jsanders

I'm looking to put a posi rear end in my 92 RS after I swap my 350 in. I know a lot of the old school muscle car guys loved retro fitting a shortened 9-Inch rear end into their cars. What is the process of fitting a 9-Inch into our 3rd gens?

built91Z28

If you want a 9", the best way is to just buy a housing made for our cars. I have a Moser and it went right in, no problems. But thats a lot of money unless you really need it.

EvilCartman

iTrader: (1)

Well, you can order one and just basically bolt it in or pick one up from the junkyard, strip off the old brackets, weld on new ones and figure out a way to attach the torque arm. Then you need axles with a Chevy bolt pattern, order new or have a machine shop drill a new pattern. I went with a bolt in package from Currie, all came to the door via UPS and bolted it in that night.

jsanders

From the looks of it maybe a 9" is a bit of an overkill for what I want to do with this car. At least for the price it will be to fit it in the car properly. What other less costly, maybe easier rear end swaps can we do that will give us posi traction? I know there is the 10-bolt but I hear these are weak, and then there is the 12-bolt out of the old bbc cars and 4x4 trucks. Should I maybe just look for a 3rd gen Z28 or IROC posi rear end to swap over? I also would not mind having rear disc brakes either.

JamesC

iTrader: (5)

Answers to swapping rears (third- and fourthgen), brakes, combination valve, parking brake cables, and speedo gears can be found below:

https://www.thirdgen.org/forums/tran...-10-bolts.html

JamesC

jsanders

I thought that was JUST about 10-bolt rears. I'm actually wanting to stay away from a 10-bolt I just keep hearing issues about them. I'm thinking it would be best for me to go with a 12-bolt.

JamesC

iTrader: (5)

I was replying to the above. Your choices are 9- or 10-bolt. Regardless the braking system will be the same.

JamesC

jsanders

Oh! lol, sorry yeah I'm reading over the whole thread again. I think I am just going to stick with a 10-bolt and have it built for my 350. I plan on having only around 350-370 hp anyways with a 175 shot.

built91Z28

12 bolt, 9 inch, or any other axle excpet a F-body 9 or 10 bolt will be the same story. Either buy a bolt in axle, or grab an old one and fab the brackets and torque arm mount. The 12 bolts that came factory on some cars are still not going to have the torque arm mount.

jsanders

Built 10-bolt it is! But I'm having trouble finding a Torsen heavy-duty diff... SLP does not seem to sell them anymore, is it a discontinued item?

jsanders

Ok, I'm now looking at the EATON diff for our 10-bolts. And please correct me on this because I'm a bit confused with what I'm reading.

I've read that the 8.5" 10-bolt NEVER came in any third gen F-Bodies. So do we have the 8.2" 10-bolt, or the 7.5" 10-bolt? I'm guess the 8.2" because the only options that EATON has for their posi is the 8.5" 28 spline, and the 8.2" 28 spline. Which do we have?

jsanders

Never mind, we have the 7.5/7.625... Hmm... How much of a pain is it to swap in the 8.5" in place of the 7.625?

sailtexas186548

iTrader: (2)

the only 8.5" is a dana44 rear thats hard to find for these cars. to swap in any other 8.5" your looking at the same process as swapping in a 9"/12 bolt/ford 8.8" etc.

jsanders

I figured as much, well I found an EATON 7.5/7.625 10 bolt 28 spline posi diff for $200. Seems like a good price to me, so that is step one in rebuilding my rear end to handle a bit more power after the 350 is dropped in...

Thanks for all the help, between reading the FAQ and asking questions I feel I'm starting to understand things a lot better.

AlkyIROC

Older cars were easier to swap in a better diff because many of them used leaf spring suspension. Reposition the mounting pad on the axle and bolt them in.

Third gens however use a torque arm suspension. No matter what kind of better diff you find in the junkyard, you'll have a hard time coming up with a strong and easy way of attaching the torque arm onto the diff.

As mentioned above, the best and cheapest way is to buy a housing made specifically for a third gen. The cheapest way is to order a 9" housing package. You get the bolt in housing and axles. It's designed to use your current brakes so they're just swapped over. The only other thing you need to provide is a center section. I found a 9" center with 4.10 gears and a 31 spline posi out of an old Bronco in the junkyard and it only cost me $100.

If you buy a complete, ready to bolt in diff in either 9:, 12 bolt or Dana 60, expect to pay close to $3000. The basic 9" housing package with axles is only around $1000

Ron U.S.M.C.

While your in there you might want to up grade from 2.73 ratio to a 3.42 and put on a LPW support cover.

jsanders

Wow, thanks for that info I defiantly did not find that info anywhere else. But I think for the power I will be making a built 10-bolt will do just fine for me.

jsanders

Yeah, already on the list haha

AlkyIROC

I pushed a beefed up 10 bolt into the 11 second range while street cars have broken them on the street. No matter what you try to do to the 7.5" 10 bolt to make it stronger, it will still have those tiny teeth on the ring and pinion. If pushed too hard, the teeth will fail before anything else in the diff will.

Best suggestion I give anyone considering a diff upgrade is to drive what you currently have. The 10 bolt can be stronger than most people believe. If you do however manage to break it, then you can consider how much it will cost to have a diff capable of handling the power.

There comes a point when you order a part because you need it no matter what it costs. You have 2 lists. What I need to have and what I'd like to have. Eventually the "like to have" list gets small. I walk into the local speed shop and ask if they have a specific part. They say yes and it costs $$$. I just say "OK, whatever, go get it from stock".

That $1000 or $3000 diff upgrade may seem like a lot now but it can be a lot cheaper in the long run than trying to fabricate a way to use a junkyard diff or spending all that money trying to beef up that tiny 7.5" 10 bolt. If it's done now, you have lots of room for upgrades later without having to worry if the factory diff will last.

Even a factory 9" isn't indestructible. I caught a cracked pilot bearing support before it failed and I was only pushing the diff into the mid 9 second range. The heavier the vehicle, the slower the ET will be before the diff can fail.

jsanders

Good way of putting it in perspective.