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Rear Brake System:

Changing Rotors, Calipers, and Rear Brake Pads on a Mercedes w123 

Written by Alan Phillips

Changing Rotors, Calipers, and rear brake pads on a Mercedes w123 (possibly for all MB's with all wheel disc brakes, but I don't make any promises)

NOTE: This is a comprehensive how-to on replacing the entire brake system from the brake line on. If your only changing a certain part then follow the steps pertaining to that part (for example: if your changing the brake pads just follow the steps that say "brake pad" or "all" in them). 

Tools needed:

  • Jack

  • Jack Stands

  • 17mm socket

  • Ratchet for use with 17mm socket (1/2" normally)

  • C-clamp or big flatblade screwdriver

  • Small tipped punch

  • Needle nose pliers

  • Standard wrench set (12mm up to 17mm)

  • Ball peen hammer

  • Friend who can swing a ball peen hammer

  • Various aerosol chemicals (WD-40, Brake Cleaner, Liquid Wrench, Chezwhiz)

Note: If your reusing the rotors use C-clamps, if you could care less about the rotors you can have fun and use a big screwdriver, more on that later.

 

Step 1 (All)

Block the front wheels and loosen the lug nuts on the side in question. Then jack the car up and support it properly with the jack stands. Remove wheel. (duh)

 

Step 2 (Rotors)

Do the same on the other side but don't take the wheel off.

 

Step 3 (All)

Remove the pins holding the brake pads in the calipers by tapping on them using the punch and hammer. Once you have one removed and the other loose you can pull the clip out using the pliers. Store the pins and clip in a safe spot, you'll need them to put the whole thing back together.

 

Step 4 (All)

Now you must remove the brake pads. If your reusing the rotors (only replacing the pads and/or the caliper) then you'll want to use the C-Clamp here, if your not reusing the rotor then you can use the flat blade screwdriver. I personally use the C-Clamp method but that's only because that's the way I learned it and it also makes me feel like a surgeon :)

  • C-Clamp method: Place the C-Clamp on the tap on the brake pad and the groove thing on the caliper, tighten it until you compress the piston a little and move to the other tab on the same pad. Keep doing that until the piston is fully compressed (easy to tell). Do the same on the inner pad.

  • Screwdriver method: Use the screwdriver as a lever to compress the piston by levering on the brake pad's tabs. Once you have a big enough gap to stick the screwdriver head between the pad and rotor you can just wiggle the screwdriver as much as you want until the piston is compressed. Once again, repeat the procedure for the inner pad.

If all you are replacing are the pads then skip down to step 10 for reassembly.

 

Step 5 (Calipers and Rotors)

Now take your 17mm socket and ratchet and loosen the 2 bolts on the inside of the caliper that look like they are holding the caliper in place (easy to tell what's what, and the facts there's only two 17 mm bolts in that area helps). Remove the bolts but keep a death grip on the caliper cause when it falls it's going to mess up the brake line if your not careful. If your replacing the caliper then go to the next step. If your not replacing the caliper then hang it carefully out of the way and skip to step 7.

 

Step 6 (Calipers Only)

Take your 12 mm wrench and loosen the bolt when the rubber brake line connects to the steel brake line (it's on the top over the little metal bridge thingy). once the bolt is free wiggle the brake line out of it's hole being careful to not contaminate the steel brake line's interior with gunk. (read cover it with a plastic baggie). If you are reusing the brake line (not recommended, but people do) then transfer the old brake line over to the new caliper. 

 

Step 7 (Rotors)

Here's where your hammer-wielding friend comes in. Go to the other side and turn the wheel as he hits the back side of the rotor through the gap left by the caliper. After a few good hits the little bugger will pop off (helps if you spray WD 40 all in where the rotor meets the hub, just make sure to then spray it with Brake Cleaner after your done).

 

Step 8 (Rotors) 

NOTE: If your adventurous you can replace the parking brake shoes but there's really no need. As a result I won't explain how to do it. It's not hard if you do though. 

Go ahead and put the new rotor on the hub. (Hard wasn't it)

 

Step 9 (Calipers and Rotors)

Making sure the pistons are compressed all the way (use a big C-Clamp) go ahead and bolt the caliper back on the Hub Housing thingy. !!!ALWAYS USE LOCK-TITE!!!

Don't forget to reattach the brake line to the rest of the system.

 

Step 10 (All)

Now take out the brake pads, turn them on their back (has a MB star on it) and smear a little bit of the brake pad grease that you got (not really needed, but thats factory recommended, it's suppose to keep down the noise).

Do that for both pads.

Now that they are properly smeared go ahead and put them in their respective slots (doesn't matter which goes where, they're the same size, shape, etc)

Once they are in and kind of aligned slide one of the pins in and kinda jiggle the pads around until it fits all the way. Put the clip in it's spot and do the same thing with the other pin. Once you have those in their spot tap them in the rest of the way with the hammer.

 

 

Congratulations, you've just rebuilt the rear brake system on your fine Mercedes-Benz. Like the rest of the care there's a awe inspiring simplicity to it that makes you just smile and wonder how those German Engineers do it.