Hello Everyone .....
Just got done a complete brake job on my 350sd.
New rotors , calipers, brake lines.
I bled the brakes and cannot get a firm pedal.???
I installed a new MC bled them again and still a very soft pedal.
Drove the car and it will only stop if you pump the pedal.
I am using a pressure bleeder.
??????
What am I doing wrong????

I also posted on the diesel forum


Please can someone help
-Anthony

Sounds like the "secret" hidden rear reservoir of the master cylinder strikes again.

There is a rear section of the master cylinder reservoir that is difficult to see. Brake fluid flows from the obvious front section into the less obvious rear section. My guess (and it's just that) is that the rear section (front brakes) is sucking air.


Best of luck,

__________________
Norm in NJ
Next oil change at 230,000miles

Thank you norm.
I did just discover that the inside of the reservoir is a maze of sections.
I heard some "Slurping" ...like through a straw......inside the reservoir.
It looks full on the outside .......
I was pressure bleeding without fluid in the pressure tank.
Ill try bleeding againthis time with some fluid in it. This will insure the MC stays full.
Ill keep you posted.
Thanks
-Anthony

Thank you guys for all the replies
I have also posted on the diesel forum.......
Before installing the MC I did bench bleed it.
After install I pressure bled the MC lines and the ABS lines.
I then started at the pass rear and worked my way to the drivers front.
Some one suggested the "secret" hidden rear reservoir of the master cylinder.
This seem to be getting fluid. I’m using 20 lbs. of pressure. Is that enough?
The pressure bleeder keeps the fluid level up in the MC.
I even tried the two man ....errrr 1 woman, 1 man bleeding technique.
Dervman ....Yes I did jack up the back end higher than the front.
Is that ABS unit a problem?
I never had this on the 300SE and I did the same brake job.
????
Any other ideas?
Is it just a stubborn air lock?
Bad booster????
ABS ....air lock??????
????????????????

Still no brakes......................
I tryed everything.???
Pressure vacuum....both.......bench bled the MC.?????
The pedal is firm when the engine is off.....
While running It goes to the floor......it will pump up on three pumps but then goes to the floor...................
I was able to run the ABS motor independent of the system.
Bled everything again back to front including the ABS unit with the ABS motor Running ....................Nuttin................

?????????????????????////
What could be wrong??

I hate to say this, but that still sounds like air in there to me. With the ABS there is considerable volume in the brake system, although I know you have bleed copious amounts of fluid by now.

All I can say is that it took quite a long time to get this same problem fixed on my brother's Chevy 1-ton with hydroboost brakes. Right side caliper took a LONG time to come clear of air, it would clear, then start bubbling again.

We eventually replaced a brake hose to completely cure this, but I'm sure you would have noticed THAT much brake fluid dripping!

All I can suggest is carefully checking for leaking hoses and bleed out each section of the system -- that is, crack the lines at the ABS on the MC side and make sure you have nice clear air-free fluid, then bleed the other side of the ABS, then each brake line. I've never had to bleed an ABS before, so can't help much there.

The rear calipers are right side up, eh?

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

The rear calipers are right side up, eh?
OOOHHHHHHH yeaaaa!
I removed the capipers again ...one at a time.....
And bench tested each one....
will try again tomorrow.......

thanks Peter....

When I did my brakes, I used the vacuum method. Both rear lines sucked clear fluid for about 2 half vacuum bottles of fluid. I thought I was done, but to my surprise, more bubbles. I kept sucking, I used about 0.5 litres of brake fluid in total for both sides.

On the rear brake calipers, are the bleed valves at the top or on the bottom of the caliper?

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1989 420 SEL