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I had something similar to this happen to me about 13 years ago on my 1st GT3. The car was about 2 years old at the time and I had just installed a new set of PS2's.
The only change that I made was the tires. The car was super twitchy at highway speeds. We could not figure out what was wrong. We ended up checking the tire build dates and it turned out that the rears were built about 7 months apart. Put on a different set with matching months and the problem was solved.
So it took a while for my plate set to arrive from Sharkwerks, but it arrived a couple of weeks ago after weeks in transit and weeks in customs. My car is now at my local Porsche dealer to have the LSD rebuilt and fix some issues we found with the chassis.
So what have they found?
The ride height at the back was around 2cm too low, also the weight distribution across the four wheels were not in line with the factory specs.
The breakaway force of the diff was only 5nm
While trying to raise the rear the technician disovered that the adjustment rings have oxidised to such an extent that they have become frozen. No amount of force or penetrating fluid could get them going again.
The result of all of this is that I am now upgrading the suspension with Öhlins Road & Track.
I have a couple of questions I hope you can help me with:
What settings are you guys running with this setup? I drive my car hard, but only track it once or twice per year. Our roads are very smooth. All help is appreciated.
According to my technician, the preload on the LSD is now too high with the set from GT Gears. Can anyone tell me what the preload should be after fitting the plate set from Guard Transmission?
Although there may be a problem, I would suggest that Matt knows what he is doing WRT the operation of the LSD and its settings! If you had questions, you should check with Matt
Thanks rbahr, I have already sent Matt a private message via this forum. I do not have an email for him as there is nothing listed on his site, but I notice that he usually responds quite quickly. They are measuring somewhere in the region of 100nm preload now.
I had feedback from Alex at Sharkwerks, he says you should not test the rebuilt LSD for breakaway torque/ preload while it is dry outside the car. In hindsight this makes absolute sense. He says that it needs five heat cycles to settle. So it looks like the dealer was just a bit over cautious.
Now I am off to figure out what settings will be best for the new Öhlins R&T setup.
I left my Öhlins R&T at its stock settings and that works fine for daily driving.
At least now we know why your car was so unsettled on the highway. These cars are very sensitive to alignment, tire pressures, and ride height/corner balance. I would start with the setting Öhlins has out of the box before contemplating any changes. You will be happy.
I had feedback from Alex at Sharkwerks, he says you should not test the rebuilt LSD for breakaway torque/ preload while it is dry outside the car. In hindsight this makes absolute sense. He says that it needs five heat cycles to settle. So it looks like the dealer was just a bit over cautious.
Now I am off to figure out what settings will be best for the new Öhlins R&T setup.
100Nm does sound high. It does make sense that the clutch parts need to be broken in, even though the manual does not indicate that.
Matt has posted his email and office phone in the past gtgears@yahoo.com
(508) 993-1733
Also check your front and rear Lower control arms... I had a rear one that developed play while at the track , and the car behave exactly as you described.. with unexpected jolts left or right while going on a straight line, which were derived from the wheel having play... It happened to me at the track and it wasnt a confidence inspiring feeling I can tell you.
best of luck!
Also check your front and rear Lower control arms... I had a rear one that developed play while at the track , and the car behave exactly as you described.. with unexpected jolts left or right while going on a straight line, which were derived from the wheel having play... It happened to me at the track and it wasnt a confidence inspiring feeling I can tell you.
best of luck!
I feel compelled to explain, that after much discussion, it was clarified that the straight-line problem was only when going on and off the gas. Pretty much ruling-out suspension problem and ruling-in LSD slip-grab-slip
I feel compelled to explain, that after much discussion, it was clarified that the straight-line problem was only when going on and off the gas. Pretty much ruling-out suspension problem and ruling-in LSD slip-grab-slip
I don't have time to review the whole thread, but even low tire pressure on one wheel will give you that result. It doesn't take much to make these cars twitch, including suspension setup, which, by the way, I have experienced, too.
More to the point, I still have the original LSD in my 04 and I'm sure it is long, long shot after 142K miles, but I don't have the issues that are described here. So, that pretty much doesn't rule out a suspension problem.
I had the same symptom you describe - unsettling when going off or coming on throttle, the more sudden the throttle input, the more unsettled the rear got. Turned out to be a stripped eccentric bolt.
I don't have time to review the whole thread, but even low tire pressure on one wheel will give you that result. It doesn't take much to make these cars twitch, including suspension setup, which, by the way, I have experienced, too.
More to the point, I still have the original LSD in my 04 and I'm sure it is long, long shot after 142K miles, but I don't have the issues that are described here. So, that pretty much doesn't rule out a suspension problem.
I summarized what has been learned in this lengthy thread, so everyone wouldn't have to read the whole thing. After 75 posts, we are w-a-a-a-a-a-y past the point of looking at low tire pressure.
But more to the point, the fact that you don't have the same handling problem with a shot LSD does not rule in a suspension problem or rule out the LSD in the OP's case. Besides, the OP determined the LSD was the cause. The fact that your LSD functions as an open differential does however explain why more people do not complain about LSD problems...they don't know their LSD is worn out.. It's ironic that the LSD, which is intended to improve handling at high speeds can have two totally different failure modes, a) the ineffective equivalent of an open differential or b) the slip-grab-slip failure mode which hurts handling in two ways 1) on the gas and 2) on the brakes but 3) not with a neutral throttle
Interestingly this issue also partially explains why C2 and C4 didn't have LSD's as standard equipment. First, they handle great with an open differential and second there would be lots of unhappy customers in the first 30k miles of ownership and a lot more warranty work on LSD's that weren't necessary in the first place..
We are still in communication with Sharkwerks and Guard Transmission. My Porsche technician is still worried about the plate pack being thicker. Can anyone with experience with these plates please tell me if this looks normal?
03-24-2020, 11:41 AM
