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I figured that I've built a few trucks, built my own engines, What the Hell I'll build my own rearend or at least give it a shot. Boy it didn't take long for me to get stumped. Called to order the carrier bearing set, that asked 8 1/2 or 8 3/4 ring gear. Its a 12 bolt out of a 75 1/2 ton truck. I did not realize they had 2 different 12 bolts in the trucks.......... Anyway on the ring gear do you measure the machined surface or all the way to the outer edge of the teeth?
 

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It's actually an 8-7/8 (8.875") inch ring gear for the 12 bolt axles.

It's not the same as the car axle and the gears WILL NOT interchange, the ring gear will fit the carrier, and the carrier will fit into the axle housing but the pinion gear shaft and bearings are smaller on the turcks than those on the cars.

The guy that asked you if it was an 8.5 or 8.75 inch ring gear needs to look in the books more closely or something. The GM 8.5 inch ring gears are only found behind 10-bolt housing covers, and 8.75's are a Dodge/Chrysler ring gear measurement, some of which are also found under Jeep Cherokee's in the 1990's.
 

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8 1/2 was not a 12 bolt

8 1/2 was the 10 bolt gm and the dana 44

8.875 is the 12 bolt

the truck one are smaller pinion stem diameter than the car ones

not real strong

car ones are technically stronger, by at least a little

good luck
 
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