I have an 7 1/2" auburn posi 3:40 out of a s-10 that I can put into my camaro's 7 1/2" rear end. I also have a '89 Formula 3:27 posi that is 7 5/8". Both will recieve 3:73's, but which is a stronger rear end that will withstand more torque. If anybody has learned from experience or knows which is better to use I appreciate it a lot.

 

The S-10 gears will only fit in a 7.6" (or 7½", or 7-5/8", or whatever else you want to call it) 10-bolt GM rear end. The 89 probably has a Borg-Warner 9-bolt, so it will not fit there.

People say the 9-bolt is stronger. I personally don't know. I do know that the brakes on a 9-bolt suck, they have got to be some of the worst disk brakes ever conceived.

There is no 3.40 ratio in a 7.6" 10-bolt. It might be a 3.42.

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"So many Mustangs, so little time..."

 

Use the 7-5/8 rear end out of the 89 car. Both of those rear ends are 10 bolts, but the 1989 is stronger. In 1988 GM changed the design of the 10 bolt by adding 28 spline axles to it. When they added the 28 spline axles they called the rear end the 7-5/8 instead of the 7-1/2. The 7-1/2 rear end is still a ten bolt but it will have 26 spline axles instead of 28 spline axles. The Borg Warner rear end is a nine bolt design and has a 7-3/4 diameter ring gear with 28 spline axles.

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