Hey guys, my 1979 z28 has the 3.43 gearing with the aweful open diff, I wanted to get a Posi unit for it... I think the easiest and cheapest option for me would be to replace the entire rear end with a used unit. (This car is being made for the street and keeping it original is a non factor).

Ive already replaced the block with a 1997 4 bolt main 350, a Crower Cam, Vortec heads, changed all the internals... it's gonna be a quick little ride, but the open diff is frustrating.

Does anyone know what Kind of units would fit that I would likely have a chance of actually finding for sale? Doesn't have to be from a camaro.

Gearing of at least 3.23 is a must... higher would be cool but with a limited budget I can't be too picky.

ALSO: I had a friend of mines father tell me if I took my car to a diff shop and asked them to "tighten the diff" I'll actually be able to spin both tires even with an open diff.

Any help or ideas would be awesome! I can't change gears or anything myself and won't be able to pay a pro to do it.

 

You need to go back and ask him to tell you in detail just how that is done. That's a new one on me. An open diff will pull the wheels evenly, if both tires have the exact same amount of traction. We know that rarely happens, and if it does, maybe for a split second till one tire breaks free. Have you scoured craigslist or ebay yet for a used unit? Replacing the whole rearend would be the easiest route, providing it's not beat to death. I'll have to look see if I have any bookmarks on cross-compatibility. You may find one from a different vehicle with the same or close overall width as yours, but leaf spring mounting points may be different, or may have coil spring mounts instead.

 

Will do- Ill be seeing him again shortly so I'll make sure to post his details on the matter.

Yeah Ive checked alot of online sales... there is one that is from an 80's+ camaro with 4.10 gearing, but I'm not sure if it would work or not.

 

There are some guides on replacing the second gen with a rear end out of some Ford models. I bought a rear end out of a '96 Explorer. It is Posi and came with disc brakes as well. The biggest drawback is that the pumpkin isn't in the same position as the Chevy's, so you'll have to deal with that. For me, I had the short side extended at a machine shop to match spec. Most adjust the rear to work with the Ford leaf and shock mount places as well. I cut all of mine off and bought Chevy spring perches, that will be welded on at a later date. She's not going any further than my driveway for some time since she has no engine, trans or driveshaft atm. So I'm not worried about it now. That allowed me to use the stock mount areas and hardware for everything. You will probably want to pick up a Ford to Chevy bolt pattern adapter as well. One thing I found on mine though, I need to pick up 1 1/2" long lug studs. 2" ones stick out past the face of my adapter and doesn't allow the wheel inner face to properly seat with the adapter face. That is easy enough to do though. It is just something I haven't bothered with yet, as I've been focusing on getting the front suspension together.

I'm sure more can chime in with exact details though. 1971BB427 was my source for a lot of my help. Looking around the web also found quite a few others who had done pretty much the same swap. A mid 90's Ford 10 bolt rear out of Explorers (and I think F150s) are equivalent to a Chevy 12 bolt rear and, as I mentioned, usually comes with posi-traction and rear discs.

For a price break down:
rear axle - 350$
Welding - 350$
Cleaning supplies (**** tons of carb cleaner) 30$
stud adapter - 75$
new axle shaft for extended side - 30$ from junk yard (my short side is within a few MMs length of my long side after being welded, so another long side shaft fit perfect.)
Lug studs - will run me 50$ when I get to it

I also cleaned it up and coated everything in POR 15.

 

There are several other GM rear axles that are a direct bolt in. The '70-'81 Camaro all interchange, as does the Firebird from same years. Might find different yoke sizes, so an adapter U joint will need to be installed if the rear has the larger TH400 size yoke. Simple swap, and cheap U joint.
As Geawiel mentioned, the 8.8" Ford is an excellent choice, if you don't mind fabricating the mounts, and also reworking the driveline, plus the 5x4.5" bolt pattern. If your wheels are dual pattern, they will work anyway.
Around my area, a 8.8" Ford from an Explorer or 4x4 Ranger is $200 at pick n pull, and on holiday weekends, they're half priced. An extra long side axle is $20, and then lengthening the tube 2 7/8" longer on the short side, is less than $100. Buying perches is about $10 for generics, and no reason for Camaro perches. They wont fit the larger 3.25" tube anyway, and if you get an 8.8", you should also grab U bolts and spring plate from the donor too. Lots of Explorers came with 3.73 or 4.10 posi, and they are a copy of the 12 bolt GM rear axle, except larger 31 spline axles, and tubes. Codes can be found on a Google search, so you can check the door tag prior to removing one from a Ford. Pre '94 are drum brakes, and later are disc brakes. So if you want to convert to 4 wheel disc, you can simply buy a later axle, and then replace the proportioning valve to adjust the braking after the swap. I used no prop valve at all on the '69 Nova, and it stops great with a stock power master cylinder.
I put one in my BBC powered Falcon gasser, and have put them in a '69 Nova, and a '70 Camaro. They'll handle all the power and torque you'd most likely see on most street vehicles, at a very affordable price.

 

Thanks for the replies! Ok... so we managed to get a used posi off of a 1979 Camaro...

How hard would it be to swap my 3.42 gearing into the 3.08 posi? is it something we could do at home? if not... how much would the labour cost roughly? we already have the parts so presumably it would just be labour.

 

I'd give them a try. Might not be the set you back in the seat launch you're looking for, but surely will help highway driving, and you might thank him later.
The difference between 3.08 and 3.23 can't be felt, and not sure the 3.42 would be much difference in feel. If the 3.08's don't get your car launched as you want, I'd go to either 3.56 or 3.73 gears. Mileage will suffer, but you'll notice a big change in launch feel.
I'd guess if you have to ask about whether you can do the gear swap, then you probably shouldn't. It takes some tools you probably don't have, and a fair amount of mechanical savvy with rear axles. Many guys who have hot-rodded for years wont try gear swaps, as it's easy to mess up a new gear set, if you don't get the lash and preload set properly. It should be less than $200 to have the gears swapped, if you currently have the parts, and they're in good shape.

 

The 8.5 Chevrolet 10 bolt rear end is pretty strong.In fact it replaced the 12 bolt rear end.I have a 1979 Z-28 RS Camaro Pro-touring car with a 500 HP plus 377 cu,inch Supercharged Small block Chevy. With a Super T-10 4 speed and an 8.5 10 bolt with a Moroso "Brute Strength" posi,31 spline Mosier axles and 3:42 Chevrolet gears.17" wheels and tires .And a 26"tall tire it cruises along at 2600 RPM at 60 MPH.I used my original rear end housing .So I know it will fit. And Z`s have a bigger diameter drive shaft with larger U-joints.I have never had a problem with this set up at all.

 

Or keep what ya got and just get a lock rite locker for you're diff ,easy to install by home mechanic,changing gears,leave that for a qualified shop . If you are just going to stomp around town 4.11s are alot of fun 3.90s are also nice, little less tire spin.