Dodge 2000 DURANGO Service Manual page 158

5 - 4 BRAKES
DESCRIPTION AND OPERATION (Continued)
FRONT DISC BRAKES
DESCRIPTION
The calipers are a single piston type. The calipers
are free to slide laterally, this allows continuous com-
pensation for lining wear.
OPERATION
When the brakes are applied fluid pressure is
exerted against the caliper piston. The fluid pressure
is exerted equally and in all directions. This means
pressure exerted against the caliper piston and
within the caliper bore will be equal (Fig. 1).
Fig. 1 Brake Caliper Operation
1 – CALIPER
2 – PISTON
3 – PISTON BORE
4 – SEAL
5 – INBOARD SHOE
6 – OUTBOARD SHOE
Fluid pressure applied to the piston is transmitted
directly to the inboard brake shoe. This forces the
shoe lining against the inner surface of the disc
brake rotor. At the same time, fluid pressure within
the piston bore forces the caliper to slide inward on
the mounting bolts. This action brings the outboard
brake shoe lining into contact with the outer surface
of the disc brake rotor.
In summary, fluid pressure acting simultaneously
on both piston and caliper, produces a strong clamp-
ing action. When sufficient force is applied, friction
will attempt to stop the rotors from turning and
bring the vehicle to a stop.
Application and release of the brake pedal gener-
ates only a very slight movement of the caliper and
piston. Upon release of the pedal, the caliper and pis-
ton return to a rest position. The brake shoes do not
retract an appreciable distance from the rotor. In
fact, clearance is usually at, or close to zero. The rea-
sons for this are to keep road debris from getting
between the rotor and lining and in wiping the rotor
surface clear each revolution.
The caliper piston seal controls the amount of pis-
ton extension needed to compensate for normal lining
wear.
During brake application, the seal is deflected out-
ward by fluid pressure and piston movement (Fig. 2).
When the brakes (and fluid pressure) are released,
the seal relaxes and retracts the piston.
The amount of piston retraction is determined by
the amount of seal deflection. Generally the amount
is just enough to maintain contact between the pis-
ton and inboard brake shoe.
Fig. 2 Lining Wear Compensation By Piston Seal
1 – PISTON
2 – CYLINDER BORE
3 – PISTON SEAL BRAKE PRESSURE OFF
4 – CALIPER HOUSING
5 – DUST BOOT
6 – PISTON SEAL BRAKE PRESSURE ON
DRUM BRAKES
DESCRIPTION
Drum brakes on all models are dual shoe, internal
expanding units with an automatic self adjusting
mechanism (Fig. 3). Nine inch and eleven inch
brakes are used.
OPERATION
When the brake pedal is depressed hydraulic pres-
sure pushes the rear wheel cylinder pistons outward.
The wheel cylinder push rods then push the brake
shoes outward against the brake drum. When the
brake pedal is released return springs attached to
the brake shoes pull the shoes back to there original
position.
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