Brake pulsating on 2012 E550AWD

Schooch

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Pulsating brakes on my 2012 E550AWD BiTurbo, replace everything new and 6-8,000 same issues. Super frustrating, any suggestions?
 

brandwooddixon

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Hi and welcome.
Some more information would be useful.
I take it that your car is an E550 4Matic?
Please describe the pulsating brakes e.g. when does it happen; when doesn't it happen; rate of pulses - fast/slow; can you hear it?
Do we take it that you have replaced brake pads, brake discs/rotors, brake fluid?
6-8,000 - is that the miles that you have driven since "replace everything new"? Was the issue ever cured?
 
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Schooch

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Yes it’s 4 matic with the AMG package. I feel it after only a few miles of driving, it feels like it’s up front. I did replace everything new after I tried turning the rotors and adding new pads. It was great for like 6,000 miles. So I changed everything all the way around, it was great for another 6,000 then it started up again. I didn’t change the brake fluid, wasn’t aware that could be an issue. You definitely feel it at higher speeds and you hear and feel it reverberating through the steering wheel.
The car is absolutely perfect except for the braking issue. I do my own mechanic work and restore cars as a hobby. I’m just puzzled how a quality ride like this can have such poor braking. When I bought the car it did was doing it. Thought it would be and easy fix, just keeps coming back. Any suggestions would be greatly appreciated.
 

mattkh

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Interesting that it is perfect for 6000 miles.
Is it to do with the tolerances allowed on the thickness of the brake pads..?
 

Mr Greedy

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This sounds typical of discs not sat totally flush on the hub. Or for some reason, the hub face not being totally perpendicular to the hub bearing axis.

Are you able to take it somewhere who can take the wheel off and measure the disc braking surface run out with new discs fitted? You would be looking for run out before 1000s of miles has had a chance to do something that might cloud the issue.


This would confirm or rule out the above, and should be a relatively cheap test if somewhere has the kit?


Testing lateral run out
 

brandwooddixon

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Do you regularly use the footbrake "HOLD" function instead of the parking brake?
 

Exp21

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You could measure with a dial gauge the discs while spinning. It could give you an idea of the issue. If it's ok, I think it's a brake pad issue?
 
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Schooch

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Do you regularly use the footbrake "HOLD" function instead of the parking brake?
I never apply the PB, I just park the car in P when I’m done driving. I’m not familiar with HOLD function. I’m seeing in multiple sites that many owners are having the same braking issues as me. There has to be an inherent flaw in the design, to many others are have similar complaints.
 

brandwooddixon

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I asked about the brake HOLD feature as I was curious as to whether you have a tendency to use the foot brake to hold the car stationary when at junctions or in standing traffic rather than the parking brake. The brake HOLD feature performs the same function as the parking brake (when the engine is running) but uses the disc brakes.

In my experience using the disc brakes to hold a car stationary, instead of the parking brake, will cause symptoms similar to what you describe, in that over time the brake pedal starts to feel like its "pulsing" under light braking as grip on the disc is gained and then lost.

This is typically caused by the transfer of pad material onto a hot disc (say after hard braking to a stop) causing a raised area, which as it has a higher coefficient of friction may gather more material as time goes by but will certainly give a patch with more grip. Some people believe that keeping a very hot disc clamped by the pads causes warping of the disc, which I suspect it could if the brake calliper piston pressures are uneven.

In any case, I try never to use the footbrake to hold my car stationary after coming to a stop and instead apply the parking brake as this allows the disc to cool without pressing hot pad material into its surface.

Many of my cars (including non-MB ones) suffered from "warped" discs in the past, but since I stopped using the footbrake to hold them stationary I've not had this issue repeat itself over the past two decades.

Its like allowing your turbochargers time to cool down after a fast run before turning the engine off and stopping the flow of cooling oil around the bearings. By the same token whenever braking from high speed to stationary I'll aim to brake hard, release the brakes and then brake again to bring the car to a halt before applying the parking brake.
 

EmilysDad

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.....

In any case, I try never to use the footbrake to hold my car stationary after coming to a stop and instead apply the parking brake as this allows the disc to cool without pressing hot pad material into its surface.

.....
so what would you do in my car that uses an electric parking brake on the disc rather than the top hat disc/drum set up that you describe? There are those that would frown on people just using PARK ;)
 

brandwooddixon

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The back brakes only account for a small amount of the total braking force and never get as hot as the front so even if there is some build up, it will never be as noticeable as on the front.

As for Park, I only knowingly put the gearbox into park before getting out of the car (mine will automatically enter park and apply the parking brake if I open the drivers door!) and never into neutral in order to save wear and tear. Gearbox failure in my E430 taught me that.
Hence when stationary but driving my car is in drive with the parking brake on.
 

MJJ

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Cars are durability tested by the manufacturers to significantly higher heat and pad transfer extremes than us drivers could ever subject them to on the road - think 5-7 full brake pressure stops from 100mph in quick succession, followed by continued application of brake pressure following that last stop.

It is possible that the E550 is borderline on brake hardware specification so it can share parts with less powerful models, but I would still expect there to be an underlying fault to cause the issues you are seeing. Fine for 6,000 miles then returning to a failure condition suggests brake components are wearing very heavily.

I think you need to establish if the disks are reaching their wear limits (when they will be more susceptible to warping) within that 6,000 miles, and you can only do that by measuring their thickness with a micrometer, and comparing to the specification of a new disk.

If they are wearing within 6,000 miles, possible reasons could be:
- As above, hub face corrosion/debris causing disk run out might be an issue - try lightly sanding the hub before fitting new disks.
- Sticking calipers, continually applying a little brake force and over heating the brake hardware - without the driver being aware. I suggest trying to drive for 10-20 miles with as close to zero braking as you can, then check the heat coming from the wheels by holding your hand close to the wheel. If there is a sticking caliper, you will feel a noticeable increase in heat from that wheel compared to the others.
- Another possibility could be blocked brake cooling ducts (if they are fitted to the E550), but I would think you would need to be working the brakes very hard (towing, or living in the mountains) before that became an issue.

Martin.
 
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