W211 SBC Brakes

[bobbyc]

Having had my E280CDI Saloon now for two years, I just thought I would pass on my experience of the SBC braking system fitted to this car.
I bought the car second hand from MB in Salisbury when it had approx. 10K on the clock. It was an excellent drive, and all went well until I heard some metallic noises coming from the back end at 40k (I do about 35Kmiles a year). I took the wheels off and found a seized caliper, with one pad down to the steel carrier plate, and hence the noise. After unplugging the SBC unit, I changed the rear pads myself, and noted only one pad on the rear axle was fitted with an electrical wear indicator, and not the pad that had worn down to metal. All was well, and the brakes went through the cars first MOT at 74K miles. At 75K miles, I again heard graunchy noises from the front end, and again found one pad down to metal, and again only one wear indicator, and not in the pad that had worn. It is interesting to note that in both cases the excessively worn pad was on the passenger side, and the wear indicators are fitted on the drivers side. Also in both cases, the pads on the opposite wheel had plenty of friction material left on them.
My conclusions are that although the SBC system is a superb braking system, its complex operation results in uneven pad wear. Fitting only two wear indicator sensors to the possible eight pads is not adequate, and I have twice been caught out without any display warnings. (Had the car been left hand drive, would it have been any different?).
I have now resolved to check all eight pads physically at least once a year, as dealers cannot be trusted to spot the uneven wear that seems to be a feature of this system. Have any other SBC equipped owners had similar problems?

 

[Dieselman]

All was well, and the brakes went through the cars first MOT at 74K miles. At 75K miles, I again heard graunchy noises from the front end, and again found one pad down to metal, and again only one wear indicator, and not in the pad that had worn. Fitting only two wear indicator sensors to the possible eight pads is not adequate, and I have twice been caught out without any display warnings. (Had the car been left hand drive, would it have been any different?).
I have now resolved to check all eight pads physically at least once a year, as dealers cannot be trusted to spot the uneven wear that seems to be a feature of this system. Have any other SBC equipped owners had similar problems?

Why not fit more pad wear sensors. Just "T" them together electrically, it's a bit of hassle but not as much as worn out pads every time.

Regarding the MOT, I'm surprised they didn't note them as too worn or even an advisory, unless the brake system wore them out after the MOT test.

 

[bobbyc]

Prety good suggestion Dieselman, it would be fairly easy to fit detectors in the opposite pad of the wheel currently fitted with a detector and connect in series. A bit more work though to run cabling across to pick up the other pair of pads on the wheel at the other end of each axle. I believe before the American been counters got involved, and started looking for ways to get costs down, Mercedes used to fit detectors in all eight pads. This would clearly be the ideal solution from a safety point of view, and would have detected my seized caliper before I started cutting metal!
Once we get some decent weather again I will look into the practicality of your suggestion, and maybe do it next summer.
I watched the guy doing the MOT, and as he didn't take the wheels off, probably coudn't see the pads that well and probably assumed that they were wearing evenly. Car passed the braking efficiency tests with flying colours.

 

[timskemp]

The uneven pad wear is probably caused by ESP intervention - I believe there was a software update that helps prevent this. Even my heavy right foot got 98k miles from the rear discs / pads.

 

[Number_Cruncher]

>>I watched the guy doing the MOT, and as he didn't take the wheels off, ...

Yes, that's right, an MOT tester can remove nothing, not trim, not covers, nothing. As an extreme example, a car with each of its wheels held on with only one bolt, if the bolts were hidden behind plastic trims would pass the MOT.

Only if the thickness of remaining friction material can be seen by the MOT tester without removing any parts is it inspected. Then, a fail can only be issued if less than 1.5mm of friction material remains - if thin, but above 1.5mm, you might get an advisory notice.

Why are the calipers siezing up?

 

[bobbyc]

Thanks for the MOT info. number cruncher. That maybe explains why it was not spotted, or ignored.
With the E Class, it was only the back caliper that seized resulting in the early pad change. The front calipers were fine, and unless whoever had the car for a year before me only changed front pads on one side only, they are definitely wearing unevenly. My previous car was a C220CDI Estate, and that also suffered a seized caliper at the rear resulting in metal to metal contact, as again, no pad wear sensor fitted on that side.
In all cases, extreme wear has been on passenger side. Is this pure coincidence, or is there some logical explanation? ....................i.e. passenger side wheels tend to hit more potholes on kerbside of the road. Does this fool some of the clever control systems into operating?

 

[w124coupe]

I replaced my front pads at 68,000 and the rears are still fine at 73,000. Absolutely even wear on both sides (same SBC-equipped E280CDI car as you but estate).

If you are still in warranty I would get it checked ASAP.

 

[benzino]

Hi all,

regarding SBC, just bought a 280cdi 211sport. how often should the sbc pump be heard making the grinding noise? on mine it seems to be every other time i press the brake pedal. is that right?should it be that often?

 

[bobbyc]

Hi Benzino, I am not sure there is any "normal" and presume the pump is activated when the fluid pressure falls below a set level. On my 280 with normal town use, the brakes are very sensitive and only require minimum pedal effort to slow/stop the car. I would guess I can hear the pump cycling for about 20 seconds every 8 minutes or so as an average.

 

[Soltan]

Hi Benzino, I am not sure there is any "normal" and presume the pump is activated when the fluid pressure falls below a set level. On my 280 with normal town use, the brakes are very sensitive and only require minimum pedal effort to slow/stop the car. I would guess I can hear the pump cycling for about 20 seconds every 8 minutes or so as an average.

Not sure I can be that accurate, but that sounds about right, although on a long drive I tend to tune it out now.

 

[Will Kelly]

hi all, so by disconnecting the SBC when i change my discs & pads will i need to have it "star" reset? what about if i change my calipers? regards will

 

[bobbyc]

Hi Will, I have changed all eight brake pads now by disconnecting the sbc main plug under the bonnet. Haven't needed to get anything reset with STAR equipment and all seems as it should.
Not needed to change any calipers, but can't see why it would be an issue as long as you bleed the system afterwards.

 

[Will Kelly]

many thanks for the reply will be changing mine before its next service @ 85k as for my calipers there are a little shabby and lets the car down i have a contact in worcester who refurbs them for very little monies, new pistons/seals?