Slight pulsating feeling when braking

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lexie

Member
Joined
Nov 25, 2004
Messages
49
Location
Belgium
Car
E240 Estate (S211/2004)
We have a E240 Estate 2004 with 46.000 km on it.

When braking (not hard braking, just for slowing when apraoching lights etc) i feel a slight pulsation. Not hard, but it's noticable and the longer the more it irrittes me. The feeling does not come from the pedal, but it feels like the braking force is slightly changing with the rotation of the wheels. One possibility I can think of is that one or more discs are not weared down evenly.

The car is currently at the stealer (second time already) for sorting this out, but for the second time they tell me they have tested the brakes and cannot see unusual readings from their test tools (whatever those might be).

I really want to sort this out. What could be the cause? What can I tell my stealer to look for?

Some history on the car:
- Last summer I started hearing a minor noise from the back of the car. It has been determined that it was a ball bearing (left rear wheel). It has been replaced and the noise was gone.
- About a month after that I got a punctured tire. Replaced both rear tires with same make and model of the originals.
- About a month after this (and a skying trip to the mountains in mid-winter) I started feeling this pulsations while breaking.

Any advice or ideas are welcome!
 
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It sounds like either a warped or corroded disk.
 
Vibration

Warped disc, hub run-out, loose wheel bearing or tyre tread separating. But 99% likely a warped disc as Dieselman says

Nick Froome
www.w124.co.uk
 
The dealer has tested all again and didn't find anything special with the brakes. They've tried with the wheels of another car on the back, and they say the feeling was gone. According to them the rear tires are to blame. I haven't been able to verify this because i don't have the time to stick around while they play with the car.
I'll try to have a word with the tire company today...
 
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Second opinion required?

Were the new rear tyres properly balanced when they were fitted?? Can sometimes cause problems on independantly sprung rears but unlikely. Sounds a wee bit like a cop out by the dealer. i.e. find someone / something to blame that is nothing to do with them????:crazy: WARPED FRONT DISCS MOST LIKELY CAUSE as has been said. :( Did you do a lot of heavy braking with a fully laden car when on your ski-ing holiday?? Also have a look at other posts on "sensotronic brakes" on the forum to see if your symptoms are similar.:confused: Otherwise seek a second opinion.;)
 
We were indeed fully loaded (4 people + luggage) on the trip.
Not really hard braking. I also pay attention to let brakes cool down when going down hill -> no long braking actions.
As we drove a few 100 km on snowy/icy roads/highways, both ABS and ESP had to kick in a few times, but not on a prolonged basis.

While reading some posts on sensotronic brakes as you sugested I remembered a few things:
- The car has been recalled twice concerning brakes. I hope they did a good job about that.
- This winter I had an isolated issue when braking which I totally forgot about. It was freezing, just left home. Drove 20 meters to first corner at very low speed (maybe 20 km/h) and it felt like it didn't want to slow down when applying normal braking pressure to the peddal. I had to put my foot down really hard in order to stop just in time. Never happened again so I thought something mechanical was frozen or something like that.

Anyway, I'll pick up the car this afternoon and try with another car's wheels to see if there is any difference. I'll switch all 4 of them to be sure.
 
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Just came back from dealer.
He said that if it would be a warped disc or something like that, then he would see the needle move on his test instruments, but it didn't move.
I must say it is barely noticable and on the way back from the dealer I had little doubt if it was still there. I still felt it, but it seems to be even less noticable. Maybe I'll feel it better when some other people are in the car.

I also took a look at the discs myself and I saw lines on them, dark gray, randomly shaped, a bit like lightning, going all the way from the outside of the disc to the inside. I couldn't feel them with my fingers. Is this normal? Is it corrosion? Can this be the reason? Am I just imagining all of this?

I'm also wondering if the frequency of the SBC pump activity is above normal. It seems to activate every 2 or 3 trips when cutting of the engine. Sometimes also when stopping at a red light. The overall frequency is about once a day.

I'm also considering the fact that one of the tires is maybe not perfectly round, as the dealer is suggesting. It seems the roads are a tiny bit rougher with this car compared to others, again bearly different. I thought this was irrelevant because I guess this could be normal and suspension / tire pressure related.

PS: Don't mind me editing my messages. I'm not English speaking and try to rectify spelling or other mistakes as I spot them.
 
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other tyres

I also took a look at the discs myself and I saw lines on them, dark gray, randomly shaped, a bit like lightning, going all the way from the outside of the disc to the inside. I couldn't feel them with my fingers. Is this normal?
difficult to say without a picture but probably NORMAL/OK
Are you now driving on the other car tyres/ wheels on the rear??
sensotronic brakes do appear to have a mind of their own, often doing routine maintenance/check type operations without your input.
 
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I just drove the car with radio and airco off (unusual and hot experience as it is quite a sunny day). The SBC pump seems to be more active than I thought it was. It activates for only 1 or 2 seconds after every 5 to 10th brake, and after every brake on pavements (I think it is called pavement: square hard stones with rouded edges resulting in a horribly uneven surface as a whole).

[offtopic]
Other things I could hear with the radio and airco off:
- Changing gear, it's a manual. Only noticable when window is down.
- CD/DVD spinning up from time to time in the comand.
Also to be noted is that the engine is quite silent. very pleased with that!
[/offtopic]

On topic again. I'm startig to think maybe I'm too picky. Should I learn to live with the bearly noticable braking pulsation? Personally when I start hearing or feeling things I tend to develop a fixation on it, this can be confirmed by anyone who has been in my cars with me ;).
I definitly know something is different than before, and it is more obvious after have driven with another car just before...
 
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Thanks already for all your input. I has given me a lot to think about.

grober said:
Are you now driving on the other car tyres/ wheels on the rear??


I think that will be a job for tomorrow when I have more time.
 
I did a quick test drive with a passenger. Tested with passenger in front seat, then in rear right seat, then rear left seat. The feeling was definitly worse when he was sitting in the rear left seat. He also told me that in that seat he even felt a vibration when not braking at all. He didn't feel anything particular in the other seats. The problem seems to come from the left rear wheel. This is also where they have changed a ball bearing last autumn and where I had a punctured tire after which I had both rear tires replaced.
 
In that case I would say it's probably a tyre out of round or a buckled rim.
 
Did not try other wheels yet. But did something else today.

I lifted the car, once for each wheel, and had a turn on the wheels by hand. I could hear the brake pads on the discs without braking. I assume this is normal since all 4 wheels did this. The sound was quite uniform. But on the left rear I could hear and feel a little change at a specific position of the wheel. I had someone push the brake pedal a little and the contrast was more noticable then, but not that much. A visual check of the spinning wheels did not reveal any abnormality concerning the shape of the tires, all 4 tires seemed to go up and down a little, but no more than a millimeter or so (as I would expect for tires of 200 euro/piece, 136 pounds).

I guess these findings point to the disc again. Or could it be the handbrake?

Would it be worth changing the rear discs anyway? Is this a costly operation? None of our previous mercs needed changing the discs, not even after 250.000+ km.
 
try the new wheel/tyres on the rear first.

Try the wheels/tyres swop first. If modern mercs are like the old ones the handbrake operates on 2 brake shoes inside a drum combined as part of the rear disc. If the caliper piston hasnt seized or the rear caliper isnt loose or the handbrake shoes/return springs/adjuster are ok. ( unlikely with your age of car) there is no problem. Discs pads are self-adjusting and will rub lightly, without binding, on the disc normally. Warped discs should show up on a properly set up dial gauge. Remember also that the discs will never be as pristine as when the car came out of the factory. The garage will only define them as "warped" beyond certain tight tolerances.
 
also took a look at the discs myself and I saw lines on them, dark gray, randomly shaped, a bit like lightning, going all the way from the outside of the disc to the inside. I couldn't feel them with my fingers. Is this normal? Is it corrosion? Can this be the reason? Am I just imagining all of this?
This could be friction material transferred from the brake pads unevenly to the brake discs as the result of overheating or heavy use during your holiday in the mountains. See the following article on The "Warped" Brake Disc and Other Myths of the Braking System courtesy of Stoptech:


http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml

You will probably have to replace the discs.
 
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I've suffered from this problem and found that sometimes a good drive with your foot hard on the brake pedal can clean up the disks, otherwise remove them and give them a good scrub with a sharpening stone and the pads a wire brushing, then re-bed the brakes.
 
....

Dieselman said:
It sounds like either a warped or corroded disk.

Very insightfull as always. Mine rear discs are corroded on the edges and will get replaced on the next service.

Any recomendations on brake discs or just to go with standard mb fare.

Regards
 
Still didn't find the time for the wheel swap. I did lower the pressure on the tires (they were still set for the trip through Germany: Fully loaded for 210+ km/h). With the normal (lower) pressure, the feeling is a bit more masked, but still noticable, especially when carrying more weight on the back of the car.

I'm pritty sure it's the left rear disc because, when giving the wheel a turn by hand, I could feel a variation which was not present on the other 3 wheels.

Dieselman said:
sometimes a good drive with your foot hard on the brake pedal can clean up the disks

I'm not sure how to do this for rear discs. Would breaking hard have enough effect on the rear discs?
 
lexie said:
I'm pritty sure it's the left rear disc because, when giving the wheel a turn by hand, I could feel a variation which was not present on the other 3 wheels.
If you can feel an uneven restriction to rotation when turning by hand, then you should report this to your Mercedes Service Centre and have them carry out the same test. They should replace the disc and pads under warranty.
 
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