4th gen rear in 3rd gen
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Joined: Nov 2000
Posts: 727
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From: Charleston, WV, USA
Car: '86 IROC-Z + Misc. project cars.
Engine: Supercharged + Nitrous TPI 355 CID
Transmission: Art Carr built Th700r4
The rear end itself is pretty much bolt in. There are some differences in parking brake cables though. You would also need rear wheels to fit a 4th gen car. Most 4th gens I have fooled with have had 3.23:1 gears, but some do have 3.42:1 and 2.73:1.
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Joined: Mar 2001
Posts: 2,047
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From: The State of Hockey
Car: 1987 Trans Am GTA
Engine: Miniram'd 383, 24X LS1 PCM
Transmission: TH700R4, 4200 stall
Axle/Gears: 9", 4.33:1
Check out the technical article on this site for more details.
But the axle is identically mounted in the car, and is 3" wider overall than a thirdgen axle. That means the wheels will stick out 1.5" farther on each side with the fourthgen axle in a car with thirdgen wheels. The car can be driven in this form without problems. If fourthgen wheels were used, the offset of the wheels would even out with the wider axle and put the wheels back into a stock position in the wheel wells. The parking brake cables will require some playing with to get them to work if you use the fourth gen rear brakes. The fourthgen rear brake cables will be needed but the bracket above the Driveshaft will work with some minor adjusting.
6-speed cars came with the 3.42:1 gear and the autos had either a 2.73:1 or 3.23:1 gear depending on if it had the performance rear axle ratio option.
But the axle is identically mounted in the car, and is 3" wider overall than a thirdgen axle. That means the wheels will stick out 1.5" farther on each side with the fourthgen axle in a car with thirdgen wheels. The car can be driven in this form without problems. If fourthgen wheels were used, the offset of the wheels would even out with the wider axle and put the wheels back into a stock position in the wheel wells. The parking brake cables will require some playing with to get them to work if you use the fourth gen rear brakes. The fourthgen rear brake cables will be needed but the bracket above the Driveshaft will work with some minor adjusting.
6-speed cars came with the 3.42:1 gear and the autos had either a 2.73:1 or 3.23:1 gear depending on if it had the performance rear axle ratio option.
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