Should the stock vicous diff clunk when locking?

[jonb-]

Simple question really. If i jack the rear of my car up and turn one wheel, i get a bit of free play, then a very obvious mechanical clunk and the other wheel starts to rotate in the same direction.

And not wanting to sound rude, lets please not start the vicous "which direction the wheel should turn" debate as that's just been done.

Thanks

[Bry]

Sounds like a mechanical lsd,my viscous lsd always rotates the wheels the same direction immediately with no play or clunk

[BenF]

Hmm, most mechanical plate diffs require some torque to lock up the rear wheels - and are quite noisy when they do.

To me, that sounds like a standard Mk2 LSD.

[jonb-]

Hmm, most mechanical plate diffs require some torque to lock up the rear wheels - and are quite noisy when they do.

To me, that sounds like a standard Mk2 LSD.

I was under the impression the vicous diffs needed some torque to lock up the rear wheels, not the plate types.

Why would the vicous allow play before locking with a clunk.

I think i need to do more research.

[jonno]

Mine clonks and bangs like a good-un on full lock, never heard a viscous LSD make any noise at all?

[jonb-]

It's not clonking when driving, only when spinning the rear axel when it's up in the air.

My current working theory is the lag for the second wheel to engage must be the fluid catching up and the clunk when the second wheel does engage is the entire vicous unit springing into life.

Probably not a very good theory, but unless it's a worn geared diff nothing else in my head makes sense.

[BenF]

Jon,

That does sounds like the standard Viscous LSD (which is very good). With both wheels jacked up in the air, car in neutral and handbrake off you can turn one wheel and after a small quiet clunk and a little motion you should see the wheel on the other side turn in the same direction.

Drop one side of the car down - and you can now turn the wheel up in the air, but you should feel resistance.

Plate type LSDs need a fair amount of torque to make the plates engage and the diff lock up. With the rear wheels up in the air, and you spinning one of them you'd not expect the diff to lock up.