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I am going to assume you mean " Inexpensive".....

You can go to any auto parts store and get a spare GM res cap..that fits the Benz res ..or just get an old Benz one.
You drill a hole in it to accept a rubber hose and then you get some air to that hose.
Use any imaginative thing you can , from an old garden pump-up sprayer , to a blood pressure testing cuff bulb.
I like the cuff bulb b/c it fits right on to the cap and they have that little release valve on them....works slick for a one guy operation...you just pump the bulb a few times and go bleed a wheel..then go back and pump it again and do the next...the trick is to watch the res for fluid level...when it gets low , you take the cap off and add some more ...crude , but cheap and cool ............all you want is a little pressure on the fluid in the res to chase the old fluid and air out the bleeders...5-10 psi is more than enough...and less is better b/c I have seen guys blow the res right off the master with as little as 25 psi...smart !!! ....plus the res is just a plastic container and will not withstand any high pressure..... if you see the sides starting to bulge out , you are using too much presure. You just need enough to move the fliud when a bleeder is opened at the other end. This test the hoses too, b/c if they are constricted inside , the low pressure in the res will not be enough to allow a good flow at bleeder, indicating a possible constricted hose on that wheel. Kinda simple, when you think about it. You are just moving a fluid and it takes very little force to move the fluid...the force requirements are when the fluid has to move the mechanical parts [ pads/shoes/etc]...but hardly any force is required in moving the fluids to bleed a system properly. You are simply chasing the old fluid/air out the bleeder end with new fluid.

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A Dalton

Fantastic advice. I actually have a spare cap from an old cylinder resavoir I can use. I have an air compressor that I can regulate down to 5psi so I will try that.

I jacked up my car this afternoon and checked for binding and general brake operation and everything seems to be in order so I will try for another bleed tomorrow when I get some time. Will post back and let you know how I I get on. Really appreciate your efforts. Have you got old Mercs as well. I am really wanting to get into an old pagoda sl but have been a bit put off by all the dramas I have had with the 250. Hopefully when I get the old girl out on the road my frustrations will be forgotten. I have restored countless BMW's in the past and none have given me as much grief. I think the reason has often been over engineering on Mercedes part. Keep it simple has always worked for me. I am interested in other peoples perspective on this one

Andy, you can buy a Motive pressure bleeder for around $55. Check online for the best deal.

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Fred Hoelzle

No, The car did not pull to one side. And , the car stopped well. But the pedal was almost floored in stopping. Very disconcerting. Pulling the pads to look for uneven wear may not really answer the question, since the car has been laid-up so long, and the 'frozen pad' condition may not have existed when the car was last driven.

You can plug the master cylinder outlets-all at once, or selectively- to help indentify the source of your problem.
Are the replacement M/Cs of the correct bore size?

my 280S /69 had that sinking padel after renewing the master cylinder.
The front left pipe was swelling up as the pedal went down.
replacement of all the five brake rubber pipes rectified the problem. The fifth is at the axle swing area.
regards
mak

I have suspected this for a while but everyone tells me it unlikely and to change the master cylinder. How much did the pedal sink. Also did the pedal only sink when the booster was activated mine only sinks when the car is on. After the booster has been bleed of vacumn the pedal doesnt sink. I have a theory that there isn't enough presure without the booster to ballon the pipes but it would be great for you to verify this before I start spending more money. I have now been through two brand new master cylinders at 500 a pop and a new brake booster.

I dont know if the cylinders are correct. I asked at the counter and thats what they supplied. Both original ATE oem mercedes parts. They both look identical to the one I took out.

I will try and block the master off. I dont want to damage the taper on the cylinder so am after some suggestions of how to do this. Someone suggested a bolt with a ball bearing around the same size diameter as the taper in the mc.

At the back of the car where hard brake line tees off there is a large junction with a cylinder attached. Does anyone know what this is. If the cylinder is filled with fluid I am wondering if it could act as an air pocket. Unlikely but I am that desparate to track this down I am happy to consider anything.

Hi paul I pulled all the pads out today and they all look ok. I rang a brake expert in Auckland and ran this sceanrio past him. He seemed to think because of the construction of most brake pads, ie thick metal backing, that if the pad flexed it would stay flexed. I think in my case I have ruled this one out. But I would like to here in more details about your case. I may be missing something.

Cheer Fred. I have spent all morning engineering my own one out of an old second hand brake resavoir cap. I havn't tried it yet. The whole system is apart again anyway. I couldn't sleep last night trying to figure the problem out in my head and ended up pulling the master cylinder off this morning to test the brake booster independantly. I have established 100% now that its not the problem and as someone else told me in this forum there is a solid mechanical connection between the pedal and the booster so its impossible for this particular booster to be causing any sort of pedal sinking.

I tell you what I have been restoring cars now for 20 years and this is the single most frustrating issue I have ever encountered. I will definitely be posting the findings no matter how dumb it makes me look. If I can save anyone else the same frustration (and money) as I have endured it will be worth it.

It been to two separate brake specialists now who have both had it for a day a piece and have come up with different causes. Both have been fixed but the probelem is still here.

The masters could be bad even though new.

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[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.

First you have to check if all pistons are free and the brake pats are not worn.

Air may be trapped is the system.
One way to get rid of it is start the engine, apply pressure on the pedal (as much as possible) and keep the pedal depressed over night.

If that does not work you can try to bleed from the bleeders with a large syringe (be very careful not to overfill the reservoir).

Rob

I suggest you actually measure the M/C and compare it to a known valid spec. I have gone through an episode similar to yours and found the M/C bore was larger than the original. If a bespoke plug is not available one can be made from a short piece of brake line and fitting. Crimp the end of the line over on itself to close it. Be very carefull using anything other that could damage the sealing area of an outlet in M/C.

I have decided to bite the bullet and have the new old cyclinder fitted with a stainelss sleeve and new seals. Spent all last night eliminating all other possibilities (thanks everyone for thier suggestion I looked at all of them).

The most likely cause is going to be internal seals in the cylinder allowing fluid to pass between the two internal chamber and be displaced slowly back up into the resavoir.

I have been on the phone to some of New Zealands best brake shops and they have all consistently said the same thing.

Man will I be gutted if its something else now. I promise no matter what the outcome I will post the results next week when the cylinder comes back and is reinstalled.

Your brake expert is correct; the pad did not actually deform. In my case, it was a Volvo 965, and every few years the problem would pop up. AS I remember it, the pads were held in the caliper by two pins that press fitted into the caliper and ran thru two holes in the pad backing. These pins would rust up, solidly enough that the pad really was not moving much, despite heavy pedal pressure. And the pads did not hang-up on the rotor either. But the limited motion of the pads resulted in a springy , soft, depressed pedal. I had 2 shops look at it, bleed everything, to no avail. It was only when I went in to replace the rotors and pads, out of desperation, that I discovered the cause. BUT, since you have determined that the pads do move freeely, this does not seem to be your problem. I would be looking at the rubber hoses, expanding. Good Luck with that beautiful car.