Synchronizer Operation Explained

[@getplaning]

I have overhauled countless gearboxes, measuring gaps and replacing parts, but this is the best explanation of how a gearbox works that I have ever seen.

[@DrivelineMaster]

Thanks for the compliment.

[@5CGQ]

What most people don't appreciate is that "grinding gears" isn't damaging the actual gears that transmit power, but the dog teeth on the synchro system.

[@DrivelineMaster]

You are absolutely correct.

[@dangeary2134]

Makes me appreciate that big truck transmissions generally do not have synchronized gearsets. I had to rebuild an entire transmission when someone had broken the main output shaft in one. No books, no drawings, nothing but brute competence. I will say, the way that they are made with dual or triple countershafts, the design is ingenious. The input and output shaft are only connected by a pilot bearing. The fact that the main output was snapped into two pieces, and the transmission didn’t fly apart is testament to the designer! The countershafts held the gears in their proper location, even though the shaft was toast! No synchronization there, just a good gear matching hand was required!

[@mikekokomomike]

I have a Kawasaki motorcycle and the factory service manual chapter on repairing the transmission has one line about " paying attention to the mating dogs ". Made me chuckle.

[@josephschaefer9163]

Not if you have old stuff with slider gears

[@josephschaefer9163]

@Franky997 grinding gears on old stuff like '47 chevy, farmall tractors, or cub cadet lawn mowers does damage the actual gear teeth. The whole gear slides to engage

[@jptrainor]

Best and only video of a synchronizer in live operation that I've seen.

[@anthonygonzalez-oit9299]

This was really well explained. The video at the end really capped it off and pulled it all together for me. Thanks.

[@132_pradyumnajoshi8]

The cleanest explanation of synchro that I have ever seen. No other video that I have referred has explained the functioning of the key, which in my opinion, brings the whole thing together. Kudos!👏

[@DrivelineMaster]

Thank you. Most comments are similar to yours. I do occasionally get one from someone who is real picky or they just like to knock me down. I appreciate the positive comment.

[@maneki9neko]

This is terrific. Details like the back cut on the engagement teeth on both the synchronizer sleeve and the speed gear, are new to me. This is shown under magnification at 2:15, and is easily missed when you have the parts in your hand. This back cut is what holds the two parts together under load, and prevents the car from popping out of gear. When an older transmission pops out of gear people will tell you with authority and confidence: 'oh, the synchronizer rings are bad'. But the synchro rings have little to do with this function. However when this tiny back cut, on on the engagement teeth of the speed gear or the synchronizer sleeve is worn away, there is nothing left to hold speed gear and sleeve together. In this case a new set of synchro rings will do nothing to fix the problem. And that is very much worth knowing.

[@DrivelineMaster]

Thank you for your comments. Please note that the back cut is not present on all synchronizer sleeves and gears. I see it missing mostly on older transmission designs. There are several reasons why a transmission will jump out of gear and worn out back cut is one of them. Normally what happens is the oil is not changed when it should be and or the driver is rough on the transmission and the blocker rings start to wear causing grinding (gear clash) which in turn chews up the clutching teeth on the gear and on the sleeve which wears away the back cut. It's often a domino effect.

[@OverlyCuriousEngineer]

One of the best videos i have ever watched about synchro mechanism. Incredible presentation.

[@DrivelineMaster]

Thank you

[@maneki9neko]

Yes. He really has all the fine details down. Gear boxes for Spec Miata racing are rebuilt all the time. However the re-builds tend to have problems. If a rebuilder replaces the bearings, the brass synchro rings, and the seals then the gearbox will shift into gears easily and the box will hold oil, but will it stay in gear? Apparently if the back-cut (2:15 in the video) on the engagement teeth between speed gear and synchro sleeve are worn, these parts need to be replaced too. Someone who is simply installing a 'rebuild kit' will miss this.

[@MarcusCromwell9]

I wish teachers at school would teach the same way. Amazing video with lots of different presentations, I don't think this could be explained any better than this!!!

[@sarthak_18]

Really sir you said true thing

[@rogergummer5173]

Given the hard job, its a reasonably good explanation.

[@maxwelld3753]

Never understood how they worked until I watched this. Very well done.

[@mikes9939]

Would be good to explain that the synchro ring is made of brass hence it's gold color. Brass is softer and is sacrificial meaning it will eventually wear out and need replacement. Brass is the perfect companion metal to press against the hard steel gear and do no damage to it as it tries to either speed it up or slow it down so the the synchro hub can slide over and complete the lockup. It's important to remember that the synchronizer assembly must adjust the speed of the entire cluster gear and input shaft including clutch disc in order to perform the lockup into the selected gear. Quite a task and shows why you must have clean clutch release so that the disc is completely free to rotate. This is a very good video, especially with the gear train illuminated with the strobe light to show what happens.

[@DrivelineMaster]

Thank you for your good comments. You are correct. One note. although these blocker rings are brass there are other blocker rings made of other materials and sometimes either lined with a friction material similar to brake lining and others that use a bi-metal design with a sintered metal inner cone that is soft with a high coefficient friction. I will consider a followup video with this additional information.

[@shaggydogg630]

We had some Mustangs rings made of paper! Replaced many.

[@Kevin-mx1vi]

​@@Franky997Can confirm that because some years ago I worked for a company that made synchromesh rings for many of the major European car manufacturers. Selector forks were also made from phosphor bronze, but of a different grade.

[@trumanhw]

@@shaggydogg630 of ... paper? No joke? No, has to be a joke. Sounds impossible.

[@shaggydogg630]

@@trumanhw compressed paper , no joke.

[@jerryscared]

Great video! Wonderful explanation. I especially appreciated the summary in the beginning of the three functions of the synchronizer.

[@Danielagostinho21]

Using a strobe light to see gears at speed mesh, Brilliant!

[@mathewshackelford8037]

Works just like a timing light

[@gleambrite2679]

You always think there must be an easier way. Loads of engineering and sleepless nights have gone into all these details to run smooth operations. Amazing and well explained. Great work.

[@LEDRavecom]

Wow, using the strobe light to show synchronizer at work is brilliant! Thank you!

[@spacetrace7021]

The ability or willing to show what you explaining just earned you a subscriber.

[@elora2525]

The best video for ASE, I watched this video 2 times before the test and still didn't pay enough attention. This video need to be watch 3 times for ASE manual transmission test

[@gsheverything_2716]

Why the test, if you don't mind me asking???

[@chadportenga7858]

Thank you! The demonstration of the synchro in action at 7:00 helps it all make sense. (The first part of the video is the nitty gritty of what makes it work. The demo shows it in action.)

[@abhijeetchilwirwar722]

A great video , actually had doubts about the internal shafts used and the sleeve and gear engagement but this video had it all covered

[@Kimbeattie]

Great video and the strobe light showing the operation was brilliant thanks from Canada

[@OwensGarage]

Excellent video, thank you. You just filled up another small gap in my mechanical knowledge.

[@NickGiamattiKeyWest]

Fantastic presentation!....Great technical detail & functional explanation! Strobe light visual on the Rotating System really brought-it-all- together! Thank you!

[@Anglgrinder-j3y]

Thank you for explaining & animating, this technology is becoming clearer, thank you

[@DORVALFAGUNDES]

Drivemaster, you're the best Master. My language is Portuguese, but I didn't understand the Brazilian videos and I understood your video. I didn't understand how the synchronized ring works but thank for you, I understand now.

[@DrivelineMaster]

Your Welcome

[@chimeragaming56]

really nothing beats a good explanation and some actual footage or hands on with my actual hands. ty for this.

[@Bushybowl]

Excellent job on the video, structured and explained perfectly and pleasure watching

[@kengarcia1461]

Really good, well explained and easy to understand demonstration. Thanks for making and sharing this video

[@xavieraxiak6866]

As the sleeve moves towards the speed gear, the keys weakly push the blocking ring ahead until the conical friction surfaces make contact. The resulting frictional torque rotates the blocking ring so that it's teeth are 1/4 tooth pitch misaligned with the sleeve teeth which causes contact of the teethes' angled surfaces. This is called "energizing". As well as causing the blocking teeth to block the sleeve, the sleeve can now apply a strong force to the blocking ring via the tooth contact, increasing friction and synchronizing torque.

[@doublebass3858]

very good explanation. The only video I found that explains the synchronizing gear in great detail

[@DrivelineMaster]

I'm glad this worked out for you.

[@diegorodriguez-lk8of]

Great fucken video don't give up you'll be up to 1 million subscribers soon. Best of luck and thanks for making things clear and simple to understand

[@aniruthdinesh9156]

Awesome Presentation, now I understand how this really works!

[@cncn9631]

Its Amazing teach Video I Ever Seen. Good Jobs

[@frankcastle8349]

Thanks for the video! An excellent explaination,best on YT for gears.

[@pablogarciavasquez6637]

¡EXCELLENT MASTER CLASS AND GREAT TEACHER GREETINGS FROM LIMA PERU!

[@dalekrinke2674]

Very good explanation of this mechanism. Thank you a bunch for your time and experience! 👍👍

[@ervinmq1955]

Great Vid. Well explained... Thanks for sharing...

[@Joeelectronicschematicsforauto]

This was absolutely awesome these videos should be in schools to teach students

[@DrivelineMaster]

They are used in all my classes.

[@nickayivor8432]

Thanks for sharing what you know with us brilliant video tutorial amazing From Nick Ayivor from London England UK 🇬🇧

[@WilliamStrawnJoe]

Any time I think I am smart, I need to watch this and realize how much I don’t know.

[@pathumsahan8372]

Also me

[@johnpower8356]

Great with strobe, I had a 1958 Mack truck when I was young no syncro’s man you had to shift just right, you get used to it. Great video

[@katojeremiahcsfg4274]

Liked the way you tried everything to make us get the idea, thanks

[@billglenn10]

Excellent video and explanation of how this works... Thank you...

[@JIm-w1b]

Kids used to say they could drag race powershift as in brute force abuse without using the clutch, but the way the synchronizer is designed, this is impossible, because the harder you try to force a shift, the harder the synchro will ride up onto the cone and fight to prevent it

[@lovesjw]

Applause! Real gentlemen applaud this good video!

[@federicomezzina5784]

Thank you for the very clear explanation!

[@keitharoo1962]

Wow, did I just learn something today!!!! Thanks!!!

[@Limeayy]

Woo, this time Manual Transmissions. If i literally had an instructor that taught like this I think it'd go into my head alot easier :P

[@luca490]

Beautiful video sir.

[@BugCrush3r]

excellent description of the synchronizer but I wish you talked a bit more about the locking keys and springs and the purpose they serve

[@DrivelineMaster]

They are not locking keys. They are synchronizer keys. They transfer the force between the sleeve to the blocker ring.

[@AndreKK-]

Best video on the topic!

[@DrivelineMaster]

Thank you.

[@ScottsGarage17]

Great job explaining!

[@Engineerboy100]

Wow!!!! That was awesome 👌 thanks you so much for posting.

[@charleskutrufis9612]

Thank You for this video. Very informative.

[@wejaith3]

Amazing video probably the best one

[@fjs1111]

You did phenomenal work putting this together and your explanations. Learned a few things.

[@DrivelineMaster]

Glad you enjoyed it and found it of value.

[@ryanhewett1663]

very informative; thank you.

[@jafersadique7492]

Very informative 👍👍

[@Tedminat0r]

Brilliant idea with the strobe light. Thanks!

[@raymondjames9734]

i want to use this to make a fixed gear / free wheel bicycle hub! never understood this before thank you!

[@MrsTiaRani]

awesome video, very well explained! many thanks

[@kalef1234]

That strobe demo was great

[@abdullahmohammed2955]

Amazing video thanks alot hope u r having a beautiful life ❤

[@elwoodgalapagos1846]

gotta love the reverb on the voice

[@skudnu5462]

so, synchronization only works when the car is moving since we need the gears to be spinning correct? engaging first gear from a standstill therefore does not need to be synchronized just like reverse?

[@DrivelineMaster]

Pretty much correct, the synchronization only takes place when the gears are spinning. Even though the car is not moving if your engine is running and the trans is in neutral but vehicle is not moving some of the gears inside the transmission are spinning. If you push the clutch pedal to the floor and move the shifter quickly some synchronization might take place. If on the other hand after you push the clutch pedal to the floor you wait about 30 seconds before moving the shift lever then all the gears will most likely be stopped.

[@heavydieselmechanic]

Good work

[@JohnSmith-ok9sn]

Exceptional video. Thank You!

[@DrivelineMaster]

John Smith from Plymouth, MI?

[@SFlores1979]

This video was great!!! Thank you for it.

[@vusindlovu8897]

Simply beautiful 👌

[@maxenielsen]

Marvelous! Thank you so much!

[@larrydykes7643]

Somebody needed to show this video to my old '67 VW bug.

[@stimpsonjcat67]

Damn fine job on the strobe use!

[@shanilkadesilva65]

Great video

[@DGQ1Q2]

Super goood video thanks

[@johng69er]

Great clear video thank you

[@utkarshkushwah8800]

Thanks for the such a nice explanatary video...

[@TheAnonymous1one]

Question: Since the small clutching teeth is what mechanically locks the free spinning speed gear to the shaft and actually transfers the power why dont we see more of those stripped vs the actually gear teeth on high powered cars? It looks like it has much less material engagement would seem to be the weak link. I would also think the narrow sleeve that couples the two together would be prone to strip out before the actual speed gear teeth would strip under high power.

[@DrivelineMaster]

1) the small clutching teeth are already 95% in alignment with the teeth on the gear before the sleeve is allowed to slide onto the gear so there is no grinding. This is accomplished by the proper operation of the blocker ring. When the blocker ring becomes worn out and can no longer perform properly that is when the clutching teeth start the grind during the shift. This is the grinding noise that can be heard by the driver between shifts and is called gear clash. The reason these tiny teeth can handle the torque comes from the total surface area contact between the gear and the sleeve. The number of teeth and the length of the teeth determine the total contact surface area. I'm not an engineer but this is something that has to be engineered into the design. They must determine the maximum torque that the synchronizer and gear would have to be able to handle and how much contact is needed.

[@brianb-p6586]

Between two gears, only one tooth on each gear is engaged with the other gear at any time. Between the parts of the synchronizer assembly, all of those small teeth are engaged at the same time, spreading the load out between them. Many small teeth are as strong as one large tooth.

[@ericbanks6644]

Fantastic video. Thanks!

[@georgespangler1517]

Thanks,,,great informative vedio of the operations

[@jamingagnier2170]

Homie sounds like Kermit the frog

[@isabelgarcia891]

Thank you great explanation

[@sasikumarmanju972]

Super video thanks good 💯

[@LibertyWarrior68]

I'm getting ready to rebuild my gearbox, so I'm learning as much as I can.

[@m.b.smoshitoa8325]

WONDERFUL MY MAN. I DID NOT UNDERSTAND THIS BEFORE BUT NOW I HAVE THE GUTS TIO GO OPEN GEARBOX. LOL MOSHITOA ( S AFRICA)

[@RC-Heli835]

That is so cool to see it working like it should. My KW T800 has an 8LL and its synchroniser has been very noisy since the heat exchanger went bad and got water into the transmission.

[@DrivelineMaster]

Try Changing the oil and put Redline Manual Transmission Fluid (MTF) in it. This stuff does wonders sometimes.

[@RC-Heli835]

@@DrivelineMaster I just have changed the incorrect 90 wt for 50 wt motor oil. That by its self worked wonders. It made it possible to where the gear shift would actually move the gears in and out. Before that I could take it out of gear and it would stay in gear. It did that one morning until the oil got warm. I ran it all day, came in and drained that 90 wt while hot and its been better ever since. Everything but the synchroniser. So mine is not slowing the gear down when all that noise is going on? I wonder if the air shifter could be sticky somehow?

[@DrivelineMaster]

Unless the manufacture says you can use motor oil instead of GL4 or GL5 gear oil I wouldn't leave the 50st motor oil in your transmission. 90wt gear oil is not the same as it would be if it was 90wt motor oil. The way they measure thickness for gear oil is different than motor oil. Once again I would recommend the Redline MFT. I know it cost more but it is worth it. Unless your transmission was designed to work with motor oil (like some honda's) you will end up damaging your transmission and costing you more $$$ in the long run.

[@RC-Heli835]

@@DrivelineMaster It calls for 50 wt engine oil. Granted Synthetic would be better but we just had a cracked head replaced at 6,389.00 on the truck and now the compressor has blown apart on the other truck leaving us stuck with a core fee. Cat wants 1,500.00 just for the core fee alone. Fleet Pride got us a refurbished for little over a grand and no core charge.

[@DrivelineMaster]

As long as the factory specification is 50wt engine oil then that is what you should use and have confidence that you won't cause any damage. This is the first trans that I know about that uses 50 wt straight motor oil.

[@andrewhanson5942]

Now THAT is some high tech mechanical engineering!

[@scattkiwiman]

thank you for showing this !

[@asemelsayed9477]

amazing work but what is the speed of the blocking ring ? is it equal to shaft or gear speed before synchronizing?

[@DrivelineMaster]

The synchronizer hub which is splined to a shaft, the sleeve and the blocker ring all rotate at shaft speed.

[@asemelsayed9477]

@@DrivelineMaster ok thanks is the key connected rigidly to the blocker ring? and how are they connecting? and how does the blocking ring return its original position?

[@mrbigheart]

thank you, sir. this is highly useful!!

[@deepsinghania6496]

This video is clear my concept

[@armedfarm3429]

After several videos trying to figure this out, I finally get it. Excellent video. Now I wonder if there would be other ways to slow shaft/gear speed. Synchro's are spendy parts "labor wise" to replace. I also wonder what fluid would cause the least amount of wear & still give satisfactory shifting.

[@DrivelineMaster]

Unless a specialized fluid is specified and the spec is 75w-90 or 80w-90 GL4 I really like Redline Manual Transmission Fluid (MTF)

[@josephschaefer9163]

Good ole stinky 80-90 gear lube is the highest temp rated fluid

[@armedfarm3429]

Up here in MN maybe a 75-85 would be a good choice. I think up in the cold states an ATF is hard to beat. @@DrivelineMaster

[@DrivelineMaster]

I don't want to give the wrong information. Most manual transmissions can not and should not use ATF. ATF can only safely be used in a manual transmission if and only if the service information or owners manual says so. Never use ATF in a manual transmission unless it has been specified by the manufacture as an acceptable winter oil option.

[@jacobwarrington1904]

Thanks for the video! Helped me study.

[@akashmore9127]

Thanks very well explained 🙏🙏🙏

[@5speedMax]

That is a very cool visual.

[@ayiideng5857]

thank you for its very explained and helpful

[@edgalaxie]

Excellent video!

[@wubbaddubbalublubme4830]

So I get that the speeds match up thanks to the blocker ring, but how do the teeth on the gear, blocker ring, and sleeve match up with each other?

[@GroovesAndLands]

The internal teeth of the sleeve match up just right to the clutching teeth (dogs) on the speed gear as well as the blocker ring. Thus, the sleeve is free to slip over them - but once it does, they must spin together. So when the sleeve is pushed towards the speed gear, the sleeve pushes on the shift keys, which push on the blocker - all towards the speed gear. The internal cone of the blocker presses against the external cone on the speed gear, developing friction and either speeding up or slowing down the speed gear until it matches the speed of the hub/sleeve/blocker assembly. Once that happens, the sleeve can be pushed over the blocker and onto the the clutching teeth of the speed gear - thus coupling the speed gear to the sleeve, and therefore the hub, and therefore the output shaft.

[@DrivelineMaster]

The blocker ring rotates with the hub but the blocker ring is not fixed to a position but instead because the connection takes place because of the keys and the cut out on the ring. The ring can rotate separately about 2-4 degrees from the hub. The teeth on the sleeve, blocker ring and gear are space about 1-3 degrees apart. Because the teeth are cut at a pointed angle they don't have to align up perfectly. The video shows that sometimes but even being off slightly when the sleeve starts to move towards the gear the points on the teeth if not perfectly aligned will slide from one side of the tooth or the other forcing alignment. Kind of difficult to explain. I hope this made sense. Imagine two really sharp pencils and trying to hold them point to point. Unless you get it exactly perfect on each point as you move the points towards each other. If you miss hitting the point perfectly they will slide off the point to one side or the other. It's like that.

[@jimcopeland4011]

One perhaps ignorant question on the final demonstration. What is the gear on the far left of the video? I assume it looks like the speed gear, and maybe I'm not adequately understanding the relationship between the speed gear and the speed gear clutching teeth.

[@DrivelineMaster]

I believe that was 1st gear speed gear. The speed gear and the speed gear clutching teeth are all part of one gear assemble. The speed gears area also the free spinning gears check out from time stamp 2:44 to view the speed gear AKA free spinning gear.

[@rogerbegin9479]

That was pretty interesting. I never knew how any of that worked.

[@oscarchitsa6548]

Well explained bravo

[@spiritspride46]

Good video. Thank you.

[@user-id3tj1gs6y]

Great video! The one part that I don't understand - how does the blocker ring prevent engagement if the gears cannot be synchronized?

[@DrivelineMaster]

Here you go. The sleeve pushes on the keys which push on the blocker ring. The job of the blocker ring through friction between the ring and the gear is to grab the gear and make it go the same speed (synchronize) so the sleeve can slide over and lock the two together. If the blocker ring is unable to synchronize the gear to its speed a lot of friction is taking place. With more friction more heat is generated. With more heat there is expansion of components. The heat and expansion is a counter force pushing back on the blocker ring. That force on the blocker ring is transferred to the keys and then onto the sleeve. The counter force prevents the sleeve from moving close enough to the gear for the clutching teeth to touch. If the clutching teeth are allowed to touch before synchronization a grinding noise (gear clash) will be heard. Hope this helps.