Brakes ok cold, sticking hot.

RedMF40 · Jun 30, 2020

I'm helping a friend who's a new dad sell his '68 Mercedes 220D.
Drove it a few times now and it's clear the brAkes are hanging up.
They'll even hold the car on a pretty good hill.

Next morning brakes are free, everything normal. Until you start driving, that is.

I'll see if I can find a photo of the car. That should help diagnose it.

Thanks for any ideas,

Gerrit

MARK ROBKE · Jun 30, 2020

I have seen brake fluid contaminated with oil and cause that problem-someone dumps the
wrong stuff into the master cylinder. Oil expands when hot, but brake fluid does not,
and that expansion applies the brakes. Mark.

marloweg · Jun 30, 2020

brake calipers or brake hose pinched of by rust but the hot part says calipers

Steve@Advance · Jun 30, 2020

If all the brakes are binding up when hot, it's the master cylinder not fully returning.

Inside the master cylinder, there is a tiny hole that opens the system to the fluid reservoir when the pedal is released. If the MC piston fails to fully return, that hole remains closed, and the system builds pressure from the fluid heating and expanding.

It can be caused by a mechanical binding or improper adjustment of the pedal, or the master cylinder piston binding in the bore due to corrosion, or the wrong fluid has been introduced to the system and has swollen the cups.

If it has been stored, or just been many years that the brakes have had any service, chances are they will all need to be taken apart and gone through. Do it now and save the shoes/pads from getting fluid soaked.

If it's had the wrong fluid introduced, bad news! Everything will have to come apart and be flushed. ALL rubber components, including hoses, replaced.

Duner Wi · Jun 30, 2020

Jack it up when all wheels turn freely. Apply brake and see if brake releases by turning wheel. Check each wheel this way. If it is one wheel I suspect a collapsed brake hose. Let us know how it turn out.

Stephen Newell · Jun 30, 2020

It might free itself up if the car was driven more using the brakes often. I had a car that sat for three years and one wheel was completely locked up and the master cylinder was sticking like that car. I just drove it around on my property until it started working
right.

504 · Jun 30, 2020

Jack it up front first,spin the wheels,one may already have drag,hit the brakes and spin them again.
If you find one dragging open that bleeder, and if that frees the brake you have a bad hose. If it
still drags then see if you can push the caliper cups in with a screw driver, leaving the bleeder
open. Rear the same thing if you have disc on the rear. I really think you will find a rear
problem,wheel cyl,parking brake,axle seal. on rear drum brakes the most over looked thing is the
brake shoes not resting on the pin,but resting on the parking brake bars.

guido · Jun 30, 2020

Hello RedMF40,

When the brakes are hanging up, check the temperature of the drums-rotors. If you find a hot side, then you can investigate further. Brake hoses that old can collapses, causing the brakes to hang up.

Usually is only one side that hangs up.
It is possible that on wheel has thin brake lining-pads, and it gets hotter then the rest, and expands enough to get tight. Or, for the same reason, a caliper is overextended and hangs up. Also check the hand brake, and make sure it is realeasing all the way.
Also check the brake to master cylinder clearance, it may need to be adjusted,

Guido..

wore out · Jun 30, 2020

(quoted from post at 18:25:49 06/30/20) If all the brakes are binding up when hot, it's the master cylinder not fully returning.

Inside the master cylinder, there is a tiny hole that opens the system to the fluid reservoir when the pedal is released. If the MC piston fails to fully return, that hole remains closed, and the system builds pressure from the fluid heating and expanding.

It can be caused by a mechanical binding or improper adjustment of the pedal, or the master cylinder piston binding in the bore due to corrosion, or the wrong fluid has been introduced to the system and has swollen the cups.

If it has been stored, or just been many years that the brakes have had any service, chances are they will all need to be taken apart and gone through. Do it now and save the shoes/pads from getting fluid soaked.

If it's had the wrong fluid introduced, bad news! Everything will have to come apart and be flushed. ALL rubber components, including hoses, replaced.

Steve, your post is by FAR the most realistic reply to this topic.

MarkB_MI · Jul 1, 2020

> I have seen brake fluid contaminated with oil and cause that problem

Brake fluid contamination is usually pretty obvious; any visible rubber parts (such as the master cylinder cover gasket) will be visibly swollen. And you probably won't be able to drive the car far enough for the brake fluid to get hot.

Sprint 6 · Jul 1, 2020

Most likely, somebody put something other
than brake fluid in the master cylinder.
Easy way to tell is if the master cylinder
cap has a rubber seal, it will be swelled
up past it's normal size. If somebody did
that, get out the wallet, it's gonna get
expensive.

Year or so ago, had a truck that was doing
this. Customer had replaced his own brake
calipers with parts from Autozone.
Autozone told him since his truck had
hydroboost, it used power steering fluid
instead of brake fluid. On their advice,
he flushed the entire system with 4 quarts
of power steering fluid.

RedMF40 · Jul 1, 2020

Thanks for the replies. I'll have a chance to look at it today, can put it up on my lift I've been talking about here (needed a little lift).

I remember an old work van had similar problem. Drove ok cold, after some miles the brakes started dragging. Finally stopped with a smoking front wheel and stuck caliper. Pulled into a place and they fixed it. Forget exactly the problem but I think it was related to a failing brake hose as some have mentioned.

I'll be able to troubleshoot a little better with the suggestions here. For wrong fluid--I doubt it. Car has been in same family since 1988 and they have done all the maintenance. I'll check though.

Thanks again,

Gerrit

showcrop · Jul 1, 2020

Someone had that on one front. It turned out to be a bad hose that was acting as a one way valve. As others have said if it is on all four wheels that points to the MC. One wheel to a hose or cylinder.

dr sportster · Jul 1, 2020

Like Guido said check for closed up rubber lines they swell shut.

Fordy20 · Jul 1, 2020

Had that same thing happen on a 69 Corvette. Bad brake hose on right rear wheel would only let brake fluid seep back slowly so brake would stick for some time after using the brakes..

RedMF40 · Jul 1, 2020

Update:

I put the car up on my lift, right rear wheel almost locked up. Very difficult to spin.
Right front a little better.
Both left wheels almost normal but don't spin freely.

Probably hold off on any repairs, selling car as-is but wanted to know what the issues are. Old used-up Benz. Thanks for the tips on troubleshooting, saved a lot of time.

Gerrit

Janicholson · Jul 1, 2020

Still could be a master cylinder. If it has dual diagonal brakes, they work on opposite corners. To find it easily get to be resisting motion, and
loosen the lines at the MC. If it frees up, the MC may have one cup not retracting past the compensating port. Jim

RedMF40 · Jul 1, 2020

(quoted from post at 19:50:18 07/01/20) Still could be a master cylinder. If it has dual diagonal brakes, they work on opposite corners. To find it easily get to be resisting motion, and
loosen the lines at the MC. If it frees up, the MC may have one cup not retracting past the compensating port. Jim

Thanks, MC is a possibility. Brake hose to that wheel looked almost new. Doesn't mean the caliper isn't sticking, but I'll check the master as you suggested.

Gerrit

Brakes ok cold, sticking hot.

RedMF40

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marloweg

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Duner Wi

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504

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