Lesson 1/Learning Event 1
Floating Caliper
The floating caliper is designed to move laterally on its mount.
This movement allows the caliper to maintain a centered position with
respect to the rotor. This design also permits the braking force to
be applied equally to both sides of the rotor. The floating caliper
usually is a onepiece solid construction and uses a single piston to
develop the braking force. This type of caliper operates by
pressurized hydraulic fluid like all other hydraulic calipers. The
fluid under pressure first enters the piston cavity and begins to
force the piston outward. As this happens, the brake pad meets the
rotor. Additional pressure then forces the caliper assembly to move
in the opposite direction of the piston, thereby forcing the brake
pad on the opposite side of the piston to engage the rotor. As
pressure is built up behind the piston, it then forces the brake pads
tighter against the rotor to develop additional braking force.
Fixed Caliper
The fixed caliper is mounted rigidly to the spindle or splash shield.
In this design, the caliper usually is made in two pieces and has
either two, three, or four pistons in use. The pistons, which may be
made of cast iron, aluminum, or plastic, are provided with seals and
dust boots and fit snugly in bores machined in the caliper. The
centering action of the fixed caliper is accomplished by the pistons
as they move in their bores. If the lining should wear unevenly on
one side of the caliper, the excess clearance would be taken up by
the piston simply by moving further out in its bore. As the brakes
are applied, the fluid pressure enters the caliper on one side and is
routed to the other through an internal passageway or an external
tube connected to the opposite half of the caliper. As pressure is
increased, the pistons force the brake pads against the rotors evenly
and therefore maintain an equal amount of pressure on both sides of
the rotor.
As discussed above, the fixed calipers use a multipiston design to
provide the braking force. The fixed calipers may be designed to use
two, three, or four pistons. The dualpiston design provides a
slight margin of safety over a singlepiston floating caliper. In
the event of a piston seizing in the caliper, the singlepiston
caliper would be rendered useless, while the dualpiston design would
still have one working piston to restore some braking ability. The
three and fourpiston design provides for the use of a large brake
lining. The brake force developed may now be spread over a larger
area of the brake pad.
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