chapter 16 bennet

8/10/2019 Chapter 16 Bennet

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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 failureanalysis on transmission components.

Troubleshoot an air shift system.


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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.


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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 maximizetransmission service life, can be eliminated.

E-250: E-250 lubricant is rated for 250,000

linehaul miles.


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Checking Oil Level

Check at each A-typeservice, typically at intervalsof 5,000 or 10,000 highwaymiles.

Avoid mixing brands,weights, and types of oil.

The transmission oil levelshould be exactly even withthe filler plug opening asshown.

Overfilling can cause oilaeration.

Under-filling results in oilstarvation.


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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 levelby dipping your finger into the oil filler hole is

not a good practice.


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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.


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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.


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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.


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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 problemssuch as hard shift or jumping out of gear.


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B Inspection PM

Air control system Check for leaks.

Bell/clutch housing flange Check fastener torque.

Clutch shaft yoke bushings

Grease clutch shaft bushingslightly.

Pry upward on the shaft tocheck for wear.

COE remote shift linkage Lube U-joints and check for

wear. Check any bushings in thelinkage 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 propertorque.

Tighten if necessary.

Output shaft assembly Pry upward on the output

shaft to check radial play inthe mainshaft rear bearing.

Check the splines on theoutput shaft for wear frommovement and chuckingaction of the U-joint yokes.


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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 oilchange intervals that are better suited to the actual operatingcondition 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.


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Caution

Using a 1-inch air gun to tighten yoke retaining nutsshould be avoided, although it is all right to removethe 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 thoroughlyclean the fasteners and their mating threads beforereinstalling.


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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 tooperating temperatures, it expands to occupy

a greater volume. If the breather is plugged,

this can cause seal failure.


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Rear Seal Replacement


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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 theseal or draw in contaminants.


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Caution

Do not over-torque the yoke nut, which can

damage the bearing.

Do not perform this operation using a 1-inch

air gun.


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Transmission

Troubleshooting Guidelines

See Table 16-2 on pages 476-477 of the

textbook.


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Towing Precautions


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Caution

When the driveline or axle shafts are

reinstalled:

The axle nuts must be tightened to the correct

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

The axle shafts properly installed (RH and LH)

The drive shafts properly phased


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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.


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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 todays 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.


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Analysis of Bearing Failures

Fretting The bearing outer race can

pick up the machining patternof the bearing bore.

It can be mistakenlydiagnosed as one that hasspun in the bore.

Contamination

Scoring, scratching, andpitting of bearing contactsurfaces identifycontamination failures.

It is caused by very fineparticles suspended in thelubricant or by the use of olderEP (extreme pressure) oils.


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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 untilready for installation.


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Timing Transmissions

Multiple countershaft transmissions must be timed duringassembly.

Timing ensures that the countershaft gears contact their matingmainshaft 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 thischapter: In the main section, it is necessary to time only the drive gear

set.

In the auxiliary section, depending on the model, only the lowrange, deep reduction, or splitter gear sets have to be timed.


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Timing the Front Section (1 of 2)

Before placing eachcountershaft 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.


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Timing the Auxiliary Section (1 of 2)

The specific gears on themainshaft 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 locateddirectly opposite the first

set marked.


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Timing the Auxiliary Section (2 of 2)

Mark the tooth stamped withan O on gear to mate withtimed the mainshaft gear.

Install the mainshaft gear inposition on the range

mainshaft or output shaft. Place the auxiliary

countershaft assemblies intoposition and mesh the markedteeth of mating countershaftgears with the marked teeth of

the mainshaft gear. Fully seat the rear bearings on

each countershaft to completethe installation.


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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 rotatingcomponents contact, pick up, and circulate oil

from the oil in the sump.

Maintaining the correct oil level is critical forsplash lubrication to be effective.


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Summary (2 of 6)

Only lubricants recommended by thetransmission manufacturer should be used ina transmission.

These could be either gear or engine oils.

It is usually recommended that the first oilchange be performed shortly after thetransmission enters service, often between

3,000 and 5,000 miles of operation in alinehaul application, or less in vocationalservice.

S


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Summary (3 of 6)

In general linehaul application, it is goodpractice 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.

S


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Summary (4 of 6)

Leakage in transmission rear seals is arelatively common problem in truck

transmissions, but one that is easily repaired.

When diagnosing transmission complaints, itis important that you confirm that the

transmission is the actual cause of the

problem before removing it for repair.

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Summary (5 of 6)

When disassembling a transmission, eachcomponent should be carefully inspected for

abnormal wear and damage.

Components that are not reusable should beordered 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.

S


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Summary (6 of 6)

Bearing failures occur because of dirtcontamination and poor lubrication.

More than 90 percent of bearing failures are

caused by dirt. Cleanliness is critical when repairing and

servicing standard transmissions.

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