Page 73 - Driving Commercial Vehicles Manual

chapter 3 — basic driving skills

Disk wheel problems
fast fact
Check your wheels before every trip. If you have disk wheels, don’t drive if
Wheel separations are you find:
usually caused by loose • loose or missing lug nuts
wheel fasteners or broken
wheels/rims, or by wheel • stripped studs
bearing failure.
• cracks in the rim.
If you find any of the following, investigate and decide whether immediate
attention is needed:
• metal or paint flakes around the nuts — may indicate wheel movement
• oil or grease leaks from the hub — if you see oil or grease, check the brake
drum area to see if there’s oil or grease on the brake pad.

Cast spoke wheel problems
fast fact
Check your wheels before every trip. If you have cast spoke wheels, don’t
Rust streaks on the rim may drive your vehicle if you find:
indicate a loose lug nut or • missing or loose nuts or rim clamps
cracks in the rim.
• cracks on the rims or hubs.
If you find any of the following, investigate and decide whether there’s a
problem that needs immediate attention:
• mismatched, bent or cracked lock rings
• oil or grease leaks from the hub — if you see oil or grease, check the brake
drum area to see if there’s oil or grease on the brake pad
• wear on the rim near the clamp or a valve stem that’s too close to a spoke
— may indicate that the rim has shifted

• rim damage — could allow the tire to lose pressure or come off.
Brake failure warning devices

All vehicles using air or vacuum brakes must be equipped with warning
devices that will warn the driver if the air-pressure or vacuum system fails.

Braking systems
Every motor vehicle must be equipped with at least two separate braking
systems. One of these systems must be mechanical, for example a ratchet and
pawl (notched wheel) or spring brake mechanism. If the foot (primary) brakes
fail, the driver must use the emergency (mechanical) brake, which requires
more time and distance to stop the vehicle.

57