Chapter 8. BRAKE, WHEEL, AND TIRE REPAIR INSTRUCTIONS

TM 10-3930-621-34

CHAPTER 8

BRAKE, WHEEL, AND TIRE REPAIR INSTRUCTIONS

Section I. SERVICE BRAKE

8-1. Description

The hydraulic brake system is of the full floating,

8-3. Brake Drum

selfcentering, self-adjusting type which consists of a

a. Removal and Cleaning. Refer to TM 10- 3930-

mechanically actuated master cylinder transmitting

621-12 for removal and cleaning procedures.

hydraulic pressure through heavy duty brake lines to

b. Inspection and Repair.

wheel cylinders. The wheel cylinders are of the double-

(1) Check inside diameter of brake drum at 45

ended type, with actuating links extending from each of

intervals, around circumference, using a micrometer or

the cylinders. The links transmit movement from the

diameter bar and thickness gages. If diameter difference

cylinders to the brake shoes. The top of each shoe

exceeds 0.010 inch or radius difference exceeds 0.005

moves freely in a wear plate, while the bottom of the

inch, resurface drum.

shoe transfers movement from the hydraulic wheel

(2) Examine drum for scoring or 'it, at checking.

cylinders. Wear adjustment for brake linings is made

Resurface drum if score marks can be felt or any heat

automatically in normal use by the self-adjusting

checking can be seen. Heat check cracks form cutting

mechanism. The shoes are held against the brake wear

edges, which quick shave off lining surfaces.

plates, wheel cylinder links, and adjusting eccentrics by

(3) Check drums for "bell mounted" or "barrel

tension springs, which maintain the shoes in equilibrium.

shaped" wear by placing drum on drum lathe and

advancing tool until it contacts drum at its high points.

8-2. Brake Shoes

Then advance tool to contact low) points. Measure the

a. Removal. Refer to TM 10-3930-621-12 for removal

difference and resurface the drum, if difference exceeds

procedures.

0.005 inch (radius).

b. Repair.

(4) If drum requires resurfacing, proceed as follows:

(1) Minor charring, dirt, or grease on brake

(a) Resurface in pairs

linings (not grease soaked) should be remedied by

(b) Machine to same diameter

buffing with sand paper or grinding.

(2) Clean shoes with compressed air and dry

which will cause rapid wear if they remain

cloth to prevent damaging shoes or linings.

(5) If-drum does not require resurfacing. polish with

Caution: Whenever handling brake shoes, be

fine emery cloth to remove discolorations or old lining

careful not to get grease or dirt on brake linings as

residue.

serious damage will result.

c. Installation. Refer to TM 10-3930-2 1-12 for

c. Replacement. Brake shoes employ bonded

installation procedures.

lining. When replacement becomes necessary, a similar

8-4. Wheel Cylinder

type of lining must be installed. Replace shoes (TM 10-

a. Description. The hydraulic wheel cylinder houses

3930-621-12) when the following have occured:

two opposed pistons, which actuate t, t. opposed brake

(1) Drums are resurfaced

shoes. Pistons, rubber ('.-I, , arid springs are held in the

(2) Lining is worn to shoe table

cylinder by pressure from the brake shoes. Open ends

(3) Grease or hydraulic fluid has soaked linings,

of the cylinder are protected by rubber boots.

causing brakes to grab or pull to one side.

b. Removal. Refer to TM 10-3930-621-12 for

(4) Charred or burned linings.

removal procedures.

(5) Lining scored deeply.

c. Disassembly.

(6) Brake shoe table worn, twisted or out-of-

(1) Refer to figure 8-1 and disassemble as

round.

follow-:

(7) Shoe is cracked.

(2) Remove, rubber , boots (2 and 9) and ,con-

d. Installation. Refer to TM 10-3930-621-12 for

necting link (1 and 10) from cylinder ends.

installation procedures.

8-1