Chapter 10. BRAKE SYSTEM MAINTENANCE

TM 10-3930-673-34

CHAPTER 10

BRAKE SYSTEM MAINTENANCE

Para

Contents

Page

Section I. Description and Data

10-1.

General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1

10-2.

Principles of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1

Section II. Brake System Maintenance Procedures

10-3.

Disc Brake Assembly Replacement/Repair . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-3

10-4.

Brake Control Valve Repair . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-9

10-5.

Parking Brake Seals Replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-16

Section I.

DESCRIPTION AND DATA

10-1. GENERAL

This chapter covers maintenance procedures for the service brake system components, as well as principles of

operation.

10-2. PRINCIPLES OF OPERATION

a. General. Hydraulic fluid to operate the service brakes is drawn from the main hydraulic reservoir by

the small (1.48 cu. in. [0.024 lt]) section (1) of the dual gear pump. The frame tilt circuit is supplied by the

same pump section. Protection for the circuit is provided by relief valve (2), which is designed to bypass when

circuit pressure reaches 1750 psi (12066.25 kPa).

Pressure to operate the brakes is supplied by accumulator (3). Pump (1) flow is used in the brake circuit solely

to maintain the accumulator charge. Pressure switch (4) is used to monitor brake circuit operating pressure

and turns on the LOW BRAKE PRESSURE warning light in the cab if pressure drops to below approximately

650 psi (4481.75 kPa).

b. Accumulator Charging Cycle. Force to operate the service brakes is produced by the precharge

pressure in the accumulator (3). When the brake foot pedal is depressed, a path is completed from

accumulator (3) through ball valve (5) to wheel brakes (6). Pressure exerted by the accumulator is applied

equally to the cylinders of all four wheel brakes (6). The path between accumulator (5) and pump (1) is

blocked at this time by check valve (7), which is seated by accumulator pressure. Check valve (7) will remain

seated as long as accumulator pressure is higher than pump pressure. Charging valve (8) will then be in the

position shown, and all flow from pump (1) will pass through charging valve (8) and the frame tilt valve (not

shown) back to the reservoir. When, during brake operation, accumulator pressure drops below a preset

pressure established by design of pilot valve (9), charging valve (8) must be shifted to permit recharging of the

accumulator. When accumulator pressure reaches its lower limit, pilot spring (10) will force the spool in pilot

valve (9) upward (as shown). Accumulator pressure is then applied through ports in pilot valve (9) to the left

end of the spool in charging valve (8), shifting the spool to the right (as shown). Since pump pressure is higher

than accumulator pressure at this time, check valve (7) will be unseated and pump flow is permitted through

the charging valve ports and check valve (7) to the bottom of accumulator (3). Orifice (11) in the check valve

seat restricts the rate of flow to accumulator (3). Orifice (12) in charging valve (8) limits flow to frame tilt

circuit while charging valve (8) is shifted to allow accumulator recharging.

10-1