Chapter 16

Standard Transmission

Servicing

Objectives (1 of 2)

• Explain the importance of using the correct lubricant and maintaining the correct oil level in a transmission.

• List the preventive maintenance inspections that should be made periodically on a standard transmission.

• Explain how to replace a rear seal.

• Describe the procedure for troubleshooting standard transmissions.

Objectives (2 of 2)

• Identify the causes of some typical transmission performance problems, such as unusual noises, leaks, vibrations, jumping out of gear, and hard shifting.

• Outline the procedure for overhauling a transmission.

• Analyze the procedure for performing failure analysis on transmission components.

• Troubleshoot an air shift system.

Recommended Lubricants

• Recommended lube– Use only the recommended lube.

• Synthetic lube– Most transmission manufacturers today prefer synthetic

lubricants. • E-500

– Eaton recommends E-500 lubricant. It is designed to run 500,000 linehaul miles with no initial drain interval required.

• E-250– Lubricant is rated for 250,000 linehaul miles before a change is

required. • Synthetics exceed requirements

– They can be expected to perform effectively through various geographic and seasonal temperature conditions.

Mineral-based Lubes

• Initial oil change– Will flush out of the transmission any cutting debris

created by virgin gears meshing– Linehaul

• Any time after 3,000 miles, but before 5,000 miles – Off-highway

• After 24 and before 100 hours of service• Oil change intervals

– Linehaul: Oil change intervals vary between 50,000 and 100,000 miles for linehaul applications.

– Off-highway: Off-highway operation usually requires oil change intervals ranging from 1,000 hours to a maximum of 2,000 hours of service.

Synthetic-based Lubes

• E-500: E-500 is designed for 500,000 linehaul miles.

• Initial drain: The initial drain interval, once considered so important to maximize transmission service life, can be eliminated.

• E-250: E-250 lubricant is rated for 250,000 linehaul miles.

Caution

• Do not add transmission lubricant without first checking what lubricant the transmission is using.

• Mineral-based gear oils, mineral-based engine oils, and synthetic gear lubes are all approved for use in transmissions and none of them are particularly compatible. Mixing transmission oils causes accelerated lube breakdown, resulting in lubrication failures.

Checking Oil Level

• Check at each A-type service, typically at intervals of 5,000 or 10,000 highway miles.

• Avoid mixing brands, weights, and types of oil.

• The transmission oil level should be exactly even with the filler plug opening as shown.– Overfilling can cause oil

aeration.– Under-filling results in oil

starvation.

Shop Talk

• Transmission oil should be exactly level with the filler plug opening.

• One finger joint equals approximately one gallon of transmission oil, so testing oil level by dipping your finger into the oil filler hole is not a good practice.

Caution

• Do not overfill the transmission. – Overfilling usually results in oil breakdown due

to aeration caused by the churning action of the gears.

– Premature breakdown of the oil will result in varnish and sludge deposits that plug up oil ports and build up on splines and bearings.

Shop Talk

• When draining transmission oil, check for metal particles in the oil. – Metal particles may indicate excessive wear

and may warn of an imminent failure. – It is not unusual for a newly broken in

transmission to have minute metal particles held to a magnetic drain plug.

Preventive Maintenance Inspections

• Preventive maintenance (PM) can help avoid failures, minimize vehicle downtime, and reduce the cost of repairs.

• Often, transmission failures can be traced directly or indirectly to poor maintenance.

Daily Maintenance

• During the drivers daily pre-trip: – Air tanks

• Drain air tanks to remove water or oil.

– Oil leaks• Visually check for oil leaks.

– Shifting performance• Report any shifting performance problems

such as hard shift or jumping out of gear.

B Inspection PM

• Air control system– Check for leaks.

• Bell/clutch housing flange– Check fastener torque.

• Clutch shaft yoke bushings– Grease clutch shaft bushings

lightly. – Pry upward on the shaft to

check for wear. • COE remote shift linkage

– Lube U-joints and check for wear.

– Check any bushings in the linkage for wear.

• Air filter– Check and clean or replace

the air filter element. • Transmission output yoke

– Uncouple the U-joint and check the flange nut for proper torque.

– Tighten if necessary. • Output shaft assembly

– Pry upward on the output shaft to check radial play in the mainshaft rear bearing.

– Check the splines on the output shaft for wear from movement and chucking action of the U-joint yokes.

C Inspection PM

• Oil life– If an oil change is required, drain and refill the transmission with the

specified oil. • Transmission oil analysis can be used to establish more precise oil

change intervals that are better suited to the actual operating condition of the truck.

• Gearshift lever – Check for bending and free play in the tower housing.

• Oil shift tower assembly– Remove the air lines at the slave valve and remove the shift tower from

the transmission. – Check the tension spring and washer for wear and loss of tension. – Check the gearshift lever spade pin/shift finger for wear. – Also take a look at the yokes and blocks in the shift bar housing,

checking for wear at all critical contact points.

Preventive Maintenance Recommendations

• See Table 16-1 on page 469 of the textbook.

Caution

• Using a 1-inch air gun to tighten yoke retaining nuts should be avoided, although it is all right to remove the nut using this tool.

• Many fasteners are bored completely through the housing.– These fasteners must have thread sealant applied to

the threads. • If oil leakage is observed at the PTO covers,

replace the PTO cover gaskets and thoroughly clean the fasteners and their mating threads before reinstalling.

Shop Talk

• Always check for a plugged transmission breather when identifying the cause of a transmission oil leak. – When transmission oil is raised from cold to

operating temperatures, it expands to occupy a greater volume. If the breather is plugged, this can cause seal failure.

Rear Seal Replacement

Shop Talk

• Do not attempt to repair a visibly worn or damaged yoke by polishing it with crocus cloth. – Minor scratches can either track oil under the

seal or draw in contaminants.

Caution

• Do not over-torque the yoke nut, which can damage the bearing.

• Do not perform this operation using a 1-inch air gun.

Shop Talk

• Wear rings that increase the original yoke diameter can cause the new seal to wear more rapidly due to increased seal lip pressure.

Transmission Troubleshooting Guidelines

• See Table 16-2 on pages 476-477 of the textbook.

Towing Precautions

Caution

• When the driveline or axle shafts are reinstalled:– The axle nuts must be tightened to the correct

torques (Refer to the specific service manual for the correct torque values.)

– The axle shafts properly installed (RH and LH)

– The drive shafts properly phased

General Transmission Removal Practices

• Caution – Ensure that the transmission does not hang by

the input shaft in the pilot bearing bore in the flywheel.

– The clutch assembly, pilot bearing, and input shaft can be damaged if the transmission is supported by the input shaft.

Shop Talk

• Engine torsionals refers to the frequency of torsional pulses delivered to the drivetrain as the force of each cylinder power stroke is unloaded into the crankshaft. – Because of today’s practice of managing

engines at slower speeds and higher torque to produce better fuel economy, lower frequency torsionals are produced and this has caused some transmission failures.

Analysis of Bearing Failures

• Fretting– The bearing outer race can

pick up the machining pattern of the bearing bore.

– It can be mistakenly diagnosed as one that has spun in the bore.

• Contamination– Scoring, scratching, and

pitting of bearing contact surfaces identify contamination failures.

– It is caused by very fine particles suspended in the lubricant or by the use of older EP (extreme pressure) oils.

Shop Talk

• Store new bearings in their shipping wrappers until ready for use.

• Used bearings should be cleaned in solvent, lubricated, and wrapped in greasy paper until ready for installation.

Timing Transmissions

• Multiple countershaft transmissions must be timed during assembly.

• Timing ensures that the countershaft gears contact their mating mainshaft gears in phase to properly distribute the torque load. – When timing a transmission, follow the OEM procedure.

• In the typical truck transmission used as an example in this chapter: – In the main section, it is necessary to time only the drive gear

set. – In the auxiliary section, depending on the model, only the low

range, deep reduction, or splitter gear sets have to be timed.

Timing the Front Section (1 of 2)

• Before placing each countershaft assembly into the housing, mark the tooth located directly over the keyway of the countershaft drive gear. – In many transmissions,

you might find that this tooth is stamped with an “O” to identify it.

• Mark any two adjacent teeth on the main drive gear.

Timing the Front Section (2 of 2)

• Mark the two adjacent teeth located directly opposite the first set marked on the main drive gear. – There should be an equal

number of unmarked gear teeth on each side between the marked teeth.

• After the mainshaft and countershaft are installed into the housing, the marked teeth should be meshed exactly as shown.

Timing the Auxiliary Section (1 of 2)

• The specific gears on the mainshaft and countershafts that must be marked differ, depending on the auxiliary gearbox design.

• Mark any two adjacent teeth on the mainshaft gear of the set to be timed. – Then mark the two

adjacent teeth located directly opposite the first set marked.

Timing the Auxiliary Section (2 of 2)

• Mark the tooth stamped with an “O” on gear to mate with timed the mainshaft gear.

• Install the mainshaft gear in position on the range mainshaft or output shaft.

• Place the auxiliary countershaft assemblies into position and mesh the marked teeth of mating countershaft gears with the marked teeth of the mainshaft gear.

• Fully seat the rear bearings on each countershaft to complete the installation.

Summary (1 of 6)

• Scheduled lubrication services are key to a good transmission maintenance program.

• Standard transmissions depend on splash lubrication, meaning that some of the rotating components contact, pick up, and circulate oil from the oil in the sump. – Maintaining the correct oil level is critical for

splash lubrication to be effective.

Summary (2 of 6)

• Only lubricants recommended by the transmission manufacturer should be used in a transmission. – These could be either gear or engine oils.

• It is usually recommended that the first oil change be performed shortly after the transmission enters service, often between 3,000 and 5,000 miles of operation in a linehaul application, or less in vocational service.

Summary (3 of 6)

• In general linehaul application, it is good practice to schedule a transmission oil change from 50,000 to 100,000 miles of service.

• Good preventive maintenance (PM) lowers the incidence of breakdowns, minimizes downtime, and reduces the cost of repairs.

Summary (4 of 6)

• Leakage in transmission rear seals is a relatively common problem in truck transmissions, but one that is easily repaired.

• When diagnosing transmission complaints, it is important that you confirm that the transmission is the actual cause of the problem before removing it for repair.

Summary (5 of 6)

• When disassembling a transmission, each component should be carefully inspected for abnormal wear and damage. – Components that are not reusable should be

ordered after disassembly, not discovered during reassembly.

• Ensure that a cause of failure is determined before reassembly, or the failure is likely to recur within a short period.

Summary (6 of 6)

• Bearing failures occur because of dirt contamination and poor lubrication. – More than 90 percent of bearing failures are

caused by dirt. – Cleanliness is critical when repairing and

servicing standard transmissions.