I have a 2012 W212 4Matic, with 153k miles. The brakes have about 60K miles on them and have even pad wear of 3–4 MM remaining all around. The car has developed a problem that is getting more pronounced. When breaking relatively hard, it feels like the car is going to spin out. The left front dives and the right rear rises, feeling like it’s going to spin around. You can feel and see the body turning from facing 12 o’clock to 11 o’clock. I’ve rotated tires, changed the fluid, had the brakes visually inspected by my mechanic and he found no apparent issue with brake lines. There are no lights on my dash so I assume the ABS wheel sensors are still functioning. The brakes don’t pull when braking gently. Struts and shocks are a year old, springs are original. What should I be looking at/checking? TIA.

Interesting. Assume you have already scanned the car for error codes. Assuming there are none, the ESP/ABS system should keep the car straight under hard braking. If my car, I would disable ESP/ABS (warning you may lose power steering assistance) and test under hard braking to see if the behavior changes (better or worse) in order to isolate the ESP/ABS system out of the picture. If it works better even if you have to hold the steering wheel tighter, you would have isolated the issue. Hopefully, I make sense. Open to be corrected. Do test in an isolated area away from endangering anyone.

Thank you for your guidance. There are no codes (iCarsoft MB v2.0) and I disabled ESP/ABS as suggested. No change to braking problem.

67,

Before the days of ABS, car pulling to one side under heavy braking for me usually was caused by different friction value of the tarmac.
Example : New tarmac one side and old tarmac one side, right after a road repair.
The condition above is both front wheels do not lock at all, just strong braking modulation. Also supension, steering and brake are healthy.

ASK :
AA. Is your wheel/rim size and ET standard ?
BB. When was last 4 wheel alignment done and show us the print out.

I am suspecting 2 possibilities :
01. The braking pressure on LEFT front caliper is stronger than the one on the RIGHT.
02. You have a rather worn out steering tie rod end at LEFT side , as such it TOE-OUT during hard braking.
Well, worn out arms bushing can cause what you are experiencing too.

Our steering alignment default is TOE-IN, but I do not know the standard scrub radius W212 have, but I suspect it is positive and that gives a TOE-OUT force when braking and accelerating,
hence the static alignment for steering is TOE-IN to compensate for that.

S-Prihadi, thank you for your response. My suspension is in good repair (inspected by mechanic, not just shade tree me) and the issue has no correlation to road surface. Agreed that it seems the left front caliper is exerting more pressure but it’s unclear to me what would cause that. It has been about two years since my last alignment so that’s worth considering for the reason you mentioned.

IF THE BRAKE :
Depending on you caliper design, it is a single piston floating caliper or a 2 + 2 pistons ( known as 4 pistons ) type caliper.

Single piston design. One side is a follower only.
Source : https://low-offset.com/workshop/floa...rake-calipers/





2 or 4 or 6 piston design, surely a fix type.



For single piston floating caliper, if the follower side jammed up, that means less braking force.
For any type of caliper, if the piston jammed up, less braking force too.

Brake fluid from leaking piston or grease can also contaminate the brake pad, and less braking force.

So your RIGHT side brake system is then the bad dude, in this case.

12 years old and 153K miles is a lot for the brake seal to work so far flawless, till now.
Have any inspection done to the brake calipers and the brake rotor thickness measured ?

I replaced the brake fluid today since it was due. I didn’t measure the rotors or fully inspect the pads but no contamination was apparent. The reservoir was full and the calipers were clean and dry so I don’t think a piston seal is failing but it’s worth investigating nevertheless.

It sucks that MB does not sell repair kit for caliper : seal + dust boot + o-ring if any, for our calipers.
To see rubbers/polymer components working in such environment of a brake caliper to last more than 10 years and 100,000 miles is in itself a marvel in engineering already.

I managed to replace all the seal kit on my front calipers because it is by Brembo, but there are crossover o-ring I can't get genuine Brembo.
The rear one I can't get the seal kit , that is by ATE

Here is my front caliper preventive overhaul :
https://mbworld.org/forums/e-class-w...-overhaul.html
https://mbworld.org/forums/e-class-w...y-achieve.html


Perhaps you can test temperature difference between LEFT and RIGHT rotor disc after heavy braking test, use IR gun or FLIR type thermal gun.
The hotter side would indicate better caliper's piston pressure hence more friction and more heat.

It would be wise to do the 4 wheel alignment first though as its been 2 years and probably pass 20,000 miles yes ?
I do my alignment per 10,000KM max or usually per 5,000KM and wheel balancing per 5,000KM. I do only 5,000KM a year now.
Afterall rear tire can last only 25,000KM there about, with its camber setting and the way I drive it.


Happy troubleshooting............

Anyone remove caliper and pads and inspect those as well as rotor?

Might be the other wheel pads are hard and glazed over so have les friction

I would just replace pads right now as 3-4mm left is not a lot throw in new rotors too.
Other possible causes for pulling are:
brake line blockage
Bad brake rubber hoses that flex too much versus the others
sticky caliper either piston or on slides.
OVerheat in brake lines causing to boil on some corners
Bad tire - belt slip, tread worn, worn funky due to bad alignment.
Suspension hardware and bushings loose, dry rot, something broke.
bad road and or leans for drainage

front rear brake bias not set correctly.
brake fluid leakage to one of the corners
Something greasy on rotors or pads on some of the corners

I would just replace pads & Rotors right now as 3-4mm left is not a lot
During this process I would really check out calipers when collapsing caliper pistons

Thank you to all for your replies. I’m confident that the issue is not due to bad wheels/tires, condition of suspension components, alignment, or road surface. I’m going to start with replacing the brake lines. While they don’t exhibit any external damage, they could be decaying internally with bits of rubber preventing the brake hydraulics from performing normally. If that doesn’t work, I will replace the calipers. I just ordered brake lines from FCP Euro so we’ll see how it goes. Thank you.

Do you have any good documentation handy for brake line replacements? About to start mine as well...

This is for the W211 https://mbworld.org/how-tos/a/merced...ke-line-386629

You can wait for @konigstiger to post some documentation. I do not recall if @pierrejoliat replaced brake lines recently, Pierre did you?

I misspoke as I am only replacing the brake hoses btwn the calipers and hard brake lines, though I just read through Pierre's 'adventure' post haha. Thanks for the link!!

I misspoke. I am replacing the f & r rubber brake hoses as well, not entire brake lines. I don’t have instructions yet but am looking.

I would suggest checking all arms and the rear subframe. The rear subframe is prone to rust. If it starts to rust, after some time the arm supports may break, leaving you with a suspended arm. That will definitely cause that exact pull to the side you were describing. I had this issue and seen others talk about it, not a pleasant surprise unfortunately. Hopefully it's not this!

Yes, did them all it was time consuming, but came out great, certainly right at the limit of my physical ability on jackstands in the garage. Take pictures before you start! Just in case you need to refer back to them, do one at a time, I also had plenty of time to see my subframe up close, despite living in the snow belt, mine was still okay. not pretty but ok. As far as I could tell the originals were steel, hard to bend even with the line bender, I took Left Coast Geeks excellent suggestion to use Copper/Nickel lines, easily bent by hand, I only used the tubing bender for a couple tight angle turns.

Any update on this problem? Reading through the thread, this sounds like a mechanical problem, not something you'll see with computer codes. Front struts replaced a year ago, I'd start there. Could be an improper installation, or a failed front left strut causing the front left to dive under braking. Could also be a very worn suspension bushing causing the geometry to shift under heavy braking load. Lastly, it may be a brake problem, either a seized caliper, or something wrong with the pads. I've seen where folks installed on of the brake pads backwards, which causes just that one corner to have a different coefficient of friction. I can't think of anything else that would cause this. Strut, suspension bushing, or brakes. Gotta be one of those. I'm thinking strut since that's what was touched last.

Argon3030, thank you for your insight. I replaced the brake hoses, but that had no effect on the problem. The current brake pads are installed correctly but have 64k on them. The struts were installed 5/21 and sway bar end links around 6/22. The suspension is fine with no significant wear to the bushings. This weekend I had a sudden low speed stop in a parking lot and could feel hard pulsations from the ABS system. Since then, problem alleviated a little bit. Perhaps the right front caliper is bad. I have replacement calipers and pads ready to install this weekend to see if that fixes the problem.

I think that's a good call, I think the front right caliper is frozen or not functioning correctly, with two new calipers, rotors and pads, you should be back to normal.

and brake lines flush until clear.

Your description reads like a frozen caliper. The infrared thermometer suggestion is a good one.

If you have calipers and pads ready to go, you should replace the rotors.

First, thank you all for your responses and thoughtful input. While I rotated the tires, flushed the fluid, replaced all hoses, disabled ABS, replaced front pads/rotors/calipers, it was to no avail. So I took the vehicle back to my mechanic, and this time they found the problem, The rear subframe is rusted and cracked on the left side. Apparently this is an issue with E and C class. I’ve read a few threads on here regarding the issue and at least one described how my car feels when braking suddenly from moderate or higher speed. Apparently this is repairable but beyond my skill set and comfort level.

Edited to ad: thank you juanmor40. He identified the problem a month ago. I missed the sub frame rot with my car on the ground but my mechanic found it on the lift.

Thank you for the follow up. I had not heard of this w212 issue before, but apparently it's a thing. I found a thread here with photos that sounds very similar: https://mbworld.org/forums/e-class-w...nspection.html