Robert -
I've seen a couple of things cause this. One is the return orifice in the
master cylinder is plugged with rust or some other foreign material. The
other (and more common cause) is a misadjustment of the brake light switch.
The way the master cylinder works is the fluid from the reservoir goes into
the cylinder in front of the rubber seal on the piston, then gets sent out
to the calipers and rear wheel cylinders when you press the brake pedal.
When you release the pedal, the piston in the master cylinder is returned by
an internal spring, and needs to travel backward far enough past the orifice
to let the brake fluid return back to the reservoir. If the brake light
switch is adjusted too deep, it prevents the brake pedal from returning far
enough, and that prevents the piston in the master cylinder from retracting
fully.
All of this said, the disk brake pads actually never retract fully - they
are always in slight contact with the rotor. There is no spring action -
only the very slight run-out or wobble of the rotors actually push the pads
(and caliper pistons) back a bit. Unlike the rear brake shoes, which are
returned by the springs within the rear brake assembly.
Are you experiencing binding of the front brakes, or just the slight
rubbing? Very slight rubbing/contact is normal, binding isn't. If one of
the conditions that I first described happens, usually the brakes start
binding the more you drive it. If the fluid can't return to the reservoir,
and the pads are rubbing, heat is generated, which expands the brake fluid,
which presses the pads tighter against the rotors, which generates more
heat, which..... you get the idea.
Wayne Kube
Plano, TX
'79 MGB V8 3.9L "Hobbes"
Logan 1925
n5wmk
----- Original Message -----
From: "packrat6" <packrat6@charter.net>
To: <mgb-v8@autox.team.net>
Sent: Sunday, July 20, 2008 8:42 PM
Subject: [Mgb-v8] disc brakes
> the disc brakes on my 79B are rubbing all of the time. not making any
> noise
> (the pads are relatively new), but they are not releasing completely when
> the
> fluid pressure (pedal) is
> released. both front wheels seem to be affected the same.
> is there some common cause for this?
> thanks for the help. robert
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