Brakes sticking - PeachParts Mercedes-Benz Forum

Phillytwotank · #1 04-08-2014, 03:00 PM

Just wanted to toss out a quick question...

What could cause the brakes to stick?

'84 w123 300d

trying to see if there is anything i can do to get home safely today before i start in on a brakes R&R as soon as i can get the parts together.

uberwasser · #2 04-08-2014, 03:42 PM

Need a bit more info. Are all four of the brakes sticking? If so it's most likely a bad master cylinder.

Just one brake, or a set (front or rear)? Could be a dragging/seizing piston in a caliper, or old brake hoses that are collapsed internally not allowing fluid to return to the master cylinder/reservoir.

One of the primary dangers of driving like this is that the fluid can overheat and lead to complete brake failure.

Phillytwotank · #3 04-08-2014, 03:55 PM

i'm about to lift it here in a little bit and see if i can narrow it down to which brakes are troubled.

Maxbumpo · #4 04-08-2014, 04:09 PM

If just one wheel, most likely the flexible brake hose is acting like a one-way valve, so the brake will be pressurized, but not release.

Phillytwotank · #5 04-08-2014, 06:28 PM

On the lift I couldn't tell that there was any problem.

Set out to go home and the brakes felt mostly normal for a while.

After the unused the brakes a few times the sticking feeling returned

Unable to maintain speed, smell of brakes, rapid slowing when in neutral, hard pedal

But no pulling... So it seems that it would be all breaks sticking evenly.

Master cylinder?

Diesel911 · #6 04-08-2014, 07:37 PM

Quote:

Originally Posted by Phillytwotank

On the lift I couldn't tell that there was any problem.

Set out to go home and the brakes felt mostly normal for a while.

After the unused the brakes a few times the sticking feeling returned

Unable to maintain speed, smell of brakes, rapid slowing when in neutral, hard pedal

But no pulling... So it seems that it would be all breaks sticking evenly.

Master cylinder?

Can you tell which Wheel or Wheels is getting hot?

When the Car is Jacked up someone has to start the Engine and step on the Brakes a bunch of times. Then you rotate the Wheels by hand and see if they release only a minimum of drag after you rotate the Wheel/s.

If it is a internally collasped Hose issue Brake Fluid won't spurt when you loosen the Brake Line at the Master Cylinder but (after you pump the brakes somemore) the Brake Fluid will spurt out when you loosen the Caliper Bleed Screw.

When the Square cross section O-ring/Piston Seal gets hard an inelastic the Piston will not return like it is supposed to. Deflection of the Rubber O-ring is the only spring action available to pull the Caliper Piston away from the Rotor.
Gunk between the Piston and the Caliper can do the same or a combination of both.

If the Brake Pads are thin and the Caliper Piston is sticking out abnormally far it also does not want to return easily.

See post #5 for a pic on how the O-ring deflection returns the Caliper Piston
1983 240d manual all 4 calipers not retracting

cooljjay · #7 04-09-2014, 02:14 AM

Bleed the brakes first, easy to do....even on the side of the road....with a 9mm wrench and a tool box to depress the peddle...that should help for a bit....i have been driving 3 years doing a once a year fluid bleed...I am just getting to ready to replace the rear hoses tomorrow...as I am getting sick of the squeaking breaks...as was said...the hoses acting like a one way valve....and also I have some large cracks in the lines.

funola · #8 04-09-2014, 08:14 AM

Quote:

Originally Posted by Phillytwotank

On the lift I couldn't tell that there was any problem.

Set out to go home and the brakes felt mostly normal for a while.

After the unused the brakes a few times the sticking feeling returned

Unable to maintain speed, smell of brakes, rapid slowing when in neutral, hard pedal

But no pulling... So it seems that it would be all breaks sticking evenly.

Master cylinder?

Have you topped up your brake fluid recently? Power steering fluid will produce the symptoms you're having.

t walgamuth · #9 04-09-2014, 10:13 AM

A mal adjustment on the brake booster linkage also can cause problems.

Stretch · #10 04-09-2014, 02:02 PM

As can flexible lines

funola · #11 04-09-2014, 02:37 PM

Quote:

Originally Posted by Stretch

As can flexible lines

"But no pulling... So it seems that it would be all breaks sticking evenly."

Flex lines? What's the chance?

Phillytwotank · #12 04-09-2014, 06:51 PM

Yes I repeat, no noticeable dragging on one particular wheel over any other and just a steady drag no pulling side to side.

Think my plan is to throw four new hoses on there and flush/ fill dot 4.

I've never done anything to the brake hydraulics since we've had this car

Stretch · #13 04-10-2014, 03:13 AM

Quote:

Originally Posted by funola

"But no pulling... So it seems that it would be all breaks sticking evenly."

Flex lines? What's the chance?

That all four lines go at once? Pretty slim chance of that happening I agree.

@Phillytwotank

Still it sounds like the hydraulic system could do with some attention - don't kill those hard lines trying to remove the flexible ones though.

Have you got one of those non contact IR temperature thermometers? Perhaps it is worthwhile checking which brakes - if indeed all - are the ones that are sticking.

Phillytwotank · #14 04-10-2014, 08:43 PM

Pulled over when they felt like sticking.

Shot the rotors with the IR

275f on the front
100f rear
Same left to right

Continued driving in a real rural area and really didn't touch the brakes for 10 miles. Coasted to a stop and shot the rotors again.

100f front
100f back

Finished my trip home three miles braking and going repeatedly. Pulled in the driveway and checked the temp again.

115f front
115f rear

Still planning on new hoses all around and new fluid. I figure that's the least I could do since I've never touched the brake hydraulic. I'll be prepared to do a MC and/or the booster next then the calipers if need be.

cooljjay · #15 04-11-2014, 01:58 AM

when you remove flex hose, also unscrew the bleeder all the way out...use the hose on a can of brake cleaner to stick in the bleeder opening...and spray the caliper out with brake cleaner....I did that on my rears the other day after I changed the hoses, it was amazing the yellow gunk that came out of the calipers...