[W126 Coupe] Brakes and air

[Dick Spellman]

Ronny,

A pressure bleeder needs to be attached to the fluid reservoir fill 
cap.  Both of the little rubber caps on the reservoir must be replaced 
(if original) with MB parts before using a pressure bleeder.

If after the pressure bleed (correct order: pass rear, driver rear, pass 
front, driver front) with 25-28lb on the gauge to clear the ABS, your 
braking should be solid.

If it is not, they probably pumped the pedal in lieu of the pressure 
bleed the first go round on you brake job.  This will likely have 
destroyed the master cylinder seal where the pumping to the floor 
resulted in travel past the build-up on the piston from years of use 
causing this seal to fail.  Hence, a new master cylinder may be needed.  
If this is the case, a close inspection of the interior lower level of 
the brake booster must be done while the master cylinder is out of the 
way to be sure no fluid has risen and accumulated on the brake booster 
membrane.  If there is a small amount pooled on the booster metal 
housing but, no obvious contact with the rubber membrane you should be 
fine with just the master cylinder replacement.  If the membrane has 
been affected the booster too will need replacement.

many shops still do the pedal pumping and swear it works fine.  But the 
above describes what happens on aging cars when pressure bleeding is not 
done as MB recommends.  Costs time, can cause loss of braking and 
ultimately cost you more money.

Good luck,

Dick

)On 12/16/2010 11:30 AM, Ronny 560sec wrote:

> My 1987 560 SEC have a major brake job for front and back and the 

> garage, I come there for the last 20 years, also decided to replace 

> the brake fluid.

> But they have a problem with bleeding out the air. After a couple 

> hours the brakes start working the should do and I drove home. I went 

> to the gas station to fill and started the engine. At that moment I 

> felt that the brakes become soft and went nearly totally down again. I 

> tried pumping, but that did not help.

> Any help and idea is needed and thank you.

>

> Ronny

>

>

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