TH400 will only downshift manually?

[D-max Man]

I have a 1985 Surburban 6.2 diesiel which originally had a 700R4 trans. but the previous owner swapped it out for a TH400. He told me that it had a manual valve body which has proved to be more of a hastle than it is worth.

So today I swapped the valve body & seperator plate with one from a known good trans. I also had to install one of the check balls which had been removed so all 6 are there now.

Now when I drive it, it still starts out in high gear just as it did before. If I manually downshift, I can only get it to go down to 2nd. (Before I had all three gears manually).

I also do not get a downshift on full accelleration but the pedal swith is working and has power to the solenoid plug on the trans when accellerator is fully applied.

The vacuum modulator is hooked to the vacuum switch on the inj. pump with the other port connected directly to the vacuum pump (and it has vacuum on it).

It has been sitting for a couple of years but I had all there gears before switching the valve body. Is there something else that gets done to the trans when a manual valve body is installed?

Any help is appreciated.
Thanks,
C. J.

[SoTxPollock]

Not too sure what year th400 you have, but the manual valve body was actuated by either moving the shift lever manually, or when put in D would upshift by vaccuum via the vaccuum modulator. The vaccuum modulation was taken from the intake manifold on gasser engines which would vary with how far your right foot was pushing the accelerator. It also had a govenor that would cause it to upshift out of first gear if you left it there too long and the rpm's went too high.
I'm not sure that your vacuum source will allow it to shift since it doesn't appear to be a varible vaccuum. You are probably stuck with shifting manually only all the time.
How did you determine that the original valve body was defective?

edit from STP, Sorry I got interupted by a lady wanting to show me pictures of her new horse, I just had to oblidge.
I'm suggesting you pull the govenor our of the side of the transmission and verify its not stuck in the open position which would cause it to force 2nd gear operation, if you free it up where it operates correctly it should go to first gear.

[D-max Man]

I was told by the previous owner that he had installed a manual valve body. If I put it into D it would go right to 3rd. gear. I could downshift into 2nd & 1st with the shift lever on the column but it would not up-shift on its own.

I used a valve body out of a trans that was in my old plow truck that I have had for 6 years and was working properly when I took it out (Maybe I should have just used the whole trans.).

It does have a vacuum switch on the inj. pump that is operated by the throttle cable.

I can check the governor that is pretty easy to do. I have rebuilt these things before but it has been many years ago and I am a bit "rusty".

[Robyn]

HI

I have built many 400's and never once installed a manual Valve body.
Some of the manual kits do different things to make the switch.

Pull the cover off the governor and see whats in there.
The governor may have been modified to stay in the open or shift position all the time.

If you are in doubt, yank the governor from the other tranny you have and switch them out.

I am a little foggy on just what all is done to modify one of the 400's to be manual but something tells me the governor had to be worked over.

Also be sure you have good vacuum at the modulator. High vacuum when the throttle is all the way to the floor and lower when its in the idle position.

Just make sure when you get it shifting that you get firm shifts.
If the shifts are late and hard rotate the vacuum valve clockwise while looking at it from the pass side. If the shifts are early and or soft rotate counter clockwise.

Late= too much vacuum
Early= too little vacuum

Make sure the vacuum pump is pulling a steady 26 inches at the pump.

If its pulsating (needle wiggling) the tranny is going to shift poorly.

Give it a look see.
Hope this helps

Robyn

[D-max Man]

Thanks for the help. I found that the governor had spring clips holding it closed, the accumulator was missing the center spring, the vacuum modulator was junk, the vacuum pump was only giving about 10-12 inches and fluctuating and the vacuum switch on the pump was leaking. Other than that all was A-OK. LOL...

Now that I have it shifting, I think my fuel filter is getting plugged up. I guess I shouldn't have let it set for 2 years eh?

[DmaxMaverick]

Well....I can't imagine why you would have shifting problems if that's all it was........

Two years on a fuel filter is kinda' long. They're cheap, eh....

Glad you got'er figured out.

[Robyn]

Well Heck I got ya close anyway ROFLMFAO !! ;0)