Hi all,
There is probably a reason that the 69 Imperial SM warns against cutting
the brake rotors: warranty experience proved it to be a problem.
I'd say that the rotors were designed to be just barely thick enough in
the first place. Weight (mass, actually) in motion is kinetic energy
and your brakes convert that kinetic energy into heat energy during a
stop. More weight means more heat during stops. The same type of brake
caliper is used on 67?-72 Dusters, Demons, Valiants, and Darts. So
Chrysler continued to use the design for 3 addition model years. Why?
Probably because those cars are much lighter and easier on the brake
components.
Cutting a rotor down to smooth the faces isn't inherently evil (unless
done purely for profit) and won't make the part structurally unsound (so
long as the machining isn't extreme). The problem is that a too-thin
rotor will not be strong enough to withstand the heat it absorbs during
a hard stop and it will warp. I'm betting that Chrysler initially
allowed minor "cleaning up" of the rotors in 67 but immediatey had tons
of warranty claims for pedal pulsation and other, similar, un-Imperial
like, brake problems. They therefore made it a no no to machine the
rotors at all.
I'm also guessing that the caliper design limited the initial rotor
thickness. With the fixed caliper, the pistons have to do all the
"taking up" as the pads wear. You only allow a piston to move so far
out of its bore before cocking is a problem so that was certainly a
concern. And the dust seals can only extend so far before they won't
seal reliably. So the engineers were walking a fine line: 1) pistons
can only extend so far out of their bores, 2) pads have to be of a
certain thickness for adequate service life, 3) calipers can only be so
wide before interference with wheels or suspension components is a
problem, 4) so rotors can, therefore, be only 0.875" thick (or whatever
the original thickness was).
With warranty claims piling up, Chrysler quickly canned the Budd system
and went to the trouble-free sliding caliper design for 1970 Imperials.
Pete in PA
Back to the Home of the Forward Look Network