12 Bolt Rear End Gear info needed!

[proud71owner]

Hey yall, im in need of a 3.07 or 3.08 gear for my 71 c/10. ...i have a 3.73 or 4.11 now. will a 3.07 or 3.08 fit the carrier i have now?

[piecesparts]

Suggestion from some experience that I have attained over my life. I recommend a new set, vice used ones. It takes a reall good rear end guy to get the gears aligned back to the same grooves that they originally run in at. If you don't get them back in alignment, you may have some rear end noise. Been There--Done that.

[raycow]

In short, no. The differential case break on the 12 bolt is between 3.42 and 3.73. It's been my experience that if you have to buy gears and pay someone else to set them up, it is generally cheaper to buy a complete rear that has the ratio you want.

Ray

[texas71]

You will definitely need the corresponding carrier. I have done this many times and have never had a issue, don't use mixmatched gears, use only a known set (GM), a carrier from another set is fine as long as it is the right one and I don't use any of those ring gear spacers, new crush sleeve with proper torque, and use the shims (put them back in the same locations), bearings, and of course bearing caps out of your existing housing, new bearings have never been a problem but don't mix new bearings or races with old ones. I have a old Chilton manual from the early 70's that shows how to check the gear mesh pattern and gives a backlash spec if you want to check it just find one of these books, from experience checking backlash it always sounds and feels like alot more than it really is. I have done this many times and have not had a problem yet, with the exception of a corvette with aftermarket gears that required shimming but that was to be expected. Knock on wood but I haven't swapped a whole housing yet because of gear ratio. Just my $.02 worth.

[cdowns]

the cheapest way is to find a complete rear out of a parts truck

[LONGHAIR]

Originally Posted by texas71

You will definitely need the corresponding carrier. I have done this many times and have never had a issue, don't use mixmatched gears, use only a known set (GM), a carrier from another set is fine as long as it is the right one and I don't use any of those ring gear spacers, new crush sleeve with proper torque, and use the shims (put them back in the same locations), bearings, and of course bearing caps out of your existing housing, new bearings have never been a problem but don't mix new bearings or races with old ones. I have a old Chilton manual from the early 70's that shows how to check the gear mesh pattern and gives a backlash spec if you want to check it just find one of these books, from experience checking backlash it always sounds and feels like alot more than it really is. I have done this many times and have not had a problem yet, with the exception of a corvette with aftermarket gears that required shimming but that was to be expected. Knock on wood but I haven't swapped a whole housing yet because of gear ratio. Just my $.02 worth.

If you have done that more than once (and got by with it) you are very lucky indeed. I have done hundereds of gear installations and it never works out like that....