996/997 GT3 Diff Rebuild: Anyone Done it?

[Steve Rance]

But it is SO effective and a whole lot of fun when you get it right. It's a pity that Porsche have tried to engineer this out of the 911. It was a technique that involved the driver as a fundamental in the extraction of performance. Surely what true driving enjoyment is all about??

[fioran0]

Agreed and you would think so. Im not sure anyone at Porsche is much interested in that anachronistic view of driving any more sadly. Top Trumps style metrics are so much easier to pump out. Its a new day and a new target of owners.

[Harris_I]

(For the record, I agree with you)

[V8KSN]

Steve, Neil

Thank you. I have learned so much from those past few posts!

I have so much more to learn though!

[fioran0]

I'm going to bump this up just to add that I read something by GT Gears earlier that was specifically discussing fitting a diff with more lock up % into the newer cars such as the 997. These are designed increasingly to have electronics do the job of the diff and are as a result given a very weak diff from the factory.

He confirmed that doing this swap does indeed move the mechanical diff upstream of the electronics, reducing or removing the amount of intervention that takes place from the electronic side of things going forward. Much better situation from the driving seat and your brakes will thank you for doing it too.

[Steve Rance]

Great news Old Chap. Thank you very much for posting

[Cunno]

Steve Rance said:

Great news Old Chap. Thank you very much for posting

Steve have you convert your diff yet? If so which way are you or did you go guard or cup parts?

[Steve Rance]

Not yet. I'm a little torn to be honest. Both options will be a huge improvement over the standard set up

[fioran0]

Steve Rance said:

Great news Old Chap. Thank you very much for posting

No probs. Not worth a post on its own but felt it was worth filing in here.

[rrroro]

Little bit of a thread resurrection… Cunno just told me about this thread, loads of great info

I had cup plates fitted to my 7.1 GT3 around 2013 and then had that rebuilt a few years later as the diff never felt quite right, I’m not sure it was fitted correctly by the place that supplied and fitted the cup pack. The 2nd rebuild felt much better, but on my last trackday last year I noticed the car being a little wobbly at the rear again. Not badly, but not really together like it used to be

So I’m having the diff rebuilt again soon, and the term Belleville washer has been thrown about. I’ve googled a bit but can’t seem to work out exactly what the Belleville washer is for. I’ve read about it helping (increase?) the preload, but I’m not sure exactly what is meant by preload either …

I think I understand what the plates actually do in the diff, but increasing the preload will do what exactly, just tighten everything up so the diff works ‘sooner’? Ie Make it lock up earlier on acceleration/ braking? I thought that was dictated by the steepness of the ramps? In which case does the Belleville washer act as a bit of a cheat to help less steep ramps trigger like a diff with a steeper set up? Thanks in advance, apologies for the stupid questions …

[Slippydiff]

Using a Belleville washer increases the static preload ie how hard it is for the wheels to turn independently with no power or braking torque being applied. The lower this preload, the more the differential acts like it is open when no torque (power or braking) is applied to it.
Whereas higher preload reduces the severity with which the plates/diff locks when accelerating or decelerating (as they’re already preloaded)

[rrroro]

Cheers slippy. So basically, using the Belleville washer means the diff will trigger with less torque being applied, so under less aggressive acceleration / braking?

Do all diffs comes with a Belleville washer fitted as standard, or are they added such as in this instance to improve performance? I’m wondering if I already have a Belleville washer and it has worn out, or if I don’t have one and it’s being fitted for the first time

(I could just ask the guys doing the work, but I like to research first so I don’t appear completely ignorant!)

[rrroro]

(By “trigger” I mean lock ^)

[Slippydiff]

The OE diff has a Bellville washer, but it's a pretty flat/weak/thin item, hence once the less than durable OE plates wear out, the diff quickly loses its preload.

A quick, cheaper "fix" is to fit a Bellvillle washer which is thicker and more convex, thus providing more static preload, however, you're still relying on the less than brilliant OE plates, hence most go with the Cup plate upgrade, this comes with a thicker, more convex Belville washer and plates with a more durable (and aggressive) friction material.

Increasing the static preload raises the threshold at which point the ramps are activated, and in the process softens their initial effect.

[Cheburator mk2]

Slippydiff said:

The OE diff has a Bellville washer, but it's a pretty flat/weak/thin item, hence once the less than durable OE plates wear out, the diff quickly loses its preload.

A quick, cheaper "fix" is to fit a Bellvillle washer which is thicker and more convex, thus providing more static preload, however, you're still relying on the less than brilliant OE plates, hence most go with the Cup plate upgrade, this comes with a thicker, more convex Belville washer and plates with a more durable (and aggressive) friction material.

Increasing the static preload raises the threshold at which point the ramps are activated, and in the process softens their initial effect.

Another trick which Porsche uses is to flip the orientation of the bellville washers. Some diffs have the cones pointing towards the middle of the diff, some have them pointing outwards. Pointing outwards on average increased pre-load by about 10-12Nm. You can also play with the thickness of the dog plates which sit between the clutch plates as well with the actual clutchplates thickness. Setting it up involves a bit of simple maths and good quality micrometers/depth gauges. And a torque wrench.

Needless to say, if you are tracking the car hard, transaxle oil changes need to happen a lot more frequently than Porsche's service schedule would suggest. The oil has a double hard task - it has to work with the gears and synchros on one hand, but also it has to lubricate the LSD. Motul 300V 75w90 LSD is probably the best...

[rrroro]

Thanks guys. I thought this thread got deleted or something as I couldn’t find it, then realised it’s in the Porsche General chat not 911. Duh…

Anyway, thanks for all the info guys, that’s been very helpful. My theory is that the cup plates weren’t set up 100% correct, so nothing a rebuild by someone that knows these cars well shouldn’t fix

Thanks again

[VPD255M]

Interesting thread, thanks everyone.

I have a 997 GT3 with the Cup friction plates and original 28/40 diff, the Cup friction plates are a massive improvement but would like a more active diff especially under braking so looking to install the 996 40/60 ramps.
It's been suggested that the Cup plates will be too aggressive with the 996 ramps and that we should switch to the Guard plates instead.

Does anyone have experience with this combination of 996 40/60 ramps and Cup plates?

[Cheburator mk2]

VPD255M said:

Interesting thread, thanks everyone.

I have a 997 GT3 with the Cup friction plates and original 28/40 diff, the Cup friction plates are a massive improvement but would like a more active diff especially under braking so looking to install the 996 40/60 ramps.
It's been suggested that the Cup plates will be too aggressive with the 996 ramps and that we should switch to the Guard plates instead.

Does anyone have experience with this combination of 996 40/60 ramps and Cup plates?

i have it in my 996.1 CS - it works a treat. No (s)PASM either... So perhaps it works well in a analogue car like the 996, but it's too aggressive for the nannied 997 platform?

[VPD255M]

Cheburator mk2 said:

VPD255M said:

Interesting thread, thanks everyone.

I have a 997 GT3 with the Cup friction plates and original 28/40 diff, the Cup friction plates are a massive improvement but would like a more active diff especially under braking so looking to install the 996 40/60 ramps.
It's been suggested that the Cup plates will be too aggressive with the 996 ramps and that we should switch to the Guard plates instead.

Does anyone have experience with this combination of 996 40/60 ramps and Cup plates?

i have it in my 996.1 CS - it works a treat. No (s)PASM either... So perhaps it works well in a analogue car like the 996, but it's too aggressive for the nannied 997 platform?

Useful to know, thanks.

[braddo]

Reviving an interesting thread.

Has anyone tried this 'friction plate upgrade kit' from design911? It's a Racing Diffs product and about £450.

https://www.design911.co.uk/p/friction-plate-upgra...

I seem to recall that the Motorsport/Cup plates are no longer available so are most people installing Guards diffs these days?