the Boss said, "if you are racing"... otherwise, my advice is play it safe.

[@arjanwilbie2511]

Next issue. The LT95 for a Range Rover needs EP 90, the same LT95 with a shorter input shaft and bellhousing needs 15 W40 motor oil for lubrication. Range is civilian use, the 101fc gun tractor military use. Any views on this?

[@GearBoxVideo]

Nope. I am not familiar with this transmission.

[@JAYJAYJAY53]

I am amazed that that tranny is worth repairing. I swear after working in the construction field with my hands all my life I can spot a hack a mile away . I would trust you any day .

[@jonb1236]

I have a new Toyota Tacoma 5 speed manual transmission that is currently using Redline MT 90 GL4 gear oil. The hotter it is outside the better it seems to shift. Some days it feels like first gear has to jump a hurdle to get to second and nothcy to third with fourth and fith gear better. The mechanic that installed the new transmission put the wrong gear oil in the first time. It literally felt like shifting through concrete. He first told me it was the syncro rings "shearing off or breaking in'' period for the new transmission. That was it for me with this guy so thats when through research I came upon the REdline gear oil and put this in at a new shop. For the first 1000 miles or so the transmission shifted like a dream so smooth until recently going back to a more tight feeeling and like described above. Do these new transmissions really have to be broken in to smooth out or could this be a gear oil problem? My clutch is a new Luk also. My thought of a new clutch and transmission would have been shifts like a hot knife through butter which i just really dont have in this new setup. Currently at 7000 miles on the new transmission/clutch. Ant thoughts? Thanks

[@GearBoxVideo]

Sounds like. Clutch release issue

[@footballandhooligans9164]

Thankyou for great education.

[@ruralrenderer]

I have Amsoil MTG GL-4 in my newly rebuilt NV4500. Should I consider changing it to Driven or Royal Purple?

[@GearBoxVideo]

No.

[@rehanniazi3596]

I always learn a lot from u

[@downunderglitchgaming6379]

Wouldn’t the temperature of the oil change the flow rate and by running that same experiment on them all at different temps get a more accurate results🤔 Has got me curious now I might experiment my self Thanks

[@GearBoxVideo]

Go for it

[@KeepItSimpleOffroad]

Great video!! Annnnd I don’t understand oils at all. What would you recommend? I have a street driven rock crawler with a 350 sm465/ np 205 and I live on Az. I have been using the mastercraft gl5 80-140 and Lucas 80-140. My thought was it’s hot here so a heavier oil but I don’t actually understand it. I do know it will melt my shoes. If you look at my KZbin channel it’s the 48 willys doing a burnout. It’s very clear you know your stuff. Thanks again!!

[@vw4x4]

Great video.... We could use a guy like you in the vanagon community to rebuild transaxles. Specially the Syncro (4x4) vanagon transaxle. Do you have any experience with these units by chance?

[@GearBoxVideo]

Never did one. Wish I had a core to rebuild.

[@ronhiggins4549]

How come no testing Redline MT 90?

[@mike-ke8qd]

Thanks for another great video!

[@ArmstrongRacing]

I show my friends and customers this video when they start telling me they want to use the cheapest fluid possible, great info here. Had a customer get gear grind after adding friction modifier to base oil instead of just buying the recommended LSD oil. What are your thoughts on this?

[@GearBoxVideo]

Friction modifiers are for rear ends with Limited Slip to prevent clutch chatter. They should never be used in a manual transmission application. Use the oil the manufacturer suggested for the transmission. Limited slip oils are for axles and should never be used even without modifiers in a transmission.

[@ArmstrongRacing]

sorry for the confusion, this was a transaxle application where the LSD and and gear-sets share the same oil

[@MXSLICK]

I always found that gl5 oils cause grinding in my manual transmissions. my understanding is that gl4 has significantly less additives designed for differentials then gl5 has. those additives don't play well with synchronizers. gl5 is too slippery.

[@GearBoxVideo]

Depends on the oil. As mentioned in the video I've built 1000's of transmissions with GL5 oil with no issues. However the new formulations of GL4 do have some advantages. There is no point in using a "classic" formulation when 50 years later we have made huge advances in oil technology in regards to polymers and chemical engineering.

[@dexter2433]

@@GearBoxVideo some time thicker is better .......funny how most car books will say 5w20 under normal use but if you dig deep you will find 10w30 or 10w40 oil is recommended under hard or extreme conditions like extreme heat or heavy loads ...now i am talking car motor or pick up motor and trans ....not race application transmissions but wouldn't you think the same apply ..i know for max HP thinner oils will give you better flow under extreme RPMs allowing at least oil even if not the best oil to be there to lubricate some but in a situation were you have a low RPM application but under heavy load like pulling a horse trailer for the life of the truck wouldn't a heavy weight 140 do better ?.....sorry for the long book but kinda needed to get were i am coming from ....and thanks for the vids and sharing of your knowledge...

[@MXSLICK]

i should also mention that dealership prices for manual transaxle oils are out of this world. I think $90/bottle here in Canada for my toyota. GL4 basically is not available through any normal retailler so one is left to just throw in some gear oil thats the right viscosity...and grindy shifting is often the result. GM has a few variations available through dealerships with synchromesh being on the thin side but also a manual transmission gear oil.

[@GearBoxVideo]

@@dexter2433 As mentioned above there are many variables using different gear boxes with different needs. Here is an example; years ago we found that people using a certain brand synthetic lube in T10 transmissions were cracking synchro rings. This brand was all the rage. People claiming that the boxes shifted great. What we found out is that as this oil heated up the rings couldn't properly grab the gear. It was a GL4 oil. So the ring would sort of skid and chatter on the gear cone eventually fatigue and crack in half. Changed to a different brand and no more cracked rings.

[@henrymorgan3982]

Cool test!

[@mattbender3197]

Great informative video, keep the up👍

[@justYouJesus1God]

My mechanic used that oil you said not to use for trans with sychros, what happens if it is used, will the gears grind and not work? Every time he fixes it, it runs and shifts smooth like butter he says, and then after a few times, it starts getting stuck again,. Is this the problem with the oil? Or is it that he still hasn't put the right gears or missing synchros on?

[@GearBoxVideo]

Could be a clutch issue

[@wayneweckwerth9080]

What do you use to determine the original center point when redoing the counter shaft, in a worn transmission case

[@GearBoxVideo]

Wayne Weckwerth You can go by the rear bore and interpolate the front bore dimensions.

[@chrisreed4974]

Paul, great video! I Have a quick question... (85 corvette 4+3) Manual i found says a gl-5 80w-90 In the manual gearbox, and a dextron ll atf in the overdrive) Street driven not hard, but an occasional "romping through the gears! 1) Do u still recommend (these days some 30 yrs later) the driven GL-4 80w-90? If not what do you highly recommend? Also in the Valvoline brand you show...is it because of the limited slip additive that it's not recommended for synchronized manual gearboxes or something else? 2) What brand and type atf fluid for the "delicate" overdrive portion do you recommend?

[@GearBoxVideo]

Driven GL4 works great as does Royal Purple 75wt max gear lube. I use Mobil one multi purpose ATF in the OD section

[@OverlandTT]

Paul, first time to your channel and this was great. Is there an additive that can help the torque converter seal after a coolant leak a couple of years ago? It's on a 2004/5 Cayenne S. thanks

[@GearBoxVideo]

Im not aware of it . Thanks for watching

[@davidteixiera8398]

Thank you sir Driven

[@evil_twit]

Don't you want to test the fluids at operating temp? They get thicker when they warm up, right?

[@GearBoxVideo]

Viscosity increases when warmed. The issue most times is how transmissions behave cold, hard shifting poor flowing oils, grinding in gear until warmed up...

[@arthurlastname974]

Hi GBV. I am a new subscriber. Thank you sir for this video, I have spent the last two weeks strait studying gear box lubricants for my np435 in my dodge. Transmission shop conversation with them yelling what does it matter, not free time or patience to talk about lubricants, I suppose I understand.... My question to you is in some (mine included) transmissions will also call for sae engine oil (mine calls for an sae 50 as an alternative).I head through someone on the web that oils don't have the same protection needed in transmission as gear oil.... I am very interested in your opinion on this. Thank you

[@GearBoxVideo]

In a 435 I would use 75 =99 wt Gl4 gear lube. Stalube from Napa or amazon

[@arthurlastname974]

Thank you sir for your response and insight.