I put a new GRR on to go along with the new VSS, but my speedo still is way off. When I'm going 55mph it says I'm going 30. I have read the sticky on how the speedo works, but I am wondering if anyone else has had this problem, or what exactly the solution is to fix it?

Thanks!

 

Stock tires? Is it bouncing or steady?
Fill out your signature so we can see what your working with

 

All stock, its steady, and steadily about 25 mph off.

 

sounds like someone might have installed the wrong speedo gear in the transfer case.

 

If its consistant with how far off it is across the spectrum, I suspect that either the wrong pinon drive gear has been installed, or that the GRR is off..

Just for giggles, remove the GRR altogether and see how it does.. and inspect the pinion drive shaft while your at it.. altho I doubt that is the issue..
then inspect the pinion gear, most of these trucks used the "yellow" gear, or the "blue Gear", but for the life of me I cant remember which went with which gear ratio..

Also inspect the wiring harness from the VSS, make sure its not chafed or open.

 

The pinion drive gear has not changed from the original, could it be broken? and the GRR is brand new, I ran without the GRR for a day or so and it was consistently around 15mph under what I was going.

 

If the Pinion were broken or missing teeth, teh speedo would jump as the missing tooth would cause a pause or skip of the gear..
I am suspecting that the "new GRR" is off.
is this "new" or your original that has been rebuilt?

You may want to talk to these guys and get some input from them..

http://www.transmissioncenter.net/sp...tm#90%20Degree
Do you have the original GRR that was on the truck?

 

I bought it from the dealer, so I assumed it was new, but I guess I'm not 100 % sure. Is the GRR supposed to make the VSS read a higher mph? or lower?

 

The new GRR looks like this:

But the original looks like this: