Tuesday, June 7, 2011

Swapping an Open Rear Differential into a Positraction / Limited Slip Differential

My Camaro has a 3.42:1 open rear differential. The 3.42 is good for acceleration without sacrificing too much gas mileage but there is just one little problem with an open rear; the one wheel peel.

It's almost embarrassing, laying only one streak of rubber. This is a muscle car!

So, to remedy the peg leg, I bought a 2.73:1 rear end with a posi 3 series carrier. Well the posi is great, but having such a high gear just won't do.  So this is where the swap comes in.

The goal here is to remove the carriers from both rear ends, swap the ring gears, and then put the posi carrier into the 3.42 rear end.

 It is a lot easier to swap carriers, instead of ring and pinions. Once you swap carriers all you have to worry about is getting a backlash of around .008" - .012".  Replacing your ring and pinion is a lot more in depth and requires a hydraulic press, among other things. Hard to do out of your garage and very easy to mess up. I recommend having a shop do this for you.

On to the swap!

What I used:

Dial Indicator with Magnetic Base
Torque Wrench
Needle Nose
Socket Set
Pry Bar
Brass hammer
Flat Head Screwdriver

First Steps

- Removed the differential cover and drained the old gear oil.
- Removed the c clamps on both sides of the carrier.


- I rotated the carrier until I could find the the small bolt that hold the center pin in. 
- After I removed that the pin was easy to pull out. Don't pull the whole pin out though. Just need enough so you can push the axles in. 
- I pushed the axles in and the  axle c clip retainers fell out into the housing.
- I removed the axles, and the carrier was ready to come out.
- I removed the Carrier. It was a little tough to get out, so I had to use a pry bar. Careful not to pry on the ring gear, or spider gears.

Carrier is out. I removed both carriers from both rear ends.

The limited slip is on the left, and the open is on the right. You can tell it is a limited slip by the spring in between the spider gears, and the limited slip has a lot more supports running through the gear mount.

Also, an original limited slip carrier for an 8.5" GM corporate rear end will have the cast number 410408N.


- I removed the ring gear from the carrier. Careful, the bolts are left handed, so "lefty-tighty, righty-loosey"
- The ring gear was pretty tight on there, I had to use a brass hammer, and a flat head to help knock the ring gear loose.

After you get it off, I don't recommend putting it on the floor like I did. You'll want to try to keep the gears and carrier a clean as possible.

At this point I swapped the ring gears, and began putting everything back in. Everything went back in the same way it came out except the limited slip carrier has the 3.42 ring gear and is going into the original rear end on my Camaro. 

After I got everything back on, I used the dial indicator to check the backlash. 

Well, I didn't have a magnetic base, so I used vice grips, a clamp, and a 2x4. Not the most accurate, but it did 0 out, so I figured it was fine. I got a backlash of .0095" which was within the range and fine. If it the backlash was out, I'd have to shim the carrier until it got to the proper backlash.

Everything looked good so I put the cover back on, lubed it up with 2 quarts of gear oil and a bottle of GM friction modifier so the clutch pack slips properly and doesn't chatter.

And since I had pulled the rear end out, I wire wheeled it, cleaned it up then painted it. I used Rustoleum hammered paints.


I'm not an expert. I'm just an enthusiast having fun with his Camaro. Use any advice at your own risk.

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