[B]Bleeding Brakes[/B]

[c49737]

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?

[sixto]

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

[c49737]

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.

[300holst]

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.

[230/8]

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

[sixto]

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

[c49737]

Originally Posted by 230/8

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

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.

[c49737]

Originally Posted by 300holst

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.

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