hey, the previous owner said that he had put the rear end of a 89 iroc on my 91 z28. how can you tell what ratio you have. I have the casting number that is on the housing. i believe that it is 22522676, but i cant really tell that the 6's are 6's. they may be 8's. and my speedo question. my electronic speedo does not give correct speed cause of the rear change. how do i get it to give correct speed. thanks
bryce

 

If its out of a 89 iroc it could be anywhere from a 2.73 to a 3.42. They had different gears depending on the model (350/305 Auto/Manual Etc...) One way you can tell is this, Use jackstands to get both rear wheels off the ground, get under the car and with a white marker or something, make a mark on the driveshaft where it meets the rearend and make on mark on the actuall rear end, then line the two marks up, now get someone to assist you, roll under the car and have your buddy turn the rear wheel one full turn and count how many times the driveline turns. Ex. if the drive line turns about 3 and a half times, you have a 3.42, if its turns less than 3 time, your a 2.73. Etc... Hope this helps you.