Dodge RAM TRUCK 1500 1995 Service Manual page 235

DRUM BRAKES I - 63
mmmm
b h a i c e s
i i i E X
page
Brake Drum Service 72
Brake Support Plate Installation 71
Brake Support Plate Removal 71
Brakelining Wear Compensation . 63
Brakeshoe Installation (11-Inch Brake) . . . . . . . . . . 65
Brakeshoe Installation (13-Inch Brake) . . 67
Brakeshoe Removal (11-Inch Brake) 63
Brakeshoe Removal (13-Inch Brake) 66
GENERAL SERVICE INFORMATION
All BR models are equipped with Delco rear drum
brake assemblies. They are two-shoe, duo-servo units
with an automatic adjuster mechanism.
' Three different size drum brake assemblies are
used which are:
® 1/2 ton (1500) models have 11 x 2 in. drum brakes
• 3/4 ton (2500) models have 13 x 2.5 in. drum
brakes
• 1 ton (3500) models have 13 x 3.5 in. drum brakes
Two different wheel cylinders are used. The differ­
ence being cylinder bore size. The cylinders used on
1/2 and 3/4 ton models have a bore diameter of 23.8
mm (0.937 or 15/16 in.). The cylinders used on 1 ton
models have a bore diameter of 27 mm (1.06 or
1-1/16 in.).
DRUM BRAKE OPERATION
Drum brakes on BR models are a semi-floating,
self-energizing, servo action design. The brakeshoes
are not fixed on the support plate. This type of brake
allows the shoes to pivot and move vertically to a cer­
tain extent.
In operation, fluid apply pressure causes the wheel
cylinder pistons to move outward. This movement is
transferred directly to the brakeshoes by the cylinder
connecting links. The resulting brakeshoe expansion
brings the lining material into contact with the rotat­
ing brake drum.
Two forces affect the brakeshoes once they contact
the drum. The first force being hydraulic pressure ex­
erted through the wheel cylinder pistons. And the
second force is the friction generated turning torque
of the rotating drum.
The drum forces both brakeshoes to move in the
same direction of rotation. Servo action begins with
the primary brakeshoe which begins to wedge (or
wrap) itself against the rotating drum surface. This
force is transmitted equally to the secondary brake-
shoe through the adjuster screw and anchor pin. The
net result is that each shoe helps the other exert ex­
tra force against the drum. It is servo action that cre-
page
Drum Brake Adjustment 71
Drum Brake Operation 63
General Service Information . . . . . . . . . . . . . . . . . 63
Wheel Cylinder Installation (All) . . . . . . . . . . . 70
Wheel Cylinder Overhaul (All) 69
Wheel Cylinder Removal (All) . 69
Wheel Nut Tightening 72
ates the wedging (or wrap) effect which produces
increased force on the drum braking surface.
BRAKELINING WEAR COMPENSATION
All drum brake assemblies used on BR models are
equipped with a self adjusting mechanism. The com­
ponents forming the mechanism consist of the: ad­
juster screw, adjuster lever, actuating lever (11 inch
brake), lever return spring and the adjuster lever
spring. The adjuster lever on the 13 inch brake, is
also equipped with a lever and tension spring.
The adjuster mechanism performs two important
functions. First, is in maintaining proper brakeshoe
operating clearance. And second, is to maintain brake
pedal height. The mechanism does so, by adjusting
the shoes in small increments to compensate for lin­
ing wear. The adjustment process is continuous
throughout the useful life of the brakelining.
The adjuster components are all connected to the
secondary brakeshoes. Actual adjustment only occurs
during reverse brake stops. Secondary brakeshoe
movement (during reverse stops), is what activates
the adjuster components.
In operation, secondary shoe movement causes the
adjuster lever spring to exert pull on the lever. This
pivots the lever away from the adjuster screw teeth.
When the stop is completed and the brakes released,
the adjuster lever pivots back to a normal position. It
is during this return movement of the lever when ad­
justment occurs. At this point, the lever comes back
into contact with the adjuster screw teeth as it moves
upward. The lever will then rotate the adjuster screw
one or two teeth as needed for adjustment.
The adjustment process requires a complete
stop to actually occur. Rolling stops will NOT
activate the adjuster components. In addition,
the adjuster screws are left and right hand
parts and must NOT be interchanged.
BRAKESHOE REMOVAL (11-INCH BRAKE)
(1) Raise vehicle.
(2) Remove rear wheels.
(3) Remove brake drums.