I just had my transmission rebuilt. Taking it out for a first drive it goes into gear just fine, but it doesn't shift into second until I let off the throttle completely. If I give it any gas it goes back to first and revs up. I thought it might be the kickdown cable, so I ran the adjustment all the way out. No change. I spoke to the guy that rebuilt the transmission and he said vacuum issue. I checked the vacuum and it's connected and has vacuum on it at the transmission. I am going to try and get some better vacuum reading tonight or tomorrow night, but I wanted to see if anyone had experienced this and could help point me in the right direction.

1980 with a 383 motor and TH-350MV4. He said it was rebuilt to handle the extra HP and has a B&M shift kit.

How do you adjust shift points if you change the cam to one that produces less vacuum? Or other mods that can effect vacuum? Or if you just don't like the shift point?

 

What kind of vacuum modulator was installed, is it adjustable?
What exactly does 'ran the adjustment all the way out' mean when referring to the cable?

 

If your unit has the downshift [kickdown] cable AND a vacuum modulator, your problem could be with either (or both) items. If the cable is mis-adjusted so that the trans is getting a signal to downshift....when it should not....that will cause your symptoms. Also, if the modulator is defective (diaphragm ruptured/torn) or if the vacuum line to it is disconnected, missing, or plugged up, you will get similar symptoms. Try to adjust the downshift cable as best you can. If that doesn't fix the problem, replace the vacuum modulator.

P.S. When you remove the modulator from the transmission, you will get a quantity of fluid to drain out that opening (est. a quart or less). It would be best to capture that oil, and if still clean, put it back into the trans when you have installed the new modulator.

 

Sounds like a stuck Governor is one possibility to me , give your car a good full throttle L1 then L2 when the rpm’s are up then D3 , this can “flush out “ the debris that’s sticking the Governor . You can remove the Governor easily and un-stick the Governor valves too

The other possibility is the shift kit has pump pressure too high making the Governor overriding the shift valve as in holding it in gear to long

possibly a stuck kick down valve inside the valve body making fluid pressure overriding the 1-2 shift valve

Or maybe the Transmission shop set the shift points to high ?

At some point you need to take the manager for a car ride

 

The vacuum modulator was installed on the transmission when I got it back from the shop. I assume it was new as it was a complete rebuild. At least that is what he told me and he has a good reputation around town. He has been willing to talk with me and I expect he will get this right for me.
When I connected the kick down cable, I had the pan off so I could see how it worked. I've never worked on a transmission, so I learning a lot here. I could pull on the cable at the carb and watch it push the solenoid (not sure that's what you call it) in and it looked like it was working as it should. There is an adjustment on the carb linkage that would adjust how much throttle is needed to engage the kick down. When I say "ran it out", I mean I moved the adjustment to the end so it should not pull on the cable until very late if ever. I am going to disconnect the cable completely at the carb end to confirm this is not the issue, but I am pretty sure it's not.
I confirmed the vacuum line it connected and had vacuum at the transmission. Last night I put a tee in the line so I could run a hose into the car and watch the gauge will driving. When I give it throttle I got down close to 10 inches and when I let off it went back up to 20ish. From when I understand, that should be good enough for it to work. It has a racing cam and make very little vacuum at idle. When you let off the throttle and it's slowing down it makes decent vacuum.

I used Valvoline DexIV synthetic ATF. Would regular DexIII make a difference? I figured synthetic was better, but IDK at this point.

I would hope that there wasn't an debris as this was freshly rebuilt, but you never know.

 

Take it back. His problem.

 

I think that is probably correct. I wanted to try and understand more before I tell him fix whatever is messed up and don't charge me any more. Everything I hear and read points to internal to the transmission and not an error I made installing it back in the car. Problem now is I have a car with no rear bumper and no tail lights that will have to drive 5 miles in 1st gear to get it to him.

 

Might be better just to have it trailered. I know it's more money, but my 2 cents worth - towards your $100.

 

I would probably trailer it. I was more making a joke.

 

I disconnected the kick down cable completely. When I pull on it by hand, I can feel it's loose at the beginning and then hits a spot and has pressure as I pull it more. I fell that is when it is pushing the kick down valve in. It all feels normal, so I think I've connected everything back up correctly. It still does the same thing. Very frustrating.

I have what I think is good vacuum. It jumps around because I'm on and off the throttle so quick. I don't want to be doing burn outs down my street to figure this out. Vacuum is around 20 when I'm rolling around 1000rpm. I give it gas and it drops to 15ish or below depending on how hard I hit it. Then back up over 20 when I let off. I put a tee in the line from the carb to the transmission and ran the hose into the cabinet so I could watch it while driving.

 

You said they put a shift kit in. There's the possibility that they messed that up or that it was defective. It's been 45 years since I put one into my brother's 74 Camaro TH350. But on one occasion we had some plastic ball roll out of position on whatever you call the plate that has various perforations to control fluid passage. We caught the issue as we noticed a bump in the previously perfectly flat plate where it had crushed the mispositioned ball. But it could have been easily not noticed. I don't know what would have happened if that ball was not where it was supposed to be, but surely something.

In any case, I'm with those who say it needs to go back to the guys who did the work and made right. Good luck.

 

For anyone keeping score, they replaced the valve body and it's shifting fine now. They didn't charge me anything. Now to finish the bumpers so I can drive it.

 

Did you drive or have it towed to shop...free if you have AAA

 

I had it towed. Don't have AAA. I do have Hagerty insurance and I probably could have argued with them over their towing policy. But, it was only $65 and not planned well, so I paid it. Could have driven it given how close the shop is, but played it safe.