Brakes still freezing. . .
 

I've changed the flexible brake lines in both front wheels, fully bled the brakes.
Still there are days, like today, when my front left caliper will freeze closed. Today it happened close to home, so I could get the car back without much trouble.
But I can't seem to figure what's wrong. And now it' cold.

I still need to figure out what's wrong with the charging system. I'm sure it's the alternator. But I need to go get it checked. Arrrgh. Not going to do any of that unless I can get the brakes fixed. Any other ideas? Could it be the caliper itself?

Thanks,

Both calipers in the rear of my 240d were seized, so it does happen. Take a close look at them, you may be able to swap sides. Usually this results in the angle the brake lines enter into the caliper not being correct, but it can work in a pinch to diagnose. If the problem switches sides, then it's the caliper. I recommend you change out calipers in pairs.

You did not rebuild or replace your calipers ? Correct ?

By ' freeze' I assume you are only saying ' does not retract from solid contact with the rotor the way it should ' ?

Not that it locks up and the tire is not turning on the rest of the drive ?

and that perhaps the way/s you know this are that the steering wheel does not want to return to straight and follow the wheels... and/or that the brake and wheel area of that tire are noticeably hot ?

If you did a good job of bleeding.....

there is a good possibility that you need to put rebuilt calipers on..

that tiny reduction... the pulling away from the rotor to ride against it but not be pressing against it .... is provided by the square brake caliper seal... ....

It is not really feasible for most people on a safety item like the caliper... which the FSM says ' do not take apart'.... to do anything except replace them with the best calipers you can find... both sides of an axle is the rule...and the same brand of caliper...

It is possible there is enough crud in between the piston and its bore to keep even proper dust shield pull back from being effective...

It is more common for the Caliper Pistons to become stuck due to Rust that forms a thick muck of Water-Brake Fluid-Rust and prevents the Caliper Piston from Returning or the Brake Caliper Piston is sticking out too far due to worn out Brake Pads and or Rotor.

If you do some internet searches you will find that the deflection and elasticity of Brake Caliper Seal (the Square cross section O-ring) is what returns it. So there is not a lot of force available to push the Caliper Piston Back.
So, if the Seal is hard and inelastic and or there is Muck preventing the Caliper Piston from returning it won't.

But, it was a good idea to change the Brake Hoses just for safety.

Correct, I didn't replace or rebuild the caliper
It DOES lock up and keep the wheel from turning. The car wouldn't go past about 20 MPH the last tenth of a mile. The left side was smoking when I got out of the car. The brake was engaged at the very very top of the pedal.
If you call smoking noticeably hot. . . :)

How do I figure out if there is crud and muck?

Thanks!

You pretty much can figure you need rebuilt or new calipers in your situation.... playing the odds....
and as others mentioned... very likely rust and crud which has accumulated over the years... even bleeding does not clean out around the pistons.... so really keeping the brake fluid moisture free is critical and most of us do not even have control over that for years before we acquire our particular cars...
Technically you can not figure out that it has crud around the piston without taking it apart...at which time it has to be renewed anyway.... you have to go by the fact that it is not retreating from the rotor properly.... there are no other mechanisms to make it retreat....only the flexibility of that rubber ring.... when the friction from whatever on the piston exceeds that rubber rebound ability ... then corrective action has to be taken....

I think it's time for some replacement calipers. If it's only one side would lead to caliper problems even more since you've replaced the hoses. I'd replace both fronts, not just one.

Yes, for many decades that I am aware of..... the rule is that you do the same stuff to both ends of any axle....

Do not overlook the master cylinder or others.
 

My 83 300D had rear brake binding 3 times, it caught fire once. It only binds after the car is driven 30-50 miles. First with a good caliper from PNP, then with a rebuilt one from Peachparts, brake hoses were replaced as well. I had the master cylinder and the caliper ( 3rd unit ) replaced but so far not with enough mileage to be 100% sure the problem is fixed. The car is in Santa Cruz. Article about brake binding and probable reasons.

Brake Parts for Cars

Sometime the problem may be more elusive and expensive than you think.

ah-kay, That is most unusual.... given how few actual parts there are in the whole system.....
Why don't you start a new thread and get back to fixing that ? Something has to be causing it... don't let that machine beat you !!!

I had to replace both rear calipers this year. At times like this I have to remind myself my car is 30 years old. One of the longest trips I ever took was to my wallet. ;)

Not to deviate from the original thread, but I thought I was respond to this. I had a similar problem, but with the front calipers on my 84 300D. The brakes would periodically stick on long drives. They would be fine for a few dozen miles, then I'd notice the car was considerably more sluggish and would run hot for a while because the front brakes were dragging, then they'd free up again. New calipers, brake hoses, and master cylinder did nothing. Turned out there was a large amount of brake fluid in the booster (presumably from a failed MC from the previous owner), and apparently the fluid was occasionally causing the booster to get "stuck" in the engaged position. Just a thought.

That is certainly a possibility.....the difference here is that she is only reporting it happening on one wheel..... if it were more rotors then clearly something higher in the ' trunk' which shared a common branch would be indicated...

Greg, I was helping ah-Kay do some of the repairs on his car. In this case it was the R/R caliper locking up. we finally replaces 4 brake lines, both rear Calipers and the Master Cylinder, then power flushed the system. the driving I did with it in town with a lot of stop and go etc... and using a IFR Lazer temp gauge, I didn`t detect a difference in temp between the Rotors. so the original problem in this case was the Master Cylinder not letting the fluid return to the reservor fully.

Imagesinthewind, since this car has been in your ownership, has there ever been any work done to the brake system? Did the PO do any brake work to the system to your knowledge?

If the system hasn`t been flushed in a long time, there can be internal damage to the MC as well as the Caliper pistons from corosion. not saying that any exterior gunk, crud, rust etc... hasn`t caused any problems. this might just be long term neglect that has cought up to you.

I would replace both front Calipers as well as the Master Cylinder and hoses.

that`s my 2¢ worth.

Charlie

That's a good question, how long has this brake fluid been in the system. Mercedes particularly states that the brake fluid be changed out every year. Especially in snow country. The brake fluid will attract and hold moisture which will in turn cause corrosion in the system.


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