Help with vehicle brake problem

[JimR]

Now here's the killer about ABS. They can't apply themselves without someone stepping on the brakes. The traction control can. Unless there is some type of linkup (screwup with the sytem that may be causing it to happen. As far as replacing the calipers and rotors being a fix for this problem. if the calipers are not stuck or sticking, replacing them will not make any difference. Your sensors should be mounted on the abckside of each wheel. I do not know how to check them. Have you checked the caliper pins to see if they are freed up? You might try removing them on that wheel just to check it out and regrease them. I still think there is a traction control issue here. I would like to know what the fix ends up being. Was your 10/03 visit to the dealer under warranty? If so I would try to use that against them to fix the problem they never fixed.

 

[Egon]

I have heard that the sensors for ABS and traction control can become coated with particles from the brake pad that have metalic materials in them. Results in improper signals to the computer and many times a missdiagosis by the tecknician resulting in costly repairs.

Supposedly ceramic pads will alleviate this problem.

I received this information from a NAPA auto parts regional sullier who took me back into the warehouse and spent at least 1/2 an hour showing me pads and rotors and telling of things to come in the brake department. I was replacing the front pads on a Dodge 2500 at the time. He recommended extreme duty pads such as are used on emergency, ambulance and police vehicles. These pads were head and shoulders above anyhing else I'd used. For rotors he advised the cheapest available because of the possiblity of warping one when stopping with heavy loads on downhills.

Little off topic but hope it will help.

Egon

 

[Junkman]

Traction control works by applying the brake to the "offending" wheel. ABS releases the fluid to the "offending" wheel. They are both independent of each other. I did think of one possibility though.... the brake hoses are damaged internally and are not allowing the fluid to return to the master cylinder after application of the brakes. It would be slightly constricted, so there is only a portion of the fluid trapped. I have seen this on older cars, but I guess that it can happen on newer ones also. Also check the wheel lug nuts. If they are over torqued and not even, they can warp a rotor. Common problem with places that use air guns to put the nuts on. If the rotors are warped, that will cause the problem, because they will be hitting the pads on each pass where it is higher than the other side of the rotor. The brakes ABS and the traction control sensors are both located inside of the differentials from what I remember about the systems. Oh... the wife said NO WAY!!! /forums/images/graemlins/crazy.gif

 

[Egon]

2. Clean your front Mercedes ABS brake sensors when you have your wheels off and are replacing your brakes and rotors. The sensors are magnetic pickups and that attract all of the metal particles that wear off your brake pads and rotors. Over time the accumulation of metal on the tip of the sensor will cause the sensor not to work properly. You may clean off your sensors by spraying brake parts cleaner on them. Sometimes it is necessary to remove the allen bolt and remove the ABS wheel sensor so you can wipe off the accumulation of metal fuzz with a soft clean rag.

Egon

 

[Egon]

In order to maintain directional stability and prevent the vehicle breaking away, the wheels should neither lock up during braking, nor should they spin when driving off.

Bosch TCS prevents the wheels from spinning. It ensures
good traction, stability and steerability when driving off
or accelerating.

Each wheel is continuously monitored by wheel-speed sensors. TCS evaluates the wheel-speed sensor signals and immediately recognises when a wheel is about to start slipping. In this case TCS is activated and regulates the drive torques of the driven wheels. This electronic wheel-slip control selectively brakes individual wheels and intervenes in the engine management.


TCS Video
Show Video

Products
ABS Antilock Braking System
Traction Control System TCS
Electronic Stability Program (ESP®)
Braking systems


The Bosch TCS components:
1 Hydraulic modulator with
add-on ECU
2 Wheel-speed sensors
3 Engine management
ECU for communication

Egon

 

[KAB]

Based on the fact that you mainly see the issue when doing highway driving / Towing and it just goes away, I would agree with junk that it appears to be a fluid overheating issue.

This is normally associated with brakes hanging up just a bit and causing excessive heat in the caliper causing the fluid to boil and apply more pressure.

Most (all) modern vehicles have a rubber gasket at the master cyl. reservoir. Under normal operation there is no need to add fluid (or bleed) the brake system. If for some reason a time in the past where the brakes might have overheated to the point where the fluid started to boil this could leave a small pocket of air in the system which is now causing the brakes to hang. The first thing that I would try is to bleed the brakes. Make sure that the fluid used to replace the fluid in the system is compatible. (If DOT3 use Dot3, Silicon use Silicon, Etc..) Might even want to get the fluid from the dealer, ouch /forums/images/graemlins/crazy.gif. When bleeding the brakes for this make sure you get the old fluid out. (You want to see clean fluid). The service bulletin indicated that replacing the caliper fixes the problem, I have to wonder if they ever bleed the brakes first? When you test drive after this you will need to put it to the same condition as when the problem is occuring.

As for ABS and traction control if it is a sensor you should either have an indicator that traction control or ABS is activated. Both system use the same sensors and control unit. (I have a bad habit of combining the two of them when referring to one or the other).

The pulsation you are referring to is probablt due to warped rotors.

If a bad brake hose was the problem you would see it more in stop and go traffic and less of a problem on oper road.

Kurt

 

[Rowski]

I can't remeber and not at work to look at a wiring diagram but isn't there a switch to turn the ESP system off? If there isn't you could pull the fuse for the system (dissable it) road test and see if your problem is gone.

I have a gut feeling that a brake pad is hanging up ever so slightly and causing the heat build up. One thing to make sure that the pad sliders (not caliper sliders) are clean and the pads can move very freely. At my shop we sandblast the pad sliders (just the area where the pad slides) and coat with a copper antiseize compound. But we live in a very heavy salt area.

Also take a look at the pads. If a pad has been overheated it will usually have small heat cracks in them. This maybe able to help isolate what is happening.

 

[bczoom]

Wow,

Great information guys. Thanks.

A couple notes/questions:
Egon - Sorry. What is that in the attachment? Were the videos, products and stuff supposed to be links? If I did a google search on Bosch TCS, will I find this stuff?

Kurt - Re. the pulsating being caused by warped rotors, wouldn't I feel that in the steering and also, wouldn't it be there all the time? Neither occurs.

Derek - Brake pad hanging up. I just had the pads replaced and I still have the issue.

I may not get to work on this for a week or 2 but here's what I'm thinking for an initial approach. Let me know if I should change this.

Order (but not yet install) a new set of rotors/pads. Regardless of the fix, I figure I should replace these. The existing set of pads only have about 80 miles on them but due to the extreme heat, I'll write them off as "cooked".

First, try to isolate the problem to see if it's TCS/ABS. I'll clean the sensors and see if I can disconnect this option through a switch or fuse or something.

If the problem no longer occurs, it would lead me to believe it's TCS/ABS related and then trace it from the sensors backwards.

If that doesn't work (disconnect TCS/ABS), do a full inspection of the braking system from the pads all the way back to the master cyl. Clean everything along the way. If nothing obvious, replaces hoses and fluid and try again.

At this point, hopefully it's fixed. If not, I guess calipers are next.

Once I've found/corrected the problem, then replace the rotors and pads. Can't see cooking another set until the problem has been resolved.

Again, thanks everyone!!
Brian

PS. I'm holding off on contacting the dealer and MB corp until I have a resolution. If their resolution matches what I had to do, my response may be a bit more tempered. If the true fix is different, a scathing letter will be sent.

 

[RoyJackson]

"The SUV is a Mercedes ML-320 with just under 37000 miles."

Time to rid yourself of that overpriced lemon and move on to an American Built vehicle (of course, that Benz may have been manufactured at the M-B plant in Alabama or Mississippi).

The Ford Explorer is a solid and proven vehicle. Try one...you'll find it to be rock solid.

Benz? Well, they were really good vehicles at one time...way overpriced taxi cabs now though. Nothing more then a Yuppie status symbol for folks who don't know any better...

 

[bczoom]

</font><font color="blue" class="small">( "The SUV is a Mercedes ML-320 with just under 37000 miles."

Time to rid yourself of that overpriced lemon and move on to an American Built vehicle (of course, that Benz may have been manufactured at the M-B plant in Alabama or Mississippi).

The Ford Explorer is a solid and proven vehicle. Try one...you'll find it to be rock solid.

Benz? Well, they were really good vehicles at one time...way overpriced taxi cabs now though. Nothing more then a Yuppie status symbol for folks who don't know any better... )</font>

Roy,

Not sure I'd call it a lemon but do concur that it's not of the same caliber/quality of an elder Benz. The ones I had it the past were better machines.

I got the ML the year they came out. I was looking for a SUV and everything I was looking at (even 8 years ago) was over $30K. Well, I thought I'd try the Benz since it was closely priced to the others. It is one that was built in Alabama. To my knowledge, that's the only place they're made.

As for moving on to an "American Built" (which in any vehicle, who knows), I did. In this post, that's my Crew Cab GMC right under the "Hoss's" sign.

I bought the SUV because it was too hard to get the kids in the back seat of my truck at the time. No 3rd door. Don't need a SUV anymore since the cars/van/truck all have doors for the kids.