Help with vehicle brake problem

jwstewar · Feb 6, 2005

This is just me reading here and taking a guess w/o actually knowing anything about truly solving the problem /forums/images/graemlins/laugh.gif. Have you checked the tire pressure? If the tires are a little low, the wheel speed sensors could be picking up that this tire is spinning faster than the others and trying to slow it down. Just a thought. At least it doesn't cost you anything to check it out.

bczoom · Feb 6, 2005

( This is just me reading here and taking a guess w/o actually knowing anything about truly solving the problem /forums/images/graemlins/laugh.gif. Have you checked the tire pressure? If the tires are a little low, the wheel speed sensors could be picking up that this tire is spinning faster than the others and trying to slow it down. Just a thought. At least it doesn't cost you anything to check it out. )

That is a good point. Actually, one of the places I had check the brakes pointed this out (that my tires were a little low). He added some pressure but the problem continued. I will check the TP again. If the one tire does have a slow leak or something... THAT WOULD BE A DANG EASY FIX!!

Rowski · Feb 6, 2005

On the side that you are having the most problem, which pad is cooked? Both the inboard and outboard pad or just one?

bczoom · Feb 7, 2005

Derek,

I'll have to check. I say "cooked" since they've received so much heat they're probably brittle. The pads are new so I may not have an answer until I pull them and put a micrometer on them.

Brian

bczoom · Feb 7, 2005

( If the tires are a little low, the wheel speed sensors could be picking up that this tire is spinning faster than the others and trying to slow it down.)

I checked the TP last night. I might have a slow leak. The tire I'm having problems with was at 24 psi. The opposite tire is 28 psi.

Now, if one tire has a lower PSI but you get the vehicle to approx. 70+ mph, will the tire with the lower PSI become more elongated (grow taller) due to gravitational force and make the TCS think it's spinning faster and apply pressure?

KAB · Feb 7, 2005

( 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.
)

Depends on how bad the rotors are warped. In the car that I drive daily for work (600+miles/wk) they are slightly warped but do not notice it in the steering wheel or braking system most of the time. (yes, they are warped, but I am waiting for aftermarket rotors and pads to become available and figure out when I will have time to replace them.)

On the MB how does the ABS/TC system indicate that it is active? Most cars have some way of notifying the driver that it is being activated.

Somebody mentions about low tire pressure. In GM vehicles that use the ABS system to indicate low tire pressure there needs to be 12lbs of air pressure in 1 tire before it indicates a low tire. So with only a few psi of difference between tire should not cause a problem. (if so it should activate in sharper turns.)

( 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.

)

While I was looking for a way to disconnect ABS/TC I would go ahead with a brake system inspection. This way you could make sure the system is in top notch.

When you removed the old brakes how did the lining wear look? Not inboard/outboard (unless 1 was good and the other was gone, Inconsistant wear here can be expected) but front/rear Top/bottom (per Pad) if this is not even then there is probably an issue with the mounting system.

I would also check for drag while the car is on jack stands.
There should be no drag (you already knew that /forums/images/graemlins/grin.gif).

Is there a traction control button on the dash somewhere?
Depending on the system, it will either turn off the powertrain mgmt, braking, or both parts of TC. Has no affect on ABS.

Try this forum. It looks like they might just have some good people like we have here /forums/images/graemlins/smile.gif : MB Forum

Good Luck

Kurt

reb · Feb 9, 2005

It sounds to me that the slow leak could very likely be your whole problem. The lower pressure would make that tire rotate faster than the others, making the computer think you have a traction problem. It would then apply the brake on that side. What bothers me is that the dealer's techs should know the system well enough to suspect that kind of problem instead of immediately looking at expensive fixes.

bczoom · Feb 9, 2005

Thanks again guys.

Unfortunately, I won't have any time to even look at this for awhile.

I'm going to get the tires fixed first.

Lazy · Feb 9, 2005

Hi
I have a 91 Chevrolet dually and the same thing happened to me. Turned out to be the rubber hose going to the caliper was collapsing and holding pressure in the caliper. I replace both hoses 3 years ago and haven’t had the problem since.

Charlie

cj7 · Feb 10, 2005

wew.. this is a trying problem....

my 2 cents to start with is the basics..

some of which have already been mentioned.

tire pressure
clean sliding surfaces - slides etc. be sure to check under any small clips that the pads may rest on.. rust can build up under these and the pad will jam .. not being able to retrack all the way from the surface of the rotor. clean and lube (neversieze) slides and contact points.

Does one pad wear more than the other?
What about the surface of the rotor? Are they all smooth no hot spots or blisters?

beyond would be sensors or some type of computer error regarding traction control or ABS

cj7 · Feb 10, 2005

Do you have a mechanic buddy that has a computer that the two of you could test drive with it? They are supposed to be able to check the functions of all the sensors and if the system is 'talking' or not. just another thought.
(if I had one you would be welcome to it)

Did anything get lodged in between the pad and rotor? or get burned into the pad or rotor?

If you have it jacked up can you turn the rotor by hand? Does each side seem to drag evenly?

bczoom · Feb 21, 2005

Hey Rick,

Sorry I haven't responded. Been out of town for the last 10 days.
To answer a couple things.
Re. checking it out with a computer, the dealer already did that and all seems well.
Outside of the punishment they've taken from the extreme heat, the pads and rotors are OK. No uneven wear or anything.

I still haven't done anything with the vehicle but I think I'll take this approach.
Order new rotors and pads but don't install until the problem no longer occurs.
Order and install new hoses. Hoses and calipers are what the dealer says will fix it but I think I may be experiencing what happened to "Lazy". I'm not going to replace the calipers since they've been checked out by 3 places (including the dealer) and the piston, slides... are all fine.
If the hoses don't fix it, I'll start the process of disconnecting the traction control, ABS...
I'll obviously get the tire pressure problem addressed.

Brian

TCBoomer · Feb 24, 2005

A couple other things come to mind....

1) Contaminated fluid--is the master cyl cover seal swollen, even slightly? Petroleum based contaminates will cause the seals to swell. Those 5 min oil change centers are sometimes known for incorrect fluid top offs. Even dealers have been known for this too...I've seen it. If petroleum based contaminates are present, then the complete hydraulic system will have to be serviced. The cyls could be flushed and rebuilt, the lines flushed, but the ABS pump and valve block assembly would have to be replaced. Also all hoses would have to be replaced.

2) Misadjusted brake pedal switch--has anyone, including yourself, recently been working under the dash near the brake pedal switch? I'm not familar with MB's switch design, but if it's adjustable and it was possibly bumped, it could cause the pedal to not return completely. You wouldn't notice it during short trips, but long trips = heat, and heat = expansion. Even a slight switch misadjustment could be the culprit.

bgott · Feb 24, 2005

And, are you the only driver? Maybe you have a left foot braker driving the car. Left foot brakers keep their foot resting lightly on the pedal and that causes lots of heat and wear. You don't do that, do you? I always check for wear and dirt on the left side of the pedal in cars I've worked on with re-occuring brake problems. That has saved me countless hours of pulling my hair out chasing phantom brake problems. Left foot brakers will jump up and down and do cartwheels screaming about how the problem isn't their fault, but, if you can get them to change their habits the problems seem to magically go away. /forums/images/graemlins/tongue.gif

bczoom · Feb 24, 2005

TCBoomer,

To be honest (shhh... don't tell anyone else), this is the only vehicle that I actually have the brake fluid periodically changed. It's been a couple years but I believe it was done correctly (by the dealer) .

Nobody has been near nor under the dash. Wouldn't the brake lights remain on to establish this condition?

Brian

bczoom · Feb 24, 2005

Brad

Yes, I'm the only driver.
The only times I use my left foot when driving are:
When I'm looking for the high-beam switch... I'm learning but it still seems like a habit.
While watching a NASCAR race. I don't want my RPM's to go down while cornering.

Brian

DaveNay · Feb 24, 2005

As aggravating and difficult to diagnose mechanical problems have been on cars for the last 100 years, we now have to look forward to the fact that as many as one third of new car warrantee claims can be attributed to software bugs.

New York Times article.

This means that if there is any connection between the computer, and the brakes (ABS, traction control, or <diety of choice> forbid any kind of "brake by wire" system), then there may be absolutely no mechanical problem whatsoever, and yet the computer could decide to apply maximum brake pressure to any or all wheels at any moment, including while driving at 70 MPH down the interstate. /forums/images/graemlins/shocked.gif /forums/images/graemlins/shocked.gif /forums/images/graemlins/shocked.gif

I am exaggerating somewhat, but it is still a very real issue with modern computer controlled vehicles.

Dave

TCBoomer · Feb 25, 2005

Flushing the fluid is something that many overlook today. Chances are if the dealer did it a couple yrs ago, you should be fine. Just make sure the cover seal is not swollen.

As for the brake lights staying on...no they wouldn't because depending on the style of switch, the switch would still make contact with the pedal, and turn off the lights. But if it was pushed in the barrel clip further, it would prevent the pedal from fully realeasing. That would keep the brakes partially applied...even if only slightly.

TCBoomer · Feb 25, 2005

Software conflicts are very common today. Even aftermarket alarms and remote start systems are causing issues. I deal with this almost all the time.

I've seen 2 way radios cause ABS activation when the radio was used on certain GM vehicles. But you knew the ABS activated because you could hear/feel it working. The fix...reprogram the computer with new software.