I have an 89 with the 5 speed. I have the 3.08 rear I think. What size are the grears? What I mean is that some are 7 5/8 and other are 8.5. To make this simple I'm looking for the parts to convert to posi with my current rear. What do I need to look out for and what do I need to get? Thanks.

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1989 Firebird Formula L03
Black with 5-Speed
Stock with Functional Formula Cowl Induction, Centerforce Clutch, KYB GR2 struts and GAJ shocks, 89k on the clock and running smooth.

 

You will need to decide if its a 10-bolt or 9-bolt. I think w/ 3.08 gears, its more than likely a 10-bolt. If its a 10-bolt, it will be a 7.65" rear axle.

If your going to get a posi, your best bet is to get a "3" series posi, and some new "3" series gears to go w/ it. Right now, with the 3.08 ring gear, your setup is a "2" series.

If your on a budget or you really like the 3.08 gears, GM did make 2 series posi's. You might be able to find one used somewhere.

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'87 Trans Am
S/D TPI retrofit including functional PassKey,
22# injectors,
Whatever chip I feel like burning,
JET AFPR, Ported Plenum,
TB Coolant Bypass, Custom Cold Air,
SSM SFC, KYB Shocks, Boxed LCAs, Wonder Bar,
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16" GTA rims,
Corvette Servo,
3.73 Posi
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Summit 1-5/8" headers, 2.5" Dynomax catback.

Best 1/8: 9.519@72.74

'97 Bonneville SSE