TRAKCAR

My guess is that our PP and Clutch overheat and there is a cooling issue.
No issue with gearbox wear, just an issue with gearbox / PP / Clutch COOLING.
Unlike Matt this has no base on any technical knowledge LOL.

IMHO:
Seems not related to the gearbox as even a new fresh 3.8RS / 4.0RS will do this after just a few hot track events within 1500 neat, slow shifting track miles.

I always changed oil at 6 days.
4.0 clutch and PP, 3.8 stuff never had any wear, they just fail where they always do.
Always ran Guard and or Motorsport LSD.

Always overheating still.
That's if overheating causes the car to not disengage the clutch fully once you come off the track.
Or I never notice it on track, but it shifts fine and I don't hammer the gear, I shift slow.

As soon as the PP/Clutch have gotten too hot and I come off the track it seems like they melted and even after a 30 minute cool down run at 60MPH it still wont completely declutch, its exactly the same as when I just got off the track.

The next day driving to work, I can hammer the car all day long and it will never do it with street driving. Next track event same thing, sticks BAD after coming off the track.
You can start the car in first gear, but it is not fully declutched but enough that it wont move. The sticking part is only when you want to take the car out of gear, not into the next gear at all.

I think the 3.8 and 4.0 clutch and PP just cant handle the HP / high temp track. Maybe it was OK for the 3.6 and the 996CUPS, but not for the 450-500HP 3.8 and 4.0 I think.

Maybe the GT2RS clutch and PP are stronger/more heat resistant
OR how can we get more cooling to the clutch and PP?

Jamie_GT3

I was just talking to JB racing about this same thing today. The postulation is that our clutches are slipping a little and making lots of extra heat. We're working on a few solutions to handle it, maybe one ready in time for my 4.2...

TRAKCAR

But the clutches come out looking like virgins?
If they'd be slipping there would be some wear?

Jamie_GT3

Maybe not, the heat has to come from somewhere. Right now we know our cars are close to the max rating on the torque levels of the disks. So the assumption is that the disk is slipping a little and making more heat than would normally be in there and prematurely aging the PP. That's what Jim and I discussed today as being the most reasonable issue...

rja

Elaborating on my discussion w/ Matt today from Guard.

He didn’t support the idea that the issue might be heat related, at least from the perspective that getting more cooling onto the gearbox is going to help (occasional grinding when attempting to pull 3rd to 4th). I am seeing the problem occur more in later sessions where I push me and the car harder as the day goes on, so it stands to reason more heat does have an effect. But as Mooty pointed out, this could be an early sign that synchro is on its way out and will get progressively worse. Certainly, I hope not.

A few things worth sharing from my conversation (some obvious or well known, some not):

- The synchros on our GT gearboxes can be readily replaced. Not cheap because of labor involved, but still far cheaper than a full rebuild or replacement gearbox.

- The syncros themselves are fairly cheap (in Porsche terms anyway) at around a few hundred dollars, so it’s common to replace others if not all while in there.

- He mentioned option of stronger motorsports syncro for 2nd. Didn’t delve into this much but I made a mental note.

- He pointed out that if indeed a syncro problem, best to jump on it early rather than wait because continued use can lead to bigger problems like worn or damaged gears, and then costs quickly begin to escalate.

- He discredited my assertion that my tendency to pull 3->4 fastest (because that’s usually down a straight) might be hard on the syncrho, and said that downshifts are generally behind such failures, and stressed importance of matching those revs well.

So based on above, I will have the fluid changed and monitor closely. If the problem continues (and certainly if worsens) then I’ll probably proceed w/ having the synchro(s) changed out.

M3EvoBR

I'll still go back to the basics. Perfect heel and toe. Use my car as an example. 15K miles decent amount of track time around Sebring at a fairly decent pace (videos on my sig. to prove). Stock clutch, not even a 4.0 clutch and also stock tranny. Car always worked perfectly. Sometimes a little notchy on the street for 1st gear, but that's about it.

What Jamie said makes sense, but I don't believe it comes from torque slipping, but yes from not healing and toe adequately and having the same effect.

24Chromium

And here I thought I knew how to heel/toe. I tracked 2 BMWs prior to the p-cars. The last BWM I had, I tracked it for many years, as well as being the DD. When I recently sold it, it had ~110k miles on it with the original clutch (and gearbox!).

If anything, I probably over-rev the engine on the throttle blip. I chalk that up to the lightweight flywheel, and ham-fisted feet. The distance between the brake and throttle pedals has always annoyed me, even with an extension on there.

So, walk me thru the mechanics of what I'm doing to the clutch and gearbox by constantly over-rev'ing the blip on my downshifts.

Mvez

In that case, just be patient on the clutch release when you over-rev the engine on the blip.

CRex

This is the most logical explanation for me. I've encountered the exact same scenarios, except it happened both ON and OFF track. Specifically, I could re-create the symptoms in spirited highway blasts with very few corners. The diff could not have been working hard (if at all) but I'd still overheat the PP. As others have said, when PP overheats gearshift doesn't like to come out of gear.

Problem's now gone away with the installation of a new 4.0 PP (but same old 4.0 clutch plate since it looked 75% new), but the hawkish part of me thinks the problem is slowly coming back at the track. In another few sessions the episode may repeat itself all over...

997gt3north

Having thought it was the synchs but now listening to what Peter has to say I will add the following.

When I first purchased my GT3 I soon after did the LWFW install and ordered a new friction disk but kept the same pressure plate as the parts are the same (as is the friction disk) but thought it best to replace the friction disk.

What I found surprising was that the friction disk in the GT3 looked how it did. I have previous experience building big HP turbo cars and learned all about uprated Pressure Plates and Friction Disks - mixing and matching them to get the right combo of streetability and the ability to hold the power to 400+ and 500+ TQ cars.

The thing that surprised me the most was the friction disk - when I saw it I just didn't believe it was enough for a 'GT3'. The mistake I thought I made later was that these are low tq cars compared to 20psi+ turbo cars but it has always been the thing that has bugged me.

I remember one time I decided to drop the clutch a little at a traffic light to see if I could do a little drag start - sure enough I remember smelling burnt clutch and that confirmed to me that the 3.6 PP and 3.6 FD work for daily driving and even on the track when proper rev matching but they are on the very edge of just not being enough.

If you now move to the 3.8 and then the 4.0, if they are still suing the same friction disk I can tell you for sure that this is the problem - 100% in my mind. Someone should pull the part numbers and see if that is what they are using.

The GT3 friction disk looks identical to the friction disk material found in the 2001 Audi S4 and 2001 Audi RS4. In these cars, the S4 has 270hp and 270tq. The RS4 has 375hp and 325tq but was shipped with an uprated Pressure Plate with an additional 400# of clamping force I believe but still the same friction disk.

Both these cars were heavily tuned. Originally when they started tuning the S4 and bumping up the boost, people just installed the RS4 pressure plate but very quickly the friction disk became the obvious weak spot - and note the RS4 came with 325tq - very similar to the 4.0 GT3. It was very obvious very quickly that this friction disk couldn't hold much if anything above 325tq - but especially when hot - it just didn't work.

I spent years doing this and working through different combinations (I had a few of these cars) - but what I eventually figured out was:
1) for the most part if you just change out the Friction Disk for a 'type 2' type Spec Friction Disk it would without a doubt handle the heat better and it would work
2) spring loaded pressure plates were not worth it - they just kept failing


My advise to the 4.0 guys:
1) pull the Friction Disk part number and actually order it and look at it
2) if it looks like the 3.6 Friction Disk or is the same part # - that is a major red flag in my opinion
3) if true, find a Friction Disk that looks like a SPEC Stage 2 or 2+ made of Kevlar

- see the spec link below
- the 3.6 Friction Disk, and I'm betting the 4.0, looks like a SPEC Stage 1
- i just can't see a 4.0 that is being tracked working with this type of Friction Disk
- if you look at what the type 2 and 2+ Friction Disks look like, that is from all my past turbo car builds what is required when you get much above 300tq once you start abusing the tranny (i.e. track time)
- since these aren't drag cars, I do not think the issue is the Pressure Plate per say (not saying it isn't) as you are not dropping the clutch and launching the car - but the Kevlar Friction Disks just handle heat far, far better


http://www.specclutch.com/products

TRAKCAR

Part #'s.

I have seen the clutch, its the spring area that cracks open, this is fixed with the 4.0 part # below, but the PP still "melts" yet, the disc looked virgin, no wear at all.

997gt3north

.......... 4.0 RS ............ 3.8 RS ............. 3.6 GT3 .......... 997 gt2 ........... 997 gt2 rs
FD 997-116-013-91 997-116-013-01 996-116-015-01 996-116-015-01 997-116-013-91
PP 997-116-027-91 997-116-027-91 996-116-027-51 996-116-027-51 996-116-027-51


- just called the dealer to get some part numbers to see if that might help
- 3.8RS as everyone knows now uses the same PP as the 4.0 - it originally was shipped out with the 997-116-027-90 part
- what I find amazing is the 997 GT2 and the 997 GT2 RS use the same PP as the 997 GT3 (996-116-027-51) but the GT2/RS gets the likely uprated FD (997-116-013-91) that is used by the 4.0 but the GT2 uses the exact setup as the 997gt3

- it is very interesting that the Pressure Plate (996-116-027-51) which was used in a bunch of gt3s, gt2s and TT worked but then was changed for the 3.8RS (a part that failed quickly) and then changed again for the 4.0 (and seems to be having issues)?

- so the original 996 part number can handle more tq (up to gt2 RS levels) and handle 8400rpms (997gt3.mk1) but somehow was not good for the last 100rpms of the mk2 cars and 4.0 - both or which are now having lots of clutch issues?

- if it was me, I think I would try the 996 Pressure Plate from the GT2/RS, GT2 and GT3mk1 with the FD from the GT2/rs & 4.0RS and see if that works


I'm guessing that whomever is manufacturing that 997-116-027-91 Pressure Plate hasn't got the specs correct


What is Alex using on the 3.9?

Jamie_GT3

I like where this is heading. I agree, I tracked and daily drove a 3800lb 500+ftlb M5 on the track and on the street, have over 12000 miles on a segmented Kevlar clutch and it's still great, no issues.

I agree that if I heel and toe perfectly then there is little wear at all on the clutch, hell one would argue if you do it perfectly you really don't even need a clutch to make the shift

It's interesting that the disk is potentially underrated and lends a lot of credence to what we're all experiencing. If the clutch is slipping, PP is getting hot and diaphragm failure happens.

It is interesting the Eddie hasn't had any issues at all... Hmmmm....

RAPID

I agree with Peter's description of the symptoms, additionally I recently have the problem with the reverse gear being stuck (parking on slight slope after tracking, I put the car in reverse to avoid using handbrake). I don't think the synchro is involved here since I hardly ever use reverse? (by the way when I say stuck, I mean really having to pull as if you want to tear it away!). Rarely a problem when doing a lap (occasionally 4th to 3rd).

M3EvoBR

Jamie and I spent some good amount of hours discussing about the symptoms and when they happen.
Without any technical proof, but using a little bit of common sense, looks like it's heat related, Not necessarily gearbox internal heat, but clutch and most precisely pressure plate heat, where the excessive heat distort the 'springs' affecting the de-clutch action. Most likely by friction (which looks like to cause the heat increase)

On my GT2, I had to be very conservative with the boost ramping to avoid clutch slippage due to the torque levels. This is easily resolved with the use of a higher clamping pressure plate and also different friction disc.

Going a little further on what work what doesn't, I have hardly seen a clutch that works properly in track environment for these cars, and also in a few other cars, just to name a few which I have experience, a Evo VIII making a decent amount of power, torque, and the most important part, RPM. All these 3 things combined would avoid a 800+WHP 10K RPM gears to go in gear.
As most of us here still want to drive the car on the street most of the Carbon carbon clutches with small diameters like the Tilton is not really the best option, so I personally opted for a Sachs kit that is able to withstand about 890NM of torque (aprox. 650 lbs/ft) and has no springs, but still uses an organic disc, so the feeling is 90% the same as the OEM clutch.