Transmission vacuum valve setup

[SimonUK]

Hi folks,

does anyone have the dimensions of the

'Valve gage block, J-33043'

specified in the military manuals for setting up the transmission vacuum valve on the IP.

Many thanks,

Simon.

[Robyn]

I have never had the good fortune of owning one of these tools or seen the dimentions.

I always start by setting the valve with the screws in the center of the slots and go from there.

With the vehicle in drive and starting off on a level road, using a light throttle the 1-2 shift is best set at about 15-20 MPH

If the shift is too late it means you have too little vacuum to the modulator.

Too soft a shift with a heavier throttle (way too soon with say 1/2 throttle) means too much vacuum.

Unfortunately its hard to describe this setting in text.
I have done so many over the years that its sort of like buttering toast.

The valve is a half hearted way to simulate manifold vacuum on the engine and use this to control the line pressure on the TH400 Tranny

Anyway
Starting with the setting in the middle will get you close.

Too little vacuum will yield late harsh shifts
Too much vacuum will yield early soft shifts

Looking at the IP from the RH side, Rotating the valve clockwise will lower the vacuum to the modulator at any given throttle position and rotating counter clockwise will raise vacuum.

This is not rocket science. As long as your in the ball park it will be fine.

If your light throttle test yields a shift from 1-2 above 25 MPH you have a tad to little vacuum.

If your shift is real quick and soft then its too much vacuum.

The vacuum control is aimed at duplicating the characteristics of a gas engine.
With the throttles closed = High vacuum. With the throttle wide open= very low vacuum.

The more throttle there is the more throttle pressure thats needed (Tranny pressure) to offset the load and shift the clutches without slipping)

Hope this helps
Keep us posted

Robyn

[SimonUK]

Hi Robyn, Thanks for the reply.

I finally fitted a new modulator to the tranny and when I reconnected the tubes to the valve the shifts were way too hard and late (no vacuum no matter where the pedal was)

I tried every possible position before removing and opening the valve.

The wee plastic link that runs in the groove and pulls the wire link to the actual valve was worn away where it runs in the groove.

as a temporary repair (which usually means till it fails again) I superglued a square bit of plastic where the link had worn away to nothing.

Just about got it set perfectly now so we'll see how long it lasts.

I've got a couple of old valves which are probably worn the same inside so i'll maybe look into fabricating a part to fit.

It may seem like a lot of hassle but a replacement is a couple of days away for me and I hate throwing away a perfectly good and probably expensive part for the sake of a 2 cent piece of plastic.

Regards from sunny (today anyway) Scotland

simon.

[Robyn]

NOW
There is such a thing as a mechanical modulator assembly that is run by a cable.

TH400 Mechanical modulator,Teckpak 40M modulator

Here is a link to a site that sells these.

The little vacuum valves you are working with are a GM part # 14057219

Best

Robyn