Brake Questions..ahh!

[KylePavao]

Ok. Well the W115 needs two things to be roadworthy. One: Good brakes, and two, an exhaust. Well, the brakes are being tough...

I first suspected the master cylinder. So I switched it with one from parts car. No difference: still stops, but extremely close to the floor. Second, tested the booster. Its working. I pump brakes, turn car on, and they return to floor.

So all I can suspect is the lines themselves. The calipers are working, so what else could be wrong other than the lines? I bled them with the old cylinder, made no difference. Suggestions??

[pawoSD]

Are the flex lines old? They could be swelling under braking pressure....thats all I know of that could cause that.

[Bodgit2]

There's likely some air in the system. Bleed and reverse bleed if needed with phoenix injector. Are the pads in correctly? If the pads aren't in correctly on one wheel, you will have the problem you describe. Does the pedal get firmer if you pump it once or twice?

[KylePavao]

The pedal never seems to firm up, and only grabs at the bottom, almost to the floor.

[punky]

Originally Posted by KylePavao

The pedal never seems to firm up, and only grabs at the bottom, almost to the floor.

Isn't the master cyl.test to pump the brakes till firm pedal then start car and pedal should drop some but not to floor?

[KylePavao]

It drops some, and not to floor. Exactly as you said.

[psfred]

You have air in the system or a busted line somewhere.

If the lines have not been replaced, this is a good time to do it, else they will probably rupture shortly in use -- they are, after all, 30 years old if not replaced yet!

Also check for leaking piston seals, they are probably iffy too.

Peter

[KylePavao]

I actually through a white sheet out, drove my car over it and pumped the brakes. It seems that there a no leaks, none of the fittings are leaking either...I am hoping it's just some air in the lines. Also the lines were replaced about 6 years ago according to records, at the benz dealer. I am going to investigate tommorow.

[t walgamuth]

no disrespect intended but are you sure you know how to bleed the brakes?
a comment: i have never personally seen a flex fail. they are extremely long lived. also a low pedal if the pedal is firm can be caused by worn pads.

[punky]

Originally Posted by KylePavao

I actually through a white sheet out, drove my car over it and pumped the brakes. It seems that there a no leaks, none of the fittings are leaking either...I am hoping it's just some air in the lines. Also the lines were replaced about 6 years ago according to records, at the benz dealer. I am going to investigate tommorow.

I hope this ain't too stupid a question, but you didn't mention yet if you bench primed the masters before installing. If so, that rules that out unless you favor the odds of having two bad masters.

[Ganaraska]

I'm thinking he does have 2 bad (used) master cylinders.

Here is a test. Go out on a gravel road or dirt road with no one around and lock up the brakes.Notice if it stops straight and smooth. Get out and look at the skid marks, see if all 4 wheels locked up. If only the front or only the rear are working, it's probably the master cylinder.

It could be air in the lines too. It can be very hard to get all the bubbles out but if you leave the car overnight all the dissolved air bubbles come out of the fluid.Bleed them again the next day and you get a firmer pedal.

[Anthony Cerami]

I had a similar problem on my 350 SD.
After replacing the master cylinder, four calipers, flexible lines, and bleeding my brains out………
Guess what?? Almost no brakes….????
The wind up was ….. bleeding the brakes with a pressure bleeder at 30 PSI.
The book said 15 psi…….Yes it needed …30 PSI …go figure …..in 10 minutes I had a firm pedal.
Now it will stop on a dime and give you a nickel change!

[KylePavao]

But yes, I bled each brake, starting with the one farthest from the master cylinder and moved my way to the one the closest. Also, I don't think both masters are bad....I tried the dirt road method this morning in the gas line behind my house, and even though I have to apply a ton of pressure, all of them seem to stop.

Also after sitting overnight the pedal seems noticeably firmer, but I will bleed again.

[Ganaraska]

If it passed the dirt road test all I can suggest is to bleed them again. The car has to sit overnight so the dissolved air can come out of the fluid, then you bleed the brakes to get rid of it.