sticky clutch weirdness

[ArthurPE]

thought this was interesting
last night when I parked in my garage I rev'ed the engine a few times while stationary with the clutch depressed (it popped out when released)
next morning (14 hours later) when I depressed it to start the car it 'stuck' in (car was obviously cooled off, 14 hours in a 70F a/c'ed garage)
I pulled it out and it is fine

so that tells me it may not be heat related?
very strange

is it spinning the clutch when cold?
do bubbles form?

[ArthurPE]

some more

car stationary
with pedal released, rev engine hard a few times...pedal does not stick
with pedal depressed, rev engine hard a few times...pedal sticks

does it hot or cold

[Dal]

Very odd thought they only did this when hot. Did anyone ever come up with a definitive answer as to why some rs4's do this ? And what part is actually causing it ?

[adsgreen]

If not temperature related then wonder if it is the velocity if the oil in the clutch.
When the clutch is engaged the problem part can not move... But when disengaged something is bouncing about and catching.

Given the scenario I doubt it would be master it slave cylinder related.

[Madmonkee]

Just to add to the mix: I give my cars beans down the slip road of the motorway up the gears then cruise control goes on, get to the leaving slip after about 10 miles dip the clutch... It's semi stuck down, mechanical over hydraulic?

[ArthurPE]

it's strange
still did it after cooling for >12 hours
only does it when the clutch is depressed and engined rev'ed, even if cold and no load
doesn't do it when rev'ed while the clutch is released, hot or cold

a new clutch seems to abate it for a while then returns

possibly friction material dust getting on the input shaft guide bushing?
clutch in pushes the throw-out bearing forward to push the springs and allow the disc to 'float', ie, no clamping/spring force
perhaps the dust deposits on the bushing, when released binds on the bearing?
I mean a flywheel/disc spinning at 130 rev/sec in an enclosed space would whip up some 'wind', probably towards the rear/bushing
perhaps the bearing/bushing tolerance is real tight

does this tranny have any openings/inspection ports on the bottom?
maybe blow out the housing with some high pressure water/brake cleaner/air?

but the way it is released when stuck, by just pulling it out makes it sound like hydraulics? but changing them does not fix it
and the clutch seems to be partially engaged when stuck?
the spring in the slave pushes the rod/fork out (but hydraulic pressure really does the work), not in, the friction plate springs (and pedal spring, but it seems to only apply force after some fulcrum point in the return arc) push the slave rod back in (and expel the fluid)
so by pulling the pedal out, relieving the pressure on the fork perhaps the springs then have enough oomph to push the bearing back? but not enough to overcome the hydraulics....and crud on the shaft makes it worse?

[ArthurPE]

interesting http://www.schaeffler.com/remotemedien/ ... pkw_en.pdf

• Release-bearing guide tubes
Check the guide tube for correct fitment. Guide tubes should be centered and parallel to the transmission input shafts. Damaged or worn areas on guide tubes may prevent the release bearing from sliding freely This can lead to judder, clutch slip, heavy or difficult clutch operation. Damaged or worn guide tubes should always be replaced as part of a professional clutch replacement. LuK-AS has a range liste within our passenger car catalogue, identified against specific vehicle applications.
Note: Audi and VW models still found to be fitted with a plastic sleeve should have them replaced with the metal version LuK-AS No. 414 0002 10.

as I noted before, ours have plastic (or used to?)

plastic


metal

[sakimano]

Interesting observation, one I've made before too while revving with the clutch engaged to scare a friend

I will bet a Coke that it is pressure plate related somehow. The jhm stage iv clutch has the same problem and it uses the stock pressure plate but replaces everything else.

Replacing slave cylinders and master don't do anything.

Replacing lines don't do anything.

I have also noticed this will happen when doing an Arthur test (fitting) if at redline you clutch in and coast. When you let off, it really gets stuck halfway or gets stiff. So now I just let it rev down or shift.

[sar]

like many i have also suffered the sticky clutch syndrome, i too thought originally that it was the sleeve that arthur has pictured.

when i replaced my clutch i bought a new guide sleeve convinced that when it was stripped down the sleeve would show some wear,
however once stripped the sleeve was mint no signs of catching or binding so i didnt even fit the new one just loba pressure plate loba clutch plate and release bearing.
15000 miles later everything still ok, so maybe it is oem pressure plate.

the original sleeve in my car was metal as was the replacement pics below.

[ArthurPE]

not sure it's the pressure plate since it does it hot or cold and only when depressed?

a couple of things I'm looking at
our car has an over centering spring, it's basically used to reduce clutch pedal force required
the first few inches require a bit more force to compress the spring
after that it 'over centers' and uses the force of the compressed spring to help push the clutch (requiring less foot force)
at the bottom inch or so it reverts back to absorbing energy

looking around I see the sticking clutch is a common Audi and other mfgs problem
it was rectified in some by adding a helper spring (clock type) to the pedal axle, which gets compressed the last few inches, this helps to make the pedal return stronger
some have removed the OCS (not recommended since it pushes the pedal out all the way)
some have put a pedal stop in, this prevents from depressing the pedal all the way (and saves the pressure plate springs from uneeded movement)
this might affect the clutch starter enable switch

when hot or has grit on the bushing perhaps the pressure plate spring or the increased friction on the bushing is just enough to hang up the OCS?

I am going to try a few things and also blow out the bell housing when I change ranny/diff fluid in the near future
also may fab up some sort of adjustable clutch stop

[ArthurPE]

like many i have also suffered the sticky clutch syndrome, i too thought originally that it was the sleeve that arthur has pictured.

when i replaced my clutch i bought a new guide sleeve convinced that when it was stripped down the sleeve would show some wear,
however once stripped the sleeve was mint no signs of catching or binding so i didnt even fit the new one just loba pressure plate loba clutch plate and release bearing.
15000 miles later everything still ok, so maybe it is oem pressure plate.

the original sleeve in my car was metal as was the replacement pics below.

IMAG0210[1].jpg

IMAG0209[1].jpg

is that bolted to the housing like the flanged one?
is there a clip that holds it down?

[redrsr]

My clutch has shown symptoms of sticky clutch for the last six months, in this time the bite point hasn’t altered and no slip
My symptoms are:-
First prime the problem, engine warm, a few spirited visits to the redline, after this the pedal will fail to return fully when slowing down at T junction/roundabout etc, as soon as you apply power the pedal springs back to normal position (can even pull it back up with your foot)
It appears my clutch misbehaves under reverse loads (engine braking) but needs the spirited driving to prime the problem
I’m fairly handy with a set of spanners but this baffles me, however, talking to a race mechanic his first question was “have you got a dual mass flywheel”, and “that’s your problem”

I’m sure Audi a, know the problem b, know the solution c, know the cost of a recall

[Timster]

I’m sure Audi a, know the problem b, know the solution c, know the cost of a recall

a, yes b, yes c, yes.

The topic has run since the car originally launched (I even uncovered an Audi workshop notice for this same issue).
They have never (and will never) offer a recall now as the car is far too old.
It's a design problem.

Seems the only way to fix is to change to an alternative clutch.

[sar]

is that bolted to the housing like the flanged one?
is there a clip that holds it down?

i never seen with my own eyes how it was attached arthur but i presume these picks from elsawin are accurate.

001.png (34.23 KiB) Viewed 5110 times

[ArthurPE]

is that bolted to the housing like the flanged one?
is there a clip that holds it down?

i never seen with my own eyes how it was attached arthur but i presume these picks from elsawin are accurate.

001.png

002.png

thanks, makes it perfectly clear
what is the texture/coating on the one you didn't use? was it the same as the one installed?

I'm pretty sure I've isolated what is hanging it up
mine seems to do it at the bottom knuckle or transiton point for the OCS, you can feel it hesitate, and I'm guessing when hot (fluid, friction springs, etc.) it just doesn't have enough force to return...at the bottom of the pedal it transitions from aborbing energy to releasing it in the middle of the stroke (to reduce leg effort required)

I'm going to make some shims to add some tension/preload to the spring, see if that helps