Tech. help please! Tranny and speedo related questions.

[99VPRGTS]

Hello all. I have a 1999 GTS and had a couple questions. I went to the track this weekend and on the way up there I had GPS on and the cars speedo was off. I had always suspected that it was a little off, the GPS just verified it! Long story short, as the car increases in speed, the speedo error increases. At 100 MPH on the speedo, the GPS speed is 89-90. My question is, did the previous owner put 3.55 gears in it? I have always suspected this as well because of how the car pulls compared to stock Vipers. The car does have 19's on the back but, as some of you know, a bigger rim/tire would make the car seem like it was going faster, NOT slower on the speedo. Where do I get a speedo calibrator and how is it done?

My second question involves the tranny. The car shifts perfect in every gear, performs flawlessly, and NEVER gets hot or anything like that. However, sometimes when I am driving, I notice that I can move the stick all the way over as if I was going to put it in reverse. Normally, there is a safety switch that will not allow this to happen if the car is moving forward. So, I have to be careful when shifting from 4th to 5th. Is there a sensor that I can swap to fix this or is it something else? There are no after market mods to the tranny other than a short shifter that was installed on the car when I got it.

Thanks for any help guys and sorry the post is a little long!

-Brent

 

[PhoenixGTS]

Jack the car up so both rear tires are off the ground. Then put it in neutral with the emergency brake off and rotate one wheel by hand. Count how many times the yoke going into the differential turns compared to one full turn of the wheel to figure out what gears are in the car. If you do have short gears you'll need a correction box for the speedometer. $125 & fairly easy install IIRC.

 

[99VPRGTS]

Okay cool I'll try that. Someone told me if the shaft turns 3.5 times for one full turn of the wheel, then I do have 3.55 gears. Where can I buy the correction box?

 

[PhoenixGTS]

Where can I buy the correction box?

Unitrax in California might not have them on their website, but if you call them they will either have them or know where to get them.

 

[mjorgensen Woodhouse]

I have a 3.55 box in stock

 

[99VPRGTS]

Okay thanks for the help. I'll check this weekend to see what gears I got.

Mjorgensen I'll get up with you on Monday.