Gripping and grumbling ZF LSD in tighter corners

[amallagh]

I'm starting to run in a new 915 gearbox with ZF LSD in my 914/6GT.
I can't remember what % slip it is set up for. Is there any way to check with it fitted in the car ?

The LSD is gripping a lot on any tighter corners. Certainly on any T-junctions or 90 degree lefts of rights, never mind any maneuvering. It is really rather loud and the plates can be heard releasing. Is this normal ?
I have a ZF diff in my RS and it doesn't do this at all.

I'm concerned something has been set up incorrectly. I checked the static breakaway torque when cold with one wheel on the ground and the other jacked up with a torque wrench on the axle nut. It is about 42-44 lbft or 57-60 Nm.
If I test it like this it doesn't break away suddenly, it is relatively smooth.

[KS]

The ZF in my old Carrera 2.7 was exactly the same - very 'clunky' pulling away from junctions, but the sound and sense of grabbing disappeared at speed. It was the same with the rally and rallycross Beetles I drove, but appeared less evident when running narrower tyres. Unfortunately I have no idea how those ZFs had been set up. Who installed the diff? Will they not know? Not much use, am I?

[jevvy]

Is it safe to assume you have done a recent gearbox oil refresh with the correct LSD compatible oil?

[911hillclimber]

If it helps...
for years I've heard LSD's cracking and groaning at low speed, ie about walking speed, on tight manoeuvres in motorsport paddocks, all normal.
My plated rear diff in my Impreza did it too.

I would think a plated diff that does not show some of this is worn or so loosely set-up to be of limited value.

My Helix LSD, non plated is totally quiet and very effective.
As said, mech plated LSD's use a different oil to the same box without an LSD.

Maybe a call to Mike Bainbridge?

[fetuhoe]

The noise is simply due to a stick-slip behaviour which will be worse at low speed than when the car is driven normally.

Have you conditioned the diff? If it has been rebuilt with new plates it may quieten down after it has 'run-in'

KAAZ suggest this method which should work on a ZF.



A slipping torque of 60Nm is moderate - it may cause a s certain amount of understeer but is not as high as I have seen on other manufacturers diffs.

An LSD oil will almost certainly help to reduce this problem but could also reduce the grip on the synchros which could increase shift times.

If you have a standard oil in the transmission you could add a small amount of friction modifier - Lucas - for example until the diff smooths out.

I would start using 50% of the recommended quantity.

The fact that an LSD doesn't groan isn't really an indication that it isn't working, just that the plates will slide over each other smoothly and evenly.

[rhd racer]

Hi Andrew

Water cooled I know, but I had a diff fitted to the Boxster last year. At low speed it locks, graunches, and generally complains, and with a lightened flywheel the car wants to stall at every opportunity. I recently pulled out of the top of our lane in the wet at 5mph in 1st and it locked and I did a very nice drift in front of two dog walkers who shook their disapproving heads at me.....

The diff was a KAAZ, and I broke it in exactly as described in Chris's post and use their gear oil. They can be shimmed to provide more slip but TBH I had my best ever season last year with it so whilst it is a PITA to manoeuvre at slow speed it is the business when competing.

So I know not a direct parallel to your diff, it might be that in competition you find it immeasurably better and like me agree that it is worth driving around the other issues?

Cheers
Wayne