Turbo 400 problems

[Rob 71 chevy]

The guy who built my tranny can't seem to figure this out so I am hoping that someone on this board can. I have had my tranny rebuilt, a turbo 400, a stage 2 shift kit installed with a 2200 stall. My motor is a 350 with a 280 comp cam, if that helps. The electronic shift down is conected to my gas pedal. I believe my rearend is a 3.08. I just got my truck back for the 4th time out of the tranny shop and still problems. If I take off, with it floored, it will shift at 4200 rpms (about 40mph). But, if I am in drive and floor it say at about 2000 rpms, it stays in 1st until I let off the gas. I took it up to 6500 rpms without it shifting. Not good for the motor. I was cruising at 50 mph, about 2500 rpms I believe, and I floored it. The tach went straight to 6500 rpms and it felt llike it went to neutral. I let off the gas and it went back into 3rd. When I am on the freeway at 60mph (about 3200 rpms), and I floor it, it won't shift down at all. I can't get it to shift from 3rd to 2nd, but at lower speeds, going from 2nd or 3rd to 1st ins't a problem, but it doesn't want to leave 1st gear until I let off the gas. This tranny is guaranteed, but I would like to be able to have some answers. I would appreciate any and all advice. Thanks.

[kxmotox247]

I'm just going to give you 2 things to think about...don't know if they'll help or not.
1) I have a 383 Chevy motor for my street rod with a CompCam 280 magnum. When I bought it, the guys at the CompCam said I had to have a torque convertor around 2600-2800 stall. I'm not sure if this is going to make any difference in your case.
2) I think you can adjust the shift points by turning a little screw inside the vacumm modulator. Unplug your vaccumm line into the vaccum modulator and use a small screwdriver to turn the screw clockwise or counterclockwise to adjust shift times.

I think you need to check your vaccumm line to the transmission. If there is a leak at all, your trans will not shift right...might not shift at all.
You might want to check to see that you are pulling vaccum off the right port to do so. I'm sure there are people on this board that might be able to say yea/nay on anything I just said. I just wanted to give you something to think about.

[lost wages]

i dont remember what it was called but when i had my tranny built there was a peice that came with the shift kit that would make the tranny stay in a certain gear till you shifted it manually, sorry not much help but it might be something to look into.

[COBALT]

A couple of things:

1. Make sure your modulator is working right. Stock modulators are not adjustable unless its been replaced.

2. Make sure your governor isn't damaged.

3. The shift kit is REALLY suspect. It sounds like something they did with the circuitry and the valve body may not be playing nice. Doesn't sound like they put the shift kit in right, or neglected to do something.

[Rob 71 chevy]

Thanks for your responses so far. I am suspecting the shift kit too. Once it shifts down, it doesn't want to shift to second unless the I let off the gas completely and wait a second or two, and then it shifts to third. Not too good when I need to merge into traffic on the freeway.

Keep sending the replies. I appreciate what I have received so far. I will be discussing these with my builder. Hopefully the 5th time for him with work?

[ChevLoRay]

I had an old-skool drag racer who has been building automatic tranny's for years, to modify my valve body for firmer shifts. It was a simple matter, involving drilling one hole, blocking another, and reinstalling it with a new modulator...specifically a smaller one. It is black, and apparently, the color of the modulator has something to do with the operating characteristics of the modulator.

In my case, he said there wasn't enough vacuum signal to operate the larger modulator for kickdowns, etc. I don't currently have a kickdown hooked up, but it will kick down into second, from drive, if I floor it. It speeds up very good and shifts firmly, but not hard enough to bark the tires. If I floor it hard enough, and the speed is right, it'll kick down to a lower gear. I think I might get better gas mileage, if I had the electric kickdown working. I bought the Lokar unit, but I think adding a button under the gas pedal might just work. Oh, I guess I'd need a gas pedal, so scratch that. Right now, all I have is the arm that the pedal contacts....one of the ball studs broke off and I haven't replaced it.

I know that this doesn't answer your question, but it offers a different view on the topic. I suspect that the problem may be in the shift kit/valve body, but could also involve the modulator, if the cam doesn't generate the vacuum needed for proper operation of the gearbox. It sucks to spend good money on something, only to have it not work like you expected it to work.

Was the tranny bad before you had it modified, or was it operating properly and you just wanted a shift kit installed? One more suggestion: Contact the manufacturer of the shift kit, explaing what you told the board, and see what their tech people say.

[71GMC_3/4T]

Disconnect the electric down-shift plug and see if the problem goes away. Then go buy an adjustable vacuum shift modulator and tweek it to where it holds until about the right point, then shifts. It may take you a few adjustments, but it will eventually be easy. Make small adjustments - at least mine was fairly sensitive.
I don't even use the electric down-shift switch. That's why they put that there lever by the steering wheel!