My Rear and code on my Z has four digits but I can't seem to figure out what they mean and my chilton manual says that for 80 and 81 there was a different code from the rest of the 2nd Gens

I HAVE A BOOKLET FROM THE USSC THAT DECODES UP TO 1981. PLEASE POST YOUR CODE, MAYBE I CAN HELP.

I think it's GM35 er 35GM sorry bout the late reply.

THAT DOESNT SOUND RIGHT. YOU NEED TO LOOK ON THE FRONT SIDE OF THE PASSENGER SIDE AXLE TUBE. YOU MAY HAVE TO SCUFF IT UP WITH A PEICE OF SAND PAPER SO YOU CAN READ IT. SHOULD HAVE A CODE STARTING WITH THE LETTERS 2PT,2PY OR PT PU PW ETC. LET ME KNOW WHAT YOU COME UP WITH.

80ZGuy,
If its the stock rear end then there was only two axle ratios offered:
Auto: 3.42
Man: 3:08

If it has a posi, it should have tag on one of the rear cover bolts saying so.
John
79Z28

Yep my car is an auto and the rear end as a tag on it sayin it's posi. So I guess it's 3:42. Thanks a lot for all the help