PeachParts Mercedes-Benz Forum - View Single Post

mplafleur · #10 06-14-2004, 11:26 AM

Rebuilding is the way to go. Kits go for little more than $20-$25 for both calipers.

My front left brakes on the 300SD were binding. So much that the ABS kept engaging and those rims were HOT!

I found that the pins holding the pads in place were not in all tha way and the collet was missing on one of the pins. I used a collet from a w123 donor car, bought new pads and fixed the pistons/bores.

I found that one piston was basically frozen and not receeding back into the bore when brake pressure was released. I removed both pistons in the caliper. One wanted to come out easily (inner) and the other wanted to stay in place. I removed the outer by holding the inner in place with a thin plate and a couple of vise-grips. I then pumped on the brake pedal until the piston finally popped out. (make sure you have something to catch all the brake fluid that will come out)

Remove the line from the caliper and take off the rubber boot and inner seal from both bores. I used a screwdrive to remove the corrosion at the outer edge of the caliper bore and then used a fine sanding pad (looks like a thin rectangular green scouring pad) on the piston surface and bore surface. Once everythin is shiny and smooth again, put in a new seal (I used the old as I didn't get the rebuild kit yet) and coat both piston and bore with new brake fluid. Insert the piston and push back into the bore. Do this with both pistons and then put on the new boots. Then put the heat shields back in the outer recess on the pistons.

Press in the rest of the way, attach the brake line. Attach the caliper, put in the pads, spring, pins. You will have to bleed the air out of the line again. Half of the resevoir may be empty though. There will be a LOT of air.

All my brake problems have gone away. The ABS doesn't activate anymore and the rims are all at the same temperature again. I will get the rebuild kit and do the same with the right caliper. It's probably a good thing to do with a 20 year old car.

Don't worry about the small pitting you will see on the surface of the piston. Most of the corrosion will go away without any sign to be left, but some will leave a small pit. It's nothing to throw away your caliper over. The rubber seal is fairly wide and any pitting will have to be a couple of millimeters in length and have some depth to it to have any possibilty of producing a leak. If it didn't leak with all that corrosion build-up, it won't leak with a smooth even surface and microscopic pits.