Transmission Troubles 87' Suburban

[cmv1274]

Transmission Troubles 87\' Suburban

My 400 automatic trans out of an 87' Suburban 4x4 will not shift out of first gear. I have changed the vacuum modulator and had a trans shop look at the governor.(He said it was good. The teeth are still in good shape, could it still be bad?)(I dont really trust the trans shop) Does anyone have any other suggestions before I replace it?
If not, Will a 350trans out of a 75' Blazer be a direct bolt in as a replacement?

 

[sdavid]

Re: Transmission Troubles 87\' Suburban

Take it to another shop. Same thing happened to my '78 Jimmy w/T350. It was the governor. Good Luck.

 

[Thunder]

Re: Transmission Troubles 87\' Suburban

Is the modulator getting full manifold vacume?
Did you check the vacume line that goes to the modulator for cracks?

 

[dyeager535]

Re: Transmission Troubles 87\' Suburban

If the modulator is hooked up correctly, try driving it and running it through all forward gears while doing so, over, and over, and over again. 1,2,3,2,1, and so on. If something is lodged in there, this is apparently the way to try and "fix" it, without tearing it all down.

The governor is extremely simple, but sensitive to anything external acting on it. The shift trick worked on my TH400, I also had the motor at about 4000RPM while doing so. You can pull the governor yourself, it just sits in the drivers side of the tranny case, held in by a square plate with 4 bolts. (been awhile, IIRC, the TH400 uses bolts to retain the governor) You can always pull it out and examine/clean it yourself.

Of course, I'm not certain the governor is the *only* reason a TH400 won't upshift, but it can be at least one.

FWIW, a modulator not being hooked up to vacuum will not prevent shifts, numerous times in my car the cheesy PO's setup (hose clamp on the wrong size hose) came loose and for days I'd drive it with no modulator influence, and wouldn't even notice.