Viscous limited-slip rear diff - useful life?

[y_p_w]

I already posted this question on the main maintenance page, but then I realized there was relevant sub-forum......

So I've been thinking of how long the limited-slip rear differential is going to last in my 2004 Subaru Impreza WRX. I've been doing some reading that the viscous fluid (due to loss of fluid properties from overheating) in many LSDs might have a useful life of about 60,000 miles before effectively reverting to open-diff operation.

I don't really abuse the car, race it, or do anything that would cause premature wear (I think). I would think that my type of driving might mean it would last longer. My main worry isn't about street driving, but the occasional times (Sierra Nevada in the winter) where I'm on snow/ice. It's approaching 60K miles, and I'm wondering when I would know it needs to be replaced.

I looked up a Subaru parts retailer, and rear differential cases with LSD go for about $700 while rear differential cases with open diffs are under $200. I'm not sure what the labor would go for though.

 

[unDummy]

Gear oil should be changed every 30k miles or 3years.

Viscous fluid isn't serviceable. But, many that are mechanically inclined, have figured out how to drain/refill the viscous diffs.

Viscous fluid should last forever. What usually happens is it leaks out, mixes with gear oil, and everything goes.

If you are capable of changing it, there are various visc's that you can tailor too. Many like to go with thicker viscous fluid for more effective slip limiting.

 

[y_p_w]

Originally Posted By: unDummy
Gear oil should be changed every 30k miles or 3years.

Viscous fluid isn't serviceable. But, many that are mechanically inclined, have figured out how to drain/refill the viscous diffs.

Viscous fluid should last forever. What usually happens is it leaks out, mixes with gear oil, and everything goes.

If you are capable of changing it, there are various visc's that you can tailor too. Many like to go with thicker viscous fluid for more effective slip limiting.


I've seen the gear oil fill/drain bolt. Just a head with a square fitting (I think a 1/2" head will work) but with all this sealant around the hole. I had bought some 75W-90 for it, but never got around to it. There's a recommendation to check it every 30K miles, but I don't know if I could crank it open and if I did I don't know if I could properly seal it.

However - I've heard that rear-diff viscous fluid tends to wear out.

 

[Solo2driver]

Yes, they do wear out. I have found a couple of seasons of autocross is all a factory VLSD is good for, and they are non-servicable. We just bought a used diff assembly for the '02 WRX racecar for about $300 and put it in (we had sharded the ring & pinion anyway, nice to get a lower-mileage unit). I'd go that route if you feel that your VLSD is not functioning up to snuff. FWIW, a VLSD needs to slip to build up heat in the silicone fluid to function properly, unlike a clutch-type or gear LSD...sometimes what people feel is "worn" is just actually the exact way they are designed to function.

 

[tprog]

Originally Posted By: unDummy
Gear oil should be changed every 30k miles or 3years.

Viscous fluid isn't serviceable. But, many that are mechanically inclined, have figured out how to drain/refill the viscous diffs.

Viscous fluid should last forever. What usually happens is it leaks out, mixes with gear oil, and everything goes.

If you are capable of changing it, there are various visc's that you can tailor too. Many like to go with thicker viscous fluid for more effective slip limiting.



Does anyone know of a source for the fluid?