Dodge RAM TRUCK 1500 1995 Service Manual page 221

B R
DISC BRAKES I - 41
WEAR
«gfcy:-
TAB
80MM CALIPER
(3/4 TON)
INBOARD
BRAKESHOE
J9405-45
Fig, 2 Model 2500 Disc Brake Caliper (80 mm
Piston)
86MM CALIPER
(1 TON)
WEAR
TAB
OUTBOARD
BRAKESHOE
J9405-46
Fig. 3 Model 3500 Disc Brake Caliper (86 mm
Piston)
A simplified cross section of a single piston caliper
is shown in Figure 1. The illustration graphically
portrays the forces at work when the brakes are ap­
plied.
Upon brake application, fluid pressure exerted
against the caliper piston increases greatly. Of equal
importance, is the fact that this fluid pressure is ex­
erted equally and in all directions. What this means,
is that pressure in the caliper bore, will be exactly
CALIPER
MOUNTING
ARMS
(PART
OF
KNUCKLE)
J9405-26
Fig. 4 Caliper Mounting (in Steering Knuckle)
the same as pressure on the piston. In other words,
pressure against piston and caliper bore will be
equal. .
Fluid pressure applied to the piston is transmitted
directly to the inboard brakeshoe. This forces the
shoe lining against the inner surface of the disc
brake rotor (Fig. 5).
At the same time, fluid pressure within the piston
bore, forces the caliper to slide inward on the mount­
ing bolts. This action brings the outboard brakeshoe
lining into contact with the outer surface of the disc
brake rotor (Fig. 5). . '
In summary, fluid pressure acting simultaneously
on both piston and caliper, produces a strong clamp­
ing action. When sufficient force is applied, friction
will stop the rotors from turning and bring the vehi­
cle to a stop.
Brakeshoe Wear Compensation
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 brakeshoes 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 be­
tween 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. 6).