Chevy & GMC Vans

Bill, make this a sticky!!!!

Originally post on AS.com

Posted by Lockdoc on May 15 2006,3:31
Here is some of the info I used to recalibrate my DRAC modules for different tire and gear sizes.

http://www.tbichips.com/drac

This is a nice calculator for calculating your input ratio.
DO NOT USE THE INFO FOR THE JUMPER SETTINGS ON THIS PAGE. I FOUND THEM TO BE WRONG MOST OF THE TIME. Use the chart on the TBIchips page
Input Ratio Calculator .....
http://www.philter.com/cgi-bin/drac.pl
This is a calculator I used for tire circumference. Fill in your known values in the "Calculate tire diameter" fields. Then click "calculate". Use the circumference found here and enter it into the "Input Ratio" calculator above instead of using your tire size.
How to calculate tire diameter.....
http://www.5speedtransmissions.com/calculators.html

Hope this helps others who need to recalibrate.

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Posted by LiftedAWDAstro on June 02 2006,12:15
I just pulled my DRAC and re-soldered the jumpers according to the posted links. My DRAC looked just like this one:

I installed two six pin dip switches on my VSSB to make it easy to change settings.. It only needs them on jumper positions 2-7. Jumper position 1 stays the same no matter what.

One of the websites listed was ambiguous regarding the differences between a DRAC (digital ratio adapter controller) and a VSSB (vehicle speed sensor buffer). A DRAC has only one set of jumpers. A VSSB has two sets. The second set is for the 4L60E and will be set as a mirror image of the other set that provides signal outputs for the speedometer, cruise control and ABS controller for the rear wheel speed signal.

The VSSB in my 93 with a 4L60E only has the single set of jumpers. It looks just like the DRAC in my 92 with a 700R4 but they are not interchangable.

LiftedAWDAstro wrote:Bill, I don't have the pics of the DIP switches we did on zam's van. If you send me the spare DRAC module, I will solder the switches in. I will PM my address.

Dean, here are a couple of pics I was able to find...

Here is snapples spare DRAC module with the 2 new 6 pin DIP switches installed.

Here is the bag, with part numbers, the DIP switches were in.



I removed the solder with a solder sucker and then removed all jumpers except for #1 on the right (no pic of this). #1 on the left is always going to be left a "0" or open so nothing is put there.







Now all Bill needs to do is compute the correct DIP switch settings based on gears and tire size and plug it right in and instant speedo re-calibration is done! I installed the switches upside down from each other so that when the switches on the right are selected according to the calculations, the switch on the left will be switched opposite based on the same switch number.

Thanks Dean!
Another step towards getting my van ready for it's Adirondack voyage this coming Labor day weekend!

BLAZER wrote:http://www.tbichips.com/drac
1990-1995 GM Truck/SUV DRAC/VSSB Calibration

It would be awesome to do a DIY recal on my van. Is there a similar hack for post-'95 models?

OBDII vehicles you can adjust the computer using a programmer my jet programmer does it i'm sure a garage with a good scan tool can do it too. I know i've seen other hand held devices that do it too but for the life of me i can't remember them, the jet ones biggest down fall is it binds to your vehicles computer and will not work on another vehicle not even just to pull codes

Thanks. I'll inquire about it next time I'm at a shop.