Rear Differential Rebuild/With Pictures

[Wanganstyle]

No heat has nothing to do with it. Its an unwanted byproduct.

Google search how a viscous lsd works: Suabru and many others use them. Bmw uses a GKN VISCO-LOK viscous on e46m3 and e60 m5; im quite familiar with it.

If it was not heat expanding the silicon viscous fluid then how else would it lock up? MAGIC???

The viscous unit is a sealed capsule with fluid and discs inside. The silicon fluid gets hot and expands: locking happens then

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[TehRaydarlover]

We are both saying the same thing.

Viscous silicone fluid still needs heat to work.

Heat comes from wheel speed differences


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No heat has nothing to do with it. Its an unwanted byproduct.

[Wanganstyle]

A viscous lsd uses a shear thickening silicone fluid not heat, hence VISCOUS lsd. The fluid increases viscosity with shear rate. The diff will lock after it reaches a high enough shear rate.

A viscous lsd uses a shear thickening silicone fluid not heat, hence VISCOUS lsd. The fluid increases viscosity with shear rate. The diff will lock after it reaches a high enough shear rate.

We are both saying the same thing.

Viscous silicone fluid still needs heat to work.

Heat comes from wheel speed differences


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[TehRaydarlover]

A diff with old pinion bearings and races and Old LSD internals is NOT rebuilt

BMW's kill the pinion bearings and races first; no amount of paint or clean up will "FIX" this.
to replace them with NEW is the proper procedure; a NEW crush washer is needed to set the drag load.




a Clutch type LSD unit locks because the basket of spider gears in the middle wants to expand when One wheel is significantly different than the other; One wheel can be airborne and unloaded; it will Lock if internally proper.

A viscous LSD uses HEAT from the wheel speed difference to lock up plates in fluid; its a REACTIONARY item that locks AFTER enough heat is put into it.

A viscous lsd uses a shear thickening silicone fluid not heat, hence VISCOUS lsd. The fluid increases viscosity with shear rate. The diff will lock after it reaches a high enough shear rate. An increase in temperature would if anything make the fluid less viscous.

[Wanganstyle]

A diff with old pinion bearings and races and Old LSD internals is NOT rebuilt

BMW's kill the pinion bearings and races first; no amount of paint or clean up will "FIX" this.
to replace them with NEW is the proper procedure; a NEW crush washer is needed to set the drag load.

I could, but BMW used a VC back there for a reason - to some extent a clutch diff still needs one axle to have a load on it. a VC doesn't.

a Clutch type LSD unit locks because the basket of spider gears in the middle wants to expand when One wheel is significantly different than the other; One wheel can be airborne and unloaded; it will Lock if internally proper.

A viscous LSD uses HEAT from the wheel speed difference to lock up plates in fluid; its a REACTIONARY item that locks AFTER enough heat is put into it.

[FredK]

Now that I've got someone's attention. Anyone know how to get the pinion out?

Either pound it out with a heavy dead blow hammer exactly in this state, or use a hydraulic press.

[z122643]

So, I installed my rebuilt diff and now I can hear my radio... funny how that happens.

Despite how bad the old diff looks the LSD is in excellent shape. I intend to rebuild this one and either keep it for a rainy day or sell it.

[z122643]

If it is good it will slip but very slowly and with a lot of resistance. Remember it's a LSD not a locked differential.

[Sean]

Ok, so, basically, it will act like an open diff is the VC is bad. If it requires a lot of resistance, but starts to slip at all, it's on it's way out. I have two LSD's, one in my car and one sitting in storage - I'll have to check them both out.

[z122643]

Car must be in gear with the front wheels on the ground. Then try turning one of the rear wheels, it will be very stiff and will slowly (very slowly) rotate the opposite wheel is the opposite direction.

If dead if will just spin the opposite wheel with no resistance.

[nando]

I think in neutral if you jack up one side of the car, you should be able to turn a rear wheel and it should be stiff.

I think mine is done because of the way the car reacts under throttle, it doesn't throttle steer as it used to and over rough surfaces I can't put power down. but it has 250k+ on it..

new ones are in the ballpark of $500.

[Sean]

How do you guys know that the VC in the diff is going out? I think mine is likely shot...but not sure.

[z122643]

So, I did not remove the pinion and just decided to replace the seals. Cleaned up nicely.

Also does anyone know what the "P" stands for?

[flyboyx]

for your purposes, i would not remove the pinion if i were you. i would just clean it really good, replace the seals and put it back together.

[DER E30]

Kool, I need to do that to my 4.27 lsd... it's stupid loose :(