Since the brake master cylinder decided to fail while I was going home
from work(70mph on the Washington, DC beltway), I had occasion to
replace it with a rebuilt this weekend. Stopping in heavy traffic by
pumping the brakes, downshifting, & pulling on the parking brake
simultaneously is not the easiest way to stop a car.
It has been 7 or 8 years since I have had to do this, & I had forgotten
all the little wrinkles, so I thought I would pass along the little bits
that are not mentioned in the manual.
Braking system is from a '78 B, even though the car is a '74- got to
like the brake booster & dual circuit. After the routine removal &
installation of the rebuilt unit, I unscrewed the brake bias switch
3-1/2 turns, per Benchley. That is, I removed the one from the old m/c &
screwed it home on the new one, then backed it off. Failing to do this
before bleeding the brakes will cause lots of problems, like soft
peddle, poor braking, multiple bleeding to no avail, etc. Using my
trusty EsiBleed with a control valve added, I bled & flushed all the
lines in about 30 min. & had a nice hard peddle. After checking for
leaks, cleaning up, I pumped the peddle a few times to be sure the fromt
calipers were full, & went for a test ride. Brakes were OK, but not
great. They acted like they still had some air, which I knew was
impossible. A friendly motorist pulled up behind me at a stop, got out,
& came up to tell me I had no brake lights. Well, at least 1 light came
on, if only in my head. Got home as quickly as I safely could, &
adjusted the brake light switch to proper functioning. Now the lights
worked, & so did the brakes. The switch was preventing full peddle
travel, so the pressure did not completely release. At least, that's
what I think was happening.
Moral is, when replacing a master cylinder, check the brake lights.
Apparently, the new cylinder has a different lenght of travel than the
old one.
Before someone asks, if you add a cheap in line shut off valve to the
Esi Bleed between the tire connection & the reservoir, you can shut off
the 30 or so lbs of pressure that will cause brake fluid to spray all
over, & just crack the valve enough to move fluid, say 2-4 lbs. Works
great, just remember to shut the valve before hooking up to the tire.
Jim Stuart
1974 MGBGTV8
1978 MGBV8 in progress
|