996/997 GT3 Diff Rebuild: Anyone Done it?

[drmark]

Cup plates the way to go - it's the stability of the back end under heavy braking that you will notice most (on track anyway).

[gt3nor]

Rebuild mine myself last year with Guard internals (Guard Transmission).
It's not hard to do, but if you want it done 100% correct you have to take a measurement first to get plates with a perfect fit as the stack height is slightly different for each differential. I recommend you check out the LSD Buster thread on 6speedonline and/or contact Matt at Guards to get all the info you need for this.

[GentlePersuasion]

gt3nor said:

Rebuild mine myself last year with Guard internals (Guard Transmission).
It's not hard to do, but if you want it done 100% correct you have to take a measurement first to get plates with a perfect fit as the stack height is slightly different for each differential. I recommend you check out the LSD Buster thread on 6speedonline and/or contact Matt at Guards to get all the info you need for this.

Thanks,

I've read about the Guard diff. Any idea on prices vs the Porsche Motorsport stuff?

[gt3nor]

I paid US$1123,- including overseas shipping for all parts needed from Guards. Don't know the exact price on the Cup parts, but I think they cost more.
Note that you have to measure the ramps inside the diff before you order to get plates that are the correct size, as far I understand Guard is the only company that will send you internals that are correct for your ramp size - they are not all the same. You either have to leave the diff out while waiting on the new internals, or you have to do the job twice - but it will be correct doing it this way.

[fioran0]

From your post in the other thread (for others reading)

GentlePersuasion said:

Not any more than they'd do the clutch (on the premise that Porsche considers the diff to be 'in spec' at >8 lbs torque) which to a normal human being, more often than not means it's fked.

Not that I'm bitter, you understand.

That is the specification for the stock diff. With it removed and one end held in a vice the other side should provide a torque figure of between 5-15Nm (3.5 - 11lb ft). If it achieves this your diff is working as intended.
Whether or not you feel it is enough is a whole other deal.

[arcamalpha]

Roughly what does it cost to get a diff rebuilt with cup plates?

[thegoose]

arcamalpha said:

Roughly what does it cost to get a diff rebuilt with cup plates?

circa £1200?

[Dave 321]

Cup plates are a great upgrade, first did mine in 2009.

But as they are a race part and not road your gear oil needs much more regular changes. There is a coating on the plates that contaminates the oil.

I change mine every 5k miles

[Cunno]

Dave 321 said:

Cup plates are a great upgrade, first did mine in 2009.

But as they are a race part and not road your gear oil needs much more regular changes. There is a coating on the plates that contaminates the oil.

I change mine every 5k miles

I've not heard of this before, where did you get your information from?

[Dave 321]

Cunno said:

I've not heard of this before, where did you get your information from?

Experienced the oil contamination by just changing the oil & put it on another forum.
Well respected porsche specialist with a lot of Porsche racecar experience commented saying about the coating on the plates contaminates the oil

[keep it lit]

common fallout with the use of Carbonetic diffs.

[fioran0]

The Motorsport diff plates are steel with a plasma sprayed molybdenum coating. The street diff plates are brass.

[LaSource]

jeremyc said:

Just had mine done.

Take a short trip down the M23 to see Nine Excellence; get them to replace with Cup diff plates.

Job's a goodun'.

+1

Ken did an absolutely superb job with mine earlier this year. Correctly shimmed motorsport plates along with some tweaks to the geo.

The car now is the best handling GT3 I've ever driven...through all the phases - braking, turn in, rotation, and exit. You have the confidence to play with the degree of rotation with the throttle pedal (e.g. slight lift to tuck the front end in, etc)

Ken can also source the Guards solution - though I opted for Porsche Motorsport plates in the end.
Highly recommend a chat with Ken.

[gt3nor]

In my opinion the ramps in a 997 GT3 should also be changed from 28/40 to 40/60 (like the 996 GT3 has) when doing a diff rebuild.

[arcamalpha]

gt3nor said:

In my opinion the ramps in a 997 GT3 should also be changed from 28/40 to 40/60 (like the 996 GT3 has) when doing a diff rebuild.

Why do you say that? I've not driven a 996 GT3 do haven't experienced the difference.

[LaSource]

My post above was about a 996 GT3.

However, be interested if anyone knows what type of diff a 4.0 has. My driving seat feeling is not as aggressive as the 996 GT3 even though the 4.0 has other evolutionary dynamics (turn in, rear bias, rear stability control, etc)

[fioran0]

Indeed. This was discussed in Steve's thread. The ramps are reduced in the 997 because it now uses the rear brakes to replicate a mechanical diff effect. As the plates wear out, the brakes take on more of the work.
Adding better plates and increasing the ramps will reduce the opportunities for the electronics to involve the brakes in this area. How much this matters on an individual level will depend on how you drive of course.

[Cunno]

fioran0 said:

Indeed. This was discussed in Steve's thread. The ramps are reduced in the 997 because it now uses the rear brakes to replicate a mechanical diff effect. As the plates wear out, the brakes take on more of the work.
Adding better plates and increasing the ramps will reduce the opportunities for the electronics to involve the brakes in this area. How much this matters on an individual level will depend on how you drive of course.

When we discussed this in Steves 997 thread, I believe you thought this was the case but not 100% sure. Is this still the case or do you have new info. Only asking as I'm looking at increasing the ramp angles in my car. one thing which is confusing is when you compare the 997 and 996 diffs the part numbers are the same, so how does the 997 have different ramp angles?

Jon

[Cunno]

gt3nor said:

In my opinion the ramps in a 997 GT3 should also be changed from 28/40 to 40/60 (like the 996 GT3 has) when doing a diff rebuild.

Have you done this? What difference did it make? What parts did you use?

[fioran0]

Cunno said:

When we discussed this in Steves 997 thread, I believe you thought this was the case but not 100% sure. Is this still the case or do you have new info. Only asking as I'm looking at increasing the ramp angles in my car. one thing which is confusing is when you compare the 997 and 996 diffs the part numbers are the same, so how does the 997 have different ramp angles?

Jon

Heres my post from Steve's thread:

"The pad wear is related to the wheels being physically braked by the ABD to replicate a conventional diff. As the actual LSD in the gearbox wears out the amount of work that the ABD would have to do would increase adding to pad wear.

The system monitors for a difference in rotational speeds of the wheels via the abs sensors and reacts when certain conditions are reached.
I would imagine that a diff with more lock would require less intervention by the system when such conditions were reached and also reduce the number of times the ABD felt it had to to anything in the first place.

I also agree that TC off means off with respect to the systems that operate via engine control, but am not 100% on whether this also includes the ABD portion. I believe that ABD remains on at all times but don't know unequivocally."

My position is still the same. I believe that its on at all times but don't know unequivocally.
All the literature I have on the systems (and its systems literature, not marketing stuff) say that ABD is not turned off when the off button is pressed. It remains active along with ABS and the electronic bias. Ive not seen anything personally to suggest that this is wrong but I have limited time with the street versions past the 996. How much pad wear you get as a result seems to depend on how you drive and the condition of your diff. Its logical that a stronger diff would prevent much of the ABD activation since it responds to ABS wheel sensor signals regarding slippage
I am an engineer so you aren't going to get anything stronger than that from me with the info I have. I've not directly measured it nor have I seen isolated results from someone who has. Ive seen data traces from brake system pressure sensors that show pressure on the rear circuit with system turned off that suggest the literature is correct but it should be considered anecdotal.