Hi Bill,
Any attempts to diagnose would be pure speculation, but that's never
stopped me ;)
Sounds like you're talking about three problems: defective brake lights,
soft pedal and disappearing
brake fluid. You didn't mention whether the brakes worked or not; if
they work OK then
you've got plenty of pressure to activate the switch. More than likely
your switch is shot.
Yes, you could be pumping fluid into the servo (bear in mind the fluid
level will usually rise a bit
after a drive due to heating of the fluid). The servo is basically a
slave and master cylinder,;the slave
activates a valve to let atmospheric pressure into the vacuum canister,
whose piston activates
the master cylinder, which applies the pressure to the wheel cylinders.
I'm working from memory--I've
had a couple of these apart--because I'm too lazy to go get the shop
manual, but there's a seal called
a "gland" seal that prevents fluid from entering the vacuum canister
(which, obviously since there's
a vacuum tends to encourage the fluid to exit). Anyway, the gland seal
can harden and get brittle
with time and will allow fluid to enter the vacuum canister.
Eventually, the canister will fill up enough
that fluid will get sucked into your intake manifold and you'll get some
smoking (white). The servos
are usually good for 100K miles or more, but if yours sat for a long
time the gland seal might have
hardened. Rebuild kits are about $80, and unless you're lucky at least
one of the cylinders in the
servo will probably need to be re-sleeved (at about $100 per). You can
always buy one of the
aftermarket replacements, but the original works pretty good and I found
the rebuild process to
be interesting.
WRT the soft pedal, if this was due to pumping fluid into the servo I
think you'd lose fluid at a
faster rate. I've found the best way to bleed these brake systems is
with pressure; I put a Schrader
valve into a reservoir top and apply about 10lbs. of air to the system.
Normal pedal bleeding can
work too, but I've never had any success with vacuum systems (e.g. MityVac).
Don't jump to conclusions; you might just have a broken switch and a bad
bleed job. The fluid
loss could be due to other reasons as well (are you sure it's not being
lost in the clutch circuit?).
bs
Bill Matthews wrote:
> Hello,
> I am stumped.
> When I bypass the brake switch the brake lights come on which leads me
> to think that the brake switch is either defective or there is not
> enough pressure in the system to activate the brake switch. The brake
> fluid reservoir is going down 1/4" in two hours driving. We bled the
> system several times but could not get rid of a little "soft" pedal.
> We can find no signs of a fluid leak. Could the servo be defective and
> be filling up with fluid? I can hear it "activate when I step on the
> brake.
> Any help is greatly appreciated.
>
> Thanks,
>
> Bill Matthews 67 BJ8
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Bob Spidell San Jose, CA bspidell@comcast.net
'67 Austin-Healey 3000 '56 Austin-Healey 100M
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