TH350 Autopsy - No Reverse

I take down a TH350 that had a catastrophic meltdown at the low reverse clutch pack, among other damage. I also cover other relevant points of inspection and some considerations for overhaul.

[@wilburnmiller1851]

Another great video, i have built the 350 with lockup, and the older ones also. Been a long time since I’ve seen the inside of a 350. 75 years old now. I’m still learning and will never stop. The 700 4l60 did not exist back then. So you taught me some new tricks for upgrading. I will say a man who knows everything can learn nothing.

[@nickstransmissions]

Thanks again, Wilburn! Yep - agree completely. I learn something new just about every transmission I touch and still consider myself a student/beginner.

[@gearheadted9210]

as an old transmission dude the manual shaft will be swedged out in some cases behind the rooster comb,,a little gentle filing will allow the shaft to easily come right out and prevent damage to the bore,keep up the great work!

[@nickstransmissions]

Thank you, gearheadted! Yep, that shaft had to be worked over a bit before it went back in.

[@30jspecial]

when mine would not reverse. i pulled out the governor. real easy takes 2 minutes. anyhow the plastic gears were melted in a half moon apple core shape . so i assume i just couldn't get out of first . the fact it was looked melted i decide to rebuild it . but you could always get a donor governor from the junkyard and see if it worked . if your governor is shredded or worn down.

[@monkeywrenchization]

PATC has the repair kit listed for $195.00. This looks the same as what I'm talking about, only difference this looks to be made from metal. It has the screws, repair plate, and wide sprag assy from 87 up. That is a good upgrade for a 350.

[@nickstransmissions]

Yep, for sure..Esp for racing and/or HD towing/hauling and serious off-road use.

[@timweb1510]

Keep up the great uploads man

[@nickstransmissions]

Thanks, Tim - will do!

[@naestrebloc9849]

Where can I find valve and / or spring replacements for a th350 valve body?

[@nickstransmissions]

Your best bet is to harvest them from another TH350 valve body, except for the boost valve which is available from Sonnax. I grab extra valve bodies from my local junk yards and have them ready to go if one comes in with a bad valve body. The other option is to install a shift kit, if the shift kit has replacement springs or valves for the ones you need to replace. Thank you for watching!

[@surplusmarty2986]

great video. I am self-diagnosing a fresh rebuilt TH350 (by me), all my gears in fwd work great. My reverse gear however, I need to tac the motor up above 1200 RPM to get it to move. any ideas where I should look when I tear apart or where a fault like that would originate from?

[@nickstransmissions]

Thanks, Marty! Sounds like one or more seals may have been pinched on the low-reverse piston when seating it into the rear of the case. That's usually the problem on these, 700R4s and 4L60Es when reverse is weak after a rebuild. You can remove the valve body, separator plate and gaskets to do an air check of the low-reverse circuit...Listen for an unusual amount of hissing coming from the piston...If you have a rubber tip nozzle, put a little pressure on it so it seals that port completely then run between 50-75 PSI to the clutch - see if you hear anything coming from the piston...If all is well, you'll hear no hissing at all...

[@surplusmarty2986]

@@nickstransmissions finally got around to doing line pressure checks. Park 1-3 pressures were at or above 125 in idle gear. Reverse, at first initial engagement sat at around 50psi. I reved the motor, it jump to 150psi and sat there in idle. When I tacked up with brake engaged, it wouldn’t go above 160psi. Also one of my pump bolts is just seeping fluid. Either way, I think the reverse piston is bleeding off pressure.

[@JonathanSmith1987]

Im having a problem on my th350 rebuild. When i clean the case and or the parts, shafts, drums ect… When they dry they start getting this white powder corrosion on them. Idk how to get rid of it.

[@nickstransmissions]

How are you cleaning your parts? Are you cleaning them in a hot tank where powdered solvent is used, pressure washing them or using a garden hose?

[@hybridmusclegarage4590]

Great Video As always!!

[@nickstransmissions]

Thanks HMG!!

[@monkeywrenchization]

Why do you fight with the intermediate clutch, and direct drum? I put a long screwdriver down inside and release the band. Pull on input shaft, and the whole front end comes out in one lump.

[@nickstransmissions]

You mean to tell me that you use common sense when dealing with those two things? Sorry man, I'm not there yet, hahaha! Yea, when I'm in front of the camera, it's like I have two left feet and two right arms. Thanks for watching as always, Peter.

[@monkeywrenchization]

@@nickstransmissions I always stood the trans up, and supported it on the rear where the extension housing bolted on. All the fluid drained down into a bucket. I don't know why it was always so hard for a guy to drain the fluid before they brought them to me. I started charging extra for draining fluid. I had to pay somebody to take it away. I never filmed when tearing one down, so I don't know what's involved with that. I could completely gut a 350 in less than half an hour using hand tools. Before I had a slide hammer, I threaded two extension housing bolts into pump, and used a crows foot to pry the pump out. The 350 had five different output shaft lengths, 6 inch extension, 9 inch, 12 inch, the short stub for 203 transfer case and the shaft for the 205 case. Some 6 inch extension housing shafts were drilled in the center to lighten them in later years.

[@nickstransmissions]

I do the same - charge extra for oil disposal but typically ask them to drain the pan before bringing me the transmission. All kidding aside, filming adds a layer of complexity that isn't apparent when watching making it not quite as straightforward as it may seem, especially if you haven't done it...My first two or three videos that I filmed for KZbin will never published since half the time I stood blocking the viewer's angle, failed to get the part of the trans I was working on in the shot or was either zoomed in too much or too far away or didn't realize the battery had died...It took about four or five tear downs before I was even half way decent with the camera angles and had reasonably good idea how to position the camera, where to place tools and other things, etc. I can rip apart a TH350 in about 20-25 minutes or so and about 30 min for a 700R4 or 4L60E...TH400s are easy - 20 minutes or less (30 for 4L80Es, 6Ls)....I don't bother inspecting anything until all parts clean so much of what you see me doing when it comes to inspection is done solely for the sake of filming.

[@monkeywrenchization]

@@nickstransmissions I worked on more 350s than any of the rest because there were more of them than anything else. I kept a lot of guys plowing snow in the winter because I have a few on hand already built, long and short stubby shafts. I did do some C6 trans, a lot simpler to do because they had less parts to deal with. The governors were touchy on them. I also did Torque Flite 727, but not as common as the Chevy GMC. One of the worst transmissions I did was the FMX. Everything was backwards. Borge Warner built that trans for Ford. The 440T4 was a headache transmission, I started to get out of trans work because of the expensive tools that were needed, and the electronic testers, and scan tools.

[@nickstransmissions]

Thank you again for sharing your experiences, it's always nice to hear from other builders and their perspectives. I don't do too many TH350s however they seem to be coming back around...I've done more of them in the past two years then the prior eight combined. Seems like folks are 'rediscovering' that transmission, perhaps driven by scarcity and upward pricing pressures on 700R4s plus spiraling costs of labor to integrate into a TH350-equipped vehicle...Once challenge confronting TH350 builders nowaways is the declining availability of good pump cores...Remans are hitting $300 and good-used assemblies are fetching $200.00 at most places. Plus any reman body or entire assembly is considered a critical core so many hard parts suppliers won't even let you walk out the door with a reman unless you have the old one to turn in. The FMX is a bizarre transmission, I've done a handful of them in the past but you can't get bushings for them and valve bodies are hit and miss. The AOD/AOD-E/4R70/75 trans are based on them but those 4-speeds are much more straight-forward to work on, thank goodness. I'll have some videos on AOD and 4R70/75 on the channel soon... Automotive 'techs' are rapidly becoming indistinguishable from 'computer scientists/rocket-surgeons' these days...