Re: [DMCForum] Urgent brake problem

["Walter Coe" <Whalt@xxxxxxx>]

I thought I would update y'all on how the brake problem
went.

Original problem was that original(?) master cylinder was
leaking out the back.  Jim bought a rebuilt master from NAPA
sans reservoir.  We bench bled it, put it back on the car
and had a sinking pedal.  When I say bench bled, that means
we put it in a bench vice, put a big philips screwdriver in
the end and cycled it several times to the end of travel.
This was with little hoses connecting the outputs back into
the reservoir.

On our second attempt and in a pinch, I pulled a known
working master cylinder from a wrecked D.  This master came
from PepBoys about a year ago.  I was the one who put it on
the car originally and bench bled it the same way I always
do.  It worked fine then.  But once on Jim's car, it needed
too much pedal travel to stop the car, and the pedal would
go all the way down when held.  Now I'm wondering if this
was a contributing factor to why the car got wrecked.  The
poor guy rear-ended a truck.

So Jim ordered a new master cylinder from PJ Grady.  As
usual, I was impressed with the quality.  This was a new
part that had a nice zinc plating that the rebuilt ones
lacked.  Lack of plating allows them to rust to no end.
Sure, it's only a cosmetic issue, but still, rust sucks.

Since then an experienced mechanic told me not to push the
plunger to the end of travel when bench bleeding because
some types of master cylinders have a weak plastic fitting
on the end that can be damaged by doing this.  So we bench
bled it, per se, while on the car.  When done, the pedal was
too soft.  Either we were having a really bad run on master
cylinders or we couldn't properly bleed it on the car.  Jim
drove it home anyway, and after a few days the pedal feels
right.  My assumption is that time & use allowed any
remaining air to find its way out of the system.

Does anyone have an opinion on if it is bad to cycle the
master to its end of travel when bench bleeding?  Sometime
I'll take an old one apart and see what's in there.

Walt

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