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Re: Brake M/C rebuild question---exasperatingly long reply

Subject: Re: Brake M/C rebuild question---exasperatingly long reply
From: Bob Howard <>
Date: Mon, 17 May 1999 18:15:45 EDT
  I've recently been through the entire rebuilding process and fought
with the pressure switch too.
  First off,  I'm 99.9+% certain that the switch will not block fluid
from passing through the line. The slider in mine slid to both extremes
during my rebuilding process duress, and it was never the switch that
caused the problems.  Others, one notes, will disagree with this. Refer
to the drawing and to your switch to see which opinion fits your car. 
  Rebuilding the MC if it's a dual line non-servo unit can be done.  It's
a pain. Although I have rebuilt MCs a dozen times before, it took me
three rebuild kits to get this thing working right.
  One of the failure modes was that there was no fluid to the rear
wheels.  In that mode, there were two failures that were involved. 1 was
that the rear wheel cyls leaked, so when there was fluid to them there
wasn't pressure.  THat was because the DPO had failed to recognise frozen
adjusters and had adjusted the brakes via the handbrake cable. Result
there was oddly worn shoes, cylinders operating at the absolute end of
their stroke,  solidly frozen adjusters, a stretched brake cable, a
broken cable and a generally pissed-off current owner. Failure 2 was that
the link that connects the primary piston to the secondary piston, it's
inside the spring, broke at the weld. The secondary (rear) piston then
went to the end of its cylinder space and remained there, held in the end
of the cylinder by the spring. No return to its park position meant that
the cylinder couldn't refill and pump to the rear again. 
  When you go to do the deed, rebuild the clutch MC at the same time.
They are on the same bracket and you might as well have at least one
  There are two circlips in the MC. One is easy to reach. The second
needs some long-nose circlip pliers that I don't have. You can remove it
with two centerpunches and patience.  Don't grasp the piston with pliers
as they will mar it and then it leaks around the piston.
  The WS manuals say that the nylon guide will fall out. They lie!  Drill
two holes in the thing and insert small self tap screws. Then you may be
able to pull it out. Or not, in which case you drill the thing so that it
breaks into two halves. Then you may be able to get them out. Or not.
Keep drilling as necessary.  A new nylon guide comes in the rebuild kit. 
  The diagram in the Haynes manual is more clear (less unclear)  than the
one in the Bentley manual. It's the same MC, but a different diagram #.
The print is easier to read in Haynes.  You don't really need it if you
draw the pieces on paper as you remove them.
  The roll pin that holds the link may be stuck. If you have to drill it
out, it's a 3/32 unit available at the hardware store.
  Do you still want to rebuilt it?  Consider the value of your time. 
Removal and replacement of the MCs and the bracket will take 90 minutes.
Bleeding takes more. Removal for the second rebuild takes more.
   Reconnect the lines before you bolt the mc bracket down.  7/16 and 1/2
inch wrenches do the job for the MCs and the bracket. 9/16 for the pedal
pivot bolt. . Make note of the pedal pivot bolt pieces as you withdraw
the bolt.  You may want to buy or make a new seal for the pedal cover
  As for me--next time I'll take the advice of the professionals.  Dump
the old one. Buy a new one.

On Mon, 17 May 1999 09:07:28 -0400 Joe Short <>
>Well, replaced the cracked rear brake hose on my '75 B on Saturday.
>But when I connected my trusty vacuum bleeder to bleed the brakes 
>came out ! I even went so far as to disconnect the hose and connect my
>bleeder to the hard line and try it from there. Still nothing. With 
>the rear
>bleeders open, I pumped the brake pedal. It felt as if the brakes were 
>It didn't go soft or slowly to the floor, but it didn't build pressure 
>pump up either. I read recent;y on the list about someone who had a 
>and replace a pressure warning switch to correct the problem, but I 
>can't find 
>one anywhere. My guess is it's time to rebuild the master cylinder. My 
>are, can I verify this before I spend money ? And, are there any 
>or thing I should know before I rebuild the M/C ?

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