Brake Problem 85 300D - PeachParts Mercedes-Benz Forum

rmmagow · #1 09-09-2012, 04:06 PM

My car has been sitting for a couple of months. I took it out today for a shake-down before putting it back into semi-daily service. The passenger side rear brake is dragging pretty badly. Pulled into the driveway and a temp check shows three wheels at around 100 degrees, the rear passenger side was smoking a little and read around 190 to 200 degrees. I had previously taken the caliper off, cleaned up the brake pins, pushed the pistons back in etc. After that the brake seemed ok. I did that about 2 weeks ago. Question, are the calipers known to rust up inside and need a good cleaning and new seals or is a collapsing flex hose the more likely issue. Pads look OK, rotor is OK and prior to putting it up this summer, all was working fine.
Thanks for any and all advice.

Diesel911 · #2 09-09-2012, 04:33 PM

It is more likely the Caliper Piston is what is sticking.
Brake Fluid abosorbs Water from the Air and eventually gravity sends it to the lowest position where it forms sort of a muck between the Piston and Caliper.
Also the Caliper Bores are not plated and can rust.

The deflection of the square cross section O-ring that seals the Caliper Piston is also the only thing that pulls the Caliper back. When it gets stiff it cannot do that. See Pic.

Some have said that if the Brake Hose is holding the pressure when you open the Brake Bleed Fitting you will get a spurt of Brake Fluid because it us under pressure.
It could do the same thing if the Master Cylinder was holding back the pressure but in your case your other 3 Calipers do not appear to be sticking so it is not likely that the Master Cylinder would be the cause.

rmmagow · #3 09-09-2012, 05:39 PM

OK, that sounds reasonable. Now, say I want to clean them up and re-build them myself. They seem pretty simple. I was thinking to pull the caliper, have someone press on the brake pedal to get the pistons to come mostly out, clean 'em and put in a new set of seals. I do understand the square seals function. The bigger question is is this a lot of work for nothing and is it just as easy to buy a pair of rebuiilds? I found rebuilt for 65.00 ea and the flex lines run about 15 a pair. I'd do both sides. The new calipers are loaded and BENDIX like mine, rotors are good (probably should just do them too). I'm tight for money BUT would rather get the nastys out of the way 100%. The rebuild kits run around 20~25 and if I take the caliper apart and its badly rusted or scored, I'm screwed anyway right?

qwerty · #4 09-09-2012, 05:45 PM

Quote:

Originally Posted by rmmagow

The bigger question is is this a lot of work for nothing and is it just as easy to buy a pair of rebuiilds?

I have had good success installing new seals and boots. But you won't know anything for sure until you examine the condition of the pistons and bores.

steeleygreg · #5 09-09-2012, 07:14 PM

I would say that, how pitted either bore or piston is depends on how long the sat unused and in this case it was not allot of time. Also the amount of pitting depends also on how long it's been since the brake fluid was changed.

Diesel911 · #6 09-09-2012, 07:26 PM

Quote:

Originally Posted by rmmagow

OK, that sounds reasonable. Now, say I want to clean them up and re-build them myself. They seem pretty simple. I was thinking to pull the caliper, have someone press on the brake pedal to get the pistons to come mostly out, clean 'em and put in a new set of seals. I do understand the square seals function. The bigger question is is this a lot of work for nothing and is it just as easy to buy a pair of rebuiilds? I found rebuilt for 65.00 ea and the flex lines run about 15 a pair. I'd do both sides. The new calipers are loaded and BENDIX like mine, rotors are good (probably should just do them too). I'm tight for money BUT would rather get the nastys out of the way 100%. The rebuild kits run around 20~25 and if I take the caliper apart and its badly rusted or scored, I'm screwed anyway right?

I have always rebuilt My own as long as the bore inside the Caliper is not too bad. Sometimes the Plating on the Piston can go bad and they can also rust.

So you need to see them first to decide if they are rebuild able.

Then there is the time Factor. Exchanging them is faster.
On the other hand people have side the quality of the exchanges is not reliable.

rmmagow · #7 09-10-2012, 08:12 AM

I've ordered two Bendix repair kits. I know I'll be able to get the caliper off. Now, what's a good method for getting the pistons to come out as much as possible? I was thinking to have someone press on the brake while the pads are removed but there are two pistons to take out right? Should I fiddle around with like C-clamps hold one piston to let the other move and just go back and forth until I can get a good grip the wiggle them out the rest of the way? I don't have access to compressed air to use that pop-out method.
The rebuild process, my plan is to thoroughly wash the caliper and pistons in hot soapy water and scrub them clean paying close attention to the bores and pistons and clean them up only with plastic non-scratch scrubbing pads. Maybe some jeweler's cloth to smooth out the pistons and bores. After a perfect rinse I'm going to dose them heavily with regular brake cleaner, let them dry and reassemble with copious amounts of brake fluid. I am wanting to avoid using any solvent based cleaners other than brake cleaner.
Does this sound OK?

Diesel911 · #8 09-10-2012, 12:21 PM

Because you have Calipers with 2 Pistons it is entirely possible that one Piston is going to come out more than the other no matter what method you use to move them out.

In Shops a typical method is to remove both Pads and inseret something thin like a piece of wood beteen the Pistons and apply compressed Air by way of an Air Gun into the hole the Brake Hose attaches to. That may of may not pop out both Pistons on a 2 piston Caliper. (Be safe when you do this.)
It works well on single Piston Calipers.

If you can get the pistons to move out a little you might use something as I did in the pic to pry them with out dinging them up.
I have ATE Brakes front and rear and my Heat Shields attach inside of the Pistons so yours will be different.

rmmagow · #9 09-10-2012, 12:59 PM

Thanks Diesel, that looks very much like how I'd try to do something like this. I'm going to try to get the caliper off tonight when I get home. Question, if I have to get rebuilt Calipers, might I be better off swapping for ATE's? They seem to be more prevalent. Are they any better/worse that Bendix? This is all my fault for not using the car. I meant to drive it a couple of times a week but fell in love with the A/C in my new-to-me clunker Volvo.

qwerty · #10 09-10-2012, 01:52 PM

Quote:

Originally Posted by rmmagow

This is all my fault for not using the car.

Replacing some 28-year old rubber is a worthwhile endeavor, regardless of the underlying reason.

macdoe · #11 09-10-2012, 02:15 PM

Awsome you took temp reading of your brakes after a drive. I can now rule out sticking brakes on mine. I got roughly 95 degrees on all four wheels to compare to your reading of three. Thanks.

rmmagow · #12 09-10-2012, 03:17 PM

Quote:

Originally Posted by macdoe

Awsome you took temp reading of your brakes after a drive. I can now rule out sticking brakes on mine. I got roughly 95 degrees on all four wheels to compare to your reading of three. Thanks.

Yeah, I bought the thing to monitor my wood stove temps in the winter. Found a million more things it's good for, brakes, radiators, tranny temps etc. Useful little new-tech device.

Diesel911 · #13 09-10-2012, 06:52 PM

I have read of no function difference between the ATE and the Bendix Calipers.

The ATE Caliper Heat Shields go into the Hole in the Piston. The Bendix Heat Shield somehow atttach on the outside of the Piston.

rmmagow · #14 09-11-2012, 12:12 PM

Good. If my Calipers are shot, I'll replace with ATE, new rotors and new flex lines. My 83 had ate and they worked fine.

rmmagow · #15 10-02-2012, 10:59 AM

Epic fail on the rebuild attempt. The caliper was just too badly damaged. I have ordered a pair of loaded, rebuilt Bendix calipers, a pair of Brembo rotors and the two rear flex lines. So essentially a full rear brake rebuild. Under $300 for the parts.
After re-building the sticky caliper, the caliper continued to lock up too much for comfort, 95 degrees on three wheels, 180 on the "bad" wheel. I ordered good quality parts so I hope to be OK. Brake pedal feels pretty nasty but I do have all new fluid in there so I am thinking it is just from the bad caliper. If time/funds permitted, I'd do all 4 but I am in a squeeze. The car really runs nice now after a valve adjustment and new glow plugs even with year old fuel in there. Damn tach is making me crazy though, it actually sprang to life for about 30 seconds then went back to sleep. Something for another time.