Clutch master cylinder question W201 & 124.
 

This is a question for those who really know the clutch master cylinder setup on a W201 and W124 well. My Haynes manual (for both W201 & 124) describes an adjustment for the master cylinder pushrod. The adjustment allows the piston in the master cylinder to return just far enough to uncover the port for the connection to to fluid reservoir when the pedal returns to its stop.

Problem is my 1990 190E has no such adjustment. It appears there is no stop for the pedal and that the piston returning to the circlip at the end of the master cylinder forms the stop. Other diagrams in the Haynes manuals also tend to agree with this setup.

I ask this as I'm still having a problem that I posted about previously where my clutch pedal take-up point gets progressively higher with increasing temperature, to the point where I can get some clutch slip. Once cooled there is no slip. The clutch plate is not worn out (according to the measuring tool) and I get no slip until everything gets plenty of time to heat up (ater maybe 1 hour driving in heat).

My diagnosis is that the fluid inlet port in the master cylinder is remaining covered by the piston. This prevents excess fluid returning to the reservoir when the fluid expands due to a temperature increase. The result is that pressure remaining in the system prevents the slave cylinder from fully retracting the clutch release lever. In the absence of any push rod adjustment it suggests that possibly the master cylinder piston seal is swollen. It appears my best option is to fit a master cylinder kit or replace the master cylinder.

Can anyone confirm that:
1. the '90 models had no pushrod adjustment.
2. my diagnosis seems reasonable.
3. that the piston seals can swell thereby blocking the master cylinder port.

Anyone had any experience specifically with the W201 or W124 clutch master cylinder? Any techs got thoughts on this one?

I don't have any experience with that because I havn't had any problems. I'm a little busy right now but you are more than welcome to have a look at mine. I have the factory CD, if I do get time I'll have a look for that.

Greg,

I remember reading your previous posting on the 190's clutch slipping.

I think what you are trying to determine is whether by using the car for "after maybe 1 hour driving in heat" that the clutch is in fact slipping, slightly.

What is the free play on the clutch pedal/linkage when cold verses after one hour of driving?

I also have the Haynes manual with its sections on the clutch. It is multi-paged, but I will try and see if there are any specific clutch related descriptions that could match what your are experiencing.

Haasman

Jim,

Thanks, I would be interested to know what information the factory CD has re the clutch master cylinder, especially the issue of a master cylinder pushrod adjustment that the Haynes manuals discusses. Mine definitely does not appear to have any such adjustment with the master cylinder itself being the stop for the pedal in the up position.


Haasman,

With time (since my thread of some months back) I have been able to observe and analyse the problem. The clutch definitely checks out OK using the measuring tool. When cold it works fine without any hint of slip, even under full throttle conditions. The take-up point is fairly high in the pedal travel but not at the top. After considerable time driving (in warm weather), the take-up point gets progressively higher to the point where clutch slip begins to occur even at moderate throttle openings (can still be driven under cruise conditions but care must be taken to avoid slip climbing hills and accelerating). When everything cools down again all is fine. On my short daily commute it is not a problem, nor was there any obvious problem through the cooler months of winter. Only now with hot weather coming and on longer journeys is the problem again becoming obvious.

I am convinced that the inlet port (from the reservoir) in the master cylinder that should be uncovered when the pedal is at the top of its travel is remaining covered. This is normally taken care of with the pushrod adjustment that the Haynes manual describes. If the port remains covered by the master cylinder piston, pressure build-up that occurs as the temperature rises, cannot be released by allowing excess fluid to return to the reservoir. In the absence of a pushrod adjustment this can only occur as a result of something blocking the port such as a swollen piston seal or foreign matter in the port. The pressure causes the slave cylinder to hold the clutch slighty released, resulting in the slipping.

I was hoping that someone my have dealt with a similar situation or can at least agree with my diagnosis. It would be easier to overhaul or replace the master cylinder than to replace the clutch, especially if the clutch is not worn out (as I am inclined to believe to be the case).

Thanks for the thoughts on the problem,
Greg

Greg,

I am unsure, but my intuition tells me that it is not an intake port problem...... but if you are correct in your analysis, test it:

Take the cylinder link off the pedal, give it a full stroke, reattach it and see if that does the trick. Then you will know, once and for all.

I am excited to hear, don't keep us waiting!


Haasman

Haasman,

Thanks, but I don't understand what you are suggesting. If you mean give the master cylinder piston a full stroke then this is what happens now with it connected to the pedal. The master cylinder piston is returning hard up against the circlip at the end of the cylinder. This appears to be the actual stop for the pedal. At this point the inlet port should be uncovered, allowing free movement of fluid to or from the reservoir.

Greg

I've always been under the impression that there are no adjustments of any kind on the clutch. My "Model Year 1984" manual (USA) has an overview of the clutch and control system and includes the following statement regarding the 201 clutch:

"The upper clutch pedal stop is no longer on the pedal bearing bracket, but integrated in the clutch master cylinder"

The line drawing shows a rubber bellows cover over the master cylinder pushrod, so I can't tell if it's adjustable or not, but to me the statement implies that there is no adjustment, and like a typical brake master cylinder I assume that the piston retracts to a snap ring or some other type of mechanical stop built into the master cylinder.

Duke

Duke,

That's exactly as mine appears. There is no stop on the pedal itself. The stop is simply the piston returning against the circlip or snap ring (visible when the rubber bellows are lifted). The pushrod adjustment the Haynes manual refers to is by way of an eccentric where the pushrod attaches to the pedal. Mine (a '90 model) does not have this and agrees entirely with the description you have given. Presumably this was a design change that occured around '84. That clears up that mystery. Now just for my problem and my diagnosis.

Thanks,
Greg

My suspicion is that you might have air in the system, and increasing temps causes it to expand, which reduces the free play, and even starts to disengage the clutch. I'd suggest a good flush before you start taking things apart.

I'm having the opposite problem - increasing freeplay to the point where the clutch drags a bit causing balky shifting. I can get more travel by pumping the pedal a few times. I suspect that my slave is on the fritz as I also spotted a trace of brake fluid nearby.

Despite bienniel flushings the slave won't last forever. Because both the master and slave are moved full stroke every time you declutch, the cup rubbers eventually wear. In a brake system there is little movement, especially at the calipers, so there is less wear over time.

I suspect I will be replacing or rebuilding my clutch slave cylinder in the near future.

Duke

Duke,

The more I think about this, the more inclined I am to flush and bleed the clutch hydraulics. I will pressure bleed it back from the slave cylinder. If I am unable to push fluid back to the reservoir then it will confirm my suspicions that the inlet to the master cylinder from the reservoir is blocked. This will also remove any possible air in the system as you suggest or possibly remove any foreign matter blocking the inlet to the master cylinder.

In the absence of a pressure bleeder I will either run a hose from the bleed nipple on a front brake calliper to that on the slave cylinder as some manuals suggest, or purchase a new and clean pump type oil can and use that filled with brake fluid connected to the slave cylinder bleed nipple (as a friend who worked as an MB tech suggested). The outcome of this will determine if I then need to replace or repair the master cylinder.

I will post my findings when I get somewhere with it, whenever that may be. I have a bit on my plate at the moment already. My father wants me to replace the water pump in his '93 E320 coupe (M104) and my brother's '92 180E (M102) looks like it needs a head gasket (which he has hinted I might "like" to help him with). In the meantime, any other ideas re my clutch problem will be appreciated.

Duke, yours certainly has the symptoms of a failing slave cylinder.

Greg

Greg in Oz,

I own a manual mutch better than a Haynes : it's a "So wird's gemacht"
(That's how it's made). It's a manual only availlable in German but a can assure you it's far more interesting than all the other, non MB-manuals.
As I own a couple of W 124's, I bought a W 201 ma

I'am sorry but the message parted to soon so her is the rest of it.

I own a couple of W 124's so the W201 manual was part of a misunderstanding. I kept it because I like it very mutch. It's superior to manuals I own in French ( a translation of the German manual ) and a Dutch one ( a translation of the French!! ).
In the German manual is clearly stated : the clutch is self-adjusting and free of maintenance. The thikness of the clutch should be verified every 20.000 km. The template to do so could be home made. If you need to, I'll ask a friend to scan a design of this template (should be made out of a 0.8 mm steel plate).
As it is self-adjusting, there is no adjustment on the push rod.
If you need more information, I"ll translate the German text for you if you want.

Danny

95300YDT-A,
I am desesperately looking for an original workshop manual for my 260E, 1988, W124, in French as far as possible. how did you get it? where is it possible to buy it?

cc 260E,

I am living/working in France 3 months every year so it was easy for me to buy this manual in an ordinary shop!
Following here is all the informations I find on this manual. I hope you can order it at the editor...if not, let me know.

"REVUE TECHNIQUE AUTOMOBILE"
No 20, Rue de la Saussière
92641 BOULOGNE BILLANCOURT CEDEX

Phone : 0 33 1 46 99 24 24

http://www.etai.fr

The editor's number of the book is CIP 727.1
Tittle:
Mercedes Benz 200 à 300 (série W 124)
moteurs 4 et 6 cylindres essence
4 - 5 - 6 cylindres Diesel (atmo. et turbo)

Include are ( for the gazolines ): 200 - 200 E - 230 E - 260 E - 300 E - 300 E 24 and for the Diesels : 601 - 602 - 603 turbo & non - turbo.
And last but not least the ISBN ( very uncommon on a French book!) :
ISBN 2-7268-7271-9

Updated at Feb. 2th 2001

Well, you know as mutch as I am! If you need a helping hand with the translation : just let me know!
Good luck,

Danny

Greg

I have been thinking about your hot slipping clutch ... (Oh baby!)

To the serious side and I don't think it has to do with the hydraulics.

Here are my thoughts: At rest, the clutch master/slave system should not ideally influence the clutch assembly at all. That is where the questions of free play comes in. I would still like to know the amount of free-play cold and when it slips.

My thoughts continued- if the inlet port was not being uncovered fully and thus the piston is not getting a full stroke and replenished, this would show up when using/pushing on the clutch pedal. You reported slipping when your foot is off the pedal.

This leads me to the thoughts regarding-

- the difference between when it does and does not slip. You say it slips after considerable amount of driving (time to heat up)

- the take-up (engagement point) is high off the floor. This is commonly associated with a worn clutch disk OR a bad pivot ball/clutch arm inside the bell housing.

-you said that the clutch disk thickness measures within spec, but because the measurement is at the slave cylinder and its amount of extension, a worn clutch arm pivot ball could give you a false reading.

-a failed clutch arm would also do this, but it seems very unlikely that the arm itself would fail. I have no experience to share with this part or its life/failure.

When you were under the car measuring your clutch thickness, did you get a chance to see if there was excessive movement of the clutch arm? This might be a telltale indicator of a pivot failure.

Unfortunately, I believe access to the pivot is the same as doing a clutch and once you are in there, might as well do it all.

Like you, I am hoping that the clutch disk is thick and happy, thus not needing any major work.

I could be off base on all this, but I continue to think about what is going on with your slipping hot clutch!

Haasman

[QUOTE]Originally posted by 95300YDT-A
[B]cc 260E,

95300YDT-A

Many thanks I had an older version of it.

I thought you had the official from MB.

For my findings with this problem, please see this thread:
http://www.peachparts.com/shopforum/tech-help/79447-i-hoping-one-mb-techs-had-experienced.html

Dear Greg,

I think your clutch problem is very intriguing. I never heard about that.
But a case is only lost when we give it up.
And we don't want to, are we.
So I decided to do a "brainstorming" about this with my Indy. He is a honest and modest AND independant MB specialist, ashamed to ask the prices he has just to survive.
MB-stealership in my home town goes to him to get all those 6xx rebuild ( and they have a famous MB-rebuilder just 15 miles away in the next town !).
Well, I'll try to explain what reasonable explanation he came up.
As you allready understood : English isn't my mother's language so I am sorry and please feel free to ask any questions. So here we go.
Neither of us believe your theory about the hydraulic system. Everything you told is correct but again neither of us could imagine that could cause enough force to make the clutch slipping.
You replaced the clutch by a new one, excluding the clutch as a cause.
But did you checked out the wear (the real thickness of the flywheel at the contact-with-the-clutch surface ? The wear of the plate pressing down the clutch to the flywheel ( don't know the correct name in your language ) ?
If you did't : do it.
If the contact surface on the flywheel is still OK ( or even when it's not ),
let eventually grind (mill ?) down the surface on the RIM of the flywheel, there where you bolt on the "pressing" assembly to compensate the weardown of the contact surface and you"ll see : no more slipping when hot !
What do you think of it ?
Don't forget to communicate us a follow up !
Thanks in advance and good luck,

Danny

I will not give up until I solve this!

Your English is just fine!

I'm sorry that you don't believ my theory but it's the laws of physics. Expanding hydraulic fluid can exert huge force, much more than is required to release a clutch. Without the ability to return to the reservoir, fluid expanding with temperature will displace the piston in the slave cylinder thus releasing the clutch.

I have not replaced the clutch since my measurement with the gauge suggests it is still OK. Without residual pressure in the hydraulics it certainly works OK without any slip. I think replacing the clutch and flywheel (dual mass flywheels such as that in my car should not be machined) would be a very expensive and time consuming option, especially considering that I have not diagnosed the clutch plate or flywheel to be at fault. Without perfectly convincing evidence of the cause of the problem, I would prefer to replace less expensive components such as those associated with the hydraulics which with the evidence I have to date are still the main suspect.

Please don't take this the wrong way. I am appreciative of the interest both you and your tech are showing. I will post more replies and further findings on the other thread at
http://www.peachparts.com/shopforum/tech-help/79447-i-hoping-one-mb-techs-had-experienced.html

Greg

Greg,

What are the exact measurements that you used to create your clutch disk thickness measuring tool?

I made the measuring gauge tool according to the dimensions in my Haynes W201 manual, my Haynes W124 manual and my Brooklands W124 manual. The dimensions in all the manuals agree. Unfortunately, none of my factory manuals (MB North America, W201, W124, M103, M104 but I don't have M102) depict the tool for a comparison. Without those manuals at hand at the moment I cannot quote the dimensions but if anyone is interested I will look them up again and post here. The tool seems to fit perfectly. I can feel it sliding onto the slave cylinder push rod.

Is this the tool and the dimensions you used?

Haasman,

That certainly looks like it. Again, without the manuals in front of me, I would need to verify the dimensions. Your diagram does look very much like those in my Haynes manuals, right down to not being drawn quite to scale, from memory. My Brooklands manual on the other hand, has a full size scale drawing without dimensions which can be used as a template for the tool, if my memory serves me correctly.

Greg

Updated tech article for the W124:

Mercedes-Benz W124 Brake Master Cylinder and Reservoir Replacement | 1986-1995 E-Class | Pelican Parts DIY Maintenance Article