Axe Murder

Hello

It may be just my pink walnut seeing false patterns in what is actually random, but if there is a mystery here I would love to hear about it.

Bought a used -05 C-class a couple of years ago. When I tried it at the vendor it was fine. Within a few weeks, the front brake rotors went slightly wobbly. Swapped them, all was fine.

Two years later, I bought an -03 E55 at the same vendor. It was fine when I tried it, within a few weeks the front brake rotors went slightly wobbly. Swapped them, all was fine.

This autumn I bought a -11 C-class at another vendor. It was fine when I tried it, within a few weeks the front brake rotors went slightly wobbly. I didn's swap them, instead they fixed themselves. The wobbliness slowly went away during a month or so.

I find this mindboggling for several reasons. None of my former cars ever got wobbly rotors, but three Mercs in a row developed it within weeks. On two the issue got slightly worse until the rotors were swapped, the third magically healed itself.

My driving is average, some city, lots of highway, and the E55 only saw a few redlight dashes and a halfdozen >150 mph runs. It's not like I hoon my cars on track or snail around like a half-blind octogenarian.

So - anyone with more insights in brake technology care to expand on this subject?

Your friendly stalker with the axe,
/AM

Plutoe

TFSTPAA

Axe Murder

Axe Murder

Oh, this old thread?
Yeah - I got tired of the C180 and got a W211 E-class instead. A nice 60k miles specimen.
And it developed wobbly disks within a month! That makes four Mercedeses in a row that instantly got like that after purchase.
Swapped them myself, and the new ones have been fine for about 30k miles now. Knock on wood.

What does TFSTPAA mean?

streborx

Are you a left footed braker?

Axe Murder

Nope. I don't believe I drive in any way out of the ordinary.

I do live at the 60th latitude though, with a lot of winter snow and salty roads. But then all cars here should exhibit the same behavior, and it is only the Mercs that have consistently had this brake thing. I have owned or otherwise used several other brands where I cannot recall wobbly brakes being a thing for 20+ years.

Axe Murder

Hello

Now my E280 has began to develop wobbly brakes again, there is a familiar pulsating when I push the pedal. More pronounced when I brake just a little, not as distinct when I brake harder.

About 17000 miles since I last swapped discs and pads. How is this possible?

BenzBopper

Sounds like a warped rotors from over heating on hard braking.

Axe Murder

Yes, I know - but the thing is that I do not think I brake hard. I move through traffic with as little perturbations as possible and keep pace with the rest.

Someone once told me that if you brake to a stop and hold the pedal depressed, your discs may warp because of uneven thermal dissipation when the pads rest against the discs. They will cool slower on that spot.

But I don't think I treat my brakes any different than everyone else. If anything, I do think of that last thing more than most I guess - though holding the brakes is usually not a choice thing.

But obviously I must do something differently, because other people don't seem to complain about wobbly brakes every second year. So perhaps I got it backwards? I should make a point of holding the brake depressed extra long after coming to a stop?

Or it could be that I actually notice? I mean, I can't count all the times I have spoken with someone and they go "Yeah, my car has been great! Never a problem!" and then you find out that the rear wiper is dead, the chair heating is dead, there are cracks all over the windscreen, the central locks only work on three doors, and the power windows require that you wiggle the button sideways.

WRC-LVR

Google "uneven pad transfer on disc brakes" Then go out and perform the recommended re bedding of the pads. Some pads are much more susceptible to pad transfer than others. Apparently the Merc OEM ones suck.....

Axe Murder

AHA! That was very interesting! And much pertinent to my situation.

I have swapped pads (and disks) many times, but I have never seen a trace of a recommended bedding procedure in any of the pad packages I have received. And I was very unaware that there is supposed to be transfer of pad material to the disk.

I do 99.99% drive gently with little heavy braking, and the brake wobble does come and go intermittently with days and weeks in between. The second point was one I was aware of, but I never knew it had to do with the layer of pad material on the disk. I thought it was thermal warping on the contact spot.

So my issue is not liekly that the disks are warped. It is that their surfaces vary in friction coefficient. That seems congruent with the behavior. I shall immediately start doing bedding procedures.

Thank you very much for resolving this conundrum I have had for many years!

Acta_Non_Verba

WRC-LVR is correct.
I've been doing disc brakes for 30 years and have NEVER seen a warped rotor on a street car and only once on a track car and those were extenuating circumstances. On a few occasions, when some have insisted the rotors were warped, I proved they weren't using a dial indicator directly on the rotor surface.

Uneven pad transfer onto the rotor is the culprit and it causes a "slip/grab" condition which can come from poor braking techniques and/or pad material that is susceptible to breakdown and depositing onto the rotor surface.

WRC-LVR

Seconded from above. I have been working on disc brakes for several decades. Street cars and track only too. SCCA and WC . In my experience, the rotor isnt warped, it is the uneven layer of pad transfer causing the pulsation. I have actually seen the pad transfer so bad that it could be measured BUT it was only 002"

We used to roll the race cars back and forward a few inches in the pits between sessions to avoid the car sitting in one position and having the hot pads transfer material on one spot on the rotor. It is pretty bad if you step on the brakes at Road Atlanta at 130 mph and the whole car shakes from the brakes. I know seasoned top notch drivers that insisted on seeing the car being moved in the pits.

Some manufacturer pad seem to suffer more from transfer than others. Some get transfer but it resolves pretty quickly to normal operation. Some are a PITA and the effect may last for a long time. I have personally witnessed the latter on my 2005 Evo the pad transfer only went away after rebedding and then lots of highway miles

YMMV

Axe Murder

I hold what you say to be truth, but there is one detail:

What is a "poor braking technique"? Is there a trick to proper braking that noone ever told me?

And is there some difference in pad materials I should be aware of the next time I swap them?

streborx

Poor braking technique? Yes - braking with your left foot. Don't laugh - I know people who were taught that this is safe and proper driving.

Acta_Non_Verba

So, a lot of folks will soft pedal the brakes...gently come to stops. This seems to contribute to the resin deposits on rotors., but it has to be combined with a brake pad that uses certain materials that are conducive to leaching from the pads and getting hard deposited onto the rotors. The better braking technique is to not apply the brake so early. Instead, come up more quickly to a stop, then apply the brake pedal more firmly. Call it aggressive braking.

I cannot tell you what pads to choose to avoid this, but some compounds out there work very well and there is no resin leaching. It also isn't necessarily related to cost either. I've seen some inexpensive pads that just don't have the problem, others do. But, the braking will make a difference sometimes on pads that do leach easily. As WRC said in an earlier post, google the procedure to bed in brakes, try that, then continue to brake more aggressively. See if it cures the issue you're seeing now. If not, then you might need to try different pads (different brand or different compound). Then too, it depends how badly the deposits are fused onto the rotors. If significant, the bedding might not work.

One observation I can share - I don't see much of a problem with cars switched to ceramic pads. I've switched all of my cars over, for years back, to ceramics on the first brake job. I've never had the symptoms that appear to feel like warped rotors., but I do brake more aggressively and do not soft stop. Ceramics, BTW, are low dust too, but the downside (almost unnoticeable) is they need a little warmup especially on cold winter days to grab the best.

Hope this helps,

Axe Murder

All right, I thank you for this!

I do indeed brake softly, and if you would ask me I would assume that it would be better for avoiding this issue. But I acknowledge it may be the opposite and shall try being a bit more stern about it henceforth. Also, next time I shall try ceramic pads to see what difference it might make.

Cheers!