4-39. MAINTENANCE AND ADJUSTMENTS (Cont)
c. Refilling Hydraulic Brake System.
(1) Prior to refilling, the entire hydraulic system should be flushed with clean denatured alcohol.
Use denatured alcohol only, as other cleaning agents will swell and
soften rubber parts in the system necessitating replacement of the part.
(2) TO flush, remove vent tube assembly (fig. 4-38) and filler cap from top of hydraulic master cylinder
and fill cylinder reservoir with denatured alcohol. As in bleeding procedures (b above), open each
wheel cylinder bleeding screw in turn and pump brake slowly until the passage of clean fluid
indicates a clean system. After flushing, repeat process using clean silicone brake fluid to force all
of the flushing agent from the system.
(3) TO refill, remove vent tube assembly and filler cap from master hydraulic cylinder and add silicone
brake fluid to a level of 1/2 to 3/8 inch below top of cylinder reservoir. Bleed system (b above).
Install filler cap and vent tube assembly.
d. Air and Hydraulic Lines and Fittings Tests and Checks.
(1) With air hose couplings (fig. 2-6) connected to towing vehicle and brakes applied, coat air lines,
couplings, and connections with soapsuds. No leakage is permissible.
(2) Leakage at couplings is usually caused by worn, damaged, or improperly installed gaskets. Install
new gaskets to stop leaks.
(3) Tighten air line connectors to stop leakage.
(4) Tighten fittings on air lines and air and hydraulic hose. Inspect lines for partial restrictions caused
by dents or kinks. inspect hose for wear, cuts, or breaks. Replace with new piece of tubing, hose
or fitting if damaged or if leak cannot be stopped.
e. Slack Adjuster Operating Test. Adjust brakes (a above). Apply brakes several times and note adjuster.
Push rod should move 3/4 inch but not over two inches for full application of brakes. If slack adjuster moves
without turning brake camshaft, replace slack adjuster.
f. Air Chamber Tests.
(1) Model M127.
(a) Leakage test. With air hose couplings (fig. 2-6) connected to towing vehicle and brakes
applied, coat air chamber's flanges, connections, and plug with soapsuds to check for leakage.
No leakage is permissible. If leakage is found at fIanges, tighten fIange screws evenIy and
sufficiently to stop leak. If leakage is found at connection or plug, tighten connector and plug.
Do not tighten flange screws too tight, as it will distort flanges and
cause new leakage.
(b) Air chamber push rod travel tests.
Purpose. Excessive air chamber push rod travel will result in damage to rubber cup in
hydraulic master cylinder. Insufficient travel will result in ineffective brakes.