Brake MC ?

["Dave C." <conner@grinten.cfm.ohio-state.edu>]

Will a bad brake MC allow air to enter the lines?

On my 89 100 (no ABS) the brake pedal is spongy.  I bled the brakes and a
lot of air was in the fluid...only seen at the left rear wheel though.  Bled
lines until no more bubbles, but now the brakes are still spongy.  Bentley
says spongy means either need to bleed brakes, or replace MC. 

Tthe pedal has never been as firm as it should be.  I've wondered about
operator error on my part re: the bleeding process.  Once when bleeding I
let the reservoir go dry and got air in the lines.  I'm not sure but seem to
remember it was at the LR wheel.  MAybe I just never got it all out, and
still haven't?  What's the trick?

Bentley say no can rebuild MC, must replace.

I tried out my new improved pressure bleeder for the first time, BTW.  It's
a 2 liter garden chemical sprayer with plastic tank.  Sprayer hose is
connected directly to schraeder valve stem in reservoir cap.  Dump fluid in
sprayer tank, pressurize with built-in hand pump, works like a charm.
Previously I'd used a method where I connected an air hose directly to the
MC reservoir and there was much less room for error due to the small amount
of fluid it held.  Also, the hand pump in tank gives excellent control over
pressure.  I installed a schraeder valve in the tank wall so I can check the
pressure with a tire pressure gauge. 

Dave C.
Columbus, OH
89 100, 87 5KS, 86 4KQ