Soft Clutch after spirited driving / high rpms
03-19-2013, 10:53 AM
#1
Soft Clutch after spirited driving / high rpms
Not sure where to place this question...did a day's worth or research with no exact results.... just a general question at this point*
Back story:
My friend and I were on our way to a friend's place (an hour drive on the highway). We took a break around the halfway mark and decided to gun it the last stretch.
Both in '05 RX8s (84k km and 174k km).
Issue:
After about 15 minutes of 5k+ rpms the clutch pedal went soft....
I don't see this as centrifugal force pulling the pressure plate off as it felt the same at low rpms....
I am running an OEM clutch assembly....pretty sure he is as well.
The clutch resumed normal operating pressure once cooled down (overnight)- for us both. Temp was around -5~0C or 23~32F
Does the heat cause the clutch pedal to be soft (or somewhere in assembly?)
Is there something to be worried about or is this normal?
Back story:
My friend and I were on our way to a friend's place (an hour drive on the highway). We took a break around the halfway mark and decided to gun it the last stretch.
Both in '05 RX8s (84k km and 174k km).
Issue:
After about 15 minutes of 5k+ rpms the clutch pedal went soft....
I don't see this as centrifugal force pulling the pressure plate off as it felt the same at low rpms....
I am running an OEM clutch assembly....pretty sure he is as well.
The clutch resumed normal operating pressure once cooled down (overnight)- for us both. Temp was around -5~0C or 23~32F
Does the heat cause the clutch pedal to be soft (or somewhere in assembly?)
Is there something to be worried about or is this normal?
03-20-2013, 09:17 AM
#6
sorry, missed that in the OP
they both did the same thing? Unless it's slipping or having shifting issues I probably wouldn't be overly concerned. The advice earlier to bleed the clutch line & slave is good. The OE clutch in general has a very soft pedal that increases over time as the clutch wears.
they both did the same thing? Unless it's slipping or having shifting issues I probably wouldn't be overly concerned. The advice earlier to bleed the clutch line & slave is good. The OE clutch in general has a very soft pedal that increases over time as the clutch wears.
03-20-2013, 05:20 PM
#7
Lubricious
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Brake fluid absorbs moisture from the air. Over time it builds up, and it DRASTICALLY lowers the boiling point of the fluid. 8 years is a long time to be absorbing moisture. You just need to replace with new fluid that meets the specs. You'll probably raise the boiling point 200 degrees F.
03-21-2013, 08:53 AM
#9
Thanks for all the advice and information! 
I definitely think it's the boiling temp of the fluid...but not sure if the line should be replaced with a non-rubber one if...lets say I go for a couple track days this summer.
I would think the clutch was getting softer over time...but it resumes a harder/stiffer feel as the car cools down again.
As for the clutch plate and spring heating up...not sure if you mean from shifting or just general heat from plate from constant rpm.
I know I was in 6th gear with the exception of one gear drop for passing. Would this cause the same result?
I definitely think it's the boiling temp of the fluid...but not sure if the line should be replaced with a non-rubber one if...lets say I go for a couple track days this summer.
I would think the clutch was getting softer over time...but it resumes a harder/stiffer feel as the car cools down again.
As for the clutch plate and spring heating up...not sure if you mean from shifting or just general heat from plate from constant rpm.
I know I was in 6th gear with the exception of one gear drop for passing. Would this cause the same result?
03-21-2013, 03:23 PM
#10
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You would only have trouble with an overheating clutch disc if you were shifting improperly. If you were staying in gear, then an overheating disc isn't your problem. Possibly a soft clutch from boiling fluid could result in not fully disengaging on clutch in, which can heat up the clutch.
However you have made zero mention of clutch smell (like rubber, only with more of a sulfuric aspect) so I'm pretty sure you don't have a problem at the disc.
However you have made zero mention of clutch smell (like rubber, only with more of a sulfuric aspect) so I'm pretty sure you don't have a problem at the disc.
03-21-2013, 08:07 PM
#11
Tuner
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RIWWP, agree with you, however, improper **** it is very wide word.
for example, shifting under full throttle - ? what is it? is it requirement or just stupid thing which can destroy your clutch immediately.
or very slow shifting, like some ladies do?
for example, shifting under full throttle - ? what is it? is it requirement or just stupid thing which can destroy your clutch immediately.
or very slow shifting, like some ladies do?
03-21-2013, 08:15 PM
#12
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Agreed, it's pretty broad. For a clutch disc heat problem to occur, there has to be excessive slipping between the flywheel, clutch disc, and pressure plate. The root cause for excessive slipping is that the clamping force is improperly engaged when not shifting or improperly disengaged when shifting. There are many ways that this can occur, including driver error by not timing the clutch disengagement and engagement properly with the shifts and throttle use. For example, shifting into gear and applying gas faster than you let out the clutch will contribute to the problem. It can also be caused by hydraulic problems not transmitting the correct amount of force to the pressure plate to get full disengagement on the clutch disc. Several other methods as well.
In my opinion, the only "proper" way of shifting is to rev-match the shift, both upshifts and downshifts. This is minimal clutch wear, nearly non-existant. It takes practice to do consistently every time, and no one is perfect, so clutch wear will still occur. If nothing else, the slipping of the clutch when you start from stopped will always wear the clutch over time. The trick to it all is simply minimizing the wear you put on it.
There is very little that you can ever do to "destroy your clutch immediately". Just about everything bad for your clutch just takes hundreds or thousands of miles off it's life span instead. Eventually, one of these will kill it.
In my opinion, the only "proper" way of shifting is to rev-match the shift, both upshifts and downshifts. This is minimal clutch wear, nearly non-existant. It takes practice to do consistently every time, and no one is perfect, so clutch wear will still occur. If nothing else, the slipping of the clutch when you start from stopped will always wear the clutch over time. The trick to it all is simply minimizing the wear you put on it.
There is very little that you can ever do to "destroy your clutch immediately". Just about everything bad for your clutch just takes hundreds or thousands of miles off it's life span instead. Eventually, one of these will kill it.
03-21-2013, 09:07 PM
#13
The Professor
Typically you are shifting incorrectly if you take more than a second to use the clutch.
Pretend the clutch pedal is 1000 degrees and you are touching it with your bare foot. You should only be on it for the minimum amount of time possible.
Damage occurs when people feather their clutch un-necessarily (though it is a major part of getting a good launch off the line).
Most people who aren't good at manual trans yet will feather the clutch because that is the only way they can drive smoothly. This is where rev matching comes in. If you match correctly you can shift instantly and perfectly smooth (no car jerking) whether it be shifting up or down at any RPM.
Then once you are good at rev matching you can practice heel-toe. (rev-matching by pressing all 3 pedals at once). And then you are an expert MT car driver.
It takes practice, but the worst thing you can do is get into bad habits early.
Pretend the clutch pedal is 1000 degrees and you are touching it with your bare foot. You should only be on it for the minimum amount of time possible.
Damage occurs when people feather their clutch un-necessarily (though it is a major part of getting a good launch off the line).
Most people who aren't good at manual trans yet will feather the clutch because that is the only way they can drive smoothly. This is where rev matching comes in. If you match correctly you can shift instantly and perfectly smooth (no car jerking) whether it be shifting up or down at any RPM.
Then once you are good at rev matching you can practice heel-toe. (rev-matching by pressing all 3 pedals at once). And then you are an expert MT car driver.
It takes practice, but the worst thing you can do is get into bad habits early.
Last edited by staticlag; 03-21-2013 at 09:13 PM.
03-22-2013, 03:30 PM
#14
Don't think there is any clutch slippage because rpms stay stable as well when fully engaged....no rpm jump when clutch is engaged*
This is definitely not my first MT car, so I'd say my shifting is a good level....although shifting at low speed/rpm I find difficult to execute perfectly without a slight pause (talking milliseconds for smooth engagement) towards the release of the clutch pedal - as to not snap the clutch into place, thus jerking the car. High rpms feel much easier to engange the clutch at the right time shifting up or rev matching down.
As for heel-toe...yet to get that down right... way too jerky and still can't match revs properly with my heel :P
But great advice/opinions again guys! Thanks!
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