BENDIX A2LS Podręcznik - Strona 4

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BRAKE APPLICATION

(ADJUSTMENT REQUIRED)

DRIVE RING-LIFTED OFF

SEATING-ROTATES RIDES

DOWN HELIX AND RE-SEATS

FIGURE 8 - ADJUSTER OPERATION

off its seat in the cylinder body. If the movement of the

adjuster shaft helix through the adjuster drive ring is less

than the axial clearance (back-lash), no rotation of the

adjuster shaft takes place. (Figure 7)

When the movement of the adjuster shaft helix through the

adjuster drive ring is greater than the axial clearance, rotation

of the drive ring relative to the adjuster shaft will occur. (Figure

8) As the adjuster shaft helix passes through the drive ring,

the drive ring, lightly loaded by the drive ring spring, will

rotate in its seat in the cylinder body. As the brake pedal is

released, the brake shoe return springs cause the brake

shoe to push the piston and adjuster shaft assembly back

through the cylinder.

BRAKES HELD ON (DRIVE RING

ALREADY SETTLED IN NEW POSITION)

SHOE RETURN

SPRING LOAD

DRIVE RING

RE-SEATED

FIGURE 9 - ADJUSTER OPERATION

BRAKES HELD ON (DRIVE RING

ALREADY SETTLED IN NEW

POSITION)

DRIVE RING

RE-SEATED

RETURN STROKE

ADJUSTMENT COMPLETED

DRIVE RING

SEATED

As the axial tolerance between the adjuster shaft helix and

adjuster drive ring is taken up, the load on the drive ring

helix forces it onto its seat. The resultant friction keeps it

from further rotation. As the piston and adjuster continue

through the cylinder, the adjuster shaft helix is forced to

rotate through the drive ring. (Figure 9) This rotation of the

adjuster shaft, relative to the piston, unscrews the adjuster

shaft from the piston, increasing the overall length of the

adjuster and piston assembly. This in turn reduces the brake

shoe lining to drum clearance.

The automatic adjustment rate is variable; each application

of the brake takes up only a percentage of the excess shoe

to drum clearance. This avoids over adjustment when the

drums get hot and expand.

Note: Due to manufacturing tolerances, it is unlikely that all

brake shoes will run at the same clearances. No

detrimental effect will result and no attempt should be

made to standardize these clearances.

MANUAL OVERRIDE MECHANISM

The manual override mechanism is used to override the

automatic adjuster to set the initial shoe to drum clearance.

This initial adjustment is made after new brake shoes have

been installed, or other maintenance work has been

performed requiring the removal of the brake drum. This

adjustment 'is necessary to avoid excessive movement of

the wheel cylinder pistons and to achieve a correct and

stabilized running clearance.

The manual override is also used to un-adjust the brakes

when removing the drum when a lipped drum condition

exists.

IMPORTANT! PLEASE READ:

The manual override should not be used as an

alternative to the auto-adjuster. It is essential that the

auto-adjust mechanism be kept in good operating

condition to insure safe and reliable brake operation.

PREVENTIVE MAINTENANCE

™

The A2LS

drum brakes normally do not require any service

except when new linings are being installed. The automatic

adjusters eliminate the need for any periodic adjustment of

the brakes. To insure safe operation of the brakes, the

following service checks should be performed.

The following is a recommended time table; the actual times

may vary depending upon the use of the vehicle and the

type of operation and condition the vehicle is exposed to.

LINE HAUL VEHICLES

Every 50,000 miles (80,000 km), six months, or 900

operating hours, whichever occurs first, perform the service

checks outlined in this manual.