See if the tip of the booster output rod is removable. If so, you can possibly shorten it and reinstall without burring up the part that bears on the primary piston of the master cylinder.

Shimming the master cylinder where it sits on the booster probably won't work well since the master cylinder usually has to seal against the booster housing to keep the atmosphere out of it.

Even if the above measures work, they don't address the root cause of your problem.

Is this car new to you? Do you know that things worked well before it was parked? I would suspect that something's preventing the brake pedal from fully returning (faulty or corroded brake light switch?) or that the booster suffered some sort of internal malfunction due to the long sit.

- Chris
Michigan

makes a good point. look at the mechanism again. maybe the adjustment is not on the rod. maybe on the pedal pendant.

tom w

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I'm completely baffled.
I had a look at both ends of the pedal mechanism and found no adjustment.
I'll check the pedal end again for brake sw keeping it from returning all the way.
My concern is if I do shim, shorten the rod, drill the mc and the problem 3mm disappears again while driving. I then have too little travel suddenly. Not that 3mm matters all that much.
MC piston punch thru was a concern as well. Not sure how thick the metal is on the piston.
I wish I had a good picture of the inner works of the booster. Might give some insight to what has happened if its booster related.
Very strange.

I did drive the car prior to parking it a yr ago. It had, what I thought at the time, bad brake hoses and loose tie rod ends. Its showing 156K miles and starts and runs as though the milage is correct. No rust Tx car.
The PO botched up the climate control system. I "manualized" the CC system while the car was parked and recently started restoring the front end and brakes.

The booster output rod seems to be captive but loose. I don't see a way to remove it. Perhaps I can make the change on the other end. It would mess up the ball end if I were to grind the rod.
I still want to find the problem before I sort to this.
Have another look tomorrow.

i looked at my 280e haynes book and if it is the same on yours, which i would think it is, the limiter for the brake pedal is actually the stop light switch. it threads into a bracket with two nuts to locate it. it can be moved in or out. i bet you will find that the po just screwed it in all the way and it is too far in. if it is missing the second nut you will need to find one so you can adjust the position.

good. this is simple to fix. and easily overlooked.

tom w

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I agree, the stop light switch (and its potential for maladjustment) sounds most promising.

Most modern cars don't use threads for this anymore. Instead, the switch rachets into its holding bracket and the installation procedure requires that you grab the brake pedal and yank it back and up, forcing the switch into adjustment. VW had a recall last year that required replacing the switch. An alarming number of owners on the tdiclub.com forum experienced dragging brakes afterward as a result of improper installation by the VW techs.

With the threaded adjustment, you need to be sure that there's a little bit of extra travel available for the switch plunger (I mean that the brake pedal lever isn't taking all of its travel up).

To put it another way, the booster input rod (attached to the brake pedal lever) as far out as it can go. The first few millimeters of input travel are effectively activating the booster.

- Chris

I had a good look today and found the pedal return stop is indeed the brake light switch.
However, there is free play there. In other words, I can move the pedal forward (depressing it) a bit before it moves the booster rod. So, the actual MC push rod stop is in the booster ass'y.

Out of desperation I drilled the MC piston, where the booster rod engages, 2mm deeper. That fixed the problem. (for now).
To test for "punch thru" I made several "stomps" on the brake pedal. So far, so good.

I'm wondering if there was a different MC for this particular chassis.

Stumped this chump!

maybe the booster is wrong.

odd

glad you solved the problem. hope it doesnt punch through the mc disc.

tom w

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Hello,
This is my first post here. I bought this 71 220D from a friend of mine who got it from a little old 80 year old man who garaged it in 1988. It has been unused since that time, has a little over 57k miles on it. Needless to say all the hydraulics were toast. The clutch pedal was all the way in the floorboard and the brakes were locked up. I replaced all four calipers, all rubber brake hoses, the master cylinder, clutch master and slave cylinders. I found this web site after I finished my work and found out that the front brakes were sticking and did a search trying to find out about the problem. I have already gone over alot of the recomendations found here in this thread but I see that the final solution was never posted. I too found that when I loosened the two bolts on the master cylinder from the power booster and pulled the master cylinder away from the booster the front brakes became free and the car would roll free. I was wondering if a final solution was ever found? This is my first Mercedes Benz and I can't believe that I have waited so long to have one, the degree of workmanship is just wonderfull to this old mechanic

Skip Callaham

Doh!
I now see after I have just posted that a solution was found, I hadn't looked at the second page of posts!
Anyway, I had shimed the master cylinder a bit with a piece of aluminum wire and it had worked but the power boost has quit working. Tonight I disasembled the master cylinder to see if anything might be wrong in there. All looks good as far as I can tell. This car came with all the original docs and maintenance records, also the factory workshop manual, it even has a busness card of the dealer that had a 1971 dime in case you had to make an emergency phone call for service

Robert,
I never did figure out what the problem was. I drilled the MC piston hole approx 2mm and that solved the problem.
Still works fine today. I never found anything out of whack on the car other than the booster rod protruding too far into the MC.
Weird.

i just remembered that the adjustment on freeplay in some cars is an eccentrick bolt on the actual pedal arm. in this case there will be a bolt that goes thru the arm that you loosten the nut on the other side and turn the head of the bolt.

i mention this on the odd chance that this might apply to your case.

drilling the piston on the mc is really giving me the willies!

i am very uncomfortable with you driving around with it like that. it seems unsafe to me.

tom w

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.