> Can anyone tell me what the term "knock-back" means in
> relation to some sort of action or reaction concerning disk
> brakes, and perhaps with lag in the piston contacting the
> rotor.
Sure. Refers to the process of the caliper pistons being "knocked back" in
the caliper by the rotor, which then means the pedal has to travel farther
(lower) the next time you use the brakes. Can be very disconcerting if
you're not expecting it, and interferes with precision driving. Not too
hard to cope with though (IMO), if you know your car and are expecting it.
The primary source of the rotor moving sideways to knock the pistons back
seems to be the stub axle flexing under hard cornering, although setting the
bearings too loose can also cause it. Some earlier TRs had a residual
pressure valve to prevent knock-back, but ISTR it was deleted during TR4
production.
There is a spacer kit available to counter-act the problem (by effectively
stiffening the stub axle). I would not suggest the kit unless you are
racing or having trouble with knock-back on the street (takes some pretty
spirited driving to cause it, IMO); since it has other drawbacks. But if it
is a problem for you, the kit is available from TRF (P/N HP660) or TSi (and
likely others). You can also buy uprated stub axles from the same sources.
http://www.zeni.net/trf/TR6-250GC/119.php
Randall
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