ok, here is the deal. i have done a lot of looking, but i can't seem to get a good answer to this question.

i have a 91 RS that has a 700R4 and 2.73s. i will be switching to 3.73s within a few weeks. i already have the correct speedo gears, so thats not a problem.



here isa pic of my VSS...its a little "hollow" so i will be getting a new one when i install the new speedo gears.

here is the question...when i get the new replacement VSS, am i getting the same one? or a different one?

the speedo gears are different sizes, and i have read that this will throw off the centerline of the VSS and cause problems. but then again, at the same time, people say that i dont need a different one. (most notably, GMTech says that i shouldnt need one...and he is as credible as anyone that i have found.)

so, any suggestions? i want to get an OEM VSS...anyone know any of the GM part number?

thanks a lot for any light you can shed on this subject...

-brian

 

There were two style VSS's that I know used on 700's starting in '87. One is the popular gear driven sensor, the other is the Permanent magnent generator, with a steel reluctor wheel pressed onto the output shaft. The PMG style is usually used on trucks, I have NEVER seen anything but the gear driven style used on thirdgens. Probably the best thing to do is pull your VSS out, and make sure you have a plastic drive and driven gear.

As far as gear combos not lining up, what gears are you using? I have the Part Numbers of the ones I used when I did 3.73s around here somewhere, but I have since done other combinations when I switched gear ratios and never had any kind of alignment issues. Just make sure you put the drive gear clip in the right hole (there are two holes).

 

Also...I assume you go two gears for the replacement, One goes in the tail shaft, the other goes onto the output shaft...you might have to move your output shaft gear to the other hole on the output shaft for them to line up...

 

You could also buy the black box that will allow changes without changing gears...I believe Summit and Year One carry them.

Tom

 

I thought there were 2 different vss'. One for 39 tooth and below and another for 40 and above. You should have to change to the 40 and above since you have a 37 tooth now I believe.