I am looking to upgrade my 2.73 gears in my '91 Z28. I'd like to go 3.42 or 3.73 and am unsure what size rear I have?

I've seen ring/pinion sets for sale but they list 7.5 and 8.5 rears... help!

 

I believe on the axle housing , passenger side towards the front of the car, there should be a three letter code stamped into it. Get those three and I'm sure someone here can decode that for you. You may have to do some cleaning. If it's stock, and you know that for sure, check the RPO codes in the rear hatch area locked compartment door on the inside. Gear ratio's are generally a "G" plus two numbers code.

 

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The only 10 bolt that was used in the 3rd and 4th gen is the 7.5, or 7 5/8 after '87. The 7.5 and 7 5/8 parts interchange and all ring & pinion sets are made the same.

 

More often than not, rust eliminates axle codes. They can, however, be found in the following 10-Bolt FAQ:

https://www.thirdgen.org/forums/tran...-10-bolts.html

JamesC

 

Q: What gears do I have?
A: Take off the cover and look

Q: Is my carrier 2-series or 3-series?
A: Take off the cover and look

Q: Do I have posi?
A: Take off the cover and look

Q: How can I tell if my rear is in good shape?
A: Take off the cover and look

Q: How many splines do my axles have?
A: Take off the cover and look

Q: Fill in the blank
A: Take off the cover and look

Q: Not sure
A: Whadddya think??


Is there a pattern here? NAAAAHHHHH... just my imagination.



You don't have a 8½". There was never a single one made for these cars. Not to worry; if your cover has 10 bolts in it, it's the smaller one. End of story. OTOH, if it has 9 bolts though, you have {drum roll please} a 9-bolt. Betchya didn't see that one coming.

In case you can't tell, this stuff is REALLY REALLY simple. Just a car. Not brain surgery or anything. And no, I didn't stay at a Holiday Express last night; actually I prefer a Courtyard or a Residence Inn. But I haven't even gone anywhere for the last 5 or 6 days, just stayed at home and went to work and school, so I've lost any benefit I'd have got from wherever I stayed.

There is NO DIFFERENCE, as far as gears, between 7½" and 7-5/8". They are completely interchangeable in every way. I don't think anybody makes 7½" gears for our rears anymore, they're all the slightly larger OD, because the larger ones fit em all.

 

Thanks, to all, for the info. I assume with a R&P change, I can reuse my posi and all, right?

 

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Aha... After swapping to the T5, I'm 100% positive I've got the 2.73s still... So, unless I can find a set of gears for the right price, I may just save the pennies and go for a 4thgen LS1 rear with the right gears so I can get the big brakes too... I'm still just running the aluminum drums currently.

 

You can get thick 3.42, 3.73 and 4.10 gears that will fit the 2 series differential that you have now. They are about $10-$20 more than the standard gears. Don't forget to get a good installation kit.

 

I may be mistaken but I went to "Camaro tech data" on this site for a 1991, Z-28 ,Camaro, TPI, 5.0, manual trans. ,and it ether came with a 3.08 or (3.42 G92 option) stock. Time to pull the cover.

 

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