Document 8RKjyNEvY04nn1ZJ3w7G4KNDm

Testing and Adjusting Power Brakes > Road test by making brake applica tion at 20 mph to see if car stops evenly and quickly. If brakes are spongy, bleeding of hydraulic lines is in order. With engine stopped and transmis sion in neutral, apply brakes several times to remove all vacuum in system. Depress brake pedal, hold light foot pressure on pedal and start engine. If vacuum system is functioning properly, pedal will tend to fall away under foot pressure, and less pressure will be re quired to hold pedal in applied position. If no action is felt, vacuum system is not working. Stop engine and again remove all vacuum in system. Depress brake pedal and hold pressure on pedal. If pedal gradually falls away, hydraulic system is leaking. There are no special adjustments for power brakes. Before investigating power system for trouble, check con ventional hydraulic brake system for usual sources of trouble. However, at same time as conventional braking sys tem is being checked, make following inspections on power system. Check vacuum lines and connections between intake manifold, check valve, vacuum reserve tank (Fig. 63) and vacuum power cylinder for possible vacuum leaks. Check fluid in master cylinder reservoir; level should be Vi in. from top of filler plug opening. Check condi tion of air cleaner hair and insert clean hair if necessary. Check mechanical con nections between foot pedal and power unit. Use only recommended brake fluid for refill. Observe brake pedal height when brakes are fully applied and engine is running. If clearance between pedal pad and floor is less than one inch, adjust shoe-drum clearance to proper setting. Spring and fall, or at least every 10,000 mi., remove intake manifold tee connector (vacuum supply) and clean. This connector tends to "coke up'' and restrict vacuum line if not cleaned periodically. Brake troubles especially peculiar to power brake system are as follows: Bleeding Power Brakes The bleeding of the integral type is the same as conventional hydraulic sys tem. Bleeding of auxiliary system dif fers in that the slave cylinder must be bled first, then the wheel cylinders. (See Figs. 59 and 60 for location of bleeder point, some have one, others two as shown.) Pedal Almost Goes To Floor: (1) Fluid reservoir needs replenishing; (2) Power brake hydraulic leakage due to compensating valve leak, hydraulic plunger seal leak, compensating port or output port fitting seal leak, leaks at wheel cylinders or in pipes and con nections. Brakes Fail To Release (Or Slow Release): (1) Bound up brake pedal mechanism; (2) Power brake unit trouble due to faulty residual check valve, excessive hydraulic plunger seal friction, faulty compensating port, excessive piston packing friction, re stricted air passage, piston stroke inter ference, sticky sliding valve, broken piston return spring. Hard Pedal: (1) Vacuum failure due to faulty vacuum check valve, col lapsed vacuum hose, plugged vacuum fittings; (2) Bound up pedal mecha nism; (3) Power brake unit trouble due to internal vacuum hose looseness or restriction, jammed sliding valve, vacu um leaks in unit caused by loose screws in piston plate or faulty packing and seals, broken reaction spring. Grabby Brakes: Power brake unit valve trouble due to reaction diaphragm leakage of faulty rubber bump er pad, sticking sliding valve action, restricted diaphragm passage. *