My car is a all stock 1989 IrocZ w/5.7 TPI L98, 4wheels discs brakes, and option G80 Positraction. DO I have a 10-bolt or 9-bolt in 7.625 or what?

 

You can determine what rear end you have by simply counting the bolts. If you count 9 than you have a nine bolt and if you have 10 you have a ten bolt . There is no telling what gears are in there now unless you pull the cover and check. Chances are your rear needs a fluid flush anyways.

 

Okay. That helps but what about the type? 7.625, 7.75, 7.6 or what? someone else please!

 

You have a 7.5" rear end. The fourth gens had 7.625" Here's a list of RPO codes for you, they should be in the center console lid. Look for these numbers to tell you the ratio of gears.

GU2 - 2.73
GU4 - 3.08
GU5 - 3.23
GU6 - 3.42
GW6 - 3.27
GM3 - 3.45
GT4 - 3.73
G80 - posi
G92 - performance

The G92 means you have the optioned gears. For example, if you see the RPOs GU6 and G92, then it means the gear size GU6 (which is 3.42) was an option. But if you see GU2 and no G92 then it means you have the normal factory 2.73 gears. G80 means you have posi like you said.

 

So do thirdgens starting in 1985.

 

GM switched from 7.5" to 7.625 around 1986 but they're still called a 7.5" diff. The only difference was the slight increase in ring gear size. Everything else stayed the same.

 

So to get new gears. Get the for the 7.625
I dont have any of those except G80. I have GH3

 

GH3 = Borg Warner (9 bolt diff) with 2.77 posi

 

thank you for getting right to the point

 

The Ring Gear dia is 7.75 for all 9-bolts

 

That doesn't mean that's the diff in the car. That's just what was in the car when it came from the factory. A previous owner could have easily installed a 10 bolt in the car if the 9 bolt failed and he found parts for it were expensive or non existant.

Climb under the car and look at the rear cover on the diff. A smooth cover is a 10 bolt (count the bolts). If there's a rubber plug in the cover to fill with oil, it's a 9 bolt (count the bolts). Extremely rare and strong and didn't come in any factory car except the SLP Firehawk is a Dana 44. It will have 10 bolts and a metal plug in the rear cover.

You're not going to find many suppliers with 9 bolt parts. Your best choice is www.9bolt.com