differentials

[MC75Z]

I am changing the 4 spd in my 77 to a 5 spd. I am putting in a 5 spd that is marked from the wrecking yard " 81 to 83 ZX ". The rear end in my 77 is stock whatever that is. I know there are several types of rear ends. Should I change the rear end to be copatible with the transmission and how do I tell the diferrence between rear ends. I have several that I can choose from but don't know which is which.

[Hrududu]

The differential in your car should be an R200 with 3.54 gears.

[ktm]

The only way to truly know the differential gearing is to remove the rear cover and look for a stamp on the ring gear. The stamp contains two numbers offset by a colon like 37:11; divide the larger number by the smaller to get the gear ratio. In this instance, 37/11 = 3.36. I have a 39/11 or 3.54 differential in my car.

I am at work and do not have access to the transmission calculator, but you will most likely want to change out the differential to a 3.90 if you use an 81 to 83 zx transmission. The 81 to 83 transmissions had a taller first gear and were mated to a 3.90 differential from the factory. It really depends on how you drive though.