8.8 Posi Trac Unit Question
- Thread starter WeinerK
- Start date
Mike Combs
Registered User
Any posi won't work in your car, I actually think that any 8.8" posi carrier will work with the independent rear suspension. If you look at part numbers for Auburn, Powertrax, and other aftermarket posi manufacturers you can see that all 8.8"/28 spline posi's have the same part number for any Ford model.
Double check this, but I don't think that you need a special posi from another SC.
With all of the shim work involved with changing carriers, I would rebuild yours or install a locker if it's an open differential. This is the only way that your old gears will mesh perfectly.
Double check this, but I don't think that you need a special posi from another SC.
With all of the shim work involved with changing carriers, I would rebuild yours or install a locker if it's an open differential. This is the only way that your old gears will mesh perfectly.
FYI, "Positraction" isn't a generic term, it's the trade name for the limited slip differential made by Eaton and used on a lot of older muscle cars. They still make basically the same thing. I have one in my SC, and it's sweet, much better than the Ford unit.
Usually for on-road you want a limited-slip differential, not a locker. The clutches in a LSD respond to engine torque, and lock to prevent wheel spin. This is what gives you a good launch at the track. A locker locks the wheels if one wheel starts spinning. That's what you need in your Jeep if one wheel is on a rock and the other hanging in the air.
Like Ed said, you need a diff with circlip retaining grooves, not one designed for axle C-clips. You should call the company tech line, don't trust what the salesman says - most of them don't know the difference.
Now, about that Eaton Posi - it doesn't have circlip grooves. The shop assured me it would work anyway, but it didn't. So they had to take the whole thing apart and machine the circlip groove into the side gears. This is several hours of labor and tricky machine work - you don't want to pay for this... luckily they had already offered to fix it for free! (But as they said... "never again!")
Rebuilding a Ford Traction-lok can be done for cheap - IF there is no damage to the unit. Often the clutches wear through the metal end plate, and it breaks apart and runs through the spider gears. If this has happened, it's toast. You should also replace your ring/pinion gear in that case. Actually I'd recommend that either way - those 3.55 gears are probably the best $170 I've ever spent on my car.
Usually for on-road you want a limited-slip differential, not a locker. The clutches in a LSD respond to engine torque, and lock to prevent wheel spin. This is what gives you a good launch at the track. A locker locks the wheels if one wheel starts spinning. That's what you need in your Jeep if one wheel is on a rock and the other hanging in the air.
Like Ed said, you need a diff with circlip retaining grooves, not one designed for axle C-clips. You should call the company tech line, don't trust what the salesman says - most of them don't know the difference.
Now, about that Eaton Posi - it doesn't have circlip grooves. The shop assured me it would work anyway, but it didn't. So they had to take the whole thing apart and machine the circlip groove into the side gears. This is several hours of labor and tricky machine work - you don't want to pay for this... luckily they had already offered to fix it for free! (But as they said... "never again!")
Rebuilding a Ford Traction-lok can be done for cheap - IF there is no damage to the unit. Often the clutches wear through the metal end plate, and it breaks apart and runs through the spider gears. If this has happened, it's toast. You should also replace your ring/pinion gear in that case. Actually I'd recommend that either way - those 3.55 gears are probably the best $170 I've ever spent on my car.
Last edited:
redknight
Registered User
3.55's
Rob.
Are you running an AOD or a 5-speed? I'm considering doing this, but I've got a few other headaches to work through first. I'm just trying to plan ahead by gathering some opinions about gear ratios. I have an AOD my self, although there are A LOT of times I would love to have a 5-speed.
Rob Noth said:
Rob.
Are you running an AOD or a 5-speed? I'm considering doing this, but I've got a few other headaches to work through first. I'm just trying to plan ahead by gathering some opinions about gear ratios. I have an AOD my self, although there are A LOT of times I would love to have a 5-speed.
