Rear LSD gear oil - 1997 Volvo 850 AWD

[V50M66]

As far as I remember it actually is an Eaton G80. Locks the same way as one - too much wheel speed variation and it locks together violently and stays that way until you let off the power. You can also spin one wheel too fast by hand with the car in the air and it will lock solid with enough wheel speed difference.

That Volvo diagram is interesting - it appears to show a 7/900 diff, as there’s no provisions on the case in the picture to bolt up the viscous coupling.

[scot850]

So for the untrained in rear diff locking units, what is the difference between the Eaton G80 and the limited slip differential in the way they operate? For me, a great learning opportunity!

Neil

[V50M66]

So for the untrained in rear diff locking units, what is the difference between the Eaton G80 and the limited slip differential in the way they operate? For me, a great learning opportunity!

Neil

The G80 and similar auto-locker style diffs use weights in the center section that fling out when wheel speed difference is high enough, causing the whole thing to lock together instantly. It operates as an open diff until this lockup occurs, so with the car in the air, you can spin one wheel and the other will spin backward, until the weights fly out at that certain speed difference and then it’ll lock it together instantly.

A traditional clutch-type LSD uses clutch packs that engage and disengage more gently when wheel speed difference increases, using clutch packs that allow a certain amount of slip before engaging. Spinning these in the air, both wheels will travel the same direction.

Two different ways to get similar results.

In the aftermarket you can also get helical LSDs, like the Quaife you can put in M56. This uses a complex gear system that distributes torque where it needs to go for optimal grip based on wheel speed and power input.

There’s also fancy computer controlled stuff, but that falls more into the realm of torque vectoring than simply limited slip. Interesting stuff if you have time to do some research though.