Mercedes-Benz Forum banner

107 Clutch Master Cylinder

10K views 37 replies 7 participants last post by  CA-280SL 
#1 ·
I've got an 81 280 SL 5 speed. Anyone got any hints on replacing the clutch master cylinder? The mounting bolts back into the side firewall, there's not enough clearance to get them out. I'm thinking I may cut or drill the firewall to get them out. Drilling hasn't worked so far, poor clearance and shallow angle.

I'm also looking at the mounting bracket. The brake and clutch pedel assemblies are mounted to an aluminum bracket. I can see that it's held by the same nuts that hold the brake booster and who knows what else!

Any help would be appreciated.
 
#2 ·
Are you certain that the clutch master cylinder mounts on the firewall? On my 1975 350SL Euro four speed, the clutch master mounts directly to the aluminum pedal bracket. There is no attachment to the firewall. See the holes indicated in the photo below. Perhaps the 280 is different from the 350 or there is a difference in how the cylinder is mounted by the year. Check for the two bolts that screw into the master cylinder.

Yes, the four nuts from the booster mounts the pedal bracket.

The reason I have mine apart now is because the aluminum bracket cracked in half. The photo shows the crack and a comparison with a later bracket I acquired. The later brackets are much better reinforced with more ribbing. Also the welding job when it cracked the first time was poor. I'll need to swap over some of the parts to change it from a brake pedal only to clutch and brake pedals, but it should work fine. Both have the same part number.

GD
 

Attachments

#3 ·
Golddragon is correct in that both my 1980 and 1985 280sl s have that same bracket. The masterclutch assy
Mounts on the aluminun bracket.. You got to remove the drivers seat from the car to get in there to remove the
2 bolts and the input hydraulic oil line from the brake resoviour and the outlet line that goes to the slave
Hydraulic line mounted on the bellhousing.
 

Attachments

#4 ·
CA, Thanks for your input. I found that I didn't need to remove the seat, but I can see that the extra space to lay down would keep my knees off the gravel. What I found very helpful is to remove the steering wheel, instrument cluster and speaker. There's plenty of room to get at the parts and bolts and I can see what I'm doing rather than feeling my way though the work and craning my neck.

GD
 
#5 ·
CA and everyone, I'm reinstalling my manual pedal assembly after rebuilding it with a used bracket from an automatic. Everything fits fine. The later model bracket is much stronger. The clutch parts swapped over well.

I have a question about the eccentric bolt that attaches the clutch master cylinder push rod to the clutch pedal. How is this off-center bolt supposed to be adjusted? Is the push rod adjusted for alignment or length?

The rotation yields only a fraction of an inch difference. I'm certain that it's the same on the 280's as my 350 and may be for other manual transmission Mercedes of that time period.

Please see attached photos.

Thanks for your help.

GD
 

Attachments

#6 ·
I did not have to adjust it. I put itback like it came and when you bleed your clutch slave clyinder that
Is bolted to the right side of your bellhousing, pressurebleed it from the bottom. Youcan actually use one
Of your wheel brakeclyinders bleeder screws. Dont firget to remove the cap from your master brake
Clyinder and check the fluid level often.
 
#7 ·
Thanks for the pics, CA & GD

Well, I'm still stuck. I managed to get the master cylinder mounting bolts off by using an air chisel to punch two holes in the firewall and then drilling them larger. Now, I can't get the pivot bolt off the shaft end. It looks like there's a 14mm nut on the inboard side with the bolt coming from the outboard side. I can't seem to get anything on the bolt head end to hold it. Looking at the pic provided by GD, it appears that the bolt head is on the inboard side. I'm going to get my phone under there and get some pic, maybe that will help. I'll try to post some pics later.

As far as removing the entire assy, can you guys give any more details on how it comes out? I've got the four nuts that hold the bracket to the firewall off. The bracket doesn't seem to feel any looser, is it held at the aft end as well? Do I need to get the steering column out of the way?
 
#13 ·
Well, I'm still stuck. I managed to get the master cylinder mounting bolts off by using an air chisel to punch two holes in the firewall and then drilling them larger. Now, I can't get the pivot bolt off the shaft end. It looks like there's a 14mm nut on the inboard side with the bolt coming from the outboard side. I can't seem to get anything on the bolt head end to hold it. Looking at the pic provided by GD, it appears that the bolt head is on the inboard side. I'm going to get my phone under there and get some pic, maybe that will help. I'll try to post some pics later.

As far as removing the entire assy, can you guys give any more details on how it comes out? I've got the four nuts that hold the bracket to the firewall off. The bracket doesn't seem to feel any looser, is it held at the aft end as well? Do I need to get the steering column out of the way?
CA is correct in his advice to you. While I've been working on mine, I wished I had removed the seat. It may as yet come out.

You may have done more damage than good by drilling and punching holes. All that's necessary to remove the assembly is the four 13mm nuts holding the bracket to the brake cylinder, one 10mm screw at the other end of the bracket, the bolt attaching the brake cylinder to the pedal and the fluid lines going to the clutch master cylinder.

If you removed the two clutch cylinder bolts (after removing the four 13mm nuts on the firewall) where I indicated on the bracket, you could have left the clutch cylinder in place. The push rod attached to the clutch pedal comes out. As far as I know, there's no other way to get the assembly out.

GD
 
#8 ·
IIRC. There is a bolt on the front attaching it to the dash frame. No leave the steering column, dont have to remove it.
Did you remove your drivers seat ? You could be a young wippersnapper that is still flexible enough to bend over backwards,
but im a old fart and taking the seat out let me lie on my back and remove everything.
 
#12 ·
CA,
Yes, thank you. I had found that one. Details are a bit sketchy, but I think I can figure it out. The drawing from the 123 shows the clutch pedal travel, but doesn't give the specification. It appears that my only recourse is trial and error or to figure out a way to hook the cylinder up to do the bubble test.

After rebuilding the pedal assembly. I now need to determine if the master clutch cylinder is bad. It doesn't feel right and was jammed. I think it may have contributed to breaking the weld on the old bracket.

GD
 
#15 ·
Thanks, guys, it's great to get some help. No, I haven't gotten the bracket out. I can't seem to get to the 10mm nut under the dash. There's a big wiring bundle that I think it's under. I clipped a tie that was holding it but that's not enough to get in there. I've decided to take the advice on removing the seat.

CA, you seemed to know how to do this, any help? I see a bolt at the front of each rail, which I've removed. I don't see a bolt at the rear, it seems to be supported by a pair of arms from the height adjustment mech. There are bolts on the height mech bracket, I"ve removed them too. The whole seat is loose now, but still seems to be held, probably at the front of the height mech.

I have an unrelated problem with the headlights you guys may be able to help with. I've got four lamps lit on high beam, only one on low. I'm thinking this has to be a relay. Any idea where the headlight relay is?
 
#17 ·
Thanks, guys, it's great to get some help. No, I haven't gotten the bracket out. I can't seem to get to the 10mm nut under the dash.

I have an unrelated problem with the headlights you guys may be able to help with. I've got four lamps lit on high beam, only one on low. I'm thinking this has to be a relay. Any idea where the headlight relay is?
Michael, The only reason I can think of that you can't access the pedal bracket's 10 mm bolt on the outer dash is because you haven't removed the instrument cluster. If that's the case, you are making the job a whole lot harder than it needs to be. I found that removing the 4" speaker helped with access also. At the firewall, the bolt on the upper left is best accessed through the round firewall port under the hood. Look for a big round rubber plug.

Yes, the bulb's burned out. Simple fix.

I hope this helps.

GD
 
#16 ·
Complete your profile with model and location using the UserCP button.

Since you state four headlights I guess yours has been converted to North American headlights. If so it is probably the headlight bulb. They are dual filament and the low one is burned out.
 
#21 ·
Bleeding

Again, thanks for all the help. I'm going to install the new master cylinder today. Any pointers on bleeding?

I've read that the best way is to connect the right front brake caliper bleed valve to the one on the slave cylinder and use the brakes to pressure bleed it. That means I'm going to have to get it jacked up enough to find the slave cylinder. I suppose I should have planned to replace the slave while I'm under there.

Probably a good time to change the oil.
 
#22 ·
I think I'm the only one here that does this:

I put 15psi pressure at the reservoir.
Crack the bleed screw on the slave and actuate the clutch pedal down and up once....and off it goes.......I use Nobette for the pedal action.
 
#28 ·
Concerning your slave

If you replace your slave be sure to get the correct part number for your car! A previous owner of my car replaced my slave with one that was exactly the same externally but had a different ID, it was larger. So the clutch pedal had to be touching the firewall and the clutch was still not fully dis-engaged. It could be shifted but would grind sometimes. It took me a while to figure it out. I almost replaced the clutch. I had to purchase the correct slave from MB, it was about $120. The correct slave had an ID of 22 mm, the one on the car was 26 mm. The bigger the diameter of the slave the less travel for a given input volume. The new slave dis-engaged the clutch just below mid stroke! Good Luck!
 
#35 ·
Thanks, I found it.

I did the conventional bleed out through the slave first to get the old fluid out. Then I did the reverse bleed from the brake caliper through the slave. I hope that gets all the air out.

Now I have to put the driver's seat back in. It wasn't working very well, I hoping to get it cleaned and lubed so both the forward/back and up/down adjustments work properly.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top