I have a ML500 and am needing help on bleeding the brakes. I was told 2 different methods of bleeding.

1. Break open the bleeder valve on the caliper then Pump the brakes
or
2.Hold down the brakes then break the bleeder valve.

All I did to deserve this was change out the rotors and pads. Dont know how air got into the system. The system was never opened. Just the pistons pushed back via a c clamp.

Which method is the correct way to do it?

What makes you think you have to bleed the brakes? Does something not feel right?

It's probably a good thing to do but consider a brake fluid flush while you're at it.

I believe that modern MBs require the brakes to be pressure bled. Possibly a more sophisticated process than just pressure bleeding, even. The old pump-the-brake-pedal method is best left to pre traction control cars.

Sixto
95 S420
87 300SDL

The brakes were very responsive and never went to the floor. Now the brakes feel very sponge and gradually go down to the floor when held for several seconds.

The spogy brakes could be air in the system although I don't know either how that could have happened.

The fact that the pedal goes down to the floor under steady pressure sounds like the fluid is getting past the seals in the master cylinder. Sometimes, when people use the "pump the brake pedal" method, they push the master cylinder piston into an area of the cylinder which has been corroded or has debris in it. This tears a gap in the rubber piston seal and ruins the master cylinder. Don't ask me how I know this.

Is it possible that when you used the "C" clamp you pushed the caliper piston in so far that it was damaged by corrosion? Check to see if there is any leakage at the calipers. If the pedal goes to the floor, pressure is leaking out somewhere, or there air has entered into the system. Did you remove fluid from the master cylinder reservoir so it would not over flow when the calipers were pushed back? If so, maybe the level got too low and air entered at that time? If you drained out the reservoir you may have been able to push the pedal down so far to re-seat the new pads that you bottomed-out the master cylinder and damaged the cups. It may be leaking into the power brake booster where you cannot see it.

230/8

How many times have you pressed the brake pedal? It could be that the calipers are yet filled from having been practically emptied of fluid. Press the pedal about half way down about a dozen times and see if that restores proper pedal feel and brake action. Don't press the pedal all the way down. You might damage the piston seals. Put your left foot under the pedal so it doesn't go all the way down.

Sixto
95 S420
87 300SDL

I havent even bleed them yet, I am just trying to figure out waht I can do.

I pushed the pistons in just far enough to slip the pads in. I didnt remove fluid from the master cylinder reservoir. I easied the piston back very slow as not to over fill the reservoir. There is absolutly no brake fluid anywhere. Not on the calipers or around the master cylinder. I cannot find a leak. But I will check around the brake booster.

Is it possible I created an air pocket when I was forcing the fluid back thru the ABS system? I was told, after the fact, that I should have broke the bleeders loose and pushed fluid out of the caliper when I was pushing the piston back. Is this true?

Hmmmm...boy, this is a bit strange, because it sure sounds like you have done all the right things. Wild guess here, is there any possibility that you forgot to tighten one of the calipers and it is flexing on the mount?

If you cannot find a leak and the pedal is still spongy, then I would have the system pressure bled. Might be a good thing anyway just to ensure all the fluid is changed out for fresh stuff.

Good luck with this.

230/8

I used to wory about this. I have seen it happen many times and it even happened to me once or twice. But I realized that the truth is that the master cylinder is shot and I would rather tear the seals in the shop instead of see it happen to a customer when they first make an unusual panic stop and press the pedal a little further than usual. Depressing the pedal to the floor is something the master cylinder is supposed to be able to do. If it cant do it replace it.

John Roncallo

I used this on my 97 E320 with great results, it is really easy to use. http://www.aep.bigstep.com/eezi.htm If you bleed or change your fluid with this, there is very little chance of getting air in the brake system.

Also, when resetting the calipers, just take off the brake fluid resevoir cap. The fluid will back up into there if needed, so much so that you may need to siphon some off.

I'm no expert on this, but I did a rotor/pad replacement on an older '75 450SE (no ABS) years ago and the pedal felt like you describe, right after I buttoned everything back up. I went into a panic, concluded I'd pushed the cup seals in the master cylinder backward or something equally stupid when I clamped the caliper pistons in to make room for the new pads. I changed the master cylinder for one I had laying around, bled everything, and guess what - same damn thing!
I talked to a MB mechanic friend of mine and he told me that the new pads/rotors need to seat themselves before that nice hard pedal feel comes back. He told me to just use the brakes for awhile and see if the situation clears itself up. Lo and behold, it did.

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1986 560SL
2002 Toyota Camry
1993 Lexus