My 86 z28 (new 360hp crate engine) now is rearendless.... i was thinking about swapping a 76 8.5" 10-bolt posi from a nova, or just buying a used 12-bolt, instead of just building a stock 10 bolt up, not sure yet.

My question is, How long or i guess wide is the stock rear axle housing from end to end? and has anyone done this type of swap before without any major issues? Any help or suggestions is greatly appriciated.

Just to add, i have a friend up the road who's been racing for about 25 years now and he said he will cut and weld anything that needs to be.

 

the single largest issue with what you want to do is how to attach the torque arm. There is simply no way to do it well, because it requires welding to cast iron, something that it not easy to do or very relieable.

If you want a better rear, you will need to buy a correct bolt in rear, either a 12 bolt, dana60 or ford 9", with the torque arm provision.

Moser, Strange, and Currie sell these rears


as for the width, mine is 62" +/- rotor to rotor

 

If swapping in a non third gen diff was so easy, just about everyone on TGO with any kind of performance would have already done it.

As mentioned above, the torque arm suspension of a third gen makes it expensive or impossible to use a diff that's not from a third or fourth gen f-body. There's no easy or cheap way to attach the torque arm onto any other differential other than a 9" with a special adapter mount which needs to be welded onto the steel housing of the 9". The adapter is available from Currie.

You could put anything you want under the car if you change the rear suspension to eliminate the torque arm but choices are limited and the easiest way is with ladder bars but that still requires a bit of fabrication. Cheap alternatives such as aftermarket LCA like the "Traction Action bars" are not strong enough to replace the torque arm.

If you're making enough power where the tiny 7.5" 10 bolt won't survive, you'll have to start saving for an aftermarket bolt in diff. Expect to pay around $2500 for a complete differential. The 9", 12 bolt and Strange Dana 60 are all roughly the same price.

A cheaper alternative is to buy a third gen 9" housing package. It includes the bolt in housing and axles for around $1000. You supply a center section and brakes.

 

thanks guys, do you think that a modified third gen 10-bolt with some mods like new axles, zexel torsen, and richmond gears would be ok with 360 hp 400 tq. i was suggested 4.10 gears with my th350

 

its a crap-shoot. steve87 posting above, had his car running 11's or maybe a little better on a beefer 10 bolt, but he is also running a powerglide which launches a bit easier that a th350/400. If you use some good sticky tires and launch hard, its only a matter of time before the ring and pinion gernade

 

I feel differently. I suspect you already have that older 8.5" available to you, and there's no reason a good fabricator in your area couldn't make you a torque arm bracket.
Use the gasket as a template, use 1" steel. Yes, this'll add even more weight, but with that made, the Currie bracket for the 9" ford could be welded to this donut thing.
I've considered this, but haven't needed to try it myself, YET. With this 454 going in my '84 Trans Am, and with junkyard 8.5s going for $75 as opposed to spending over $1500 for either a properly-done 9" or a 12-bolt....

 

I was using a TH350 with the 10 bolt. By the time I installed a powerglide, I already had a 9" under the car.

Yes it's possible to do some sort of fabrication to make a torque arm work with some other diff but you do take the risk of something failing. The suspension has a lot of forces put onto it and you want to make sure whatever is fabricated can handle the stresses.

Typically by the time you're done swapping over brackets from a 10 bolt donor diff and fabricating some sort of torque arm mount, it could be easier and cheaper to just buy a proper bolt in diff. That is providing the diff you decide to use is the proper width and doesn't need to be narrowed as well.

 

well i don't really plan on slamming the car around to much. Im hoping to be L60's on the rear. Based on what everyones saying im thinking that it would be a safer and cheaper rout to build up a third gen 10-bolt. Im also leaning towards the third gen 10 bolt only because my engine only makes 360hp at the crank, so if properly built, it wouldn't have any issues right?

 

V6 cars have broken 10 bolts on the street and it's survived behind BBC cars on the dragstrip. No matter what you do to try and beef it up, it will still have the tiny ring and pinion and that's always going to be the weakest link in the diff.

Aftermarket 28 spline axles, solid crush sleeve, rear cover with bearing cap supports like the one offered from LPW and welding the axle tubes will help but it's still only a bandaid patch for the small diff.

You can also use the diff exactly like it is and if or when you break it, decide if the added expense for a better diff is worth it. Running a high HP engine means more than just the engine. The entire driveline needs to handle all that power.

 

And there's one other option, if you can track one down: There were some Dana 44s made for these cars. Not installed by GM, but cast with a torque arm pad. They had an 8.5" ring gear.

 

yeah, good luck finding one. And if you do it will be trashed, or cost more than a new bolt in 12 bolt or 9"

 

If you do find one in good condition, it will probably cost the same as a 12 bolt or 9" unless you really luck out and find one in the junkyard.

The Dana 44 was put into the SLP Firehawks and was available over the counter from GM. It's been discontinued for some time now so the only ones you'll find are now in cars.

7.5" 10 bolt - Smooth rear cover with 10 bolts holding it on
9 bolt - Has 9 bolts holding the rear cover on and has a rubber fill plug in the cover
Dana 44 - 10 bolts on the cover and has a metal fill plug in the cover.