996/997 GT3 Diff Rebuild: Anyone Done it?

[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.

[nxi20]

I put 997 GT2 ramps (steeper than the 996) in my 996 with Cup plates in the end. It cured the lurch I used to get coming on the power out of roundabouts(!) which was sometimes so violent it used to feel like a wheel was loose. Oddly, I only ever felt it on the road, never on track...

[Cunno]

fioran0 said:

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.

Thanks, that helps, I think I'll give it ago.

[gt3nor]

Cunno said:

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?

I did my own rebuild on my 996 GT3 with parts from Guards.
My 997 GT3 came with a rebuild diff with 40/60 ramps and Guards internals already, so I don't know how it was on stock ramps. But it grips like h*ll now.

[jackwood]

Cunno said:

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

Have you ever had your diff plates replaced?

[gt3nor]

Pictures:
https://www.facebook.com/media/set/?set=ms.c.eJw9y...

[ttdan]

Cunno said:

. 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

Good question. What are the ramp angles on each then?

[Cunno]

jackwood said:

Cunno said:

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

Have you ever had your diff plates replaced?

Yes twice, both times with cup plates

[Cunno]

ttdan said:

Cunno said:

. 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

Good question. What are the ramp angles on each then?

997. 28/40
996. 40/60

[Cunno]

gt3nor said:

Cunno said:

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?

I did my own rebuild on my 996 GT3 with parts from Guards.
My 997 GT3 came with a rebuild diff with 40/60 ramps and Guards internals already, so I don't know how it was on stock ramps. But it grips like h*ll now.

How often do you track the car and at what rate are the rear pads wearing out? At present mine eats it rears on standard pads every 5 TDs and R29s seem to last about 7 TDS, but the discs are taking more hammer.

[ttdan]

Cunno said:

ttdan said:

Cunno said:

. 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

Good question. What are the ramp angles on each then?

997. 28/40
996. 40/60

Thats the angles for the 996 cup car, street car the same them but with the same part number as the 997?

[skijumper]

Get the Guards plates and washers, they are a way better than the Cup ones. Slightly more expensive but cheaper in the long run.
Give Matt a call, he's so clued into what GT3 owners want, having supplied hundreds of diff and gearbox parts. The build quality
of his parts are top quality.

[Cunno]

ttdan said:

Cunno said:

ttdan said:

Cunno said:

. 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

Good question. What are the ramp angles on each then?

997. 28/40
996. 40/60

Thats the angles for the 996 cup car, street car the same them but with the same part number as the 997?

So I'm told hence the confusion, will now have to have a look at the GT2 ramps