4. Place rags under booster and master cylinder assembly. Disconnect all hoses and
pipes from booster and master cylinder.
5. Plug hoses, pipes, and booster ports to prevent entry of dirt, water or other
contaminants.
6. Remove hardware securing power booster to bracket and remove booster
assembly.
Do not carry brake booster by accumulator, allow brake booster to fall on
accumulator or expose brake booster to heat or flame. It contains high pressure gas and
can leak under pressure and explode if heated.
1.7.2 Repair
Repair of the power booster/master cylinder assembly is not recommended. If faulty,
replace entire unit.
1.7.3 Installation
1. Position power booster assembly on bracket and secure booster with its mounting
hardware. Tighten to 30 ft-lbs torque.
2. Bleed air from master cylinder.
a. Fill reservoir with DOT 3 brake fluid.
b. Using two plastic or rubber tubes, each approx. 5 inches long, place one
end of each tube into one of the master cylinder ports and place other end
in reservoir.
c. Move booster piston back and forth until no more bubbles appear.
d. Remove tubes and connect brake lines to master cylinder.
3. Connect brake lines to master cylinder and tighten.
4. Connect fittings to power booster and tighten.
5. Bleed air from Hydro-boost unit as follows:
a. Fill pump reservoir.
b. Crank engine for several seconds with coil wire or fuel pump wire
disconnected. DO NOT START ENGINE.
c. Check fluid level and add if necessary.
d. Start engine.
e. Turn wheels, lock-to-lock, twice.
f. Stop engine.
g. Discharge accumulator by depressing brake pedal five times.
h. Repeat steps (a) through (g).
CHAPTER 3 OVERHAUL AUGUST 31, 2008
1 GENERAL REPAIR PAGE 13
M140 Tow Tractor Manual No. 46054
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