WHOA!!! Brake failure!! W124 - Page 3 - PeachParts Mercedes-Benz Forum

Parrot of Doom · #31 12-29-2006, 07:34 AM

Silly question time - do you have mats in your car, and had the mat managed to move up behind the brake pedal and restrict its movement?

jbach36 · #32 12-29-2006, 11:39 AM

Quote:

Originally Posted by DrLou

I think there's more to this - and it hasn't been discussed yet here...

First off, my main car (testbed, laboratory, etc.) is a diesel 126, so don't know how much of this applies to your 124. Given that caveat, here goes:

My vacuum pump has never failed, but I understand it may go like this if it ever does: As they start to go, they are known to start dumping engine oil into the brake boost line (the big plastic pipe between the pump and booster body). Because this line has ports which supply vacuum to the shutoff system, EGR, climate control, etc, any number of symptoms may result as this oil creeps into vacuum lines. It isn't hard to imagine that one of these might be an intermittent loss of brake boost. A very common effect is loss of the vacuum shutoff function.

In my case, a small occlusion of 'crud' in one of these ports completely blocked the vacuum shutoff circuit. After cleaning the port, problem solved!

Before getting too crazy with replacing everything: spend 15 minutes, remove this vacuum line, and be sure it's clear.

Lemme know! Lou

Interesting thought. One guy said the vacuum either works or it doesn't, and so far, it's working. Unless he's wrong and it goes down hill little by little.

Thanks,

Jeff

jbach36 · #33 12-29-2006, 11:40 AM

Quote:

Originally Posted by Parrot of Doom

Silly question time - do you have mats in your car, and had the mat managed to move up behind the brake pedal and restrict its movement?

Thanks for the tip, but nooooo way. Once your brakes go hard and you are basically rolling with no brakes, it ain't the mats. They will at least give when you press down harder.

Jeff

mctwin2kman · #34 12-29-2006, 02:38 PM

Did you or the mechanic change the brake fluid? Do a bleed to make sure there is no air? Just a thought, since when water gets into brake lines it is not ever a good thing and can cause issues like this!

Benz300 · #35 12-29-2006, 04:13 PM

some of the "opinions" here in the post have nothing to do with a hard pedal scenario that you posted.
fluid changed, master cylinders, and brake lines should not give you a hard pedal.
Once again, this forum is great if you're not dealing with such important issues as brake failures. but for something this important please do yourself a favor. take a trip to the dealership !

jbach36 · #36 12-29-2006, 10:30 PM

To respond to 2 posts:

1) The brake fluid was changed back in June when I bought the car. No problems until the hard pedal. No leaks, no nothing.

2) As Benz300 said, brakes are not to be fooled with. You don't want to take advice from novices. I'll listen to ideas, but the bottom line rests with my mechanic. Again, I didn't take it to the dealership, not even a MB specialist, but a general mechanic who I think is pretty competent. He drove it after I had the problem, which occured just that one time, and the brakes worked fine for him. Shince he could really see no problem since everything was working fine, he did a best-guess estimate that the problem was the booster, and replaced it. Too bad the problem then happened a 2nd time, just a week after the booster was replaced. So this time, he replaced the hose. Hopefully all will be well.

Jeff

Hirnbeiss · #37 12-31-2006, 12:12 PM

Someone mentioned a '68 Chevelle with no power assist. That's a horse of a different color. It would have had drum brakes, which are "self-energizing" (the shoes basically pull themselves against the drums), meaning they didn't require power assist. They just faded easily.
Disc brakes, being squeezed from the sides, are not self-energizing, and require power assist.

justinperkins · #38 01-02-2007, 12:35 PM

Quote:

Originally Posted by jbach36

To respond to 2 posts:

1) The brake fluid was changed back in June when I bought the car. No problems until the hard pedal. No leaks, no nothing.

2) As Benz300 said, brakes are not to be fooled with. You don't want to take advice from novices. I'll listen to ideas, but the bottom line rests with my mechanic. Again, I didn't take it to the dealership, not even a MB specialist, but a general mechanic who I think is pretty competent. He drove it after I had the problem, which occured just that one time, and the brakes worked fine for him. Shince he could really see no problem since everything was working fine, he did a best-guess estimate that the problem was the booster, and replaced it. Too bad the problem then happened a 2nd time, just a week after the booster was replaced. So this time, he replaced the hose. Hopefully all will be well.

Jeff

I think you're making a bad choice by taking your Mercedes to a general (non-Mercedes) mechanic. They are special and require a skilled and knowledgeable professional. When somebody doesn't have particular knowledge of your vehicle, it's common problems, etc.., they are just applying what they know from working on other vehicles (American, Japanese) which sometimes works and sometimes doesn't work.

It's been my experience that a general mechanic (non-German specialist) will misdiagnose and do an unsatisfactory job (i.e. create a new problem and/or not fix the original problem).

I love my German cars too much to let any old dude touch 'em. Between living in California and Austin I have only found one shop that I truly trusted. Sadly, that shop was in Sacramento and I no longer live there.

jbach36 · #39 01-09-2007, 10:51 PM

Specialists are good, and sometimes less expensive in the long run. But there are other times when I just feel waaaaay hosed. I needed an alignment recently, and the specialist was like, $145. The "general" place, Marietta Alignment, specializes in alignments, just not necessarily MB's. Cost $50. Each has their advantages. In the case of brakes, I had no clue what was wrong. I thought maybe it was an air bubble in the lines or something, and I'd replaced the brake fluid a few months before with that mechanic, so I went back to him. Turns out, it was something more serious.

jeff

kerry · #40 01-10-2007, 12:42 AM

I've posted two threads with a similar problem. One on the diesel discussion and one on here.
My 77 300d is also losing its power assist. It has vacuum and the boost seems to be consuming vacuum as the brake pedal is pushed since the vacuum guage drops 3 or 4 inches as the pedal is pushed, but there is little to no power assist. In other words, everything appears to be working, but it isn't.
I'd like to know exactly what the problem is.
It doesn't seem to me that the mechanic has given a clear diagnosis of the cause of the failure described in this thread. So far I don't see a clear reason to think the problem was the hose. What was happening with the hose to cause the problem?

compress ignite · #41 01-10-2007, 02:00 AM

If it happens again ...AND the operator survives...New Vacuum Pump.(Assuming
You've replaced the rubber brake lines.)

Hatterasguy · #42 01-10-2007, 12:09 PM

Quote:

Originally Posted by kerry edwards

I'd like to know exactly what the problem is.
It doesn't seem to me that the mechanic has given a clear diagnosis of the cause of the failure described in this thread. So far I don't see a clear reason to think the problem was the hose. What was happening with the hose to cause the problem?

Because his mechanic doesn't know anything about W124's and is shotgunning parts.

Hirnbeiss · #43 01-10-2007, 12:44 PM

Since gas engines never or seldom have power brake problems that I know of, the problem is most likely due to the diesel-specific components, which are the vacuum pump and (potentially) the vacuum line with check valve.

Ich tippe auf die Pumpe.

kerry · #44 01-10-2007, 12:57 PM

Quote:

Originally Posted by Hirnbeiss

Since gas engines never or seldom have power brake problems that I know of, the problem is most likely due to the diesel-specific components, which are the vacuum pump and (potentially) the vacuum line with check valve.

Ich tippe auf die Pumpe.

I think this is an important insight.
What about the vacuum pump and its systems could be causing problems if it seems to be producing adequate vacuum? In my case, this seems to be happening.
I will check the check valve.

Deezl · #45 10-19-2009, 02:07 PM

Jbach and Kerry,

I've had this same problem on my W124.

How was it resolved?