Strange W124 Troubles

[Sp!ke]

Over the past few days I've developed a very odd problem in my manual gearbox W124.

After sitting in stop start traffic for a while, the car develops a sort of high pitch whine. Once this whine starts, in a seemingly random fashion, the clutch pedal sinks to the floor and the clutch doesn't disengage. If I get a toe under the pedal, I can lift the pedal back up and on the second or third try, it works... for a few minutes before it does it again. As you can imagine, this is really scary to drive like this.

When the engine is not hot, the clutch is fine and there are no noises.

Both the clutch slave cylinder and master cylinder were replaced yesterday, still the same problem.

I'm now assuming something untoward is going on inside the clutch housing but I'm somewhat baffled as to what it could be and I'm very reluctant to take it to any clutch specialists as Its likely they'll just throw in a new clutch and potentially not fix the underlying problem.

Anyone experienced similar or may have an idea what it is?

I'm really not looking forward to doing this job, especially without a ramp.

 

[BlackC55]

Thats a new one on me.

What condition is the clutch plate and springs?

 

[Sp!ke]

The clutch is all original @ 180,000 miles.

 

[230K]

Hi

It could just need bled, i think from memory that they have to be reverse bled. I think i recall the brother inlaw having a similar problem with a 190D manual. I will text him and try and get him to read & reply.

230K

Update, i have texted him hope he comes on and helps.

 

[BlackC55]

Maybe it might be worth wipping the box out and having a look as you can't see anything from the outside.

The box removal is easy on the floor as the box is very light.

 

[BlackC55]

Good point 230k.

Start there Sp!ke

 

[Sp!ke]

I dont think it needs a bleed or reverse bleeding as its the easiest thing in the world to bleed as once the slave cylinder is removed from the casing, the clutch feed is almost perfectly vertical and gravity bleeds with ease.

You put clutch fluid in at the top,wait ten minutes until its dripping out of the bottom with a nice steady flow - easy. It also wouldn't explain it being perfect when cold, nor the noise it makes when hot.

Worth double checking as you say though. If you do get a response from your Brother in law that would be appreciated muchly.

Gearbox removal is easy from the floor you say? Might be for you but I have to say, I'm a bit trepidatious about doing it. ...

[edit] I almost forgot to say that the noise is worse on a left camber or when turning right, so it sounds like something is rubbing internally, possibly rubbing and generating heat and maybe boiling my clutch fluid in the slave cylinder.

Initially I thought the noise was a wheel bearing or disk but the noise continues when stationary so it kind of rules them out.

 

[Dieselman]

Check the free play at the master cylinder when the pedal is released. It sounds like there is no free play so as the fluid warms and expands it applies pressure to the release bearing causing it to overheat and make a noise. In turn this passes more heat to the fluid which then boils causing the limp pedal.

Free play allows the intake port of the master cylinder to allow fluid to retreat back into the reservoir properly.

 

[Sp!ke]

That sounds very plausible Dieselman.

I did see something about shimming the pedal adjuster in the Haynes manual and wondered what it could be about so promptly ignored it. I will check it out.

 

[grober]

There may also be a "clutch assist" spring on the pedal. Once the fluid is vapourised then this spring will self-actuate the pedal giving the mysterious movement to the floor?

 

[Number_Cruncher]

>>clutch doesn't disengage

Sorry Spike, I'm probably being thick, but, do you mean;

the clutch pedal sinks to the floor, and you can engage gears just as if the clutch were pressed in the usual fashion - i.e., no drive transmitted from engine to gearbox

or

the clutch pedal sinks to the floor, but, it's just as if the clutch is up, and you can't select gears, and reverese crunches (or do MB manuls have synchro on reverse?) i.e., drive is still being transmitted even though the clutch pedal is on the floor

 

[andy_k]

does this thread ring any bells Sp!ke?

I seem to remember Bob having all sorts of problems getting it to bleed properly

 

[grober]

does this thread ring any bells Sp!ke?

I seem to remember Bob having all sorts of problems getting it to bleed properly

Merc recommend using a pressure bleeder.

 

[Sp!ke]

This is true if the slave cylinder is in place when bled as it is higher than the lowest point of the clutch pipe.

However, if you remove the slave cylinder and let it hang down, its really easy to bleed.

The old thread talked of nothing but changing the slave and master cylinders (which I've done).

I think dieselmans on the right track. I think there's been constant pressure on the release bearing due to there being no slack. If the bearing is in less than perfect condition, it might have got hot and transferred the heat to the clutch pipe, increasing pressure further until eventually either something is seizing or the fluid itself has boiled.

I could set some slack in the clutch pedal travel and see what happens but I suspect that the bearing is damaged and the problem will return.

The clue is the noise in time with the problem. Clearly something mechanical is wrong rather than just being a bleed problem. If it were air in the system expanding, I'd expect to have some clutch slip and or a reduction in clutch performance when cold.

 

[Mark300SL]

I think dieselmans on the right track. I think there's been constant pressure on the release bearing due to there being no slack. If the bearing is in less than perfect condition, it might have got hot and transferred the heat to the clutch pipe, increasing pressure further until eventually either something is seizing or the fluid itself has boiled.

That was my first thought when hearing it

Maybe the whistle is the braking system equivalent of an old fashioned kettle

I could set some slack in the clutch pedal travel and see what happens but I suspect that the bearing is damaged and the problem will return.

The clue is the noise in time with the problem. Clearly something mechanical is wrong rather than just being a bleed problem.

Couls you not release the slave cylinder from its mounting whilst the car is still in "error" mode and making the noise ?
I have never dealt with a manual MB so I have no idea if this is possible

This would tell you
1. If the cylinder is getting too hot (burned fingers )
2. If the noise persists when the pressure is released you may be able to localise it (ie hydraulics or gearbox)
3. If the noise abates whilst releasing the cylinder you may be able to provoke it by pressing the actuator manually (removing the hydraulic system from the equation)

If it had got too hot then the noise could easily be a release bearing that has run dry after too many miles/years and the heat generated expands the bearing just enough to protest

 

[Number_Cruncher]

>>I could set some slack in the clutch pedal travel and see what happens

If fluid runs through when you bleed, then, the port in the master cylinder *must* be open, i.e., the pedal must be retracting far enough. After that, the system is self adjusting.

As per my question above, what happens when the pedal is on the floor?

 

[Sp!ke]

When the pedal is on the floor the clutch is engaged.. meaning it'll stall if I stop.

Eitherway, I think the gearbox needs to come out to inspect the clutch mechanism properly.

 

[Number_Cruncher]

>>I think the gearbox needs to come out to inspect the clutch mechanism properly.

I think you're right - I imagine you'll find the fingers of the diaphragm spring have worn away.

If you're taking the gearbox out, I would obtain a new 3 piece clutch kit ready to go in before you start. Even if the clutch looked OK, it wouldn't be a sensible move not to replace a 180k mile clutch while you have the opportunity.

 

[Sp!ke]

I removed the gearbox today and fitted a new clutch kit. The job took a little over 4 hours to do in the street.

Rather worryingly, the old clutch didn't look bad at all and neither did the release bearing or any other component. No signs of any wear or cause of the noise I was hearing. Also rather surprised to find a dual mass flywheel in there on such an early car. This was also removed and checked but seemed to be within service limits. A quick call to Mercedes for a price of a replacement flywheel soon helped me decide whether to replace it or not ...£620 +VAT Thanks but no thanks.

I've just come back from an extended drive and so far, no more noise and all seems well. The real test is to get stuck on the M25 for a couple of hours in bumper to bumper traffic. If its going to fail, that's when it'll do it.

Since the problem still hasn't been pinpointed precisely. I'm still not 100% convinced I'm out of the woods just yet.