Plate type LSD

Plate type LSD

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1602Mark

Original Poster:

14,971 posts

140 months

Saturday 29th May
quotequote all
Recently fitted a brand new LSD that included uprated sintered clutch packs. Had the diff case refurbished, vapour blasted and all new bearings. All done by a well established specialist with a good reputation.

Refilled with Castrol Syntrax 75W140 LSD oil.

Ran the car for less than a 100 miles and it started to sound bloody awful. It also stopped locking if provoked.

Sent the diff back to the builder who said that it had 'lost preload'? He then readjusted I presume and sent it back.

All seemed better for a short drive and we were then back to sounding like a 'welded diff', no locking and the rear end feeling squirrely under braking. Especially if slowing into a bend, no matter how shallow.

This time the LSD went back to the manufacturer who said that the clutch was very dry and the oil was very black. They also said there were a couple of 'odd size shims not fitted by them'. Anyway, the adjusted it but said there was pretty much nothing wrong with the LSD and have returned it. It'll be back in the car next week.

The final remark was that maybe a clutch LSD just isn't for me?


In the past I have only had BMW LSD, in my old E21, E30 325, E30 M3 and E46 M3 but none made any sort of racket. Is this because they're not as hardcore as an aftermarket LSD? Is it usual that a clutch type LSD is noisy to the extent that you'll wince going around roundabouts and pedestrians will look bewildered?

Why would diff oil go black after such a short time?

Mark


Galveston

628 posts

166 months

Saturday 29th May
quotequote all
My experience of after market plate diffs is that they always sound and feel awful, just as you describe.

jimPH

2,345 posts

47 months

Saturday 29th May
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Yep, for a road car I wouldn't run a plate diff,I know they're better than a helical TBD, but the road manners don't make them enjoyable.

I think the wavetrack has the best of both.

Escy

2,985 posts

116 months

Saturday 29th May
quotequote all
They can be a bit noisy. You can add more friction modifier to the oil or change the way the plates are stacked but you'll trade functionality for less noise.

1602Mark

Original Poster:

14,971 posts

140 months

Sunday 30th May
quotequote all
Escy said:
They can be a bit noisy. You can add more friction modifier to the oil or change the way the plates are stacked but you'll trade functionality for less noise.
What's the deal with friction modifiers?

Escy

2,985 posts

116 months

Sunday 30th May
quotequote all
This is the blurb for the Redline stuff I used

Limited slip or posi-traction units will often chatter without use of this product or a gear oil with a similar modifier, so add only enough to eliminate the chatter and avoid making the plates or clutches too slippery.

My gear oil didn't use it so I added in some. Your gear oil has this in it already but you could try a little bit more.

GreenV8S

28,860 posts

251 months

Sunday 30th May
quotequote all
It might depend on the brand, and probably the ramp angles and preload, but plate style LSDs are not inherently noisy.

My V8S has run for many years with what I understand is GKN diff internals similar to Ford Cosworth 2wd. For the first hundred miles or so it was quite notchy in slow tight corners and you could feel the transmission winding up then releasing, but after that it feels just like any open diff in normal driving - and spins both wheels under power.

Maybe what they're saying is that brand of plate LSD is not for you. What brand is it?

jimPH

2,345 posts

47 months

Monday 31st May
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GreenV8S said:
It might depend on the brand, and probably the ramp angles and preload, but plate style LSDs are not inherently noisy.

My V8S has run for many years with what I understand is GKN diff internals similar to Ford Cosworth 2wd. For the first hundred miles or so it was quite notchy in slow tight corners and you could feel the transmission winding up then releasing, but after that it feels just like any open diff in normal driving - and spins both wheels under power.

Maybe what they're saying is that brand of plate LSD is not for you. What brand is it?
Probably needs rebuilding, plate diffs need regular maintenance. I've got a standard GT2 plate diff in my 997 gearbox, but I know it won't last long, especially with the power I'm running. I've read them not lasting more than a few trackdays, so I'll be fitting a wavetrac next. Guards are probably better, but my car is predominantly road driven.

chrisch77

375 posts

42 months

Monday 31st May
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Sintered LSD discs are better suited to competition use than a road car. You would be better off with carbon fibre faced discs or molybdenum plasma sprayed discs for improved NVH and progression of the diff locking characteristic.

A traditional ‘Salisbury’ LSD is preloaded using a very high spring rate disc spring, so when you fit new discs they bed in and lose thickness very quickly in the first bit of use, which then leads to a big drop off in the spring force providing the diff preload, as you have recently seen. For this reason you don’t really want to be fitting new discs particularly sintered ones unless you plan in a rebuild after a few miles to reset the preload.


1602Mark

Original Poster:

14,971 posts

140 months

Monday 31st May
quotequote all
GreenV8S said:
Maybe what they're saying is that brand of plate LSD is not for you. What brand is it?
J3Driveline - I should make it clear that this isn’t a moan or complaint though. I’m simply trying to get a better understanding and see what (if anything) I can do to make it more suited to my needs? J3Driveline have been great thus far and tried to help solve my issues.

It does say on their website that noise should be minimal but I was unsure why the oil would be black after so little use? I understand the characteristics of a plated LSD may not be suited to my needs but what’s the difference between this and the LSD in my old M3’s?