I would make sure the reservoir is completely full and bleed again --
the back chamber is filled by overflowing the front one, and it's
quite easy to have it go dry.
A MityVac works great, so long as you remember that you are going to
pull air in the bleeder valves and won't ever get air free fluid.
Once you get clean fluid out and there are no big air bubbles, it's
full and free of air, you can ignore the stream if tiny bubbles
leaking in the threads. Big slugs of air, you have a leak or the
reservoir is going empty on you. I've chased that particular problem
for ages once or twice.
The pedal, with the engine running, should have about an inch of free
play, become firm quickly, and stay firm, with added pressure
resulting in more braking effect with very little movement downward.
A sinking pedal under light pressure, mysterious loss of fluid, no
brakes unless you pump them, and excessive travel with less than
normal braking power all indicate a bad master cylinder, usually from
worn out seals on the back piston.
Check to make sure the rear pads are clean and move easily -- they
get stuck much more readily than the fronts, and can give you goofy
brakes, too. Lack of wear on the rear rotors is a hint here.
Peter
On Oct 22, 2010, at 7:25 AM, Dillon, Meade M CIV SPAWARSYSCEN-
ATLANTIC, 53310 wrote:
Rich,
I suspect your bleeding method isn't working too well.
I have the "Power Bleeder" which pressurizes the reservoir, if
you'd like to
borrow it. You'll need to make sure the two rubber sensor caps on
top of
the reservoir are in good shape prior to pressurizing.
The "old school" way of two people working together, one pressuring
via
pumping the brake pedal and the holding with the second opens/
closes the
bleed valve to allow fluid/air to escape works well but you risk
destroying
the seals in the master cylinder if fluid changes have been
neglected and
there is gunk beyond the normal range of travel that the seals hit
when the
pedal sinks to the floor.
I used to use the gravity drain method, and just attach hose from
bleeder to
a drain bottle or can and let physics pull the fluid out. Slow,
but safe
and effective. Now I can do the job with MORE POWER!
-Max
-----Original Message-----
From: mercedes-boun...@okiebenz.com [mailto:mercedes-
boun...@okiebenz.com]
On Behalf Of Rich Thomas
Sent: Friday, October 22, 2010 7:40 AM
To: Mercedes Discussion List
Subject: Re: [MBZ] Brakes, again (300SD)
Yes, all 4 in the proper sequence, twice. I'm thinking I should
put some
teflon tape on the bleeders to seal up those threads a bit and keep
the air
from getting in my bleed tube (using a Mityvac), though I don't
think it is
going back into the calipers. At first they were a bit mushy after
I put on
the new caliper and filled it and bled it a bit, so I went around
the car
again and then it was better, pretty much as it was before I
started the
exercise.
I'll take a look at the bushing, but the pedal does not seem to
have play in
it, just takes some travel to start brake engagement. I guess they
aren't
"touchy!"
--R
On 10/22/2010 7:21 AM, Rolf wrote:
Check the bushing on the brake pedal where it meets the rod that
goes
into the booster. If this is missing or deteriorated then you get
more
travel before braking. Otherwise is sounds like you need to bleed
more. Did you bleed all 4?
-Rolf
On 10/22/2010 7:14 AM, Rich Thomas wrote:
So I got the new caliper on and hooked up, and system bled as best I
could (there seems to be a lot of air leakage around the bleed
nipples) with new fluid. The pedal feel is not a lot different from
before, still seems to have about an inch of travel before getting
much braking, and seems a bit soft though the brakes work OK. Might
this be a master cylinder issue, or is that just the way they are?
--R
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