back up worn linings, rotors, drums, or rear brakes out of adjustment are the most likely causes. The proper course of action is to inspect and replace all worn component and make the proper adjustments.
SPONGY PEDAL
A spongy pedal is most often caused by air in the system. However, thin
brake drums or substandard brake lines and hoses can also cause a
spongy pedal. The proper course of action is to bleed the system, and
replace thin drums and substandard quality brake hoses if suspected.
HARD PEDAL OR
HIGH PEDAL EFFORT
A hard pedal or high pedal effort may be due to lining that is water
soaked, contaminated, glazed, or badly worn. The power booster or check
valve could also be faulty.
PEDAL PULSATION
Pedal pulsation is caused by components that are loose, or beyond
tolerance limits. The primary cause of pulsation are disc brake rotors
with excessive lateral runout or thickness variation, or out of round
brake drums. Other causes are loose wheel bearings or calipers and
worn, damaged tires.
NOTE: Some pedal pulsation may be felt during ABS activation.
BRAKE DRAG
Brake drag occurs when the lining is in constant contact with the rotor
or drum. Drag can occur at one wheel, all wheels, fronts only, or rears
only. Drag is a product of incomplete brake shoe release.
Drag can be minor or severe enough to overheat the linings, rotors and
drums. Minor drag will usually cause slight surface charring of the
lining. It can also generate hard spots in rotors and drums from the
overheat-cool down process.
In most cases, the rotors, drums, wheels and tires are quite warm to
the touch after the vehicle is stopped. Severe drag can char the brake
lining all the way through. It can also distort and score rotors and
drums to the point of replacement. The wheels, tires and brake
components will be extremely hot. In severe cases, the lining may
generate smoke as it chars from overheating.
Common causes of brake drag are:
- Seized or improperly adjusted parking brake cables.
- Loose/worn wheel bearing.
- Seized caliper or wheel cylinder piston.
- Caliper binding on corroded bushings or rusted slide surfaces.
- Loose caliper mounting.
- Drum brake shoes binding on worn/damaged support plates.
- Mis-assembled components.
- Long booster output rod.
If brake drag occurs at all wheels, the problem may be related to a
blocked master cylinder return port, or faulty power booster
(binds-does not release).
BRAKE FADE
Brake fade is usually a product of overheating caused by brake drag.
However, brake overheating and resulting fade can also be caused by
riding the brake pedal, making repeated high deceleration stops in a
short time span, or constant braking on steep mountain roads. Refer to
the Brake Drag information in this section for causes.
BRAKE PULL
Front brake pull condition could result from:
- Contaminated lining in one caliper
- Seized caliper piston
- Binding caliper
- Loose caliper
- Rusty caliper slide surfaces
- Improper brake shoes
- Damaged rotor
A worn, damaged wheel bearing or suspension component are further
causes of pull. A damaged front tire (bruised, ply separation) can also
cause pull. A common and frequently misdiagnosed pull condition is
where direction of pull changes after a few stops. The cause is a
combination of brake drag followed by fade at one of the brake units.
As the dragging brake overheats, efficiency is so reduced that fade
occurs. Since the opposite brake unit is still functioning normally,
its braking effect is magnified. This causes pull to switch direction
in favor of the normally functioning brake unit.
An additional point when diagnosing a change in pull condition concerns
brake cool down. Remember that pull will return to the original
direction, if the dragging brake unit is allowed to cool down (and is
not seriously damaged).
REAR BRAKE GRAB OR PULL
Rear grab or pull is usually caused by improperly adjusted or seized
parking brake cables, contaminated lining, bent or binding shoes and
support plates, or improperly assembled components. This is
particularly true when only one rear wheel is involved. However, when
both rear wheels are affected, the master cylinder or proportioning
valve could be at fault.
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