Speed Sensor Buffer DRAC

[Joe Fortenberry]

I have a 1988 Chevrolet C1500 Silverado. It calls for a speed sensor buffer. We, my mechanic and myself cannot find it. On later models it is located under the glove box. not so on this model. Where is it?

[Mikebtte]

You most likely have a 700R4/4L60 and not a 4L60E. 4L60E had the DRAC and you would swap it for a Box with DIP switches or add them yourself. 

4L60E was not used until 93. You have a TV Cable and will need to approach a little different in fixing your issue.

[riverbanks]

That part is only on four wheel drive, speedometer correction for four low

[Joe Fortenberry]

Riverbanks; When you say a TV cable are you saying literally a cable? if so I have not seen anything like it. 

[Mikebtte]

TV cable runs to the throttle body and controls pressure in the transmission for shift points. Should be adjusted using a pressure gauge.

You should have a cable coming off the transmission going to the speedometer for speed.

The DRAC was used as a buffer box to send a digital signal received from the transmission to the ECM/cruise and the dash on new year model trucks.

88 had no DRAC but 89 did. If you received and early 89 its possible to have one. It will look like one of the many combinations below. In the Vans it was behind the dash on the drivers side, on the trucks it was behind the glove box.

Warrperformance offers units with a DIP switch installed if needed. Also a usefull source of information on the units.

 

https://warrperformance.com/?product=modified-gm-drac-to-adjust-for-different-tires-gear-ratios-tbi

 

Edited December 23, 2019 by Mikebtte

[Joe Fortenberry]

I do not have a cable coming off the transmission going to the speedometer nor can we find a DRAC. However one of my mechanic friends even gave me one for possible use. It is definitely not under the glovebox or anywhere under the dash.  That's why we're so befuddled. 

[Mikebtte]

That makes since as the 88 had no DRAC, I think you are good on that point. Forgive me as it has been a while, You should have a 2 wire sensor putting out a magnetic pulse the the speedo and a TV cable at the throttle body.

 

 

Edited December 23, 2019 by Mikebtte

[riverbanks]

Yup,educated me too,been a while also,can't explain my post,cause I didn't see the drac,I assumed it was not on 2 wd ,found more good info on udmodule.com

[James A Thomas]

I have a 97 GMC sierra and I was told I need a speed sensor buffer I was told also it’s behind the glove but the part store doesn’t have a clue what I’m talking about 

[CouchRider]

I have a 97 Tahoe &speedometer is 10 mph fast wheel and tire are factory size and I’ve already changed the VSS  in transmission..

What can I do next to correct this problem?  97  Tahoe 4x4  5.7 Vortec I’m getting doesn’t have drac. 
Does anybody know if it has one or not and where it is . Or what else could be causing my speedometer to be 10 mph fast.

[Austin s]

This issue ever get solved? I have the same issue with a 1997 GMC Sanoma 4.3l 4L60E. Speedometer is off by 10 MPH at 70 and after driving a while it causes the trans to shift hard and code for p1870 which is a general trans component slippage because the truck isn’t moving as fast as it the computer thinks it is. Could this be a PCM issue or is there a DRAC box?