5th and 6th gear slip when boost hits
#1
Instructor
Thread Starter
5th and 6th gear slip when boost hits
2003 996 Turbo
6 Speed
1st - 4th gear seem okay, but if I'm cruising in 5th or 6th gear and I floor it...the rpms shoot up from 2500-4000 and the car doesn't go anywhere. I've never heard of a clutch slip in only 2 gears. Any idea what this is?
6 Speed
1st - 4th gear seem okay, but if I'm cruising in 5th or 6th gear and I floor it...the rpms shoot up from 2500-4000 and the car doesn't go anywhere. I've never heard of a clutch slip in only 2 gears. Any idea what this is?
#2
Race Director
Anytime you get a disconnect between engine speed and vehicle speed in a manual it is either clutch slippage or tire slippage.
Unless you tell me you are driving on very slick pavement I'm going to guess the car's clutch is slipping.
If find it hard to believe if pavement not slippery/slick the car could with its 4 wheel drive system break all 4 tires loose at 2500 rpms in 5th or 6th and keep them broken loose for long enough for revs to rise like you report. That's some impressive power output.
Besides if the tires were slipping shouldn't you see the traction/PSM light in the dash come on? My Turbo's tires broke loose once under hard 1st gear acceleration and a light off to left side of the dash flashed on momentarily. I didn't bother to get out the manual and see what it could have been. I'll do that after I post. I need to be more familiar with the manual and the car anyway.
Sincerely,
Macster.
#5
RL Community Team
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I don't think there is any chance that the tires are breaking loose with the RPM at 2500 in 5th or 6th gear.
So you have no issue with clutch slippage when going WOT in 2nd gear starting at 2500 RPM?
So you have no issue with clutch slippage when going WOT in 2nd gear starting at 2500 RPM?
#6
Instructor
Thread Starter
Non whatsoever. 1st-4th is strong as a mule. 5th-6th WOT sounds like a C4 Transmission with a big stall.
#7
Race Director
In 5th and 6th (and even 4th) gear torque multiplication diminished and clutch under more load especially if engine in the sweet part of its torque band and then with the pedal floored. If the clutch has any weakness at all slippage almost guaranteed.
Clutch. (Or possibly the clutch actuation hardware somehow faulty and this results in some pressure being applied to the clutch under hard acceleratio in the higher gears which causes the clutch to become partially disengaged and thus slip. Still, almost certain the tranny will have to come out in order to determine the exact cause and perform the necessary repairs. A qualified technician's opinion should be sought out before ok'ing such work.)
Avoid slipping the clutch any in the higher gears to avoid overheating the flywheel to the point it may not be reusable.
Sincerely,
Macster.
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#8
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It looks like your clutch has failed.
The pressure plate is not up to the task with 500ft lbs of torque.
Run up thru the gears, 1st, 2nd and 3rd then quickly shift to 5th..
The RPM will bog or race to redline.. This is a classic test to "check the condition of your clutch" If it races to redline then your clutch is toast.
You are making some good power, I have a clutch on the shelf. The decision right now is> do you keep your dual mass flywheel or upgrade to a lightweight flywheel.
You have to be carefull about burning your dual mass flywheel, if you get it hot and burn the surface you will need to purchase a new one $968.00 worth..
The pressure plate is not up to the task with 500ft lbs of torque.
Run up thru the gears, 1st, 2nd and 3rd then quickly shift to 5th..
The RPM will bog or race to redline.. This is a classic test to "check the condition of your clutch" If it races to redline then your clutch is toast.
You are making some good power, I have a clutch on the shelf. The decision right now is> do you keep your dual mass flywheel or upgrade to a lightweight flywheel.
You have to be carefull about burning your dual mass flywheel, if you get it hot and burn the surface you will need to purchase a new one $968.00 worth..
#10
Race Director
Kept my foot down well long enough that if the clutch was going to slip it would have. Tires didn't break loose either.
Tried the same thing again going up hill in 4th gear. Same results save I only saw 0.7 bar boost. (My info is the engine is set up to produce just 0.7 bar (max boost and of course stock) but that sometimes a reading of 0.8 bar is possible though an artifact of the boost gage or something.)
Not sure what margin these clutches have. If you have a mod'd car and I think I read you do -- chip mod at least -- it could be the engine's putting out more power enough more power, or in a peaky way, that overwhelms the clutch and it slips.
One can't know the condition of the clutch either. It might be on its way out and the extra power is just the final straw.
One thing that occured to me while I was testing: That your clutch doesn't slip in the lower gears could be the chip limiting power/torque output in the lower gears to avoid undo drivetrain stress. I know of, second hand, at least one automaker who does this with its manual equipped cars (BMW and its 5 series fitted with the V10 engine) to apparently lessen the wear and tear on the car's drivetrain that dumping all 500hp and 383ftlbs of torque which is kind of low ain't it, considering our Turbos kick out 413ftlbs, this mighty (ahem) V10 can put out.
Sincerely,
Maccster.
Last edited by Macster; 10-25-2009 at 08:41 PM. Reason: Added my Turbo info.
#11
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Macster there just isn't enough load in the early gears. There is a direct relation between time and load. The gear ratio's and road resistance that has a effect on the clamp force/pressure plate and clutch disk.
#12
Instructor
Thread Starter
#13
Race Director
I did mention in an earlier post that one possibility was the torque multiplication in the lower gears did reduce the load the clutch had to deal with and lack of slippage in the lower gears was a result of this.
Sincerely,
Macster.
#15
Instructor
Thread Starter
A little update:
I can't get the clutch to slip now. Today was a much warmer day. 72 degrees vs. 50 when it was slipping. Took it to my indy and we couldn't reproduce the 5th, 6th gear issue that I had the other day.
medtech is right. It is in fact still on the factory clutch with 70,000 miles on it. Never replaced. When I first got the car, I couldn't get it to slip if I tried when it was stock. Kevin's ECU flash combined with a little cold weather may have been too much for the old stock clutch to handle. We also found a transmission mount needed to be replaced. Fixing it tomorrow and will update.
I can't get the clutch to slip now. Today was a much warmer day. 72 degrees vs. 50 when it was slipping. Took it to my indy and we couldn't reproduce the 5th, 6th gear issue that I had the other day.
medtech is right. It is in fact still on the factory clutch with 70,000 miles on it. Never replaced. When I first got the car, I couldn't get it to slip if I tried when it was stock. Kevin's ECU flash combined with a little cold weather may have been too much for the old stock clutch to handle. We also found a transmission mount needed to be replaced. Fixing it tomorrow and will update.