GT3 RS with failed limited slip diff. Please advice
05-30-2011, 06:09 PM
#16
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I had my local dealer look over my Gen 1 RS because the warranty is soon to expire. They told me that the clutches are completely worn out in the LSD. my question is how dangerous is the car to drive on the street? I'm suppose to go on a 1,000 mile road trip in a few days and I can't decide if I should take the car or not. A few weeks ago I drove the car 850 miles in three days and did not feel anything unusual at all! (spirited driving). So do I park the car and forget about it until it is repaired or drive it another 1,000 miles? Thanks!
Just don't push it until you fix it.
You can also install the clutch packs from a 996 cup car. Cheap and easy fix.
Incidentally, I just decreased the rear brake bias a bit by changing rotors and it has suppressed the rear tail-wagging under threshold braking at higher speeds (say about about 80-100mph.) I was paying careful attention because I was anticipating that reduced rear bias would increase the tail-wagging and "rear steer" under heavy brakes or tease the ABS or some aspect of SC (it's a 997.2 RS) into intervention -- that's complex to explain, but if you imagine the rears are now about 1% reduced, then the differential bias could become greater because the brakes are not serving quite as much differential slip resistance. The car's also running 345 Hoosier R6, which introduces two other factors -- the car is already hooked up unless the driving is untidy; and, a characteristic of the A6/R6 is initial "skate" which gives the yaw sensor something to think about. Fortunately, not apparent issues whatsoever, if anything, the 1-1.5% decrease has reduced the willingness of the car to go into ABS, making me question whether the considerable increase in rear brake bias in the 997 GT3 over the 996 GT3 brought some unintended consequences where the decision was made to compromise a little threshold limit in favor of better performance at lesser degrees. Maybe I'm just accustomed to stopping a 911 on its nose. Maybe the track had good grip that day. Maybe, maybe, maybe. Nothing scientific about my work. Pleased to find my car still has a functional LSD (noticeable through the carousel T6 at Sears on a cold track) but I know it's only a matter of time.
So you think that you found the magic optimum braking bias without using the equation: braking force at the tire versus weight on that tire?
Excellent! Now I have to find it for my car : )
"I was paying careful attention because I was anticipating that reduced rear bias would increase the tail-wagging and "rear steer" under heavy brakes. "
Increasing front bias by definition promotes stability.
Overdoing it will cause your stopping distances to go up.
No tail wagging involved.
05-31-2011, 05:00 AM
#18
To rebuild your diff? $1,000 - $1750 sans shipping and local labour to remove and reinstall. Look up LSD Buster thread to see how mikmyu took his out and reinstalled if you want to do it yourself.
New diff = much more money + more labour + no real benefit unless you drive Cup cars for a living...
New diff = much more money + more labour + no real benefit unless you drive Cup cars for a living...
05-31-2011, 10:10 AM
#19
Burning Brakes
Thread Starter
There seems to be a difference of opinion here. Some say not to push it until it's fixed and others say not to worry, you will not notice a thing unless you push it well beyond reason. Does anyone think the car will not be safe driven at 75%?
05-31-2011, 10:30 AM
#20
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75% of your normal driving limit, or 75% of the limit of the car?
I have driven my previous car (993) with a busted lsd, and at 210 km when braking hard I had to be quite alert to avoid the back of the car catching the front. That was around 75% of the limit of the car, it was also my limit...
I have driven my previous car (993) with a busted lsd, and at 210 km when braking hard I had to be quite alert to avoid the back of the car catching the front. That was around 75% of the limit of the car, it was also my limit...
05-31-2011, 11:02 AM
#22
Burning Brakes
Thread Starter
Rapid, yes 75% of the car.
05-31-2011, 11:49 AM
#24
Rennlist Member
My diff has been blown for well over a year and I still track the car all the time. It's exactly as described elsewhere in the thread -- a little squirmy under hard braking and you can't get on the power quite as much as you'd like coming out of the turns.
No big deal at all.
No big deal at all.
05-31-2011, 03:21 PM
#25
Nordschleife Master
If you guys are tracking these cars with blown diffs, please be sure to run an aggressive oil change service interval (2-3 events per change). If you look at the LSD Buster thread or the recent article in European Car you'll see pictures of blue plates from 997 cars because they get hot when they slip on each other and don't bite. It's probably not enough extra heat to damage anything (I am just guessing here and only a gear box temp gauge would tell for sure how much hotter they are getting) but it's going to kill your oil more quickly. For the protection of the longevity of your gearbox change your oil often if you are going to delay maintenance on your LSD and continue running the car hard at the track.
Regards,
Matt Monson
Guard Transmission LLC
Regards,
Matt Monson
Guard Transmission LLC
05-31-2011, 04:24 PM
#27
Nordschleife Master
05-31-2011, 04:38 PM
#28
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Blown Diffs are no big deal on street cars nor the odd track time car.
However, to those who wish to increase their track time experience to a high standard and practice will want a built LSD.
Only makes sense to have a proper LSD if going through the trouble/expenses to align high end suspension upgrades and addition track wheels/slicks....
One who tracks often should want the most out of their car...... proper LSD is no exception.
However, to those who wish to increase their track time experience to a high standard and practice will want a built LSD.
Only makes sense to have a proper LSD if going through the trouble/expenses to align high end suspension upgrades and addition track wheels/slicks....
One who tracks often should want the most out of their car...... proper LSD is no exception.
05-31-2011, 09:00 PM
#29
Race Director
06-01-2011, 01:03 AM
#30
Burning Brakes
Thread Starter
Thanks for all the helpful comments. Feeling much better about the situation! I asked my service manager how much $ it would run me if it wasn't covered under warranty. 6K + was his answer. I'll let Porsche pay for it this time.. Next time I'll go with the guard.