997,1 GT3 LSD refurb/upgrade options

[Cunno]

Hi

There seems to be a lot of noise about the standard LSD plates in 996/997 diffs being made out of chocolate and not lasting very long. This isn't strictly true. Pre load of the clutch pack is very low from factory (5 to 15 NM) and only a very small amount of wear on the clutch pack results in zero pre load on the diff. This results in effectively an open diff.

There are 3 options as recommended by Matt at Fearnsport.

1. Cup Clutch pack. (Matt did not recommend for road use this is too aggressive, this pack was designed for use with slick tyres on Cup cars and road tyres simply don't have enough grip to brake away the diff resulting in a car that pushes)

2. Gaurd Transmittions Clutch pack (A great good quality replacement clutch pack which results is far more pre load than the factory set up, around 50 NM from memory)

3. Fearsport uprated Belville Washers. (The new washers are thicker and more pronounced than the factory washers, this puts more pre load on the original clutch pack. Obviously the clutch pack still needs to be serviceable but mine at 40,000 miles were).

I chose the upgraded Belville washers from Matt and fitted them myself. Quite easy and can be completed with the gearbox in the car.

My standard "Chocolate"clutch plates. Since the upgraded Belville washers were installed the Diff has worked absolutely fine and I've completed a number of track days without issue. Car now has 47,000 miles on it.

Hope that helps.

Kind Regards

Are you talking 996 or 997 here? This thread is titled 997.1?

 

[Cunno]

Looking at photos, they look like 996 ramp angles?

 

[johntyboy]

Looking at photos, they look like 996 ramp angles?

Yes should have said the Diff is from a 996 GT3. I thought the main difference between the 996 GT3 and 997 GT3 LSD's were the ramp angles. The point regarding the clutch plates and pre load would still be relevant.

If my post is miss-leading or not relevant I'm happy to delete.

 

[Cunno]

Looking at photos, they look like 996 ramp angles?

Yes should have said the Diff is from a 996 GT3. I thought the main difference between the 996 GT3 and 997 GT3 LSD's were the ramp angles. The point regarding the clutch plates and pre load would still be relevant.

If my post is miss-leading or not relevant I'm happy to delete.

No not at all, always interesting to know there's a 3rd option available, and I'm not sure whether clutch plates are same, but I do believe that the ramp angle difference between the 996 and 997 is one of the keys to wear and why the 997 diff is concidered to be useless and wears out while you don't here the same about 996 diff even though many parts are same.

 

[johntyboy]

No not at all, always interesting to know there's a 3rd option available, and I'm not sure whether clutch plates are same, but I do believe that the ramp angle difference between the 996 and 997 is one of the keys to wear and why the 997 diff is concidered to be useless and wears out while you don't here the same about 996 diff even though many parts are same.

I think 996 GT3 do suffer with LSD wear issues, my car had very little (possible no) track time when I bought it at 30,000 miles, and by 40,000 the diff had gone and it was very noticeable on road driving.
I also have a pal with a 996 GT3 RS with 9000 miles, diff gone in that as well.

Of course Matt at Fearnsport would be able to confirm one way or the other. He was very good to me.

If indeed the Belville washer would solve the 997 LSD issues, its a much more cost effective option. Think the washers were about £350. Add to that about £100 worth of consumables and a day in the garage and its all done.

 

[johntyboy]

For info, just looked on Porsche PET and the 996 and 997 GT3 do share the same clutch plates, part number 950 332 983 36.

Kind Regards

 

[Senoj]

I have standard clutch pack plates and FS's washers on my 996. All works well.

Worn cup plates came out but they'd been installed incorrectly hence why.

 

[Cheburator]

Comment about the light pre-load meaning that effectively you have an open diff isn't quite correct. It means that if the plates aren't worn it will bite less progressively rather than be open completely as described in an earlier post

The only way that you can get an LSD to become 'open" is when the friction surfaces of the clutch disc are galled and they slip when engaged with the dog washers between them. Unfortunately, the only way to determine wear isn't the Porsche pre-load test which is sufficiently vague, but to split the LSD and to inspect the clutch pack. At least it's super easy to do.

Racing Diff clutch packs are widely used in the Drift Community on Turbo Nutter cars with double the bhp/Nm of our cars. No complaints about longevity or quality.

Last but not least - another cheeky way to increase pre-load instead of buying the crazy expensive washers is to flip the OEM ones. But again, you can go one step further and fit thicker dog washers for the same effect...

However if your clutch discs have a galled surface, your LSD will pass the Porsche breakaway torque as per the Workshop manual referenced earlier with flying colours, but your LSD will still be ***** on track or on the road...

 

[Cunno]

The The only way that you can get an LSD to become 'open" is when the friction surfaces of the clutch disc are galled and they slip when engaged with the dog washers between them. Unfortunately, the only way to determine wear isn't the Porsche pre-load test which is sufficiently vague, but to split the LSD and to inspect the clutch pack. At least it's super easy to do. only way that you can get an LSD to become 'open" is when the friction surfaces of the clutch disc are galled and they slip when engaged with the dog washers between them. Unfortunately, the only way to determine wear isn't the Porsche pre-load test which is sufficiently vague, but to split the LSD and to inspect the clutch pack. At least it's super easy to do.


Super easy, can you elaborate please?

 

[Diggermeister]

As I understood it all, the big problem on the 997.1 is the ramp angles. This is what's different from the 996 gen 1 and 2 cars.

They traction control system was designed to use ABS to augment the diff. It worked, but at the cost of cooking rear pads faster than fronts on track days.

You can do all you like with preload, or different plates (yes I'm sure some are better than others), but the physical interaction of the ramps is key.

 

[Cunno]

As I understood it all, the big problem on the 997.1 is the ramp angles. This is what's different from the 996 gen 1 and 2 cars.

They traction control system was designed to use ABS to augment the diff. It worked, but at the cost of cooking rear pads faster than fronts on track days.

You can do all you like with preload, or different plates (yes I'm sure some are better than others), but the physical interaction of the ramps is key.

.

Total agree on 997.1 makes a big difference for cars which are tracked, I would also add increase ramp angles on a street car is probably to aggressive

 

[Diggermeister]

You definitely feel the Guards setup lock up under braking.

It's excellent on track and on the road, pootling round, you never get it, but it would be awkward in those 50:50 situations, where you brake a bit too hard but were not really intent on pushing on and making progress. Like a half-hearted rugby tackle.

 

[Cheburator]

Cunno and diggermeister,

I am not good at multi quoting... but here are my 2c...

Opening the diff on our cars is very easy (relatively speaking) as you don't need to remove driveshafts from the car. Once they are down from the diff output flanges, you can remove the former. Since you aren't changing bearings, as long as you keep the shims as you found them, there should be no changes to the backlash of the diff. Once the flanges are off, then you can remove the diff covers, once they are off, the LSD casette with the crown wheel can be removed. Splitting it open isn't difficult and then you can inspect the plates. Having a good bearing puller is helpful, but not essential.

if you are rebuilding, having a precise vernier depth gauge and basic maths skills is all that you need. All torque values are in the WSM. The beauty of the 996/7 transaxle is that it's old school. It is designed to be rebuildable, or that ratios/LSD can be swapped in the field. Hence it allows even oiks like me to have a play...

As for the ramp angles - both of you are spot on. 996.1 and 2 have 40/60 diffs, while 997.1 and 2 are much weaker at 28/40, expecting the ABS and rear brake calipers to do much of the work... we know how that worked out in real world...

 

[Diggermeister]

It's not really a job I'd personally want to attempt. I'd certainly not want to do it without a decent ramp.

Plus, don't forget, to open the diff, you need to drop the gearbox oil too.

Good "how to" video here:
Skip first 45 seconds of bollocks.

 

[Cheburator]

It's not really a job I'd personally want to attempt. I'd certainly not want to do it without a decent ramp.

Plus, don't forget, to open the diff, you need to drop the gearbox oil too.

Skip first 45 seconds of bollocks.

I rebuild a whole car's drivetrain using axle stands and a pair of Arcan 2t low entry alumium jacks, so it's doable, but yes, I'd have rather had a good two-post lift on hand.

Changing transaxle oil should be done a lot more often than the official Porsche schedule dictates, especially if the cars is on sticky rubber and sees hard road and track miles. The £100 cost every two years max is a good investment, considering that Porsche increased the prices of everything transaxle related yet again...