My 85 iroc is making a clunking sound in the rear.Can someone tell me what size rear it is so I can buy the correct parts. It's a 10 bolt with 3.42's. I'm wanting to switch gears and put a posi in but have no clue what rear I have or what posi I need. I'm thinking either 3.73's or 3.90's if they make it for my rear.Anyone have any sugestions or info for me? Thanks

 

7 5/8 ring gear.

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'89 SHAGGY IROC
L98, W/C T5, all free stuff,T.E.S.,HOOKER CAT BACK,KYB,ACCEL8.8,JET fan sw. etc. 14.8@ 95.7MPH w/ auto, can't wait for the first T5 run.
so much to do , so little money

 

Usually still refered to as a 7 1/2"

 

Nothing wrong with 3.42. You wouldn't want anything bigger if it's an automatic. Have a look at the axle code (stamped on the front of the passenger side axle tube). For 3.42 gears, if it's 8JC or 8KA it's open; if it's 8PR it's a limited slip. If it's an Eaton limited slip, you can't tell by just turning the wheels; you have to spin one of them at over 100 rpm before the clutches engage. In my opinion, 3.73 is the ideal ratio for a stick if you drive it on the road much.

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1985 Yellow IROC-Z 5.0 HO, T-5 3.73 Torsen, 4 wheel disks
PFCM pads, GTA wheels, Koni yellows, B&M Ripper, Dynomax

 

I checked my bill sheet that I found under the rug and it says GU6 3.42 Axle Ratio, but no where could I find any other rear codes. When I jack the car up and spin the tires they go opposite ways. I have the J65 4 wheel disc brakes. Whats the GU6 mean?
Thanks guys