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Chapter 27. Wheels and Tires. Objectives (1 of 2). Identify the wheel configurations used on heavy-duty trucks. Explain the difference between standard and wide- base wheel systems and stud- and hub-piloted mountings.
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Chapter 27 Wheels and Tires
Objectives (1 of 2) • Identify the wheel configurations used on heavy-duty trucks. • Explain the difference between standard and wide- base wheel systems and stud- and hub-piloted mountings. • Identify the common types of tire-to-rim hardware and describe their functions. • Explain the importance of proper matching and assembly of tire and rim hardware. • Outline the safety procedure for handling and servicing wheels and tires. • Describe brake drum mounting configurations.
Objectives (2 of 2) • Perform wheel runout checks and adjustments. • Properly match tires in dual and tandem mountings. • List the major components of both grease- and oil-lubricated wheel hubs. • Perform bearing and seal service on grease-lubricated front and rear wheel hubs. • Perform bearing and seal service on oil-lubricated front and rear wheel hubs. • Perform front and rear bearing adjustment. • Describe TMC wheel-end procedure. • Outline the procedure for installing pre-set bearing wheels.
Shop Talk • Learn how to identify stud- and hub-piloted disc wheels: Improper torquing procedure and sequencing of stud-piloted wheels is a major cause of wheel failure. • With the cone locknut design, a flat washer is seated directly against the wheel face. The nonrotating washer prevents galling of the wheel surface.
Shop Talk • Revolutions per mile data on the drive axle tires must be correctly programmed to the chassis data bus. • Whenever tires are replaced or swapped on a vehicle, ensure that you check and reprogram tire revolutions per mile to the appropriate controller on the chassis data bus. • This data is used to calculate and broadcast road speed data to the instrument cluster, engine, transmission, collision warning, and other controllers networked to the data bus.
Shop Talk • Contrary to the beliefs of some truck drivers, tire pressure cannot be checked with a hammer. • The only condition a hammer can identify is a completely deflated tire. • Tire pressures must be checked with a pressure gauge. In fleets where this is not a driver’s responsibility, it must be done by a technician.
Shop Talk • Manufacturers of speed restricted tires, such as the off-highway lug caution operators not to exceed the speed limits and guidelines in their manuals. • To alert the operator, a decal located in the cab warns of the limitations of speed restricted tires.
Shop Talk • Tires are a major fire hazard when trashed and stored in large quantities. • Once a tire fire has ignited, it can be almost impossible to extinguish. • Federal and state regulations have made operators and garages liable for ensuring that tires are stored and disposed of legally.
Caution • You cannot learn tire and wheel service procedure from a book alone. • Before working on tires and wheels make sure you have received some hands-on training.
Caution • When handling tire assemblies, remember to lift properly, using your legs rather than your back.
Caution • Never raise a vehicle with a jack placed under a leaf spring. • When the wheel has been raised, use heavy-duty axle stands placed under the axle and do not rely on a hydraulic jack alone.
Shop Talk • The valves used on truck tires are known as Schrader valves, identical to those used on cars and bicycles. • It is probably the only common component found on all vehicles ranging from a bicycle to the heaviest off-highway earth moving equipment.
Shop Talk • Disc wheel nuts for right side wheels generally have right-hand threads, and wheel nuts for left side wheels usually have left-hand threads.
Caution • Igniting quick start (ether) inside a tire is a common but dangerous practice used to seat tire beads. • The explosion that results depends on the proportions of air and ether combined inside the tire. • Get this mixture wrong and you could injure yourself and others.
Caution • Watch your fingers and back when installing tire/rim assemblies onto cast spoke wheels. • It is good practice to wear gloves, and lifting with the tire/rim behind you is easier on your back.
Caution • To check and tighten the inner wheel torque, first loosen the outer wheel nuts several turns and tighten the inner nuts, then retighten the outer nuts. • To avoid losing the seating of the outer wheel when checking the inner wheel torque, loosen alternate outer nuts, tighten the inner nuts, and retighten the outer nuts. Then loosen the remaining outer nuts, tighten inner nuts, and retighten the outer nuts. • OEMs suggest that disc wheels require weekly inspects and torque checks.
Shop Talk • If pulling more than one wheel, be sure to keep all of the components of each wheel together and separate from the other wheels.
Caution • Never allow a bearing roller to be spun by compressed air because the friction that results can damage the hard surfaced contact areas.
Caution • Never use oxy-acetylene torches to heat aluminum hubs. • This type of localized heat can weaken and often destroy the aluminum. • If an oven is not available, you should replace the hub and bearing assembly as a unit.
Shop Talk • To ease the installation of the bearing cup into the hub, the cup can be cooled (by dry ice or in a freezer), a procedure that stresses both the bearing cup and hub more evenly. • Aluminum hubs are required to be heated in an oven to get the cup to drop into place.
Caution • Never pack wet bearings with grease. • Grease coated wheel bearings inhibit the ability of gear lube to properly lubricate the bearing assembly.
Caution • Never hammer or use a punch directly on any part of a seal. • Force must be applied evenly around the outer edge to avoid cocking the seal. • Wheel seals are expensive. Failed wheel seals are more expensive because of the labor required to replace them!
Shop Talk • The reason dry bearings are seldom used on current equipment is that grease does not lubricate as effectively as gear oil. • Gear oil has a much wider temperature operating range than grease.
Caution • Avoid using brass drifts to drive out wheel seals if you plan on reusing the bearing— brass particulate is difficult to remove from a bearing.
Shop Talk • Wheel seal replacements are routine service facility activities. • Because of the cost of seals, trainee technicians do not commonly practice seal replacement in a training environment. • The first couple of times you replace wheel seals in a real-world setting, read the instructions and ask questions. The bottom line is that if you experience comeback failures after replacing wheel seals, your days as a truck technician will not last long.
Summary (1 of 7) • Wheels and tires must be properly inspected during daily driver inspections and on preventive maintenance schedules. • Improperly mounted, matched, aligned, or inflated tires create potentially dangerous on-road situations. • Wheel bearings and wheel seals are key to keeping the wheel assemblies turning smoothly and safely.
