In Chapter 6, you studied the service of disc brake caliper
hydraulic systems. In this chapter, you will learn how to diag-
nose and service the disc brake system friction components.
Pad and rotor service is very similar for every kind of disc brake
system, varying only according to size, mounting method, and
whether the caliper has a provision for a parking brake.
Variations, where they occur, will be noted in the text.
Common Disc Brake Problems
The most common disc brake problems are noise and
pulsation. Common brake noise includes squeaks and
squeals from brake shoe and rotor contact. Disc brakes
commonly produce high pitched squeals or squeaks when
the brakes are applied. This is often caused by glazed or
worn pads, but may be the result of polished (overly
smooth) rotors, excessively hard pad material, or the wear
indicator contacting the rotor. A grinding or rubbing noise
when the brakes are applied may indicate the pad linings
are worn and the metal shoes are contacting the rotor. Clicks
and knocks are produced by loose pad-to-caliper contact.
Pulsation is a type of vibration. It is usually felt as a side-
to-side motion in the steering wheel, or an up-and-down
motion in the brake pedal, or both, when the brakes are
applied. Pulsation is usually caused by variations in the rotor’s
surface. Long use or excessive heat can cause the rotor to
develop thickness variations, high spots, or warping.
Pulsation is also caused by hard spots (places in the rotor
which have become overheated and lost their original finish).
If heavier than normal pedal pressure is needed for
braking, this may be caused by worn or excessively hard
210 Auto Brakes
Figure 13-1. Troubleshooting chart listing problems that can occur with disc brakes.
Disc Di Di Di sc sc sc Brake B B B ra ra a ke ke ke Problems P P P ro ro o bl bl bl b em em e s s s (All) (A (A (A ( ll ll ll ) ) ) )
C Co Co Co diti nd nd nd it it it io io io Pos n P n P n P os os ible si si si bl bl bl e e C Ca Ca Ca uses us us es es
R Re Re Re ar ar ar Di D D D is is is c c c B Br Br Br ke ak ak ak e e P Pr Pr Pr bl ob ob ob le le le ms ms ms
High-pitch squeal only when brakes applied
High-pitch squeal only when brakes released
High-pitch squeal at all times
Metallic grinding when brakes applied
One pad worn more than the other
Brake pedal pulsates
Excessive pedal effort
Glazed linings or polished rotor.
Pad wear sensor contacting rotor, replace pads.
Splash shield contacting rotor.
Pads worn down to metal.
Sticking caliper.
Caliper piston or slides sticking.
Caliper misaligned.
Excessive rotor runout.
Normal ABS operation.
Glazed linings. If linings OK, problem is in power
booster system.
Vehicle rolls when in gear with parking applied If resistance felt when moving, rear brakes OK.
If resistance is not felt, rear caliper pistons sticking or
parking brake cable misadjusted.
Vehicle rolls with parking brake applied Rear caliper pistions sticking.
Parking brake cable misadjusted.
brake pads. Another cause of a hard pedal is an over-
heated brake system. Overheated rotors and pads have a
poor coefficient of friction, meaning the pedal must be
applied much harder to have the same braking effect.
However, before assuming the cause of a hard pedal is the
disc brakes, check the brake hydraulic system and any
power assist units.
A spongy pedal can be caused by caliper and mount-
ing hardware flexing. This is usually not a problem unless
the vehicle is designed to operate with high hydraulic sys-
tem pressures. Extreme caliper or bracket wear, cracks at
the mounting points, or loose bolts can also cause a
spongy pedal.
Rear disc brake defects include all of those previously
mentioned, plus specific problems involving the parking brake.
Sticking pistons or cables are the usual cause of problems. The
parking brake can stick in the applied or released position.
Pads and rotors that wear out ahead of time are often
caused by driver habits, or severe usage, such as mountain
driving or trailer towing. If the pads are wearing unevenly,
check for a sticking piston or slide pins, misaligned caliper,
or flexing. Figure 13-1 lists common disc brake problems
and their causes.
Caliper and Pad Service
While calipers and brake pads are similar in basic
components and operation, there are many differences in
design. These differences are in the areas of mounting,
noise reduction clips and insulators, and fasteners. These
are addressed where applicable.