mis3

I was driving today and the brake wear malfunction popped up. The message was "Brake Wear. Visit workshop".

Is there anywhere in the menu to check if this is the front or rear brakes?

Pads and rotors were all replaced at around the same time 42k miles ago.

johny1989

this describes the front pads reduced thickness. on avrg you will have an other 5000km depending on how hard you break.

rear break system holds no pad thickness sensors. at least on the 209 s i have seen

mis3

Really? No brake sensor in the rear?

My driving consists of mostly city driving so 42k miles seems OK.

I usually change the rotors at the same time as pads change, as per MB recommendation. Do you guys follow this practice?

johny1989

no way rotors . my rotors are on 120 000 km an may have at least an other 20 000 km.

unless you really really break like in circuit on every trip

Rudeney

There should be one sensor on the front and one on the rear. There is no way to know "which" sensor has been triggered - you'll just need to check the pads.

Generally, the rotors are good for one set of pads. Even if they are still in spec once the pads are worn, they will probably be just barely in spec. You can replace pads, but it's likely that before you get through the, the rotors will fall below spec and possibly warp. I just went through this at 70K miles - 2nd set of pads about 50% worn, but original front rotors were shot. I replaced the rotors with drilled/slotted "Frozen Rotors". Love them! I have Porterfield pads, but will probably go back to OEMs when it's time.

mis3

The front pads should wear down faster than the rear.

However, I did feel that I have to step on the parking brake lower than usual lately.

Rudeney

The parking brake has nothing to do with pad wear. It uses a separate shoe and drum system integrated into the rear rotor.

mis3

Good to know. I thought the parking brake would use the rear brakes.

Is there any way I can adjust the parking brake? I notice that I have to step much further down lately.

Also, should I replace the brake wear sensor when replacing the pads?

My challenge is I will have to buy all the hardware from the dealership and bring it to the indie for installation. I will have to make sure all the necessary parts before hand.

Rudeney

The parking brake can be adjusted:

http://benzbits.com/w203/ParkingBrakeAdjustment.pdf

Once the wear sensor triggers the warning, it must be replaced. They are $5 each. I'd go ahead and replace both.

mis3

Thanks for the WIS. Looks like the Parking brake adjustment can be made without removing the brake caliber and pads.

Since all the rotors/pads were changed at the same time 42k miles ago, chances are only the front rotors/pads have to be replaced. I will replace the wear sensor at the same time.

mis3

I went to an indie today and he checked, I would need pads on all 4 corners. He actually removed the rear right wheels and showed me the pads were worn to close to nothing.

He said that I could re-use the old rotors in the rear. I asked if he would turn the rotor and surprisingly, he said no need. This is strange, not sure if I should take his advice.

Rudeney

Unless a rotor is warped, there is no need to turn it. And then, turning it will likely remove enough stock to make it too close to minimum spec that it won't last much longer. The proper procedure for re-using in-spec rotors is to "knock them down". This involves sanding them with low-grit paper to knock off the shine. This isn't to remove minor imperfections (ridges, valleys) but simply to rough their shiny surfaces so they mate better with new pads.

mis3

What grit of sandpaper would you recommend?

One more thing. The front brakes are supposed to wear much faster than the rear. Apparently, my front and rear brake pads are worn almost the same. Strange.

Rudeney

I generally us 80 or 100 grit. The objective is just to knock the shine off and remove surface contaminates.

My brake pads also wear fairly evenly.

mis3

Ok. Thanks. I will bring a 80 grit sanding block in case I can reuse the old rotors.

I went to the dealership to buy all items today and I will go to the indie tomorrow for the brake service. I bought all pads and rotors as well as 2 brake wear sensors. I can return the parts that I don't use.

If the old rotors are re-usable, can I lightly sand them down while they are still on the axle? My indie would not want to remove the rotors unless I wanted them changed.

Rudeney

You could sand them while on the car, but it will be more difficult. I use a power tool - one of those vibrating multi-tools that can act as a triangular pad sander or a scraper/cutter. I usually remove the rotor and lay it flat on the bench, then run the tool all around it until the shine is gone. It is an extra step to get the rotor off - you have to remove the caliper, and sometimes the rotor is frozen to the hub - but it is the best way.

mis3

Oh. I misunderstood. I thought the rotors have to be sanded lightly, like rough it up a bit to mate with the pads. I did not know they need to be sanded by power tool!

I think this indie would just replace the pads without doing anything to the rotors. He charges me $90 per axle. He said the labour cost would be lower if I chose not to change the rear rotors.

mis3

Just a follow up.

I went to my indie for the brake job. He repalced all pads and only the front rotors. He measured the rear rotors and found they were just a bit thinner than the new one and suggested to leave them. He did not remove the rotors to install the new pads. I drove home afterward and the braking was fine. I will return the new rotors and save the $150CAN. Another $30 saving in labor cost as well for not removing the rear rotors.

He also adjusted the parking brake. It was 9-10 clicks before and is now 4 clicks.

Shrumsjs

MB are designed to wear the pads and save the rotors, that is why so much break dust. I have been doing my own break work on all of my nie Mab through the years. Showed my daughter how to change pads and she does her own on her R350. on my 08 clk350 there are two drive pin that hold a clip in place, drive them out, remove clip, force calipers open and tap pins back in. If your rotors are worn replacement is one small screw and tap off rotors. Lug bold secure rotors to hub and wheel. Is you do not replace the $8 sensor wire it may not reset the warning light. Break jobs are each on MB. I did buy a good low profile floor jack from Harbor Freight and always use jack stands.