W124 brake shudder

[TimFreeh]

I've been fighting a brake shudder problem on my 91 300D 2.5 turbo and I've pretty much run out of ideas on what could be causing the problem. I'd appreciate anybody's comments that has faced this problem...

A bit of history - I bought the car with 36K miles, when I first got the car the front brakes exhibited a bit of brake shudder at high speeds. It was not terribly bad and I thought at the next brake pad replacement I would replace the rotors to solve the problem, I then drove the car for 3 years and about 75K miles with the slightly shuddering brakes.

My pad wear light came on and I replaced front and rear pads (Pagid) and new front rotors (Teves) I turned the back rotors as they were under the wear limit. The newly refreshed brake system initally performed flawlessly - no brake shudder at any speed, smooth and straight stops. All was right with the world. After about 2K miles I noticed a slight shudder and after 5K miles the front end is now shuddering enough to rattle my teeth in high speed stops. I also now have a bit of brake squeal at low speeds... Very nice. I've also noticed that the shudder seems to vanish during panic stops.

I have a dial guage and have checked the runout - it is approx .001 on the left side and .0015 on the right. Both specs are well within tolerances (.0045) Wheel bearing preload was checked and found to be correct, no play in the tie rods or ball joints, car tracks straight and true down the road.

Any ideas or should I just call my dentist and schedule regular filling replacements?

Tim

[whunter]

Hello TimFreeh
Suggestions
Possible cause listed by cost:
#1. Flex brake hoses failed internal, very cheap fix.
#2. Rear brake calipers bad, overloading front, cheap fix.
#3. All brake calipers bad, binding, not cheap fix.
#3. ABS system mechanical failure, very expensive fix.

[JenTay]

my money is on the bad caliper.

when new pads were installed you had to push the piston back which kind of exercised the piston so it worked fine for a while.

the shudder is coming from the piston staying in the 'pressed' position and not 'relaxing'.....really technical terms huh?

i had that problem with the driver side rear caliper.

[TimFreeh]

Thanks for the responses. I think I follow your technical terms...

I'm not convinced its a caliper issue. The car has had regular brake fluid changes every year. When I chanced the pads I did not have to use a c-clamp or a prybar to move the pistons in the caliper - I was actually able to reset the piston pushing it with my HAND. It moved very freely.

Whunter

How could a bad hose cause a brake shudder? If the hose was bad why did the brakes work perfectly for a few thousand miles?

I was hoping to hear from somebody that had faced this problem and fixed it. I'm not exactly crazy about the idea of replacing calipers, pads, rotors, brake hoses and the ABS computer.

I've been reading thru some old posts - the next thing I'm going to check is the floating caliper pins. If there is excess play in the pins it could cause the caliper to vibrate. I'll let you know how it goes....

Thanks -Tim

[psfred]

Worn floating pins will cause the brakes to "clank" when applied, and the pads will wear tapered from front to rear (not top to bottom).

I suspect your problem is REAR rotors -- if they were under minimum thickness to begin with, they were bad, and if had them turned, they are surely too thin now even if they weren't to start with.

Check the REAR rotors for runout -- they will make the front brakes act funny when they get synchrnized right. They also vibrate badly themselves. Check the rear pads for excessive wear, too -- if you have a stuck piston, it will be on the rear. A stuck one up front you would certainly notice, the car will
"dive" badly to one side, even with zero offset steering. Quite a ride, if you've not had the experience.

Also, make sure the rear pads haven't collided with the anti-rattle spring -- this will cock the pistons in the bore on the caliper, causing drag, hard pedal, and eventually warped rotors. You will have to rebuild the calipers if they are stuck -- usually the dust boot is gone, and the piston and bore must be cleaned before they work correctly, and it's silly to put a used seal back in.

Did you use OEM pads? Padgid, Textar, ATE, Teves are all OEM. Most other pads will cause squeaks. However, a stuck piston can cause OEM pads to squeal, too -- so will corrision and dirt in the pad slots.

You may also have something loose up front -- vibrating brakes isn't a common complaint on the W124.

And last, did you rough up the front rotors when you installed them (or did the shop?). W124 rotors are turned, not ground, during manufacture, and there is a distinct spiral left on the rotor surface. If the friction surface isn't roughed with coarse sandpaper, the pads will groan for some reason, and this may both wear the pins excessively and cause the rotor to get "wavy".

[TimFreeh]

Psfred

Thanks much. The rear rotors were just above the wear limit after resurfacing, I think they were 7.4 mm and the wear limit was 7.2 if memory serves.

I never considered the rear brakes as the problem - if the rears were causing the problem that would explain why under very hard braking the shuddering pretty much disappears since most of the brake load is on the front wheels. I think I'll just replace the rear rotors and see what happens - I'd like to change one thing at a time to see if I can isolate the failure to a specific component. I'll also check the pad orientation.

The replacement pads (front and rear) were Pagids, rotors were Teves. I've heard about using sandpaper to "rough in" the rotor surfaces but I've never done it. What is the procedure? Just use 100 grit paper until the surface is roughed up a bit?

The sliding pins on the front caliper seem to be pretty lose in the bores. One of the pins has 2-3 MM of play, the others seem to be about 1 MM. Do you know how much play these pins should have? I can't seem to find any information about checking these pins in any of my service manuals.

Thanks again - Tim

[whunter]

Hello TimFreeh
My response is very long.
I tried to keep it as short as possible.

This is what automotive Engineers call a SAFETY issue.
The brake flex hose on any car is durability tested to roughly 125% of vehicle life, current production domestic cars = ten year 125,000 miles, in real life, things happen that can reduce or extend the life of a flex hose.
Rolls-Royce states in the owners manual on all post WW2 cars that the hose life is eight years and lists the flex hoses as a regular maintenance item.

On a car with ABS brake system.
One or more failed flex hose can:
#1. Act as a one way valve. (Caliper hangs up and warps rotor.)
#2. Act as a restriction. (Massively reduced flow to one or more caliper overloads the other calipers, overworks the ABS and warps rotors).
#3. Act as a plug. (Total blockage of one or more caliper, overloads the other calipers and warps rotors).
#4. Destroy the ABS distributor and/or pump slowly. (Overworking the system at all times, not designed for full time use, drastic reduction in life).
#5. Act as a terminal failure;
Final failure mode can be:
#A. Hose seals shut with MAX ABS pressure on caliper during a panic stop, and never releases = brake pad drag + possible fire.
#B. Hose weakens to the point that it ruptures = 50% brake system loss, odds are during an abrupt stop.
#C. Hose seals shut with NO pressure on caliper during a panic stop and you loose 1/4 of your stopping ability.
#D. Cause the ABS distributor and/or pump to fail when you need it most.

This can occur at any time.

[psfred]

I don't believe the pins should have detectable play -- the floating part of the caliper should move smoothly in and out only.

Are the pads uniform thickness or are they tapered? If tapered, you definitely need to replace the pins (and pads).

Just use the sandpaper to make the surface of the rotor matt in appearance. Fastest to use an angle grinder with a coarse sandpaper pad, only takes a few seconds that way. Otherwise, the brakes groan.

Check for even pad wear on each axle, inner and outer -- if you have a bad brake line or sticking caliper, some pads will be thicker than others -- it's normal or either the inner or outer pad in a caliper to be thinner, but they should be the same as on the other wheel.

Peter

[TimFreeh]

I replaced the rear rotors and the shuddering totally disappeared. Many thanks to psfred - I would not have considered the rear rotors since the shuddering seemed to be coming from the front end. I would have bet my life on it but it was clearly a rear rotor problem.

I did re-check my instillation notes and the rear rotors were about 1 mm over the wear limit after resurfacing. I did find that the right rotor seemed to have quite a bit of brake dust inside the parking brake drum - maybe I adjusted the parking brake too tightly and the rear rotor heated up and warped?

At any rate the car stops smooth and straight once again - I won't be having any more MB rotors turned.

Tim

Tim,

Do you use spray on tire detailing treatment? Using this will cause brake shudder because it causes the areas where it hits to take on a different friction level than the other areas.

I'm glad you found the problem. I just thought I would point this out in an effort to keep it from happening again.

Have a great day,

[TimFreeh]

Larry

I do use wheel cleaners to remove brake dust but I do not use tire cleaners. Are you talking about the stuff that makes the tires look nice and shiny?

Its funny you mention that though - I did get the impression that at very low speeds it almost felt like the "shudder" was caused by the pad grabbing at certain points of the wheel rotation. This was easy to notice at 1-2 MPH and I wondered if maybe this behavior would cause the shudder I was experiencing at higher speeds. It's hard to describe but the feel was different from a warped rotor (at least to my flawed powers of perception....)

The other thing that really drew me away from thinking the rear rotors were the problem was that when I was very low on fuel the shudder was most pronounced, after I refilled the tank (with 80lbs diesel fuel) the shudder dropped off considerably. I just assumed that the additional fuel weight was reducing causing more work to be done by the rear brakes and less by the front binders. Therefore the problem must be with the front wheels... I still can't quite explain this dynamic.

Thanks again to everybody.

Tim

[stevenstevensteven]

Originally Posted by psfred

Worn floating pins will cause the brakes to "clank" when applied, and the pads will wear tapered from front to rear (not top to bottom).

I suspect your problem is REAR rotors -- if they were under minimum thickness to begin with, they were bad, and if had them turned, they are surely too thin now even if they weren't to start with.

Check the REAR rotors for runout -- they will make the front brakes act funny when they get synchrnized right. They also vibrate badly themselves. Check the rear pads for excessive wear, too -- if you have a stuck piston, it will be on the rear. A stuck one up front you would certainly notice, the car will
"dive" badly to one side, even with zero offset steering. Quite a ride, if you've not had the experience.

Also, make sure the rear pads haven't collided with the anti-rattle spring -- this will cock the pistons in the bore on the caliper, causing drag, hard pedal, and eventually warped rotors. You will have to rebuild the calipers if they are stuck -- usually the dust boot is gone, and the piston and bore must be cleaned before they work correctly, and it's silly to put a used seal back in.

Did you use OEM pads? Padgid, Textar, ATE, Teves are all OEM. Most other pads will cause squeaks. However, a stuck piston can cause OEM pads to squeal, too -- so will corrision and dirt in the pad slots.

You may also have something loose up front -- vibrating brakes isn't a common complaint on the W124.

And last, did you rough up the front rotors when you installed them (or did the shop?). W124 rotors are turned, not ground, during manufacture, and there is a distinct spiral left on the rotor surface. If the friction surface isn't roughed with coarse sandpaper, the pads will groan for some reason, and this may both wear the pins excessively and cause the rotor to get "wavy".

I'm embarrassed to say that I've waited far too long to replace my rear pads and rotors, even though the OEM parts have been sitting in the closet. On the driver side the pads were indeed colliding with the anti-rattle spring, and the dust boots are gone on the calipers. However, the pistons are not ceased, and retracted very easily with a C-clamp.

Given that the pistons are not ceased, can I simply replace the dust boots without rebuilding the calipers and bleeding the entire system? Or, is it necessary to bleed the system in order to replace the dust boots?

Furthermore, I'm tempted to temporarily reassemble with the new OEM rotor and pads, and to deal with the calipers at a later date. Any comments or insights on how much of a safety issue this might be. I'm in a bind for time this weekend, and would like to be able to delay this for a weekend when I can perform a rebuild, if it is indeed necessary.

thanks in advance for your assistance.

[vstech]

the dust boot is needed, and if the calipers are fine, there is no problem changing just the boots/shields.

[Graham]

Originally Posted by TimFreeh

I replaced the rear rotors and the shuddering totally disappeared. Many thanks to psfred - I would not have considered the rear rotors since the shuddering seemed to be coming from the front end. I would have bet my life on it but it was clearly a rear rotor problem.

I did re-check my instillation notes and the rear rotors were about 1 mm over the wear limit after resurfacing. I did find that the right rotor seemed to have quite a bit of brake dust inside the parking brake drum - maybe I adjusted the parking brake too tightly and the rear rotor heated up and warped?

At any rate the car stops smooth and straight once again - I won't be having any more MB rotors turned.

Tim

Just read this thread. I have similar but not exactly same symptoms. This is on a 98 E-Class which used to have smooth braking. I now get a judder, that seems to come from passenger side rear (but experience has told me that problems are not always were they seem!)

I have inspected all brakes. Pads look OK and rotors are within spec. Rears disks had some circular wear marks. Tried to sand then out. I also roughened up the rear pads, put some Silguide on pins. Everything seems to work OK. But judder is still there. Car tracks straight when braking.

I have a dial indicator. Is there any trick to measuring run-out of rear disks?

Hoses are another possibility. Never replaced them. How do I do it? Just disconnect, catch fluid and bleed later? Or is there a trick?

Rear disks are original, so perhaps I should change rear disks/pads and see if that cures problem, at least as first step. Maybe hoses too?

[stevenstevensteven]

Originally Posted by vstech

the dust boot is needed, and if the calipers are fine, there is no problem changing just the boots/shields.

great, thanks.