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Advice on replacing the rear differential

Hi All,

I want to know how precisely a replacement differential’s case must match the size of the old case. How tightly must the axle fit into the differential case? Can there be any play at all?

Here’s the situation: I ordered a limited-slip differential for an icy-road upgrade, but when I got the old differential off and tried to press on new bearings, I discovered that the new differential case was slightly larger than the old; the diameter of the sleeve on the outside of the new case (where the bearings must be pressed on) is 1 3/4", whereas the old one was 1 1/2". If I buy new bearings and racers, do you guys think there is any chance the diff case will fit? Also, the inside of the sleeve (where the axle goes in) is 1 1/4" on the new differential, whereas the old one was 1 3/16". That’s an extra 1/16" of play for the axle if I measured right, and of course I’ll need a different set of bearings for the new case. Can this LSD work, or do I need to return it and try again?

Finally, my differential plug appears to have rusted shut. Any advice on getting it open?

Thanks for the expert opinions.


I’d return the differential and get the one that actually matches up with your vehicle.

I assume you’ve driven with a limited-slip diff on icy roads. I didn’t like it because when both wheels spun, it could get dicey quickly.

If going with a non slip for icy conditions you are going to find something out…My 89 Mustang GT has a non slip and when I lived in NJ it was a nightmare. Both wheels would spin and would end up with the rear following the curvature of the road and end up against the curb. Actually if on a flat road the rear would try going in circles…Great for drag racing but not on icy roads unless using chains. I even had the winter snows on, With only one wheel spinning the other would keep the car straight in the rear.

There’s no way that differential is going to fit in your car. Try again.

Limited slip is made for deep mud, snow and acceleration on dry pavement. It is not made for ice. One rear tire needs to have maximum directional traction when accelerating on ice. Traction control, not mechanical limited slip is your best option. Stay with the standard differential as suggested by most.

I’m afraid I misspoke. Ice is not the main problem in Buffalo; it’s sudden, heavy snowfall that leaves four or five inches of powder on the road. They salt the roads heavily, so until it falls below -18 with the windchill (which happens, but not often) the roads aren’t icy. So I think I’ll try out the LSD anyway, but I’ll keep the open differential in case it turns out to be a mistake.

I appreciate the advice from everybody. I’ll try to find a better fitting differential.

Do you already have new winter tires? That’s the first place I’d spend my money.

I’ll be investing in winter tires as well.

What are you working on ?
Did you buy an o.e. locking diff or some racing thing ?

A differential change should be a snap with no alterations.
Not only should the bearings and axles fit , but the ring gear geometry must be perfect too.
Already too many red flags. Don’t go any further . return it and get the right one.

I’m working on a 1996 Sonoma 2wd. I bought a duragrip positraction from Yukon, but you’re absolutely right: after consulting the manufacturer’s catalog I realized did buy the wrong differential. I’m going to return it.

As long as I’m returning it for a new one, can anyone tell me whether a helical gear system like the Detroit Truetrac might have a better chance of improving traction while driving in snow over a clutch-based positraction LSD like Yukon’s model?

If the Detroit system is a locker-type system, you will get better driveability with the clutch-style LSD. Those lockers are great in mud, sand, and snow, but will get you in serious trouble on wet pavement. The LSD is much more forgiving for street use.