W123 Clutch hydraulics (?) misbehaving

[tsa]

Hi all,

first I'd like to say thanks to everyone here, whose brains I've been able to pick when it comes to troubleshooting a few minor issues with my '85 W123 estate.

Within a fortnight, and in less than 30 miles local driving, my clutch pedal started to loose its "bite" gradually, until it has become difficult to disengage the clutch. Most noticeable from neutral and into first gear. And during my second to last short trip, the brake warning light started flickering, and has ended up staying mostly lit.

After searching and reading, it seems that I have a problem with either the clutch master or slave cylinder, or the hose (pipe?) between them. The latter may perhaps be most likely due to the timing of the brake warning light? This since the clutch hydraulics is fed from the brake master cylinder reservoir.

Based on the cumulative experience of how the W123s work and (sometimes) fail, what is the most likely part causing this grief? Suggestions on further diagnostics & remedial actions most welcome.

I hope you don't answer the master cylinder, since I've seen comments about how inaccessible it is, behind the pedals . . .

Many thanks

 

[SMS]

Check your brake fluid level to see if the back chamber that supplies the clutch is full. If empty, fill and pump the pedal a few times and check for leak.

 

[optimusprime]

Leaking fluid in the area of each cylinder will tell you what parts the culprit. First i would bleed the hydraulic system . Top it up and try it for a few days .If it still plays up .Then its the seal replacment job for you . Some times you could get a seal kit . But i think now its a master cylinder, and slave clinder replacment . Mind you get the right slave cylinder on the clutch 2 types were made for your car and only differance is the plunger arm length. In that i mean the cylinder is the same but plunger is not.

 

[tsa]

Thanks, SMS and optimusprime, for very helpful comments. When the brake warning light came on, I had a quick look under the bonnet and saw the brake fluid reservoir was near the max level, but wasn't aware at the time that the clutch hydraulics shared the same container. This morning I could see that the rearmost compartment was nearly empty. Topping it up and pumping the brake pedal didn't restore pressure, so a full bleed procedure will be required. I also noticed that the cotton braided rubber hose from the reservoir and through the torpedo wall didn't look very "shiny", so at a minimum this rubber hose will need replacing before proceeding with the bleeding. The connection between the clutch master and slave cylinder obviously needs to withstand pressure, is it a solid pipe or flexible (steel braided) hose? If the latter, it may well also have to be replaced before bother trying to bleed the system.

[Edit - I forgot to mention that the warning light stayed unlit after I topped up the fluid level]

 

[optimusprime]

Hose will be flexible with a braid weather it is steel i dont know ..If you see damp on the parts it tells you its leaking as you know. Never had to change out a hose .When mine went down it turned out to be the seal in the slave cylinder. And the car i had were both brake and clutch are stand alone system not like your tandem system.. I dont want to frighten you , ,but i think on your car, to have a problem on the brakes or the clutch it will loose fluid . Then a leak in the clutch line would put the light on for the brakes. I would do a check on that one for sure.

 

[tsa]

Thanks again, optimusprime for helpful advice.

I've now got time to look a bit closer, and think I have an idea of where the master & slave cylinders are. In this picture:

I take "1" is like the rubber hose feeding the master from through the torpedo wall, it looks dry, i.e. no evidence of a leak. "2" must be the master cylinder, again no obvious fluid leak. I assume "3" is a solid hydraulic pipe that feeds the slave cylinder.
Checking underneath isn't the easiest task with the car on the ground, but in this picture

I guess the slave cylinder is somewhere behind the bracket and inside the green circle? The dirt on the gearbox looks damp, could hydraulic fluid have leaked out in and made it look like this? From a faulty slave cylinder seal?

I really should have got myself a Haynes manual, my German "So wird's gemacht" book doesn't say how to replace either cylinder, nor where they are. However it describes a reverse bleeding procedure involving a hose between one brake caliper and to the bleed nipple on the slave cylinder, using the brake pedal to pump fluid through the caliper, and up through the slave & master cylinders and back to the reservoir. Hopefully that procedure can make the bleeding easier, once I've had a go at the slave cylinder.

Anyone here having a surplus Haynes manual for the W123? This car has been too reliable for me to have needed one earlier

 

[optimusprime]

The slave cylinder is to the left of picture not in the gearbox support area more on the bell housing .Its a manual you need . So you can locate the parts on the car .I will see what I can find on line, in manuals for free . It will be to-morrow now I am afraid .

 

[optimusprime]

Do a GOOGLE search on this - ozbenz.net on the results look in to this one ozbenz real mercedes benz enthusiasts Then look at the one you need .

 

[tsa]

Do a GOOGLE search on this - ozbenz.net

Great tip - we should consider us lucky lots of these cars found their way to Oz and not only Africa; thereby we get useful advice back!

Manual clutch issue - OZBENZ

The tip I read about bleeding the slave from the right brake caliper should have indicated to me that I should have looked for the slave on the right side of the gearbox . . . . where I now realised it sits. Access doesn't seem to be too bad.

Also interesting to read AMG (OZBENZ Admin)'s comment that the clutch hydraulic line should have its fluid replaced at the same time as the brake lines - not sure if that is common practice even in brand specific garages.

In an older thread here I saw eurocarparts was mentioned as a source of new clutch M or S cylinders - still OK, or should I look elsewhere for them?

Thanks again

 

[Druk]

It’s entirely possible you have leak on the rear brakes which would have the ultimate end result of emptying the reservoir? Since the clutch cylinder take-off point is above that for the brake it’s the clutch that would be the first to be affected by a falling fluid level.

I have a manual gearbox R107 and the clutch has its own deticated fluid reservoir. eBay is your friend.

 

[grober]

some pictures of the clutch slave cylinder position

from
717.412 (5 speed manual gearbox) refresh - PeachParts Mercedes ShopForum

 

[optimusprime]

TSA where do you live ? And yes Eurocarparts is as good as it gets other than the main Mercedes dealers. Druck I am sure all information will be useful .And are you saying that you can do a mod on them so its a stand alone clutch master as well.

 

[grober]

There seems to be a bit of confusion about the clutch master cylinder/clutch slave cylinder/ clutch fluid reservoir [ which is a section of the brake master cylinder reservoir] This walkthro of the W201 clutch master cylinder replacement - same as the W123 afaik may help a bit. Druk's suggestion for a separate clutch fluid reservoir seems a sensible mod if there's room for it.
Replacing the clutch master cylinder on W201 and other models | OldMerc.net

 

[tsa]

It’s entirely possible you have leak on the rear brakes which would have the ultimate end result of emptying the reservoir? Since the clutch cylinder take-off point is above that for the brake it’s the clutch that would be the first to be affected by a falling fluid level.

Very good lateral thinking there! However the fluid level in the frontmost brake part of the reservoir has remained OK through all this; in fact it's the reason I was fooled into thinking that the fluid levels were OK, since I didn't know that the reservoir in fact doubles as two. Here is mine:

After I filled the rear clutch part, some of the fluid has already drained out, so the level can be seen to be lower than in the brake compartment.

My reservoir (and cylinders) may well be similar to those fitted to early year W124's, since my estate was built in the autumn of 1985, when the W124 sedans had been out a while. Did the W124's have separate warning lights for the brake and clutch hydraulic lines?

 

[grober]

Very good lateral thinking there! However the fluid level in the frontmost brake part of the reservoir has remained OK through all this; in fact it's the reason I was fooled into thinking that the fluid levels were OK, since I didn't know that the reservoir in fact doubles as two. Here is mine:

After I filled the rear clutch part, some of the fluid has already drained out, so the level can be seen to be lower than in the brake compartment.

My reservoir (and cylinders) may well be similar to those fitted to early year W124's, since my estate was built in the autumn of 1985, when the W124 sedans had been out a while. Did the W124's have separate warning lights for the brake and clutch hydraulic lines?

Don't think so whereas your reservoir appears to have two?
Mercedes-Benz W124 Brake Master Cylinder and Reservoir Replacement | 1986-1995 E-Class | Pelican Parts DIY Maintenance Article

 

[Druk]

After I filled the rear clutch part, some of the fluid has already drained out, so the level can be seen to be lower than in the brake compartment.

My reservoir (and cylinders) may well be similar to those fitted to early year W124's, since my estate was built in the autumn of 1985, when the W124 sedans had been out a while. Did the W124's have separate warning lights for the brake and clutch hydraulic lines?

My 1986 S124 had exactly the same arrangement as this. Twin reservoirs with sensors in each. You have to rid yourself of the notion that the rear half of the reservoir is for the clutch. It’s a tandem brake system whereby if the fronts fail for any reason there will still be a modicum of braking in reserve. And vice versa. The rear sensor is there for the brake fluid level and is the same one as fitted to automatic cars.

The fact that the lazy bastards chose to tap into a safety related brake circuit to provide the clutch with hydraulic fluid is a disgrace. It should have been provided from the start with its own stand-alone reservoir.






.

 

[tsa]

Thanks once again for good advice.

I finally managed to get the car up on a couple of ramps, so I could get a look at the slave cylinder. It certainly would have helped with double jointed fingers, with the downpipes conveniently restricting access . . .

Anyhow, I could see a moist spot next to the flange, and a drop of fluid at the lower joint of the bell housing. I guess most of the fluid leaking "out" ends up on the inside of the bell housing. I assume what has happened is corrosion of the slave barrel, due to H2O contamination of DOT-4 not replaced as often as it should have been. And then the seal blew when I noticed lack of pedal resistance, accelerating the leak, until I had difficulties disengaging.

Online, both eurocarparts and GSF list having a slave cylinder (aftermarket or generic part of unspecified origin) in stock (at GBP 47 and 46, resp.!), but with no info on the length of the piston rod. Not sure about the quality, either. My local MB dealer usually needs to get W123 parts sent from the Vaterland, in a week or so, I'll pop by them and ask how much their part is.

@ optimusprime: I'm in Surrey, updated details now.

 

[tsa]

Don't think so . . .

My 1986 S124 had exactly the same arrangement as this. Twin reservoirs with sensors in each. You have to rid yourself of the notion that the rear half of the reservoir is for the clutch . . .

Ooops - guilty as charged :-(

Anyhow, a couple of years ago I went over the brake system, and fitted new (rebuilt) rear calipers. They must have been of extremely poor quality if they've started leaking already, will look at that once I have a working clutch again. My relatively sudden loss of clutch pedal pressure & proper disengaging hopefully only points towards the clutch hydraulic line.

Now that I know that the clutch hydraulic is simply a piggy-back parasite of the rear brake line, I agree that a separate reservoir for the clutch line is the logical way of designing those systems.

This car is so more confusing and difficult to work on compared to my motorcycles!

 

[grober]

Right looking at your picture the slave cylinder part no appears to be A2012900011 this has been replaced by A2012900311 [ manufacturer TEVES] according to Merc's own EPC
Slave Cylinder, clutch OE Number A2012900311 buy online
I would go with SACHS or ATE but check the price of the MB PART also

 

[Druk]

Also, in my experience, it’s possible to replace the new operating rod with the existing one if the new one happens to be of the wrong length. You may also find a plastic packer piece under the cyl flange and it may come out in bits but be sure and replace it with something of similar thickness.