TH350 not shifting by itself, must manually shift

[Skull Leader]

After jumping a curb recently, it knocked something outta wack in my TH350. I can start in 1st, then let off the gas like a clutch to have it ease in 2nd when I shift manually, then I can shift manually into 3rd with no problem. If I stop, it goes back to neutral. Is this something I can fix without a major rebuild, maybe something external? I checked everything near the tranny and nothing jumps out at me. It is on a 1981 K5.

I also have a wrecked 87 with a TH700-R4 just sitting around, would that be a normally easy swap? Any help would be great.

 

[boz42]

Sounds like you knocked a vacuum hose off for the modulator. Just check to make sure all vacuum lines are hooked up. There is one on the back of the transmission.

 

[Skull Leader]

Excellent, now I'm getting somewhere. Is all this on the top of the transmission? I could have sworn I checked everything, but I will doublecheck. Thanks.

 

[boz42]

The vaccuum hose on the transmission is near the tail, on the back between the trans & t-case.

On the engine side it could be anywere around the carb baseplate or on a vacuum tree behind the carb.

 

[Skull Leader]

Ahh, I guess I didn't inspect close enough. I'll check those locations, thanks again.

 

[Dafey]

If you crawl under the pass side about the front of the door its pretty easy to see that way.Mine keep falling off until I replaced the 30 yr old vac hose LOL

 

[Skull Leader]

I looked underneath today, and everyting is connected like it should be. Could it be the modulator itself, and is that a pretty straight forward and cheap replacement?

 

[dyeager535]

I hesitate to say with certainty anything automotive, but it certainly shouldn't be anything to do with the modulator. Modulator controls shift firmness (and to a VERY small extent, shift RPM's) the governor is what controls shifts.

 

[Snowman1000]

mine does the same thing if it sits out in the cold during the winter. Except mine will stay in first unless you shift it but once if warms up a little its fine. I also have a TH-350 I dont think this really helps any but is also a little goofy.

 

[Skull Leader]

I hesitate to say with certainty anything automotive, but it certainly shouldn't be anything to do with the modulator. Modulator controls shift firmness (and to a VERY small extent, shift RPM's) the governor is what controls shifts.

I'm guessing the governor is internal? If it is I might look towards the swap.

 

[BKinzey]

Swap should be straight forward as the TH350 & 700r4 use the same adapters.

Then again if the governor is anything like the 700's it should be a cheap & much easier replacement.

 

[Dafey]

mine does the same thing if it sits out in the cold during the winter. Except mine will stay in first unless you shift it but once if warms up a little its fine. I also have a TH-350 I dont think this really helps any but is also a little goofy.

Mine only does it in 3rd for about a 1 1/2 miles.
It sounds just like when I had a leak in my vac line between the trans and the metal tube up by the carb.Something cheap to replace just to check... :shrug: