Most of us hate to take tests…but this is one test you get to give. See if your WW2 jeep will pass!
a. Introduction. If the hydraulic brake system, and the drum and brake shoe clearance are satisfactory, when brake pedal is depressed with sufficient force to set brakes firmly, the pedal will have a “solid” feel, with at least 2 inches of floorboard clearance. During the initial 1/4 to 1/2 inch of pedal travel, the pedal should move freely (if pedal clearance is correctly adjusted). The sub-paragraphs below furnish probable remedies for various behaviors of a defective brake system, based on the behavior of the brake pedal as a symptom.
b. Pedal Has Less than 2 Inches Floorboard Clearance. Adjust clearance between brake shoes and drums.
c. Pedal Has a “Springy” Feel. This is usually evidence that the brake shoes are improperly set, or have been relined with incorrect thickness of lining. Improper shoe setting would indicate need of a major brake adjustment. Before making a decision on this type of condition, road test the vehicle (or test it on a brake machine). This will indicate a “hard” pedal and a “poor” stop, if these conditions are present. After road or machine test, pull wheels, check lining thickness, contact, drum condition, fit of shoes to drum, and anchor adjustment, to determine exact cause of difficulty.
d. Pedal Has a “Spongy” Feel. Bleed air from hydraulic system.
e. Pedal Jams or Binds. Check for mechanical interference; also check for broken piston stop wire in master cylinder. Check master cylinder mountings and linkage, and if a booster is used, check mechanical linkage between master cylinder and booster.
f. Pedal Goes to Floorboard and Can Be Built Up by Pumping. If pressure can be built up, hold down hard to see if pressure will decrease. After holding l/2 minute, reduce pressure on foot without releasing pedal, and press lightly to see if pedal moves down under light pressure. This test will reveal a master cylinder cup which is thin, permitting fluid to bypass within the master cylinder without showing signs of leaking on the outside of the master cylinder.
g. Pedal Goes to Floorboard and Cannot Be Built Up by Pumping. Check fluid level in master cylinder reservoir. If insufficient fluid is present, test brake pedal action and perform operations described under new symptom. If sufficient fluid is present, continue with operations described in this sub-paragraph. Where accessible, feel the master cylinder boot to determine if wet with brake fluid. Squeeze boot with fingers; if fluid is expelled around or through boot, it is an indication that the master cylinder is leaking and should be removed, inspected, repaired, or replaced. If no evidence of leaks is apparent at the master cylinder, inspect all fluid lines along the frame, all hose and hose connections, the bottom edges of all brake flanges, and the inner side wall of tires for signs of brake fluid leakage. If no external signs of leaks are found, but pedal still leaks off under pressure, pull all four wheels and inspect the wheel cylinders. If no external fluid losses are found, but pedal “eases down” under constant but light foot pressure, it is a good indication that pressure is bypassing within the master cylinder; in which case, remove and repair or replace.
For even more maintenance information, you can get a copy of TM 9-803 (including other important jeep maintenance manuals form Amazon.com – The Complete WW2 Military Jeep Manual.