Bad center Viscous Coupler

[prove_it]

I've heard a blown center viscous will cause wheel noises and weird hopping while turning hard, but what about causing the front wheels to spin but not the rear during a launch. 715 is now doing front burnouts without any other issues, so started wondering if the center viscous has failed. It will spin the fronts for a second or two before gripping. Tight turns are quiet and peaceful. Anyone got ideas?

 

[jepherz]

If anything, what you describe is that your center diff is working. If you picture the center diff feeding two axles, one to the front and one to the rear, with enough slippage of either (front wheels spinning while rear are planted or vice versa), enough slippage simply heats up the viscous fluid and locks the clutch together, forcing the front and rear axles to spin at the same rate.

Keep in mind both the front and rear diffs are open on a stock, US VR4 though. So the slippage to the front axles, for instance, could all be occuring through one of the front wheels spinning.

 

[EMX5636]

If the car is still moving, then I think you can rule out center diff, t-case or axle failure. Either one of those usually feels like a slipping clutch without a welded center diff. I guess the VC could be going bad. You said only happens on a launch correct?

 

[prove_it]

Yea, noticed my front tires are bald versus 8/32nds rear too. I do push corners, but they were new less than 6k miles ago. Rear is a 4bolt too, by the way.

 

[jepherz]

Quoting EMX5636:
If the car is still moving, then I think you can rule out center diff, t-case or axle failure. Either one of those usually feels like a slipping clutch without a welded center diff. I guess the VC could be going bad. You said only happens on a launch correct?



Sorry, I meant VC in my reply. I guess I was considering the VC locking up when bad (this happens if you tow a car with 2 wheels on the ground) but I suppose it could fail fully open too, which would potentially result in the symptoms you described.

A used VC is less than $40 from jacks and you can swap it out pretty easily while on the car.

 

[prove_it]

I've got two spares already. I'll be throwing a clutch in soon now that it's finally had enough. Thought I'd get some opinions first before trying. It seems odd, since all the failed ones I've seen have failed solid and locked up, not locked open.