4. Use crocus cloth or a hone to remove deposits or minor surface irregularities. If
bore does not clean up readily, replace cylinder.
5. Inspect tapped holes of cylinder for thread damage. Use a tap to clean up minor
damage. Replace cylinder if threads are damaged due to cross-threading or of or
fittings.
6. Check passage in bleeder screw. Use a piece of fine wire to open passage if
blocked. Also check threads for damage. Replace bleeder screw if threads cannot
be cleaned up.
7. Piston movement should be smooth.
1.6.4 Assembly
1. Lubricate cylinder bore, spring, cups, and pistons with clean brake fluid. Install into
cylinder. Open side of cups and flat side of piston must be toward inside of cylinder.
2. Install rubber boots making sure they engage grooves on cylinder.
3. Install bleeder screw into cylinder but do not tighten.
1.6.5 Installation
1. Position wheel cylinder, install and lock washers, and tighten to 15-20 ft-lbs
torque.
2. Spread brake shoes apart enough to allow projections of brake shoes to engage
cylinder properly.
3. Connect brake line to wheel cylinder. Tighten tube fitting firmly. Do not over
tighten.
4. Bleed brake system as described in Chapter 2. Check for leaks when bleeding
system.
5. Install brake drum as described in paragraph 1.5.4.
After initially mounting wheel and tire assembly, recheck lug nut torque
after the first hour of operation and after the first 8 hours of operation. After this, check
monthly or every 250 hours, whichever comes first. Do not lube wheel studs as it will result
in inaccurate tightening torque. Failure to follow these procedures could result in wheel
mounting failure and loss of vehicle control.
6. Install wheel assembly and tighten 9/16 lug nuts (rear) per Chapter 2. Remove
safety stands and lower tractor.
1.7 POWER BOOSTER/MASTER CYLINDER ASSEMBLY
A hydraulically operated unit called a “power booster” supplies the power-assist to the
master cylinder, much like the vacuum booster found in most automobiles. The power
CHAPTER 3 OVERHAUL AUGUST 31, 2008
1 GENERAL REPAIR PAGE 11
M140 Tow Tractor Manual No. 46054
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