I need TH350 help and the other “usual” forums (ie places dedicated to vehicles that use TH350’s exclusively) have not come up with much trouble shooting help, so I'm hoping someone here can help, as this is now preventing me from bring my Vette home. If this posting is wrong, please delete.

I have 350C (lockup converter) in my 84 Monte Carlo, trans has 180k miles and is untouched except for routine fluid changes. Trans will not grab second, either upshifting or downshifting automatically or manually. Other wise it runs fine and seems solid in shifting.

The trans starts out fine in first with the shifter in “3”, and will hold it to redline even with light throttle if I don't let up on the pedal before shifting straight to third. When I manually upshift the trans it does the same thing, 1st straight to 3rd, with nothing while I shift into 2nd.

Downshift from third into second and the trans will free wheel until I bring the revs up enough to engage everything and push the car OR it will shift straight down to first, even when shifter is in second. Does both. Pop it into first and it will go to first.

Was fine until shortly after having it smogged on a roller dyno. Fluid is at proper level and smells fine, TV is adjusted correctly, and modulator lines look good (no leaks)and modulator doesn't appear to be leaking internally (no white smoke from exhaust. Today I changed out the modulator for a known good one, no difference in shifting, no second gear, just 1st to 3rd. Checked old modulator and it looks and operates off the car fine.

I have the Ron Sessions TH350 Handbook, and the troubleshooting list has nothing on a missed 2nd gear, or constant 1 to 3 upshift.

Except for this issue, the dang thing runs fine. Any other thoughts on things to check, or am I at the service life (long one too!) of the trans? I will rebuild/replace if needed, but don't want to spend the time or money right now if I can avoid it.

Thank you for any input,
Tom

 

Take it in. The intermediate band is gone.

 

Sounds like it is time for a rebuild. I cannot offer anything better but at 180k miles, I would say you have gotten your monies worth out of it. Hopefully someone will chime in and have a better answer.

 

Could be the servo the runs the band, but at that kind of miles? Rebuilding a TH350 is not that much. DIY for under $150.00 There are a couple of tools that make it easier/faster, but it can be done.

 

Had exactly the same problem and fix with a 1971 Ford C6 behind a 429 SCJ.

The end snaps off the second gear band - a known problem - 106k miles.

Replacement one is stronger.