i got a question here i have a grand to rebuild my rear bullet proof i cant really afford the 12 bolt. but isnt that just the housing cant i buy the same quality parts the 12 bolt uses and stick em in my 10 bolt housing or is there something i can do thats really damn strong for a 1000 bucks

help isappreciated

 

No. The ring gears are different sizes, I believe the axles are different, Etc, etc. They are just two totally different rears.Only way to get a 12-bolt is to break down and spend the $2k

 

Your stock 10 bolt housing is a 7.5" or 7.625" ring gear. The 12 bolt is 8.875. The ring gear and carrier can't even physically fit inside the 10 bolt housing.

GM produced 3 differnet 10 bolts. The 7.5" which is the late model diff, the 8.5" which was the most popular and an early 8.2". Nothing about these three 10 bolts have anything in common except how many bolts hold the rear cover on. The shape of the rear cover isn't even the same between them.

The only way you're going to get a 12 bolt or a 9" that's a direct bolt in is to buy an aftermarket housing. Your other option is to find a junkyard diff and completely change your rear suspension to find some way to mount it. Third and fourth gens use a torque arm suspension. There's no easy way to mount the torque arm onto a junkyard diff.

The absolute cheapest way to go is to buy a 9" housing with axles. That should be somewhere around $1000. After that all you need is the center section. You could pick one up from a junk yard or find one at a swap meet that has a posi and gears that you would want. The main thing is to get the carrier and axles with the same splines. Small is 28 spline. Large factory is 31 and will do for most people.

Getting an aftermarket 12 bolt housing and axles isn't much better and will probably cost more to piece it all together.

 

Not completely true. A 12-bolt? Yes. A 9"? There is another way. My buddy just put a 1989 5.0 9" in his '93 Z28. Seeing 3rd and 4th gen rears interchange, I imagine if it fits in a 4th gen, it could easily be put in a 3rd gen. He had to do some modifiying. Only grinding down one part I believe. He's registered on here, I'll try to get him to post how he did it.

Either way though, he's got a 3.89 Posi 9" in his car. And he got the rear for $200.

 

im so confused guys. is there a way to make my 10 bolt hold up to 300 to 400 horse i defiently will be going with 373 or 342 i have to get the posi differential eaton or auburn whos stronger weld the tubes get the gridle and maybe some new axles i was told solid crush sleeve and all new bearings and seals with this work for me for a thousand gimmie me some more info to

 

Before I switched to a tranny with a transbrake which needed a stronger diff I ran a 7.5" 10 bolt. I ran 11.2's before finally installing a 9" for a better gear selection.

Welded axle tubes, LPW rear cover, solid crush sleeve, 28 spline aftermarket axles.

Putting in a junk yard 9" is easier than a 12 bolt. The 9" housing is steel. The 12 bolt is cast. An aftermarket mounting bracket is available that can be welded to the 9" housing that allows you to attach the torque arm to. All the other mounting hardware for the springs, shocks and LCA can easily be swapped over.

The biggest thing about swapping in a junkyard diff is making sure it's the right size. The third gen diff is narrow so there's not a lot of factory diffs the proper size. A factory 12 bolt diff the right size is out of a first gen f-body. Good luck finding one of those. 9" diffs are a bit easier to find. A car diff is the best because it puts the pinion in the center. Early Cougers and Mustangs are about the right size but there are many othersI use a 9" housing out of a 1970 F100. The pinion is offset to the passenger side 2". If you have to go through all the trouble of shortening a diff, it will be cheaper to buy an aftermarket one.

 

you mean a ford 8.8. its basically a ford copy of a 12 bolt.