Swapping gears and adding a posi to a differential

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Mar 11, 2007 | 02:12 PM

Theman0188

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Joined: Oct 2006

Posts: 96

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From: Monroe, LA

Car: 76 Corvette Stingray

Engine: 350

Transmission: TH350

Axle/Gears: Stock

Swapping gears and adding a posi to a differential

I have a 92 firebird and a non running 89 formula 350. I want to put the posi unit and the gears ( I believe 3.42s) from the formula 350 in my other rear end. Everything is still stock. I dont know if one is a 9 bolt and the other a 10 bolt, one a 26 spline, the other a 28 spline. Needless to say i need some answers. Are they different, and can I exchange them?

Mar 11, 2007 | 07:03 PM

Kevin91Z

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Joined: Jul 1999

Posts: 10,950

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From: Orange, SoCal

Car: 1990 Pontiac Trans Am

Engine: 355 TPI siamesed runners

Transmission: Tremec T56

Axle/Gears: 12-Bolt 3.73

The '89 should have a 9-bolt, and if its a single cat car, it will have 2.77 gears, and if its a dual cat car it will have 3.27 gears.
Its basically a bolt-in, but the brake lines might not match up.

Mar 11, 2007 | 07:17 PM

sofakingdom

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Car: Yes

Engine: Usually

Transmission: Sometimes

Axle/Gears: Behind me somewhere

The 89 should have a 9-bolt, the 92 will have a 10-bolt. NOTHING WHATSOEVER will interchange inside them if that is the case.

You could swap the entire rear over, but not the carrier and gears from one housing to the other.

To tell if they're a 9-bolt or a 10-bolt, count the bolts. If there's 9, it's a {drum roll please} 9-bolt. If there's 10, I'll let you figure out what it is.