I was hoping one of the MB techs had experienced this - PeachParts Mercedes-Benz Forum

Greg in Oz · #1 11-11-2003, 11:25 PM

Whilst I have had some very helpful replies, of which I have been appreciative, no one has experienced or been able to offer a definite answer to the problem I have regarding the clutch in my 190E. Pressumably the relatively small number of manual transmission Mercedes means that there is less likelyhood of someone else having encountered this problem. That's why I thought my best chances would be with one of the MB techs here.

To save me explaining the problem again, you can see how the story unfolds from my previous threads. They are (most recent first):

Clutch master cylinder question W201 & 124.

"High" clutch pedal problem. Any ideas?

190E clutch replacement. Any tips?

Whilst throwing a new clutch at it may temporarily mask the problem, I don't believe it is fixing the real cause. Rather than blindly replacing parts I would prefer to have either diagnosed the cause myself or have a well informed diagnosis from someone with previous experience with the problem. I would be very appreciative if any of the techs here can advise of experiencing the same problem. My concern is that if I give up, and get a workshop to fix it, they may end up blindly throwing parts at it which I am quite capable of doing!

Thanks,
Greg

autozen · #2 11-12-2003, 07:05 AM

Greg,
I have read through much of the previous threads an am trying to take a Sherlock Holmes approach. Given all the things you've done and all the suggestions, I question the validity of your clutch plate wear test. I don't have any info on the new style clutches, because they are almost none existant here in Calif. I do have the little tool that slips into the slot on clutches from the 60s and 70s, and I had to look in the book each time to see if the notches should be showing or not to indicate a worn clutch because I couldn't remember. I used a factory manual, but Haynes and other after market books are notorious for getting things bass ackwards. Why don't you state your exact test procedure, and perhaps someone out here can attest that you are reading it right. Once you dissengage the clutch, it is out of the picture. In 30 years as a MB mechanic I have never seen a clutch try to apply itself slightly to cause slipping.

Peter

Greg in Oz · #3 11-13-2003, 12:07 AM

Peter,

Thanks for taking the time to read the previous threads and to reply here. For us amateurs it is always reassuring when a tech can inform us that he has struck the same problem and advise the correct fix. Obviously due to the rarity of manual transmission Benzes, knowledge of the answer to such an obscure fault is hard to find.

Since I plan to give the 190E an oil and filter change this weekend, in addition to a coolant flush and change (now that I have eliminated all the minor coolant leaks). It is probably also time it had a brake fluid flush and change as well suggesting now as a good time to investigate the clutch hydraulics.

I will take your advice and again check the clutch wear with the tool and advise of my findings (ie. whether or not the notches on the tool are visible). Depending upon the outcome of this check, I will pursue the possibility of a problem with the clutch master cylinder. By attempting to reverse pressure bleed the clutch hydraulics I will hopefully get a better idea of the state of the hydraulic system. At the same time I will also bleed and replace all the brake fluid.

If all seems well with everything cold, I will then take the car for a drive to get everything hot before the oil change. By driving for long enough (they are forecasting a hot day Saturday), I should be able to get the clutch slip to occur. I will again check for clutch wear and whether all still seems well with the hydraulics, including whether any pressure remains in the clutch hydraulics without the pedal depressed (which would suggest an obstruction to the fluid returning to the reservoir).

I will carefully make a note of everything and post my findings here. Thanks again for your help.

Greg

95300YDT-A · #4 11-13-2003, 09:41 AM

Greg in Oz,

I mailed a reaction on this forum but unfortunately, I posted it on your former thread No. 79274. So I hope you are still subscribed to that forum.
Please feel free to ask any questions : auto-trannies are rather a rare in old Europ so manual trannies are far more common here!

Danny

Greg in Oz · #5 11-17-2003, 06:24 PM

On the weekend I investigated my 190E clutch problem further.

Firstly, using the measuring gauge tool as depicted in various workshop manuals, I again checked for clutch plate wear. With the tool inserted in the slot at the slave cylinder it pushed in such that the notches on the tool were not visible. According to my manuals this suggests that the clutch is NOT worn out.

Next I connected a "one man" bleeder (ie. bleeder hose with one way valve) to the slave cylinder bleed nipple. I then opened the bleeder nipple. Some residual pressure escaped immediately. My trusty assistant (aka wife) then pushed the clutch pedal ("is that the one on the left?") while I observed. What came out could best be described as resembling well used diesel engine oil! It was black. After much pumping of the clutch pedal and topping up of the reservoir, we eventually had clean fluid flowing and all the rubbish out of the system. Whilst the car had always been serviced at either authorised MB dealers or reputable independants, it was obviously all too difficult to flush the clutch hydraulics while doing the brakes. This had proved that it was at least possible to draw fresh fluid from the reservoir into the master cylinder, ruling out any blockage in the hose between the two. Again, I checked for clutch wear with the measuring gauge (since I now knew there was no residual pressure possibly holding the slave cylinder piston rod partialy extended). Again, the tool indicated the clutch to be OK.

At this point I decided to try a test drive. Immediately I noticed the clutch engagement point was much lower in the pedal travel, where I would expect it to be. After driving for a short time the clutch engagement point was getting higher in the pedal travel. After around half an hour with everything hot (it was a hot day at around 35C) it was possible to get clutch slip by barely touching the pedal.

With the car home again, I opened the slave cylinder bleed nipple to find the system under pressure. Obviously, the fluid could not return via the master cylinder to the reservoir to relieve pressure build-up due to expansion with temperature. This pressure is what is causing the slave cylinder to hold the clutch partially released.

The following morning, with everything cool again, I decided to try pushing fluid back to the reservoir via the master cylinder. I connected a snug-fitting vinyl hose to the right front brake calliper, and had my wife press the brake pedal ("that's the one in the middle, right?") while I opened the bleed nipple to fill the hose with fluid. I then attached the other end of the hose to the bleed nipple on the clutch slave cylinder. With both bleed nipples open, I asked my wife to start pressing the brake pedal. The hose blew off the nipple at the slave cylinder with great force. Again we attempted the same procedure while I held the hose firmly at each end. Fluid escaped around the bleed nipples but it was not possible to get fluid to flow back to the reservoir via the master cylinder. At this point I decided I could not do much more short of dismantling things. I again bled the clutch hydraulics and also did all the brakes after a brake fluid change.

My conclusion from all of this is that fluid can be drawn from the reservoir as required, but cannot return as is necessary due to expansion. Earlier systems with an adjustment at the master cylinder push rod would allow the master cylinder piston to be adjusted so as to allow the return of fluid to the reservoir with the pedal in the up position. In the absence of any such adjustment on my later model car (as postings by others have verified), I can only assume a fault with the master cylinder.

My next step will be to remove the master cylinder and dismantle it to try to find the cause. I have checked the price and availability of one should I need to replace it. This may be some weeks away yet as my father's '93 E320 coupe (M104) water pump is becoming more urgent and will have to take priority over my 190E which is at least still driveable. I am mindful though, that with pressure remaining in the clutch hydraulics that the clutch release bearing will be doing a lot of work it was not intended to do. I must also take care not to allow the clutch to slip when things get hot either.

Thanks to all who have posted replies. I will keep you informed of any developments as they occur.

dmorrison · #6 11-17-2003, 07:42 PM

Let me add.
I do not nor have I worked on an hydraulic clutch system. But reading you last post it seems to me that
1. Dirty fluid. you probably have rust in the hydraulic system.
2. pressure was "trapped" after applying the clutch, using the hydraulic pressure. This pressure did not bleed off after use.
Check the lines for rust and contaiminants. Also check for return lines that could be clogged with debris.
This would mean checking the lines all the way form the pedal to the clutch actuator.

Just my 2 cents.

Dave

mbshop · #7 11-17-2003, 10:45 PM

if the pressure goes away when you loosen the line at
the clutch master cyl, then its the cylinder assuming you
checked that the clutch is returning correctly.
do you have some play in the pedal? you should.
if the pressure does not release then you need to
check the clutch hose.

george

ctaylor738 · #8 11-18-2003, 10:18 AM

I agree. I would replace the slave cylinder and the flex hose as a first measure. The slave because that is where the foulest of the water-laden old brake fluid collects, and the hose because they are prone to swell shut after some years of use.

Two more observations:

I had a 124 with a 5-speed for many years. I did not ever notice a change in the clutch play or pedal travel as I drove the car from a cold start to fully warmed.

I fought this exact problem on an XKE. Same basic arrangement. Following experienced advice, replaced slave, hose and master cylinder to eliminate them as problems. Clutch still slipped when engine warmed up. Clutch lining thickness was OK. Was advised that remaining causes were glazing of clutch lining and weak pressure plate which apparently also happens over time. Both can cause slippage as engine/clutch warms.

Greg in Oz · #9 11-18-2003, 07:26 PM

Thanks everyone for the interest in this problem.

Dave,
Yes the fluid was dirty but I have flushed everything and am getting clean fluid when I bleed it now. This is not to say that there is still not a problem, which there obviously is. There are no "return" lines as such. The one line between the reservoir and master cylinder and the one line between the master cylinder and slave cylinder are the only lines in the system.

George,
I agree. The only problem is that once I have gone to the trouble of doing all that is necessary to open a line at the master cylinder I might as well continue with the job and completely remove the master cylinder. The master cylinder resides in the area of the pedals and precautions must be taken to prevent fluid spilling inside the car. Access is also confined.

Chuck,
Yes, I am aware of hydraulic hoses "closing down" and restricting the flow of fluid. This is a common problem with brakes. With my clutch, most of the line between the master and slave cylinders is metal with only a short length at the slave end being flexible. The supply line between the reservoir and master is a flexible hose but this is OK as I can draw fresh fluid from the reservoir. I can understand you never noticing any change in the behaviour of the clutch in your 124. If mine did not have a fault it would not exhibit any change either. I don't consider there to be a problem with the clutch plate since there is no slip cold, nor hot IF the pressure is released from the hydraulics. It is only when pressure builds up with temperature that any slip occurs. Warning of this comes with the clutch release point getting higher in the pedal travel. With that pressure released the clutch works fine and the release point is midway in the pedal travel.

I will post my findings when I explore the problem further. As far as replacing parts, I would prefer to start with the less expensive and more easily replaced items such as the hydraulics, especially considering this is the suspect area at this stage. To remove the transmission and replace the clutch and possibly the flywheel only to find they are not at fault would be a costly waste of effort.

Thanks again for all the interest,
Greg

autozen · #10 11-18-2003, 09:59 PM

Greg,
I have just emailed this thread to Gilly who works at a dealership in Wisconsin. You may have never heard of it, because it is a small insignificant state,however, I have a fondness for it, because I was born there. At any rate I have asked him to see if there are any TSBs ( technical service bulletins) on the subject. You have done a marvelous job reporting on your procedures and it is appreciated by everyone trying to resolve your problem. Nothing pisses me off more than someone who doesn't even have the courtesy to state the model and year of the car in question. We'll keep working on your dillema until we get a solution.

Peter

Greg in Oz · #11 11-19-2003, 01:27 AM

Peter,

Thanks for taking the time to consider this and for involving other techs like Gilly. Wisconsin may be small (do I detect that you may be trying to stir Gilly?) but I have indeed heard of it! Despite never having had the pleasure of visiting the USA, like most Aussies I still hear much of your country. Whilst Australia is similar in area to the USA, we have a much smaller population. As such, much of what we watch on TV and read originates in the US. Kids here would probably be able to list a larger percentage of your large number of states (and cities) than kids there would be able to list of our small number of states and cities. Anyway, I digress.

It may be a couple of weeks before I can explore the problem further as I have other things requiring my attention (including my father's M104 water pump).

One interesting point to add is that I mentioned the problem to a friend who works as a tech for a BMW dealership. He stated that the same problem has occured with some BMW clutches. Obviously with more manual transmission BMWs around the problem is more well known in those circles. Another person I mentioned it to who spends considerable time working on cars stated he struck a similar fault on a locally produced GM Holden Commodore. In that instance the long spring within the master cylinder had broken. This prevented the piston completely returning which in that situation resulted in reduced piston stroke with a resulting dragging clutch. Unfortunately in that situation, unnecessary expense was incurred in the unnecessary replacement of the clutch before the real fault was found.

With all the evidence available to me at this point I really believe my master cylinder to be the culprit. It really comes down to whether I simply purchase a new one and replace it, or remove mine and dismantle it first in search of an explanation for the cause of the problem.

I would be very receptive to any similar experience others may have had or to any TSBs relevant to the problem. Again, thank you for all the constructive input everyone has contributed. We will get to the cause of this and solve it. I will keep you posted.

Greg

ctaylor738 · #12 11-19-2003, 09:49 AM

I re-read all the posts last night. I also looked on the 124 CD and my other manuals in vain for a cut-away of the master cylinder. The C-class Haynes manual has some excellent pictures of the MC and SC disassembled. It also states that there is no adjustment so I think the 202's have your setup.

It states "...as wear takes place on the friction disc ..., the pressure plate automatically moves closer to the friction plate to compensate." Huh? How does this work?

Anyway, here are my candidate theories at this point in descending order of (my) probability:

1. Corrosion in SC after 13 years without fluid change has partially blocked the line connection preventing full fluid return.

2. Flex line deteriorated, not allowing full return.

3. Metal line damaged or corroded, same result.

4. Check valve in MC malfunctioning not allowing full return.

5. Obstruction in pedal mechanism not allowing MC piston to return fully, blocking hole to resevoir.

6. (New theory). Clutch wear or malfunction of mysterious self-adjustment mechanism is causing the the MC piston to not return fully, blocking hole to resevoir.

Can you somehow test 5 and 6 by verifying that the MC piston is returning fully up against its internal stop?

MrCjames · #13 11-19-2003, 11:58 AM

Hello Down Under

I have not read through all your posts so let me apologize to you if some of my suggestions have been mentioned previously.

I encountered a couple of different clutch complaints over the years and here are a couple of suggestions I can offer.

1) The pushrod may be a ball socket, ensure it is properly seated in the clutch master (snaps in)

2) Pressure bleed the clutch in the reverse manner (through the clutch slave back to the reservoir)

3) Replace rubber hose near the trans, if not done already

4) Over center spring (only a suggestion)

5) Ensure the pivot points and or pins on the pedal assembly are not worn

6) Consider new nylon bushings where possible

I vaguely remember some sort of information on the clutch system for all cars. I will need to sift through my piles to find it.

Good Luck

Greg in Oz · #14 11-21-2003, 02:45 AM

Chuck,

I imagine the W202 may well run the same setup. The W201 and W124 do. I agree that the slave cylinder may not be in the best condition although faulty clutch slaves usually leak fluid externally past the piston and don't allow full clutch disengagement (the reverse of my problem). If I am going to start replacing hydraulic components, I would prefer to start at the top and work down. My feelings are still that the fault is at the master cylinder. I'm pretty sure the master is returning fully as it forms the upper stop for the pedal travel. Attempting to pull the pedal higher does not result in any additional travel. In fact, the clutch pedal "helper spring" gives an over-centre action that pushes the pedal up in the upper part of the pedal travel and pushes the pedal down in the lower part of the pedal travel (without hydraulic pressure in the system to resist this).

MrCjames,

In reply to your points:
1) Since the master cylinder forms the upper stop for the pedal the pushrod must be seated otherwise the pedal would travel too far up.
2) I did try reverse pressure bleeding. Being unable to achieve this confirmed there is a blockage to the return of fluid from the master cylinder to the reservoir. Bleeding in the normal direction was possible though.
3) Haven't replaced this hose yet. I will probably do so once I open the system to investigate the fault further.
4) Over-centre "helper" spring seems fine.
5) & 6) All pivots etc. seem fine with no obvious wear or play anywhere. Car has "only" travelled 220,000km.

Thanks again for the replies. I will post updates when I get further with it. Fortunately, the problem is not severe and only become obvious after extended driving. For now, it is not preventing me using the car for my regular shorter trips.

Greg

190E 2.3 rur rur rur · #15 12-13-2012, 04:23 AM

boys, there was a lot of time that passed.
Did you ever fix the hose to the reservoir?
I see it available from a German car dealer online where i live. and after all this time, did you resolve the issue? those parts are all available that you have considered throughout these threads. i just cant help wondering what keeps you from performing the inspections of the parts in question. and also, taking measurements, using an inspection mirror, flashlight, and comparing it to another car. if i couldn't learn the answer at the wr yard, i would at least have some inexpensive (diagnoser ) parts to take home. then, theres working units sitting on car lots, and driven by techs, at your selling dealer. if they wont help i would ask a stranger. what i can offer you is two anecdotes of pressure build. i saw a pickup truck that was having hot brakes caused by the pushrod clip. the last person to assemble had a clip that sheared a piece trapped. that small shard was keeping the mc piston from returning, blocking the compensating port. unexplainable with logic. it had to enter when the pedal was pushed and just dropped in. but how could it get in that position? blown by an airhose from another work station in the same shop? fallen in during a bench bleed procedure? the second was a design issue of lightweight economy cars. a weak shake brace design resulted in a whole line of vehicles that had pedal linkage attatched to weak metal. hard application led to brake drag. you gotta inspect, measure and compare, that is the diagnostic steps we refuse to pay for and seldom receive as a result. if you get wind of this story, let me know what did fix it. please

:EDTI for readability:
Boy, there was a lot of time that passed.
Did you ever fix the hose to the reservoir?
I see it available from a German car dealer online where I live.
After all this time, did you resolve the issue?
Those parts are all available that you have considered throughout these threads.
I just can’t help wondering what keeps you from performing the inspections of the parts in question, and also, taking measurements, using an inspection mirror, flashlight, and comparing it to another car.
If I couldn't learn the answer at the wrecking yard, I would at least have some inexpensive (diagnoses) parts to take home, then, there’s working units sitting on car lots, and driven by techs, at your selling dealer.
If they won’t help I would ask a stranger.

What I can offer you are two anecdotes of pressure build.

I saw a pickup truck that was having hot brakes caused by the pushrod clip.
The last person to assemble it had a clip break trapping a small shard, keeping the master cylinder piston from returning, and blocking the compensating port.
Unexplainable with logic, it had to enter when the pedal was pushed and just dropped in.
But how could it get in that position?
Blown by an air hose from another workstation in the same shop?
Fallen in during a bench bleed procedure?

The second was a design issue of lightweight economy cars.
A weak shake brace design resulted in a whole line of vehicles that had pedal linkage attached to weak metal.
Hard application led to brake drag.
You need to inspect, measure and compare, that is the diagnostic steps we refuse to pay for and seldom receive as a result.
If you get wind of this story, let me know what did fix it.
Please.
:EDTI for readability:

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode