220D, 1972. Both rear calipers are binding against discs. This seems to indicate a bad master cylinder, not calipers since both calipers going bad at the same time is unlikely.

Do you agree or disagree? What do I look for to help diagnose the problem?

Lange, the check is in the mail this weekend!

Agree.

Crack both rear bleeders and let the pressure off the rear pistons. Drive the vehicle and don't touch the brakes. Elimination of the problem confirms the m/c.

Brian - do not understand. How do you drive the vehicle and not touch the brakes?

.......very carefully........and not very far.

Or, just jack up the rear of the vehicle and see that the calipers are not gripping the rotors........your choice.

Brians advice is excellent.

As a comment, it would not surprise me if both were actually stuck. I cannot think of a time I have had this happen though.

__________________
[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.

Fellas, just checked the calipers and they were up against the rotors. Turning the wheel by hand was doable, but required some effort, they did not rotate freely. Recommend rebuilding the m/c or get one professionally rebuilt on line?

To establish the master cylinder is involved you have to release a bleeder at least. If the rear wheels then turn substantially easier then you know it involves the master cylinder.

So far it seems you have really done nothing. Actually it sounds more like a pair of old unused calipers that have some cylinder drag. Yet until you release the pressure in the brake system if any there is no way to absolutly know.

For all practical purposes the calipers keep the pads very close to the rotors. They do not back off to actually allow a really visable space even with all new components. There are no return springs. The turning rotor not being absolutly true wobbles a tiny amount loosening them to some extent. Sometimes the friction drag on the caliper cylinder sealing rubber may contribute a little as well. So the only sane test is rotating the wheels. Very slight drag may even still be possible on a good system. But not much if any.

It is unwise to leave brake systems sitting a long time between uses in most climates. Also not replacing the brake fluid on ocassion is costly. The water contamination in the fluid over time does corrosion damage. Especially to the pistons in the calipers. Then the rust inhibits free movement by hanging up on the rubber caliper seals. The pads must also move along their guides well. The guides can develop rust as well. They should have a periodic touch of lubricant. Again a maintenance thing.

I fully realise the majority of cars out there have very old brake fluid that really should have been changed out several times at least but never where. The majority of cars do not recieve adaquate maintenance.

All manufactures want brake fluid flushed and replaced periodically. Since you can still turn the wheels by hand it is unlikley the master cylinder is involved. Old tired calipers are a very common thing. Loosen a bleeder to separate as suggested.

Thanks Barry123400. Will get to that sometime this week in that I am hosing down all the threaded connections in the brake system with Liquid Wrench. Each day I hose 'em good to prepare them for turning.

It is also possible that your flexible brake hoses have collapsed internally. If you loosen the nipple on one side and it releases the other, it is the master cylinder or a kinked metal line (I don't believe that you have a common flexible hose which services both rear calipers). If you have to loosen both nipples to free both sides, it may be the flexible hoses.

My W126 has a stuck piston on each rear caliper....it happens. Both sides have one stuck piston. I am replacing the lot of it tomorrow. New: Calipers, Pads, Rotors, Parking Brake Shoes, and brake fluid.

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

You didnt mention if the car was actively used or sat. If it sat, frozen calipers is a very likely scenario.

__________________
http://superturbodiesel.com/images/sig.04.10.jpg
1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
#1994 E320 Cabriolet
#1995 E320 Touring
#1985 300D Sedan
OBK #42

Couldn't wait till Thursday to find the answer! We just went out to the garage.
One thing to note. After driving the car around the neighborhood we park it in the drive which has a small incline. The car will sit without rolling when it is not in gear and the parking brake is not on. After sitting overnight I get in and push the clutch in the car will slowly roll backwards acting as if the calipers are not sticking.
On with the story. We popped the bleed screws loose to relieve pressure, but it has had no effect on the calipers.

Yes, the car has sat for about 2 or 3 years without any real use. Maybe driven six times each year during this period.

Any ideas, or is this a replace parts as you go until the answer is found?

Replace the calipers and discs. What happens is the dragging brakes heat the disc to the point where it expands. As Mathieu pointed out, releasing the pressure should haver resolved the issue. I do not recommend driving the car in this state.

__________________
http://superturbodiesel.com/images/sig.04.10.jpg
1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
#1994 E320 Cabriolet
#1995 E320 Touring
#1985 300D Sedan
OBK #42

Roger that. Will order soon from PeachParts.com

They list two brands of calipers. Do I need to match up brands with what is on the car or will the car accept either brand?

Is a rebuild something to be performed by a rookie mechanic? Seal kits are twenty bucks, calipers nearly one hundred. Is there more than seals to deal with? Scored pistons would make a real problem from what folks have posted so far. Just hate seeing my son spend 200 bucks on parts so soon!

You require the pistons to be still in good shape to attempt doing them with a kit. That means you have to remove them from the caliper to inspect. Be careful if you attempt to do this. Your climate is as rough as mine on calipers if left sitting.

On a 123 type ate or bendix are the caliper suppliers. As long as you buy both sides substitution is fine. Ate is usually cheaper. Your 220 may be simular but you should check.

Right now I am trying to get a set of caliper pistons to retract or slide a little easier. I have a method that has worked for me several times over the years. I cannot recommend it though as brakes are critical.

On a mercedes two piston caliper I pull the pad on one side. Using a much thinner than the pad pry bar in the resulting space. . Then I press the brake pedal about four times driving the sticking piston partially out.

I then load a syringe that is available to any junky at a drug store. Inject a silicone lubricant into the top of the boot. I then pry the piston back in as far as it will go. Repeat this several times to see if less effort is required with each try. If the piston is getting as loose or sliding in as I think it should I replace the pad and do the other piston by removing its brake pad in a simular fashion.

I used to use brake fluid but became aprehensive of its hydroscopic tendencies. The brake fluid seemed to eat the rust though if a small amount was present. The silicone is not hydroscopic but is not compatable with normal brake fluid either. I never had a caliper leak or develop repeat problems either.

So I now suspect dot 3 or 4 brake fluid I used to use produces better results. Since otherwise the calipers are history usually it costs nothing but some time to attempt this. If substantial rust had developed on the piston I think it has become too late for this approach. This is obvious as the pistons will not free up properly though. To determine how things are progressing use a laser thermometer to measure the disk temperature after a short drive.

Another good test on a two piston mercedes caliper when you think it is about loose enough. Using pliers if you compress one piston by squeezing back the pad tangs the opposite piston should tend to move its pad out a little. Fresh rebuilt calipers are easier to deal with of course.

Again I cannot recommend this approach although it has worked many times on many of my cars. Brakes are just too critical a function to deal with. I get away with it without any complications.

Others may not have my judgement on this method though. You really have to decide if a locked up caliper might occur for example. Not worth the risk if you do not have a feel for this.

A working mechanic does not have the time to even attempt this approach. You want the piston to slide back in pretty easily remember. I really do not know if the average member is observent enough to do this in a safe way. There is no doubt if things are not progressing as I feel they should I stop. Then rekit the caliper or replace it.

Thought I would just bring this old thread forward as it is pretty quiet and dragging calipers are a somewhat constant problem with cars that have sat around a lot.