Help with vehicle brake problem

[bczoom]

Hey everyone,

Sorry this is long but I want to describe as best I can since it doesn't make sense to me.

I've been having a sporadic problem with the brakes on my SUV.

On occasion (but getting to become more often), one of the front calipers seems to be applying pressure without me using the brakes. The last 2 times it occured, I was on an interstate traveling about 70.

It applies enough pressure and heat that I start to get a shudder sound but feel nothing in the steering. When I pull over and check it, the rim is too hot to touch and there's actually smoke coming off the pads.

It's most common in the front right but have noticed it once on the front left. On one trip, it was front right on the way there, front left when I got home. /forums/images/graemlins/confused.gif The only times I've noticed it (and I check the heat after every drive) is when driving at higher speeds or pulling a trailer (but probably only 2000#).

I've had 3 brake shops and the dealer check the calipers. Per all, the slides and pistons are fine. I had the fluid replaced by the dealer about 2 years ago.

The SUV is a Mercedes ML-320 with just under 37000 miles. Unfortunately, it's out of warrantee. As of today, they found a TSB on this where it has happened to a couple others. They're fix is to replace the calipers, rotors and pads. They said this fixed it.

My question is, if the calipers "seem" OK by 4 places, how/why would replacing them fix the issue? What's making the caliper piston engage when just driving down the road?

Any help appreciated.

BTW. Dealer wants over $1000 to replace the calipers and rotors. Not doing that since I'm selling as soon as this is resolved. Do I assume correctly that places that sell calipers on the internet are OK?

Brian

 

[tc35dforme]

I've had calipers sieze...ie: not slide in and out .... causing a constant drag, but never an sporadic thing.

Could it be related to a traction control or ABS control / sensor issue ? My Pontiac van has that problem right now. The connector is corroded and computer can get a read on the speed....so to speak.

 

[KAB]

What year is the Vehicle?

Brake issues that you arer describing can be caused by a quit a few items. (not in any order)
1. Slids (checked and appear to be ok)
2. Bad caliper. Piston hangs on the caliper.
3. Bad brake hose. The hose starts to seperate on the inside and acts as a 1 way valve.
4. Air in the system. (could have been waiting for the right time to show up) Unlikely unless serviced recently.
5. Bad ABS system.
6. Bad master cylinder.
7. Fluke? Has the problem persisted? Consistant?

From re-looking at your post some of these can probably be eliminated.

Does this only happen while driving on open roads?
What is done to relieve pressure before continueing on?

At 37000 miles most manufactures will usually assist in repair cost, unless you are out of the months of coverage by quit a bit.

More info would help.
I would not necessarily replace the calipers unless your symtoms match what the TSB is saying the problem was.

Kurt

 

[JimR]

Either someone is throwing you a bone about the caliper or you have a big problem. I would pull the suspect caliper off the wheel. Leave the brake line hooked up. Put a C-Clamp over the back of the caliper and collapse the piston. Back the clamp off and have someone step on the brakes slowly. Watch the piston to see if it jerks out or slides nicely. If it jerks the piston is sticking. I would pull the piston out anyway and inspect it for crud on the sides. Clean it up with steel wool and wash it off. Apply brake fluid to the piston before installing it. You can slide it right back in using a thin item to work the outer seal back over the piston. If the piston checks out ok, then you have a bigger problem. The ABS should not be applying pressure as it only works when you step on the brake. Since it is only one wheel I would suspect a bad caliper. Do you have traction control on that car? That may be another item to look at. That system applies brake pressure to whichever wheel is slipping on the drive axle. A bad sensor could send a signal to the system to apply brake pressure to that wheel.

 

[Junkman]

I know your pain when it comes to warranty repairs on a Benz. They won't do anything for you even if it is 1 day out of warranty. I believe that they are living on a reputation that was earned when they were good cars, but for the last 10 years, the cars are not the quality that they used to be.
Getting back to the problem. I believe that this is a result of the brake fluid expanding as a result of heat. The solution to fixing this problem is to have the master cylinder removed and adjust the push rod further away from the cylinder, assuming that the design is the same as most other cars. I don't see how the rotors can have any bearing on the problem, but a sticking caliper could. I wouldn't have the work done by a Mercedes dealer, but rather some other service facility. The Rotors from Mercedes are about $75 each and new pads will run about $40. I have no idea as to the cost of the calipers, since I have never had to replace one. If you decide that it needs the calipers replaced, send me a PM and I can give you the name of a reputable rebuilder that you can have them UPS'd to and they return by UPS within 48 hours. I know that if you buy the calipers from Mercedes, they will be a small fortune. You could also get used calipers, but I am not certain that they are going to be a better deal than having the old ones rebuilt. If you are thinking of replacing the car, I wouldn't do anything other than trade it now before you get into any expense that will not be recovered in the trade. I would let the next owner (dealer) deal with the problem. Chances are that the car will be wholesaled a few times before it will ever see another retail buyer and in the interim, one of them will repair the problem during the safety inspection getting it ready for resale.

 

[JerryG]

Does it have traction control?

 

[JimR]

They probably want to change the rotors as they may have warped do the the heat from the brake being applied for such a long time.

 

[bczoom]

Thanks for the responses.

Let me see what I can respond to in a single post. Again, sorry, it's long but if you guys can get me out of this, I'll be most grateful.

In general, the vehicle does have traction control and ABS. It is full time AWD.

JimR - I figure the rotors are toast. No choice but to replace. Dealer wants $93 each. Online (OEM) are around $48. I'll also replace the pads.

</font><font color="blue" class="small">( What year is the Vehicle? )</font>

1998 (I don't get around much...). Maybe that has something to do with it. The vehicle just sits around.

</font><font color="blue" class="small">( Brake issues that you arer describing can be caused by a quit a few items. (not in any order)
1. Slids (checked and appear to be ok)
2. Bad caliper. Piston hangs on the caliper.
3. Bad brake hose. The hose starts to seperate on the inside and acts as a 1 way valve.
4. Air in the system. (could have been waiting for the right time to show up) Unlikely unless serviced recently.
5. Bad ABS system.
6. Bad master cylinder.
7. Fluke? Has the problem persisted? Consistant? )</font>

The problem is sporadic. I drove it to/from the dealer this week and it didn't occur. It was mostly suburban driving (mix of stop and go and speeds up to 55). It didn't happen for them on the test drive(s) either. Prior to this week, my last 2 trips on the open road, it occurred.

</font><font color="blue" class="small">( Does this only happen while driving on open roads? )</font>

Lately, it seems so. I had the maintenance records pulled and I did report in 10/03 that the problem occurred when towing approx. 2000#.

</font><font color="blue" class="small">( What is done to relieve pressure before continueing on?)</font>

Honestly, I do nothing. I have a .45 with me to put it out of MY misery should it actually come to the point I have to walk.

</font><font color="blue" class="small">( At 37000 miles most manufactures will usually assist in repair cost, unless you are out of the months of coverage by quit a bit.)</font>

Being a 1998, they could care less (other than taking my $1K to replace the calipers).

</font><font color="blue" class="small">( More info would help.
I would not necessarily replace the calipers unless your symtoms match what the TSB is saying the problem was.)</font>

The description that was read to me from the TSB wasn't very descriptive. They said they replaced the calipers and rotors and "voila", it worked.

JimR - I had 4 places check out the calipers. I only told 2 about the issue. They all came back with the same response (calipers are fine).

Your posts do have me wondering if it's a sensor. I mentioned in my original post of a "shudder" but I'm now wondering/thinking this may be the ABS or traction control trying to engage. /forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gif /forums/images/graemlins/shocked.gif If this vehicle spends most of its time doing nothing, do the sensors get bored (read - quit) and just don't know how to respond? How/where do I test them? Any idea where they're located?

Junk - As for my problem, what would generate enough heat to expand the brake fluid? If it works out to be the calipers, I'll take you up on your offer for a place that has calipers.

As for your first comment... Oh the pain of owning a Benz. Never again... /forums/images/graemlins/mad.gif I spend A LOT of $ on vehicles but neither this dealer (who sells all kinds of cars) nor MB will get my $ again. The General Manager and MB corp. will be getting a nice long letter letting him know why next week. They will not be doing the brake work as the $1K they quoted was for a pair of rotors and calipers + installation. That's it...

Brian

 

[Junkman]

My Benz has traction control and ABS, and I can tell you that I have never had any problems with either. If the fluid gets hot from the brakes dragging, then it will expand. Since you have added some more information about the car, I will take another stab at it. The traction control applies the brakes momently to stop that wheel from turning when it sees that the opposite wheel isn't turning at the same speed. This is done to give traction to the wheel that is turning slower, by stopping the faster wheel. Hope that this makes sense to you, since this is how it was explained to me. My car has a yellow light on the dash that shows when the traction control is engaged. It might be a malfunction in the traction control, but I have my doubts. If you really get disgusted with the car, send me a PM with the details, IE: color, options, etc. and how much you want for it....... I would consider adding it to my stable of cars. I would take it with its associated problems. Junk.... Yes, I am serious....

 

[bczoom]

</font><font color="blue" class="small">( The traction control applies the brakes momently to stop that wheel from turning when it sees that the opposite wheel isn't turning at the same speed. This is done to give traction to the wheel that is turning slower, by stopping the faster wheel. Hope that this makes sense to you, since this is how it was explained to me. My car has a yellow light on the dash that shows when the traction control is engaged. It might be a malfunction in the traction control, but I have my doubts. If you really get disgusted with the car, send me a PM with the details, IE: color, options, etc. and how much you want for it....... I would consider adding it to my stable of cars. I would take it with its associated problems. Junk.... Yes, I am serious.... )</font>

Junk,

Yes, I do understand how traction control works and the light does blink yellow on the dash when engaged.

That reminder, coupled with the "pulse" or "shudder" I previously mentioned, and the fact the light is not coming on the dash makes me now wonder if it's ABS related. The traction control and ABS "should" be the only things that make that noise. If the traction control light isn't coming on, would that negate is as being the issue and make it more of an ABS issue?

Brian