Looks like it's brake time - Page 2 - PeachParts Mercedes-Benz Forum

JimSmith · #16 09-13-2002, 07:15 PM

Warden,

I have written on this subject a couple of times, and while I do not consider my practice controversial, I am a little puzzzled that the common practice seems to be so different.

I always flush the brake lines and calipers with new fluid, every time I change the pads. I do this because brake fluid is susceptible to absorbing moisture, and when it does, it can lead to early caliper problems. Living in the Northeast, I also replace the rear pads before they wear down as far as the fronts because they can build up corrosive iron/carbon dust that can lock the rear calipers up by bonding the metal backing of the pad to the close fitting guide surfaces on the caliper. This leads to one side of the caliper, or both, becoming non-functional (one of the two pads on the caliper wears and the other one doesn't). Anyway, MB recommends the brake fluid be replaced at least every two years, and brake fluid is cheap.

I use Castrol GTX (DOT 4 or 4 plus) LMA brake fluid. I think nearly any DOT 4 fluid is likely ok, but I have had good results with the Castrol product for nearly twenty years now.

If you change the fluid at the same time as you replace the pads, you put a 7 mm or 9mm closed end wrench (can't remember at the moment) over the caliper vent nipple, which you might want to soak in WD-40 or some other penetrant. Then slip a tight fitting hose over the nipple, and direct the other end of the hose to a small glass jar. When you get the pins out of the pads/calipers, and the pads are ready to be removed, open the vent line and when you shove a large (Sears Craftsman) screw driver between the disc and the pad, you will find prying the pad back against the piston to drive the piston into the caliper a simple, easy task. The old brake fluid will run into the jar and will in all likelihood be black or at least darkly discolored.

Take the time to really jam the pad all the way back against the piston to drive the piston all the way back into the caliper bore. If, after you remove the first pad, the new replacement will not go in, it is most likely a problem with crud building up in the corners of the guide surfaces that is preventing that last little bit of motion to get the piston all the way in. If this is the case, use your screw driver to scrape the surfaces in question, and brake cleaner, followed by some scrubbing with an old toothbrush. I have read that there is a perception that some pads are too thick. I have never found this to be the case, and have had the openning seem too small many times. It has always been the collection of burned brake dust and metal wear particles that collect behind the pad backing of the old pad as the lining wears. Once the stuff is there, and you shove the pad back, it "squeegees" the stuff into a pile behind the pad, and no amount of shoving the pad back is going to get the piston to move into the caliper any further.

Also, remember to one pad at a time. If you take both out of a given caliper at one time, you run the chance of having the piston you are not pushing on pop out of the caliper when you push on the other one. That is a real pain in the behind.

So, the finishing up part, after you get both pads in one caliper, is to bleed the brakes after you flush the old stuff out. I typically did this as a one man operation, but with my sons now taking an interest in cars, I get an assistant. If you don't have an assistant, once the end of the hose in the jar is covered with fluid, you can pretty much do the bleeding operation yourself. With the end covered, no air gets back in and you can fill the reservoir and pump with the pedal, then go out and shut the vent valve (do not remove the hose), and check the condition of the pedal. If it is spongy, repeat the process. Repeat the process for each wheel.

Good luck, and I hope this helps, Jim