Having the hand brake work isn't a sure fire indicator that the brake shoes are
adjusted
correctly, or that the hardware is all correct. On the Spitfire, the hand
brake is a very
separate circuit from the hydraulics.
Basically, you want the rear brake shoes to be as close to the drum as
possible without
dragging when the brakes are released. If the wheel cylinder cannot float in
the backing
plate, or the drums are out of round, you'll get a false drag which will result
in a low brake
pedal.
You can get an idea if it's in the rear by going ahead and pumping up the
brakes,
setting the hand brake, and relaxing the foot pedal. Give it whatever time it
likes
to allow for a low pedal again. If you've now got a high and firm pedal, you
can
be reasonably certain the problem is in the rear, having to do with the brake
shoes retracting too far. If the pedal is again low and able to pump up, it's
most probably in the front brakes.
The calipers stick the piston seal against the bore wall. Ideally, the piston
can slide easily in the bore, adjusting for wear of the pads. In reality, they
tend to get stuck in the bore, and pull the piston back too far. This is a big
cause of low but firm brake pedal that pumps up. Eventually, the brake pad
wears enough that the piston moves and pops the seal free, temporarily
solving the problem.
Less likely but possible is that the pad itself is doing the binding.
If it's rusted to a rattle clip and flexing it instead of sliding against
it, it would push the piston back too far when the brakes are
released. The pins can do the same thing, holding the pad from
sliding and resulting in a twist.
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