996/997 GT3 Diff Rebuild: Anyone Done it?

[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

[Steve Rance]

I am fitting a motorsport diff pack to my 997 and changing to a 40/60 asap.

I have now collected my car. Very nice example but it was obvious straight away that the diff is not effective under both braking and acceleration - even at gentle road speed the car is relatively unstable under braking. It needs a lot more diff control for my needs. Lovely chassis though. Very tight. The PASM on normal is reasonably well judged on the road but the damping control isn't good - and it doesn't like a trail. but I knew that already. Pasm on sport is hopeless and the control is even worse. In normal, it's not a problem on the road unless your driving to avoidance and you need to load the nose. Going back to the diff - i'd definitely advise a stronger component set, and for a driver who wants more help out of his or her car at 10/10ths, i'd definitely go 40/60 as well. jury is out on the benefits of a final drive change.

[skijumper]

The Guards ramps have 2 settings, 40/60 and 50/70 for more track focussed cars. I set mine at 40/60 and am delighted with
the way the car handles. Race cars set the diff at the more aggressive 50/80 setting according to Matt.

[fioran0]

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?

The 996 and 997 part numbers are not the same and the ramps are very much different on both.

[Cunno]

fioran0 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?

The 996 and 997 part numbers are not the same and the ramps are very much different on both.

Ok what am I missing?

Ring set 950 332 983 05
Gear set 950 332 983 02

According to the Porsche web site and the 996 & 997 Kat these parts are the same numbers on both cars?

[fioran0]

ttdan said:

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

Only the early 996 cup used a 40/60 diff. The later 996 Cup used a slightly more aggressive diff ramp angles of 45/65 that continued through 997 Cup and RSR. Worthy of note is the difference in preload between the street and race diffs. The Cup diff runs with a preload of 150Nm give or take. The spec for the 996 GT3 diff is 5-15Nm. Thats quite a difference.
As per my earlier post. The 996 and 997 diff part numbers are also not the same. There is probably some confusion as the 996 part superseded to a 997 part number but there are two distinct numbers for each group of cars.

997 332 083 90 is the part for the 996,
997 332 083 91 is the part for the 997.
The 997 part ending in 91 very much uses 28/40 diff ramps, the 996 part which is now on a 997 number definitely does not. You do not want to get this mixed up if you are buying a new diff for a 996 which needs the 40/60.

Edit to tidy up the formatting of my phone post.

Edited by fioran0 on Monday 5th January 01:47

[fioran0]

Cunno said:

Ok what am I missing?

Ring set 950 332 983 05
Gear set 950 332 983 02

According to the Porsche web site and the 996 & 997 Kat these parts are the same numbers on both cars?

Thats not the diff you are looking at. Part numbers for the diff are in my post above.

[fioran0]

nxi20 said:

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...

IIRC the 997 GT2 uses the exact same diff as the 997 GT3 with the same 28/40 ramp angles.
Edit: Did you use Guard product actually? They have three product lines for the GT3 that are labelled (GT1, GT2 and GT3). Perhaps you got a GT2 and misinterpreted it as being from an actual GT2?

Edited by fioran0 on Sunday 4th January 20:48

[Cunno]

fioran0 said:

Cunno said:

Ok what am I missing?

Ring set 950 332 983 05
Gear set 950 332 983 02

According to the Porsche web site and the 996 & 997 Kat these parts are the same numbers on both cars?

Thats not the diff you are looking at. Part numbers for the diff are in my post above.

Thanks I now see were your getting the part numbers from. Is that not the number to buy a complete new diff? Can you not buy the internals as per the cup plates to upgrade? What part within the diff sets the ramp angle I thought it was the ring set?