1986 300E Rear brake Issue - PeachParts Mercedes-Benz Forum

ashbyrp · #1 10-23-2003, 03:15 PM

Any and all help is welcome, as I have no clue where to start.

Here's the story: Driving home last night my car felt as if the parking brake had engaged (I checked, it was not). The drag worsened, but I only had a couple of blocks left, so I pushed it

. Got home to red hot rear rotors (both sides). After a few minutes of cussing myself, I heard an explosion. I later found a large chunk of the left rear caliper under the car. (see photo)

Here's what I know: I will have to replace the blown caliper. It is only smart to replace both rotors and pads. Maybe smart to replace the other caliper while I'm down there.

Here's what I don't know: What caused the problem. I suspect the parking brake because both sides were hot. I don't want to replace the whole rear brake system just to have this happen again.

Help!

Paul

ashbyrp · #2 10-23-2003, 03:44 PM

The brake pedal felt normal. Good pressure, no sinking. No loss of fluid. Now it hits the floor- but with a gaping hole in the caliper I think that's normal.

euronatura · #3 10-23-2003, 04:10 PM

Years ago, I was a partner in a brake shop here in central america.

Given the information that you gave in your listing a couple of things could have happened.

1) The pistons on your rear calipers got stuck and caused consistant braking. This could be due to the seals within the calipers gone bad.

2) What I really suspect is that the seals in your master brake cylinder went bad and caused consistant braking on your rear tires. That is why both of them were hot. If it were just one tire I would suspect that it was just the caliper.

You did not mention what vehicle this is? I do not know if there are additional valves or hoses in the braking system or it could have been caused by the ABS? Though I highly doubt the ABS.

Your line of attack:

1) Repair rear calipers. (new pistons and seals)
2) After this, check your master brake cylinder. if bad change out the master brake cylinder also.
3) If there are additional valves or hoses check these also for blockage.

yal · #4 10-23-2003, 04:48 PM

Whats your mastercylinder like? How was pedal feel?

MikeTangas · #5 10-23-2003, 07:09 PM

If the problem isn't in the master cylinder it coiuld very well be the rubber hose for the rear brake line, collapsed internally. The parking brake is a completely separate system on these cars and not likely involved in the matter (the park brakes are purely mechanical not hydraulic).

euronatura · #6 10-23-2003, 07:15 PM

There you go! Thanks for the extra imput Mike, I could not remember if this model had a rubber hose in the rear brake lines.

On another note that I forgot to mention in my earlier posting is that you have to make certain you use PREMIUM quality brake fluid, preferable MB original. I mention this because I have seen in the past that the seals in the Master Cylinder and the Calipers(I am sorry if not useing correct terminoligy - I am translating directly from Spanish) can deteriorate or swell due to poor quality brake fluid!

ashbyrp · #7 10-23-2003, 07:27 PM

The car:

1986 300E
200,000+ miles
abs system

The parking brake was always loose- would hold on small hills, but not on large hills. I rarely use it, and have not used it in the last month.
What are the symptoms of master cylinder failure? How does the pedal feel (change)? The brake pedal felt normal before the problem, although normal for me may have not been normal. Is there any way to check the master cylinder? The part is not too expensive, so I may replace that too....any suggestions

paul

psfred · #8 10-23-2003, 07:44 PM

Pressure got trapped in the system, rear brakes only, and when they got hot, the pressure got higher.

It did not vent with the car stopped, and the caliper failed.

I've never even heard of a caliper failing like that, it must have been as hot as all get out, and could also have been defective to start with, but blow up??????!!!!!

Replace both rear calipers, I'd not trust them if they got that hot. Replace the rotors, too, they are surely warped from getting cooled by the pads in one spot and air on there rest, plus they've been severely overheated.

Then I would bleed ALL the old fluid out, front and rear, and check operation. Replacing the hoses isn't a bad idea either, but you should only have one wheel lock up from a bad hose, not both, unless there is a section of hose before the "t" to the rear wheels.

I would be tempted to replace the master cylinder, too, just to be safe. I suppose brakes that won't let go are better than brakes that won't work, but still.....

Peter

euronatura · #9 10-23-2003, 07:45 PM

Paul:

Usually you can tell if the master cylinder is failing if you pedel is going to floor *somethimes slowly - sometimes fast) when you are braking and basically the car is not stopping as it should!

If the master cylinder was clogged (seals swollen not allowing release of pressure) where it caused that the rear calipers would have locked up, then you would not have really been able to tell other than what you wrote, that the back rotors and calipers were red hot.

As for suggestions, what I would do if I were in your shoes, is rebuild/fix or change out the rear calipers (rebuild is changeing the seal and the piston. Then from there, check the hose that MikeTangas mentioned. If this hose has an internal blockage (like the master cylinder would did not allow release of pressure) that could have easily caused the consistant braking and therefore meltdown/blowout of your rear calipers. If from there, you have not resolved the issue, then go onto the Master Cylinder.

Now how can you check all of this. After getting the rear calipers installed and set up, start bleeding the system. If you are not getting any fluid out the rear calipers or they still lock up, then check the hose. If the hose is not blocked, then onto the master cylinder.......

Also, while checking the system and hose, check the hose for cracks or signs of old age. If it shows signs of old age then you need to change it. Also, if the hose has a bubble on it (I have seen this before) change it. Under extreme pressure and the lack of the release of pressure the hose could develop a bubble - usually near the clamps/fittings and this is not uncommon if the hose develops an internal blockage.