4-34. ADJUST BRAKES (CONT).
Do not work under trailer unless the wheels of the truck and trailer are chocked, the trailer is
on level ground and the truck engine is shut off. Failure to chock wheels of truck and
trailer could cause serious injury or death to personnel.
An assistant must be in the truck cab at all times while checking brakes under trailer to
prevent truck movement. Failure to have an assistant in truck cab to prevent truck
movement could cause serious injury or death to personnel.
Do not hook up trailer drawbar or trailer safety chains while checking brakes under truck.
If trailer safety chains or drawbar are hooked up, the trailer could be dragged if the truck
should move, causing serious injury or death to personnel.
With the aid of an assistant, start truck and
allow air pressure to build up to 100 psi (689
Measure distance between center of large
clevis pin (7) and bottom of brake
chamber (1) (measurement C), with brake in
released position. Record measurement.
With the aid of an assistant, apply brakes
while measuring distance from center of
large clevis pin (7) to bottom of brake
chamber (1) (measurement D).
The adjusted stroke must not exceed two in. (51 mm), or damage to the brakes may result.
The adjusted stroke should be as short as possible, but not so short that the free stroke is
less than 5/8 in. (16 mm).
The button must be pulled out before turning the manual adjusting nut or damage to
equipment will result.
The difference between the measurements D and C is the adjusted chamber stroke.
Pull out button (2) and turn manual adjusting nut (4) on slack adjuster (3) to adjust the brake. The
adjusted stroke length must not exceed two in. (51 mm).