Section VI. AXLE ALIGNMENT PROCEDURE

TB 9-2510-242-40

Section VI. AXLE ALIGNMENT PROCEDURE

6-1 Perform Pre-alignment Activity. Before aligning axles, complete all frame structure repairs. Make repairs

according to applicable paragraphs of section V. Inspect all suspension items for damage and repair or replace as

necessary. Suspension items to be inspected are grouped into three categories: springs, axles, and wheels.

6-2 Normalize Suspension Loading. The trailer's suspension assembly shall be in a normalized (relaxed) working

position and free of abnormal stress before making required measurements. Perform the alignment on a level floor.

There shall be no load on the trailer other than permanently attached fittings or standard accessories that remain on it at

all times.

6-3 Position Trailer. To ensure that the suspension is in a normalized position, keep the trailer on the level floor area

and move it back and forth at least two times. The distance moved in each direction shall be no less than one complete

wheel rotation. During this back and forth movement do not engage the trailer's brakes.

6-4 Check and Adjust Lateral Position. For all measurements, use a calibrated tape measure. The center line of the

axle and the center line of the semitrailer shall be within 1/4 inch of each other. Trailer alignment measurements are

a. Determine Lateral Position. To determine the lateral position of each axle, measure the distance between

each wheel (tire sidewalk, rim edge, brake drum edge, brake backing plate) and frame side rail edge or web. The

measured dimensions, A and B for each axle, must be within 1/4 inch of each other.

b. Adjust Lateral Position. When the A and B dimensions exceed the 1/4-inch allowance, jack up the trailer frame

so that the axle's wheels are off the floor. Loosen the axle mounting bolts and shift the axle one-half of the difference

between A and B in the direction of the smaller dimension. Re-tighten the axle mounting bolts and lower the wheels back

onto the floor. Recheck the A and B dimensions. Repeat the positioning procedure until the lateral position is correct.

6-5 Check and Adjust Longitudinal Position. The longitudinal (fore and aft) position is a check of the axle's

perpendicularly (squareness) to the trailer's center line. The front (No. 1) axle shall be checked and adjusted first.

Additional axles are then checked and adjusted using the No. 1 axle as a point of reference.

a. Axle No. 1. Determine the longitudinal position of the first axle by measuring the distance from the lunette

(kingpin in the case of semitrailers) to each end of the axle's centerline. The measured dimensions, C and D, shall be

within 1/8 inch of each other. When the axle does not have a distinctive feature that locates its centerline, place a piece

of masking tap on each hub, measure each hub's diameter, and locate and mark each hub's center on the masking tape

with a fine point pen or pencil. If the difference between C and D exceed 1/8 inch, jack up the