New calipers on, but trouble bleeding brakes - PeachParts Mercedes-Benz Forum

merrim19 · #1 10-23-2006, 01:45 PM

Vehicle: 1986 300E 228K

A broken rear axle let me to change out the rear rotors and pads. Due to whatever reasons the calipers decided to freeze up, so I figured I might as well replace them too. Everything bolted on fine, but I have air in my rear lines. Front brakes work just fine, but rears arent grabbing the rotors at all.

So air in the lines is causing the calipers not to grab, I must bleed all brakes. No problem, done this many times on other cars. Manual pumping the brake and releasing the preasure out of the nut on the caliper.

The preasure does push air out, but air must be getting in somewhere because I have been purging the lines systematically for a long time. Same amount of air and a little fluid comes out.

Possible problem with the master cylider? But then why do my front brakes keep working. I'm hoping I'm just missing something obvious, like this peticular car must by running in order to purge the breaks, or that it can not be done manualy, without a powered system.

Any ideas? I'm stumped and winter in rolling in.

Arthur Dalton · #2 10-23-2006, 01:49 PM

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Make sure you have fluid in the compartment for the rear brakes..the fluid has to overflow the front res to get to the rear........

MattBelliveau · #3 10-23-2006, 02:16 PM

As stated in the previous post, you almost have to overfill the MC to get fluid to the back breaks. Went thorought this in the spring after blowing a brake line. Thought I was looking a@ a new master cylinder. Also, make sure the rubber lines that hook up to the calipers are pliable.

mbdoc · #4 10-23-2006, 03:05 PM

Make sure the calipers are on the correct side...bleeder screw at the TOP..

If they are on the correct sides then making sure that the reservoir is FULL to the point of overflowing is the key to bleeding.

riethoven · #5 10-23-2006, 03:55 PM

Get a Mitevac to bleed the brakes. That way you can do it with one person. If I were replacing my rear calipers, I would also replace my brake fluid at the same time. You can use the Mitevac to suck out the old fluid, then pull the reservoir off (it is just pushed into the master cylinder with rubber grommets so it pulls off with no tools) and wash all the old grunge out of it and put it back on. Now fill the fluid up to the top and bleed away. Do not touch the brake pedal while the reservoir is off.

I would also think about replacing the flexible lines that go to the calipers while I was doing the other work.

Mercedes recommends replacing the brake fluid annually, preferably in the spring.

This is my 500th post!