I just got a rearend for my '92 RS that came out of a '87 IROC and plan on puttin 3.73s in it. The question I have is when I do the install what do I need to have to make my speedometer correct? Is it electronic or mechanical?

 

the speedo cable goes into the transmission not the rear end

you will have to replace the speedo gear when you change the gear ratio

 

your speedometer is electrical on a 92

 

also is the rear end fromthe iroc a 10 bolt or 9 bolt.........9 bolts are hard to find parts for..........and the 87 will have 26 spline axles if it is a 10 bolt..........the rear in the 92 is a 28 spline.

 

Ok, so I didn't have a clear cut question. The rearend that I bought came out of a IROC. I am swapping it in place of the rearend that came factory on my '92 RS. But before the IROC rear goes under my car it is gettin a set of 3.73s put in it. And since my first question about the speedometer being electrical or mechanical was answered. My next question is how do I go about having my speedometer read correct once I put the IROC rear under my car with the 3.73 gears?

 

What he is saying is if you got a Borg Warner out of a 1987 IROC with the L98 350 TPI then you will have to settle for a very limited choice of rear gears. I found 3.70's from ringpinion.com

 

if your tranny has the speed sensor that has a gear on it you can change the driven gear out,but if it has a reluctor wheel type sensor,i can't help ya on that.....sorry

 

So, where would I go to get the driven gear to go in the tranny? And how hard is it to install?

 

you should be able to get them from any chevy dealership.

it is very easy to install, you unscrew the speedo cable where it goes into the tranny, undo the bolt that is holding the threaded piece in, pop out the old one, put the new one in

 

http://www.thirdgen.org/calibrate-speedometer