Suburban Drac Module

[Caesard3]

Does anyone know about the Drac module. I had problems with my Suburban shifting (stuck in low gear). First they changed the electronic control module. That worked for a few weeks then started doing the same thing. Then the Drac module which seems like it fixed the problem. The dealer said this has nothing to do with the shifting problem. My mechanic said it did and also got the part from a junk yard. The dealer said you could not do this also.
Trying to figure out who is right.
Thanks

[Bo185]

What year truck is it?
Engine, trans and such?
Sounds like a mid to late 90's.

It could be a number of things wrong but with out more information who knows!

The VSS runs through the DRAC to the computer on some trucks but not sure which truck you have.

[Black Dog]

On a '91 Sub I have, the DRAC (actually called the VSSB - vehicle speed sensor buffer) works intermittantly. When there is no speed signal output:

The speedometer does not work.
The torque converter will not lock.
The engine idle does not drop when in gear and moving (it normally does this to provide best engine braking).
The rear wheel ABS controller will set a code 9 (flashes the brake warning light), and the ABS will quit working.
The Check Engine light will come on once in a while - definitely not every time the VSSB quits.
I assume that EGR does not work, but I have never checked for sure.

Otherwise the truck runs and drives like normal, and it does shift through all of the gears. If you have an electronic controlled tranny (4L60e or 4L80e), i would guess that you would have a lot more tranny related symptoms.

[boxxerace]

Hey B.D. I take it you dont have your VSS sensor hooked up because you have a different tranny / case combo? (Np205 my guess.)

Curious, what tranny do you have?

[Black Dog]

Originally Posted by boxxerace

Hey B.D. I take it you dont have your VSS sensor hooked up because you have a different tranny / case combo? (Np205 my guess.)

Curious, what tranny do you have?

It is a stock 2WD '91 Suburban with a 700R4. The VSS is hooked up. The problem is with the VSSB, a small circuit board the is located under the dash. This board takes the signal from the VSS, and scales it according to the gear ratio that you are running, and then it generates scaled signals that go to the computer and to the RWABS controller. This board only works part of the time (when it is above about 70 degrees fahrenheit to be exact), so it is easy for me to see what effect you get from not having the speed signals to the computers. Every morning when I get in the truck the board does not work until it warms up above 70 degrees, then it keeps working until it cools down again. You can also make it stop working by running the A/C since there is a duct that almost touches the VSSB under the dash.