Document DGXzD052vZy3B2806QJOJm9yM

BULLETIN NO. S-73-9U TO ALL UNITED SALES REPRESENTATIVES SUBJECT: BRAKE LOCK TROUBLE SHOOTING GUIDE The following outline lists operating problems which could possibly be enemintered and test procedures to be used to determine which part of the system is possibly malfunctioning. Brake Lock Will Not Hold -- 6-6601 1. Check "Hot" lead from power source at dash control switch with test lamp. If test lamp does not light, check/ replace lead. If test lamp lights, switch on dash control switch and check switch terminal that leads to brake lock. If test lamp does not light, replace dash control switch. If test lamp does light, move to brake lock and check incoming lead from dash control switch. If test lamp does not light, check/replace lead from dash control switch. If test lamp does light, check for poor ground. If ground is good, brake lock is faulty or sticking. 2. To check brake lock, leave dash control switch in "On" position and place jumper wire across the two terminals momentarily. A "clicking" sound should be heard. If this "clicking" cannot be heard, brake lock solenoid is either defective or valve is jammed. To check valve and seals, remove brake lock from vehicle and mount in vise. Hold brake lock at large gold hex portion with wrench and remove \" plug stamped "out let." Remove and check valve assembly for swollen rubber parts. If all rubber parts appear to be good and valve moves freely in brake lock, the solenoid is bad and brake lock should be replaced. If rubber parts are swollen, the entire brake system should be checked for contamination and flushed before rebuilding and re installing brake lock. Brake Lock Will Not Release -- 6-6601 1. Check dash control switch to see if it is in the "Off" position. Next, disconnect lead from power source and reapply brake pedal. If brakes release, dash control switch is shorted internally and should be replaced. 2. Check and make sure brake lock has not been installed between master cylinder and a remote brake booster. 3. Disconnect line at inlet side of brake lock. If brakes release, problem is not in the brake lock. Check vehicle for brake system malfunctions. If brakes do not release, disconnect line at the outlet side of the brake lock. If brakes release, brake lock is faulty and should be replaced. 4. If brake lock is faulty, check as outlined in preceding section. General -- 6-6601 & 6-6602 1. If the brake lock seems to release by itself after a short time, check entire brake system for leaks as this will cause a like condition. 2. Install brake lock to actuate all four wheels only on trucks equipped with a vacuum booster. 3. The 6-6602 lever lock is a manually actuated control valve and should be replaced if the action of the lever lock seems erratic. If the valve sticks in the on position and the brakes will not release, test as with the 6-6601 brake lock to determine if lever lock is at fault. (See Section 3, Under Brakes Will Not Release.) i 13