90 740 GLE 16V Spongy Brake System

Hi all,
I just replaced my front pads, bleed the entire system, no leaks found,
went for a ride and found out that brakes are spongy. If the ignition is
off, brake is normal, but when the ignition's on, pedal is all the way to
the floor. I have to pump it in order for the brake works. It wasn't like
this prior to replacing pads. What cause this problem?
Thanks for any help in advance and may God bless everybody.

 

Sounds like you didn't bleed it well enough and have air in the system,
there's a proper order to open the bleeders in, it can be tricky to get all
the air out.

 

If you've bled the line properly then my suggestion is to check the
thickness the rotors, how old are they?. If you've changed brake pads but
the rotors are past it's life then you will feel the brake pedal being
spongy and/or going down more than usual. Also make sure that the reservoir
cap is clean and seals well.

Not sure if you did it this way but as a rule of thumb when bleeding the
brake line start at the farthest calliper from the brake fluid reservoir and
work your way closer. Also it really helps to have someone pump the brakes,
as you bleed and replace the brake fluid. Remove almost all of the old brake
fluid with a turkey baster before adding fresh fluid. Put a block of wood
under the pedal to prevent the piston from bottoming out in the master
cylinder. Then tell your helper to step on the pedal and press
down gently but firmly. Open the bleeder valve and watch the fluid as it
flows through. If you don't get any fluid movement at the rear brakes on a
car with ABS, close the bleeder valve. Have your helper turn on the ignition
and apply the brakes once, then turn off the ignition and just lightly rest
his/her foot on the pedal. Open the bleed valve slowly. If a stream of fluid
flows from the valve, allow it to come for about 10 seconds, then close the
valve and add fluid to the master cylinder. Depending on the system, the
pressurized reservoir may push out enough fluid. Or the flow may continue
only if the helper presses down on the pedal. On most cars, the flow will
start and continue without the preliminaries-only the helper's foot pressing
on the pedal.

When the pedal hits the wood block, tell your helper to hold it there. Add
fresh fluid to the master cylinder reservoir again and repeat the procedure.
When the fluid color changes from grungy black to some thing closer to what
the new fluid looks like, you can stop. Close the bleeder valve and go to
the next wheel brake. Be very sure to add fresh brake fluid up to the level
in the reservoir every single time.

Before you do the final top-off have your helper apply the brakes over and
over, to exhaust the high-pressure reservoir of the ABS. This will cause the
level in the master cylinder reservoir to rise slightly. It may take 25 to
35 pedal applications to do this, but when the level stops rising after a
couple of dozen, that should be it. If you don't do this, the reservoir
might overflow under some conditions.


Hope that helps.

 

You either managed to get some air in the system, or the extra travel on
the master cylinder while bleeding it disturbed the crap sitting out of
harms way in the unused portion of the master cylinder, which has ground
up the seals. If that's the case, you'll need a new master cylinder to
fix the problem.

--
Mike F.
Thornhill (near Toronto), Ont.

NOTE: new address!!
Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)