engine and drivetrain Soft clutch

[Laurent1602]

Hi

My clutch started feeling very soft suddenly while driving. It almost needs no force but still works perfectly! There's no loss of brake fluid neither, reservoir is still topped up. This makes me believe there's no leak but I'm still puzzled what it could be...

Thanks for you replies!

[percy]

It could be helpful if you offered more detail regarding your ride, including general condition, and any recent work performed.  Not clear whether your clutch is engaged mechanically or by hydraulics, but since you mentioned no loss of brake fluid I will assume that with you are employing hydraulics.

 

Loss of  brake (clutch) fluid would indicate failing hydraulics so that you would likely feel a soft pedal or a pedal requiring multiple pumps to fully engage/disengage the clutch.  But hydraulic problems could still remain - without fluid loss.  Not unlike a problem more often associated with old or degraded brake hoses, an older or defective hose can swell internally, restricting fluid movement and pressure release.  At it's worse, degraded flexible hydraulic hose can act as a one-way valve, resulting in pressure to the slave cylinder that does not fully abate, despite taking your foot off the clutch pedal.  The net effect is similar to leaving your clutch pedal slightly depressed or a power assist.  

 

Another possibility is that one (or more) of the pressure plate springs or "fingers" has failed or is failing.  This might explain reduced pedal effort.  The clutch could still function, but the clamping force of the pressure plate/disk/flywheel would be far less than optimum.

 

Other possibilities could involve the clutch fork and the bell housing pivot upon which it rides.  Without lubrication, the pedal effort increases.  It seems counter intuitive and a long shot, but misapplied grease above the actual contact points "could" work its way down to the friction point. 

 

IF you had a mechanical clutch linkage, I would look to recently lubricated, tightened or replaced linkage.  But that brings up the possibility that your pedal assembly is laden with dirt and rust.  If you were one of those folks who spray or drop oil into the pedal box area, it might lubricate things, but if the linkage is worn, maladjusted or contaminated with dirt, the fix might be short lived.  Failing motor mounts or transmission mount might negatively affect mechanical clutch linkage operation.  Conversely, replacing mounts might make mechanically controlled clutch operation smoother and requiring of less pedal effort.

 

hth

Edited May 21, 2015 by percy

[roadhog0]

Spring broke in the hydraulic pedal box?

[PaulTWinterton]

Spring broke in the hydraulic pedal box?

Good call! That's the next place I'd look.

[Laurent1602]

It could be helpful if you offered more detail regarding your ride, including general condition, and any recent work performed.  Not clear whether your clutch is engaged mechanically or by hydraulics, but since you mentioned no loss of brake fluid I will assume that with you are employing hydraulics.

 

Loss of  brake (clutch) fluid would indicate failing hydraulics so that you would likely feel a soft pedal or a pedal requiring multiple pumps to fully engage/disengage the clutch.  But hydraulic problems could still remain - without fluid loss.  Not unlike a problem more often associated with old or degraded brake hoses, an older or defective hose can swell internally, restricting fluid movement and pressure release.  At it's worse, degraded flexible hydraulic hose can act as a one-way valve, resulting in pressure to the slave cylinder that does not fully abate, despite taking your foot off the clutch pedal.  The net effect is similar to leaving your clutch pedal slightly depressed or a power assist.  

 

Another possibility is that one (or more) of the pressure plate springs or "fingers" has failed or is failing.  This might explain reduced pedal effort.  The clutch could still function, but the clamping force of the pressure plate/disk/flywheel would be far less than optimum.

 

Other possibilities could involve the clutch fork and the bell housing pivot upon which it rides.  Without lubrication, the pedal effort increases.  It seems counter intuitive and a long shot, but misapplied grease above the actual contact points "could" work its way down to the friction point. 

 

IF you had a mechanical clutch linkage, I would look to recently lubricated, tightened or replaced linkage.  But that brings up the possibility that your pedal assembly is laden with dirt and rust.  If you were one of those folks who spray or drop oil into the pedal box area, it might lubricate things, but if the linkage is worn, maladjusted or contaminated with dirt, the fix might be short lived.  Failing motor mounts or transmission mount might negatively affect mechanical clutch linkage operation.  Conversely, replacing mounts might make mechanically controlled clutch operation smoother and requiring of less pedal effort.

 

hth

 

Thanks for the long and complete reply! My apologies for the short opening post, I was quickly typing it before I had to leave which is never a good idea.

The car has had no recent work to the clutch or braking system. The fluid was last replaced last year.

My clutch is using hydraulics indeed. I have checked the fluid level again today after standing still a couple of days in the garage now and it's still perfectly at the same level and no hydraulic fluid underneath the car.

Because it started so sudden, I don't expect the problem being a swollen hose and pumping multiple times also doesn't make any difference.

 

A broken pressure plate spring could definitely be the problem, is there a way to check that without having to take the clutch out of the car?

 

 

Spring broke in the hydraulic pedal box?

 

 

That was the first thing that came on my mind as well, but unlike the E9 I can't see the springs under the pedals. The pedal box is only accessible from underneath the car I believe?

Edited May 21, 2015 by Laurent1602

[PaulTWinterton]

You say that the clutch is working as it should, so Roadhog0 may have the simplest solution.

Check your pedal box first. Pull back the carpet, underlay, and rubber cover. The spring is on the left side at the base of the clutch pedal. Confirm that it is working as it should. If it's broken, or slipped that could be your fix.

Good luck.

Edited May 21, 2015 by PaulTWinterton

[Laurent1602]

You say that the clutch is working as it should, so Roadhog0 may have the simplest solution.

Check your pedal box first. Pull back the carpet, underlay, and rubber cover. The spring is on the left side at the base of the clutch pedal. Confirm that it is working as it should. If it's broken, or slipped that could be you fix.

Good luck.

DSC02001fx1.jpg

 

Well, since it's that simple I'm out to check it right now! 

[peterschop]

Well, since it's that simple I'm out to check it right now! 

 

Simple indeed........... unless you have the one piece carpet. While you are in the pedal box, make sure it is dry and no fluid has leaked in from the clutch MC.

[Laurent1602]

Simple indeed........... unless you have the one piece carpet. While you are in the pedal box, make sure it is dry and no fluid has leaked in from the clutch MC.

 

There you say it... I have a one piece carpet, damn   

 

Just checked it, everything is fine, no fluid!

 

And now the mindblowing part (at least for me). I just started the car to put it back in the garage, and the clutch felt normal again. Another thing I suspected was that it was engaging a lot earlier when it felt soft, that too was again gone. Very strange sice I drove the car today for 60km without any improvement. 

[percy]

 

I just started the car to put it back in the garage, and the clutch felt normal again. Another thing I suspected was that it was engaging a lot earlier when it felt soft, that too was again gone. Very strange sice I drove the car today for 60km without any improvement. 

 

 

 

You probably have worn seals (or wear in cylinder bore/s)  in either/both the master and slave.  This would explain no fluid loss. 

This might also explain hydraulic pressure and pedal effort changes.

 

Pedal feel/pressure could vary with heat and as you pump the pedal priming the system, especially if the system is worn or in need of maintenance.  Older, worn slave and master are prone to losing pressure when sitting for long periods.  By way of example, an E9 that hadn't been driven for months had a soft pedal when first started.  No visible fluid loss either.  with a couple of pedal pumps, the pedal became firm again. The best cure would be to replace seals or worn bores, along with fresh fluid - but for the foreseeable future, a quick bleed seems to keep her on the road.  To be sure, this is not exactly the same thing as brakes with which no one can afford to gamble.

Edited May 21, 2015 by percy

[Laurent1602]

You probably have worn seals (or wear in cylinder bore/s)  in either/both the master and slave.  This would explain no fluid loss.

 

This might also explain hydraulic pressure and pedal effort changes.  Pedal feel/pressure could vary with heat and as you pump the pedal priming the system,  In my experience with 02 clutch hydraulics, older, worn slave and master are prone to losing pressure when sitting for long periods.  E.g., an E9 that hadn't been driven for months had a soft pedal when first started.  No visible fluid loss either.  with a couple of pedal pumps, the pedal became firm again.  The best cure would be to replace seals or worn bores, but a quick bleed seems to keep her on the road. 

 

I agree with your explanation but this doesn't seem to be the case here. It first happened when I was on a drive (after 10km or so) and when I started it today (so when it was cold) it felt soft. I'm really wondering what it could be... For now I'll just see if it happens again.

[percy]

I agree with your explanation but this doesn't seem to be the case here. It first happened when I was on a drive (after 10km or so) and when I started it today (so when it was cold) it felt soft. I'm really wondering what it could be... For now I'll just see if it happens again.

 

 

I did not mean to suggest that heat would normally or noticably affect clutch hydraulics operation.

 

You did not indicate how long ago the clutch hydraulics were serviced or replaced.   Rubber seals do not last forever.  Even with regular fluid changes, degradation or deterioration is usually a lengthy process.  At some point there are tell-tale signs of wear, including quirky pressure issues (as you describe). Fluid discoloration can be another sign of wear (but not necessarily impending failure.)   A compromised hydraulic braking system tends to be more attention grabbing, e.g., when the brakes pull or require more pedal effort to stop, or don't stop the car the way they should.  We tend to be less demanding about clutch hydraulics, as the clutch either operates as it should - or it doesn't.  Remember, I used the word "tends" so some may be accutely aware of this. 

 

At some point seals develop micro-tears that grow in size until you lose pressure and the system's performance becomes less-than-acceptable.  Separate and apart from seals, cylinder bores can develop pits, scoring and rust  that makes it difficult for anything but the newest flexible seals to perform well.  Cylinder wear can also promote additional and premature wear on otherwise decent seals.  Unfortunately, there is no practical way of determining wear other than physically examining the bores and seals.  The good news is it's not the worst job in the world and bleeding is relatively simple..

 

Your narrative  suggests your seals and/or cylinder bores are showing wear signs.  In my uneducated-long distance opinion, it is hard to tell how long you can nurse the situation along (could be days, months or years) , but the clock is ticking.

[Laurent1602]

Well, I have no idea how long ago the master and slave cilinder have been overhauled. I own the car for a little over three years now and except fluid changes I never really bothered about the clutch so it would absolutely make sense to be wear of the sealings. The brakes and brake hoses however have been completely renewed so no worries there.

I'll just see how it goes now as I don't have the time to do much on my car for the coming weeks. If it's going to be a recurring problem I'll probably renew all cilinders and the brake master cilinder as well, as that is the only part of the braking system that's not yet replaced.

Thanks for the nice and informative write up!

Edited May 21, 2015 by Laurent1602

[Laurent1602]

The problem has become worse, until I couldn't keep the clutch in for more then a couple of seconds. Definitely a leak. It turns out that the slave cilinder is leaking, but I can't get it out!

I want to get it out in the direction of the green arrow, but to do that I of course have to remove the other end from the linkage with the clutch (red arrow) but I can't get it out. I can push it far enough backwards, but it doesn't bend enough to get it past the linkage. What am I doing wrong?

Edited June 6, 2015 by Laurent1602

[percy]

The problem has become worse, until I couldn't keep the clutch in for more then a couple of seconds. Definitely a leak. It turns out that the slave cilinder is leaking, but I can't get it out!

I want to get it out in the direction of the green arrow, but to do that I of course have to remove the other end from the linkage with the clutch (red arrow) but I can't get it out. I can push it far enough backwards, but it doesn't bend enough to get it past the linkage. What am I doing wrong?

ImageUploadedByTapatalk1433624957.201849.jpg

 

If you are saying you can't fully decompress the piston, then you can always try opening bleeder and/or feeder hose.  Follow with compression from large Channel locks, clamp or similar.   

 

 

If you are saying the slave is stuck, did you remove the circlip not shown in your picture?  It would be on the left side of the aluminum boss.

 

On severely rusted/corroded slaves I have resorted to removing hose and bleeder, spraying with penetrating oil followed by a good whack from a dead blow hammer. 

 

From a different model, but something like this?

Edited June 6, 2015 by percy