Shifting Issues

[Tonner]

Now that I have my project driving, I've noticed the TH350 does not want to shift up into 3rd. I don't have a tach, but it's screaming before it shifts. The last time I took it about a mile down the road and couldn't get it out of second. The cable that connects to the throttle is a bit weak in it's recovery. Could that be it? Do I have to pull the transmission to replace it?

[GASoline71]

That cable is the "kickdown" or "passing gear" cable. If it is adjusted improperly it could be holding your transmission in 2nd gear. Disconnect it at the carb and drive your rig around and see what happens. If it shifts into 3rd without it hooked up, then it is probbably not adjusted correctly. Also, If it's not hooked up, you will have to manually downshift when needed.

Gary

[Tonner]

Also, do I have this connected correctly?

[Tonner]

Test drove with the cable off and it still gets stuck in second. I tried manually shifting down to first and back up to make sure the shifter wasn't stuck. I can feel it click into every position just fine.

[geezer#99]

Check the vac hose and tubing down to the vacuum modulator on the back end of the tranny. Could be loose or missing.

Where’s your throttle return spring?

[Steeveedee]

Right, could be the modulator vacuum line or the modulator itself. Does it scream before shifting into second? The detent cable adjustment should be checked, although at this point, it doesn't seem to be the problem.

[davepl]

Did anyone try feeding the detent cable back down it's sheath a bit? I wouldn't assume that just because it's disconnected, it's fully retracted.

[Steeveedee]

Good point!

[Tonner]

I used the throttle return spring to hold back the cable while it was back on. That way I know it's all the way back in the sheath. Same result.
The vacuum line looks good and when I took it off and blew air through, it sounded clear. How do I check the modulator itself?

[Steeveedee]

It is still possible that the detent cable is not adjusted properly. But if it was OK when left to sit, it would be OK now. You can take the modulator off and hook it to vacuum to see if the piston moves. Don't hook it to the truck vacuum with the modulator off, you'll have a mess on your hands. It is possible that after having sat long enough, the valve in the valve body could be stuck. This is about as far as I am willing to go in terms of recommendations, as I am not a transmission expert.

[Boog]

A long time ago I had a 350 trans that stopped upshifting. Mine turned out to be the governor. Seems like it had a plastic gear that had worn down. Boy, that was a long time ago.

[Tonner]

I pulled the vacuum modulator and verified that the piston is free. The valve inside the case also moves freely. I backed the adjustment screw out on the modulator a couple times and that didn't help. I'll look at the governor next.

[Domingo]

I had something similar. When I drove it easy it will shift hard but when I drove it hard it would shift fine. I had the vacuum line hooked to ported vacuum when I switched to manifold vacuum it started shifting normal.
I would suggest switching the vacuum

[Tonner]

I have it on the manifold behind the carburetor. That's about as strong as it gets, right?

[Domingo]

Make sure you have vacuum at idle

[GASoline71]

Do you still have the stock steel vacuum line that goes down to the modulator? A lot of times it gets replaced with a long rubber vacuum line that can colapse when vaccum is applied.

Gary

[Tonner]

It's still the steel one. I blew air through it to make sure it was clear.

[demian5]

Pull the governor.