PeachParts Mercedes-Benz Forum - 380 SEC Brake trouble

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380 SEC Brake trouble

Hello All.

I just purchased my first Mercedes. A 1983 380 SEC. I love this car. It has some issues as you would expect from a car 26 years old. Love it none the less. I have a question about the brakes I hope someone can help me with.

I needed to replace the front right caliper. I did so. Pads are fine and the job was straight forward. I bled the brakes. Front left, rear left, rear right and finally front right. I had a nice solid pedal feel when finished. When I started the car to take it for a test ride the pedal went almost to the floor. I shut it off and double checked for leaks and fluid level in the master cylinder. No leaks and master cylinder just below max line. No leaks around the master cylinder or the brake servo (booster). What am I missing? Does this point to a problem with the brake servo? If so are they repairable? Any leads on getting one used?

Thanks for any ideas or assistance.

Christian

Quote:

Originally Posted by Crausch (Post 2331447)

Any leaks at the booster will be inside it, not outside. Does it hold vacuum? If you pump the brakes with the car off, does the pedal rise and hold? Is the pedal squishy or just low? And when you say "low", do you mean it's return position is low or the point at which it engages the brakes is low?

Is your brake light on? Did you use an OEM caliper or Autozone junk?

When you changed the caliper, did you clamp off the line or did you accidentally allow the brake resevoir to become empty?

Do you have any braking power at all? If so, is it power assisted or do you really have to mash on the pedal to get it to stop? Did you check for leaks at all 4 wheels (and wherever the bleed screw opening is pointing) as well as all of the brake lines? If the brake lines are rubber, what's their condition?

Pumping the brakes repeatedly with the engine running can deplete the vacuum reserve in the booster, so try driving it "normally" if the brakes are stopping the car.

Before you replaced the caliper, did you drive the car? Was the pedal higher then?

Quote:

Originally Posted by dhjenkins (Post 2331479)

Any leaks at the booster will be inside it, not outside. Does it hold vacuum? Think so.

If you pump the brakes with the car off, does the pedal rise and hold? Yes.

Is the pedal squishy or just low? Low.

And when you say "low", do you mean it's return position is low or the point at which it engages the brakes is low? Point of engagement low.

Is your brake light on? Went out after caliper replacement. Came on after bleeding lines.Went off after short test trip.

Did you use an OEM caliper or Autozone junk? OEM caliper (Girling sp?) 60 with mercedes star on it.

When you changed the caliper, did you clamp off the line or did you accidentally allow the brake resevoir to become empty? I disconnected the line. And immediately threaded it into the new caliper. Lost very little fluid if any.

Do you have any braking power at all? Yes. If so, is it power assisted or do you really have to mash on the pedal to get it to stop? Very easy to engage the brakes and car stops predictably.Did you check for leaks at all 4 wheels (and wherever the bleed screw opening is pointing) as well as all of the brake lines? Yes. Looked at each caliper individually, Scanned the underside of the car looking for any signs of wetness. Saw nothing. Will double check. If the brake lines are rubber, what's their condition? They are rubber and old but look fine. Again no signs of swelling or degradation.

Pumping the brakes repeatedly with the engine running can deplete the vacuum reserve in the booster, so try driving it "normally" if the brakes are stopping the car. Durring the test ride about 1/2 mile the brakes where used normally and worked fine just engaged low. NY inspector said he will not pass car for inspection with low engagement.

Before you replaced the caliper, did you drive the car? Was the pedal higher then? I did drive the car for only about 6 miles. Honestly don't recall pedal height.

thanks for the help.

Christian

Rebuilt the left rear caliper on a 380SEL last week and put in a new master cylinder. Found out the hard way that the rear brake portion of the brake reservoir is surprisingly small. We could get maybe three pumps (the old "up" / "down") on the bleeding of the rear brakes before it sucked air into the system. After that we made VERY sure that the reservoir was kept full during the bleeding, which resulted in a very nice hard pedal.

Redo the bleed, making very sure you keep the fluid level up!!

I second the re-bleeding, only this time just gravity bleed it.

Open all screws just enough for fluid flow, capture fluid with clear tubing & 4 jars and just stand at the reservoir and keep filling it until you've gone through an entire big bottle of fluid.

The problem with the 'unscrew, push & rescrew' technique is that the pressure you exert on the pedal turns big air bubbles into many small air bubbles in the entire system.

Thanks All. I will give it a go and see what happens. I will post my results if i am able to get to it tonight.

Thanks Again

Christian

Well I did the gravity method to the brake system yesterday and everything worked well. The pedal height of engagement is higher. Thanks for the assistance.

Christian