First off, this is my first post and I would like to say that this is a great site! As in the subject, I have a speedo ? . I have a 91 RS and have searched and read all info about this on the site. I bought this car 2 years ago. It had the 305 tbi, a 700 R4, and ran 2.73 gears. After having the car for a little over 6 months, I had a new GM 350 Ramjet put in the car. I put about 10k miles on the motor and then put the car in the garage because the trans started slipping. That was 1 year ago. Over the past 2 months, I've had the trans rebuilt and 3.73 Richmonds installed. This leads to my question, how do I calibrate my speedo? I checked under the dash, and the car no longer has the factory ECM, just the harnesses. Am I overlooking something? I've looked for the DRAC unit and can't find it. I've got the car completely gutted and am in the process of pulling all the GFX off because the car is going to go into paint. Any help would be appreciated!

 

You'll need to swap out the speedo gears themselves

Here is the how to article along with some part numbers.

http://sethirdgen.org/vss.htm

 

Thanks very much! I thought I would have to change those out, but someone told me that it would have to be done with a drac or a dip switch because it was an electric speedo. Again, thanks!

 

The vss buffer box on your 91 tbi should be about a foot from the ecm. About half way from the ecm and the center of the dash, just remove the lower cover on the passenger side, its tucked up in there between the outer dash and heater ducting, has I think 7 wires going to it and one screw holding it in place.

I dont know if its tweekable or not, but thats where it is.

You might have to change gears like Jaysz28 said.

HTH

 

The box is called a DRAC, and yes, they are tweakable if you have some soldering skills.

http://www.614streets.com/drac.html

And a calculator I wrote to make the math easy.

http://www.philter.com/cgi-bin/drac.pl

Teeleton

 

Ohhh

Priceless articles there.

Specially for the electronically challenged like myself

later
Jeremy

 

Thanks Teeleton.

Great info, might come in handy on a future project.

 

Ok, I still can't find the DRAC unit. I have located the ECM and a little yellow box marked "ac delco spark plugs". I can't find a little white box anywhere. Anymore ideas?

 

Acually....you don't have a DRAC, it's a speed buffer and the location is right where it was discribed.
A DRAC uses a reluctor, we have a mag pulse generator.
So, changing the gears is the way to go.

 

Thanks!