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Chapter 22. Driveshaft Assemblies. Objectives (1 of 3). Identify the components in a truck driveline. Explain the procedures for inspecting, lubricating, and replacing a universal joint. Describe the various types of wear a universal joint might experience.
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Chapter 22 Driveshaft Assemblies
Objectives (1 of 3) • Identify the components in a truck driveline. • Explain the procedures for inspecting, lubricating, and replacing a universal joint. • Describe the various types of wear a universal joint might experience. • Outline the procedure for sourcing chassis vibration.
Objectives (2 of 3) • Define and explain the importance of phasing. • Explain the importance of driveline working angles and how to calculate them. • Troubleshoot some typical driveline complaints. • Describe the procedure for balancing a driveshaft.
Objectives (3 of 3) • Describe the operation of a hydraulic retarder. • Explain how an electric retarder operates.
A Stand Pipe • Ensures constant lubrication and prevents dry startup.
Shop Talk • When replacing a hanger bearing, make sure you look for and do not lose track of the shim pack that is usually located between the bearing mount and cross member. • The shims set the driveshaft angles and omitting them will result in a driveline vibration.
Shop Talk • Clean grease fittings thoroughly to remove accumulated grease and abrasives before use. • Any contaminants on the zerk nozzle can be forced through the nipple into the bearing during lubing.
U-Joint Lube Schedule • See Table 22–2 on page 650 of the textbook.
Shop Talk • On-highway operation is generally defined as an application that operates the vehicle running less than 10 percent of total operating time on gravel, dirt, or unimproved roads. • Vehicles running more than 10 percent operating time on poor road surfaces are classified as off-highway in terms of preventive maintenance.
Warning • If grease is only seen to exit from three of the four trunnion seals, the bearing is not properly lubed and will almost certainly fail. • You must take the appropriate corrective action when U-joints fail to take grease. • If a driveshaft separates because of a U-joint failure, it can take out air tanks, fuel tanks, and generally cause damage that greatly exceeds the cost of replacing a single U-joint.
Caution • Half-round end yoke self-locking retaining bolts should not be reused more than five times. • If in doubt as to how many times bolts have been removed, replace with new bolts.
Caution • When removing a driveshaft with half-round or flange-type yokes, support the weight of the driveshaft with a sling before separating the U-joints.
Caution • In cold temperatures, you should drive the vehicle immediately after lubricating driveshafts. • This activates the slip spline assembly and removes excessive lubricant. • Excess lubricant in slip splines can freeze in cold weather to a wax consistency and force the breather plug out. This would expose the slip joint to contaminants and eventually result in wear and seizure.
Shop Talk • Before removing a driveshaft, mark the slip yoke assembly and tube shaft with a paint stick to ensure the correct phasing alignment on reassembly. • If the shaft assembly is to be cleaned before reassembly, use a steel scribe to indent alignment marks.
Shop Talk • If only one end of the driveshaft requires service, disconnect that end, unscrew the slip shaft seal (dust cap) from the slip yoke assembly, and then separate the driveshaft at the slip joint. • When removing the entire driveshaft, disassemble one end at a time, laying the disconnected end on the floor carefully. • When reassembling, be sure that the arrows or marks on the shaft and slip joint are in line to keep the driveshaft yokes in phase.
Caution • If the bearing cap binds in the yoke bore, gently tap with a ball peen hammer in the center of the bearing cap. • Do not tap the outer edges of the bearing cap because this could damage either the bearing cup or the yoke.
Caution • Once in use, bearing caps and their trunnions should remain matched. • Also, never take assembly shortcuts by installing only the new bearing caps on a used trunnion, as this will usually result in a rapid failure. • Regard a U-joint cross, its four bearing assemblies, and mounting hardware as a unit and replace as such.
Caution • It makes sense to remove the grease fittings when installing a driveshaft. • If they are knocked against the yoke, they tend to shear. You can easily reinstall them after the driveshaft has been installed.
Chassis Vibration Diagnosis Flowchart • See Table 22–3 on page 659 of the textbook.
Driveshaft Troubleshooting Guide • See Table 22–4 on page 664 of the textbook.
Summary (1 of 7) • The components of a driveshaft assembly include the following: • Yoke • Universal joint • Slip spline • Hanger bearing • Propeller shaft(s) • The purpose of U-joints is to connect drivetrain components when allowing the driveshaft(s) to operate at changing angles.
Summary (2 of 7) • Two types of driveline arrangements are used to transmit torque to the drive axle carriers: the parallel-joint type and the nonparallel or broken-back driveshaft type. • Because of U-joint action, when a drive yoke turns at a constant rpm, the driveshaft speed increases and decreases once per revolution. This fluctuation in driveshaft speed requires the U-joints to be in phase.
Summary (3 of 7) • Driveline vibrations are caused by loose yokes, excessive driveshaft radial runout, slip spline joint radial play, bent driveshaft tubing, and failing U-joints. • A U-joint puller should be used to separate a universal joint from a yoke assembly. • Avoid using high impact tools such as sledge hammers, because driveshaft damage can result.
Summary (4 of 7) • After removing the U-joint cross and bearing cups from a yoke, inspect the yoke bores for bore alignment, damage, and metal burrs. • Burrs can be removed with a rat tail or half round file and emery cloth. • Measure the yoke bores for wear using a go- no-go wear gauge and check yoke bore alignment using a machined alignment bar.
Summary (5 of 7) • When diagnosing driveline vibrations, it should be noted that they often originate elsewhere in the chassis. • An electronic inclinometer is the preferred instrument for measuring driveline component angles. A protractor also may be used.
Summary (6 of 7) • A hydraulic driveline retarder uses fluid friction as the means to retard driveline rotation. The principle is similar to that of a torque converter. • The principal components of a hydraulic driveline retarder are vaned rotors and stators.
Summary (7 of 7) • Electric driveline retarders operate by absorbing the energy of motion by converting it first to electrical energy using an eddy current principle, and then dissipating it as heat. • Both hydraulic and electric driveline retarder operation can be electronically controlled.
