How effective is the stock viscous LSD rear end?

[benspilk09]

My car is relatively easy to break traction with while turning right. I assume it just lights the 2 inside tires up, since it does not cause it to go sideways.

Turning left is more difficult and the rear kicks out when it happens, much like you'd expect from a car with an LSD.

Is this normal for a stock VLSD? Mine feels "normal" turning the wheels by hand, there is a ton of resistance to make the wheels turn independent from each other while on jack stands. However, it feels like it is just marginally better than an open diff when you are breaking traction.

Is my diff abnormally weak? Or are they all like this?

If it is relevant, I have a 4 bolt rear diff in my car and of course have the factory VLSD.

 

[lenny 15]

My car is relatively easy to break traction with while turning right. I assume it just lights the 2 inside tires up, since it does not cause it to go sideways.

Turning left is more difficult and the rear kicks out when it happens, much like you'd expect from a car with an LSD.

Is this normal for a stock VLSD? Mine feels "normal" turning the wheels by hand, there is a ton of resistance to make the wheels turn independent from each other while on jack stands. However, it feels like it is just marginally better than an open diff when you are breaking traction.

Is my diff abnormally weak? Or are they all like this?

If it is relevant, I have a 4 bolt rear diff in my car and of course have the factory VLSD.

Not sure how strong they were originally, but i'm sure that after nearly 30 years, they are not what they once were. If you want to upgrade I'd send it into Jon at TRE for the Evo LSD upgrade and rebuild. I'm probably going that route eventually.

 

[randman2011]

[EDIT]With use, the fluid in a viscous LSD will break down, turning it into an open diff. The more it gets used, the faster it will decay. They are not rebuildable.[/EDIT]

People used to say that the viscous CENTER fluid would be worn out by 100k miles. I don't know where that number came from or if it is supposed to apply to the viscous REAR as well, but I will say that I was able to break all four tires loose last week when I accidentally did a pull in 1st thinking it was 2nd, so at 122k miles my viscous center is still kicking. I've never noticed a handling difference between viscous and open rear differentials. With how they function ("clamping force" is delayed) they make more sense as a bad weather traction device than a sporty handling device.

I'm more concerned that you have a handling difference depending on which direction you're turning. That's not something I've ever experienced in any car, VLSD, mechanical LSD, or open. Well, I guess except for the husband's old Sebring coupe, but that had a salvage title and turned tighter in one direction than the other. Is your steering rack centered such that you can turn the wheel equally far in both directions? Shocks healthy on all four corners? Tire pressures equal left-to-right? Your experience in right turns is what I would expect with a non-functioning VLSD. Weight transfer on the stock suspension lifts the inside rear tire or at least removes enough weight that it breaks loose and just spins, wasting your power. With a functioning rear VLSD, you would get the same spin at first but the LSD would gradually lock (something on the order of 1-2 seconds) and you'd be able to put power down again. The stock suspension will allow a lot of weight transfer, but I don't think it would be enough to break the front inside tire loose also. Turning left, I have no idea what is going on. Granted I'm on a 2g platform and not 1g, but the only time I've EVER gotten oversteer on pavement was lift off oversteer and that was on a GST Spyder.

 

[benspilk09]

Being able to cut donuts left handed, but not right handed is typical open diff behavior. The right tire just spins turning right, but both will typically spin if you're turning left. There is an inherent torque bias.

My Center diff seems to work fine, as it still breaks the rear loose. It just behaves more like an open diff than what I'd expect from a "good" LSD. I didn't know what to expect from these things, I suppose there is a reason that the evo doesn't use a viscous LSD. I just did a 4 bolt swap and the rear diff came from a bone stock car with 90k miles. It felt like it was in good shape, as far as I could tell by hand.

I didn't let it spin for very long, I lift as soon as it breaks traction. Maybe I didn't let it build enough heat to lock it, but I also didn't want to blow up my new diff by overheating the VC.