What would i need to look for to know weather or not iv got the stock rearend in my 86 IROC car? Can i find out what gears came in the rear end with my VIN number? and then will i find a way to tell what the rear end ratio is by looking at it?

the whole reason is becasue the speedo is about 10 MPH too fast when im going about 55. i think the wheels are the stock size too.

 

The only way to tell what rear you have is to get the casting number off of it and take off the rear cover to look at whats inside. RPO codes only tell you what the car came with from the factory and not whats in it right now. If you run the numbers and count the teeth you will be able to cross reference that info with whatever your RPO codes say. If they don't match then you have another rear gear of some sort.

 

yea see i was hoping that actually counting wasnt the only way, but i guess so. i also thought that i could get a close idea with the calculator equation thing on this site but i would need to know my real speed, which i dont becasue the speedo is messed up haha

 

You could get an idea by jacking it up and counting how many times the driveshaft turns for ever time the rear turns, but it's probably time to change the diff lube anyway.

 

hmm, is there any interval that is set for changing the diff lube? certain miles or such?

 

Now would be a good time to change it. You don't know when the last time it was changed or if it was ever changed at all.

 

ill take that advice and do it sometime soon.

and whats the easiest way to count teeth? i was imagining puting a piece of tape or something on a tooth to mark it, as long as it will stick good enough

 

Gear ratios are stamped on OD of ring gear by all MFG's. The east way.

 

oh ok, but im new to the gear thing, can the ring gear be original and the other be different? i dont think so i think they have to go together right? just wanna make sure, i like learning as much as i can about stuff like that.

 

Gear & pinion are a matched set. Never sold seperately.