advance help

[lostinthesauce]

In need of help. I have a vacuum advance on my distributor and an electronic or plug in on my transmission. is there a conversion kit or shunt that i can use to connect the two systems? took out the transmission with the plug in on the transmission for a vacuum advance on the transmission but the damn thing has a broken shift shaft... now i must put the other transmission with the plug in order to get my truck running again. thanks for your time in advance:finish:

JB

 

[raycow]

In need of help here, too.
What kind of truck - year, make and engine?
What kind of transmission - the one with the plug-in?
What kind of transmission - the one with the "vacuum advance"?

Ray

 

[lostinthesauce]

In need of help here, too.
What kind of truck - year, make and engine?
What kind of transmission - the one with the plug-in?
What kind of transmission - the one with the "vacuum advance"?

Ray,

My truck is a 1969 Chevy Pickup, 3/4 ton, 350, with what appears to be possibly a TH400 tranny.
There appears to be an electrical connection on the transmission for the vacuum advance, but the distributor is vacuum. On my other tranny which is also a TH400, the same vacuum valve that is found on the distributor is also located on the passenger side of the transmission closer to the front...so in an older setup you would have a vacuum line thats runs from the back of the distributor to the transmission to allow the transmission to shift thru gears.....my truck will only shift gears when you rev the motor to high RPM's and then ket off the gas, only when this step has been completed will the transmission shift....this is an AT teansmission by the way....thanx for your help

JB

 

[raycow]

It sounds like you may have misinterpreted the purpose of some of the devices on your truck.

The vacuum can on your distributor is for spark advance only and has nothing to do with the transmission. It should be connected to the carburetor or intake manifold.

The vacuum can on your transmission is a vacuum modulator. This tells the transmission how far your throttle is opened, because there is no mechanical throttle valve linkage on a TH400. If this device is not getting vacuum it will think the throttle is opened farther that it really is, and that will delay the point at which the transmission shifts. In other words, the shifts will occur at higher rpm. The modulator has nothing to do with the distributor and should also be connected to the carb or manifold.

The electrical connection on the trans is for kickdown when the throttle is opened fully (again, because of no mechanical TV linkage). You should find a kickdown switch somewhere on the carburetor or throttle linkage if the truck was originally equipped with a TH400.

There is a very good Chevy truck forum at chevytalk.org and I strongly recommend that you discuss your problems over there. Scroll down the list of forums until you get to "Trucks-Vans-SUV" and then look for the 67-72 forum.

Ray