The Stack

Drive Gear (Input). A drive gear or driving gear is one that drives another gear or causes another gear to turn.

Driven Gear (Output). A driven gear is one that is driven by a drive gear or a shaft.

An idler gear is a gear wheel that is inserted between two or more other gear wheels. The purpose of an idler gear can be two-fold. Firstly, the idler gear will change the direction of rotation of the output shaft. Secondly, an idler gear can assist to reduce the size of the input/output gears whilst maintaining the spacing of the shafts. (Wikipedia)

They are stronger and quieter.

The load.

They must both have the same gear pitch.

Input and output shafts, main shaft and counter shaft gears, and shift mechanisms.

any drivetrain arrangement in which an output speed exceeds input speed. For instance, most transmissions have over drive ratio options, meaning that transmission tailshaft speed exceeds engine crankshaft speed.

The output shaft of a transmission.

Another name for the auxiliary section of the transmission.

You'll have a 5 speed front box, almost all of the time, regardless of how speeds the whole thing is.

Outside diameter

Root diameter

Tooth surface or flank

Pitch line

Pitch diameter

Fillet radii

Addendum

Dedendum

The air system.

the number of teeth per given unit of pitch diameter in a gear.

36 teeth / 6" diameter = gear pitch

teeth count / diameter = gear pitch

Output speed equals input speed.

It reduces output speed.

It increases output speed (overdrive).

sliding gear, collar shift, and synchronized shift

A single countershaft transmission that uses a sliding gearshift mechanism has a main shaft and a countershaft supported parallel to each other. To change from one speed/torque range to another, gears on the main shaft are moved longitudinally until they engage the desired gear on the countershaft. To effect this movement, spur-cut sliding gears are used. These have a shift collar integral with the gear. When the driver makes a shift, a shift fork or yoke engages with a collar on the gear and slides it on the main shaft until it is brought into mesh with a mating gear on the countershaft.

Shift Gear (Splined to Shaft)

Shift Collar

Driven Gear (Rides Free on Shaft)

Shaft

Put the sliding clutch on top of it and see if it can slide all the way down. If not, it's not straight enough.

A bottoming condition occurs when the teeth of one gear contact the root of the mating gear. Bottoming seldom occurs in a two-gear drive combination but is more common in multiple-gear drive combinations. The mating action of a two-gear drive combination tends to thrust the gears apart, so bottoming is unlikely in this arrangement.

Its main function is to bring components that are rotating at different speeds to a common or synchronized speed. In a transmission, a synchronizer ensures that the main shaft and the main shaft gear about to be locked to it are both rotating at the same speed. The second function of the synchronizer is to actually lock these components together. If the driver and the synchronizer are both doing their jobs, the result is a clash-free shift.

The term backlash describes rotational free play between mating gears, usually measured with thickness gauges or a dial indicator. All intermeshing gears should have some backlash to permit heat expansion of metal and proper lubrication. Out-of-specification backlash results in noise and rapid wear. Backlash increases as mating gears and shaft bearings wear.

The drive side of gear teeth is in contact with teeth of another gear while torque is being applied. Usually the drive side of gear teeth is subject to the most wear. The coast side of gear teeth is opposite to the drive side.

The shift bar housing, also known as the shift rail assembly, houses the components required to convert gear stick movement into range gearshifts within the transmission.

To determine the direction of rotation of gears in a transmission, you should face the front of the transmission—that is, the end that couples to the engine.

Clockwise and counterclockwise.

Washer

4th

3rd

Washers

2nd

1st

Washers

Roll pin

Key

Splined main shaft

Snap ring

Reverse

Spacers

Sliding clutch

Snaprings

Spacers

Sliding clutch

Snaprings

Spacer

Sliding clutch

One sliding clutch controls first and reverse shifts, another controls second and third shifts, and a third controls fourth and main gear engagement. Note: The main drive gear is not shown (in the diagram), but remember that this is part of the input shaft/drive gear assembly.

- Helical gears have more teeth in contact than a spur gear.

- Spur’s straight teeth minimize the possibility of popping out of gear.

- Helical gears are quieter than spur gears.

- Helical gears permit the tooth load to be evenly distributed.

- The main disadvantage of helical gears is the axial thrust they create in operation.

47 teeth on bottom/driver's side and 45 teeth on top/driver's side.

Helical gears are generally what’s in backboxes.

Spur gears are generally what’s in frontboxes.

Timing is the procedure used to time interacting mechanical components. See timing marks.

Timing marks are a means of marking gear set teeth before installation so that they can be placed in proper mesh in the geartrain.

Engine torque is transferred through the clutch to the input shaft of the transmission, which drives the gears in the transmission.

It let's you move at different speeds and in different directions. It is the driver’s means of managing drivetrain torque and speed ratios to suit chassis load and road conditions, such as a fully loaded standing start to cruising at highway speeds.

Light-duty truck transmissions have a limited number of gear ratios and a single set of gears called main gearing, contained in a single housing. Most heavy-duty truck transmissions consist of two distinct sets of gearing: the main or front gearing and the auxiliary gearing located directly on the rear of the main gearing.

Auxiliary gearing compounds the available ratios in a transmission. Most heavy-duty trucks use at least one compound, whereas some use two compounds.

The three stages of contact through which the teeth of two gears pass while in operation are coming-into-mesh, full-mesh, and coming-out-of-mesh.

The relationship of input to output speeds is expressed as gear ratio.

Torque increase from a driving gear to a driven gear is directly proportional to speed decrease. Therefore, to increase output torque there is a resultant decrease in output speed and vice versa.

The major types of gear tooth design used in modern transmissions and differentials are spur gears and helical gears.

A heavy-duty standard transmission consists of a main shaft and one, two, or three countershafts.

Standard transmissions can be generally classified by how they are shifted. Sliding gear, collar shift, and synchronized shift mechanisms are used to effect shifts in standard transmissions.

Synchronizers have two primary functions. First, they bring two components rotating at different speeds to a single, synchronized speed; and second, they lock these components together.

Block or cone and pin synchronizers are the most common in heavy-duty transmissions.

Mechanically. Either a direct-actuated, shift tower assembly, or, in the case of COE trucks, a remote-actuated shift tower.

Most current compounded transmissions use air controls to effect shifts in the auxiliary section, though some older trucks used gear levers for both main and auxiliary section shifts.

An air-actuated gearshift system consists of an air filter and regulator, slave valve, master control valve, range cylinder, and connecting air lines.

Auxiliary section gearing can be optioned to include a third gear in addition to the high- and low-range gears. This third gear is engaged or disengaged by a splitter shift system air activated by a button on the shift lever.

A transfer case is an additional gear box located between the main transmission and the rear axle. Its function is to divide torque from the transmission to front and rear drive axles and, in addition, to option driving force to the front axle.

The accessory drive requirements on trucks are met by using power take-off (PTO) units. Hydraulic pumps for pumping loads off trailers and compressors for blowing loads off sealed bulk hoppers would be two examples of PTO-driven equipment.

The six types of PTOs, classified by their installation, are side mount, split shaft, top mount, countershaft, crankshaft driven, and flywheel.

an integral filter regulator used on many standard shift truck transmissions.

see axis.

point about which a shaft, rotor, or component rotates.

the gapping or play between mating gear teeth usually measured with thickness gauges or a dial indicator.

a truck or tractor that locates the driver cabin in a forward position directly over the engine. There is no hood.

a gear problem caused by excessive wear in intermeshing gears or bearings. Climbing occurs when intermeshing gears move apart sufficiently for one gear to climb over the apex of its mate.

gears positioned to remain in permanent mesh, not engaged and disengaged by shifting action.

a transmission ratio option in which the input and output shafts rotate at identical speeds, that is, engine speed.

any gear that drives another.

a gear that is driven by another.

term used to describe the components that move a vehicle down the highway from the engine, transmission, propeller shaft(s), drive axle carrier, drive axle shafts, and drive wheel assemblies. The engine is the prime mover of the drivetrain and the role of the transmission is to manage the output ratios.

term used to describe the transmission shaft through which output torque is primarily routed. Term is used in both standard and automatic transmissions but the role played by the main shaft in each differs.

any drivetrain arrangement in which an output speed exceeds input speed. For instance, most transmissions have overdrive ratio options, meaning that transmission tailshaft speed exceeds engine crankshaft speed.

the mechanical flow path that conducts motive power through a system or component. For instance, the powerflow through a transmission in a specific gear ratio would be the sequential routing of the torque flow path through those gears that are actually engaged.

the act of rotating. Gears, shafts, wheels, and rotors are all subject to rotation.

the manifold on top of a standard transmission that houses the shift rails, usually three, to which shift yokes are connected; the shift tower assembly mounts on top of the shift bar housing. Also known as shift rail housing.

the fork-shaped components that connect shift rails with the sliding clutches in a standard transmission. Also known as shift yokes.

any of a number of types of air or hydraulic actuators.

an auxiliary transmission used to split drive torque from the main transmission between rear and forward drive axles; also known as a dropbox.

minor indentations on the shoulder or in the valley of a bearing race, usually caused by improper installation.

a bearing or journal failure characteristic in which the contact surface picks up and then wears on the original manufacturing machining pattern. Also used to describe the rubbing wear that results when two clamped components expand and contract during heating and cooling at different rates.

a condition caused when a sliding clutch is forced out of engagement.

occurs in transmission gearing, usually when pulling under full power or decelerating with load momentum driving forward movement. Worn sliding clutch teeth walk out of engagement with the gear.

the procedure used to time interacting mechanical components. See timing marks.

a driveline yoke repair kit consisting of an interference fit sleeve that is installed over the seal race.

used on Allison automatic transmissions to alter shift speeds. Changing the position of the adjusting rings determines the retaining force of the valve springs in the valve body.

any of a number of different types of add-on filters used in hydraulic circuits. Often installed on an Allison transmission after a catastrophic failure to remove particulate debris.

a device that allows a circuit to be vented to atmosphere; used on reservoirs, axles, etc.

the rpm at which an engine is overloaded to the extent that it begins to either lug or stall; a factor in performance testing of automatic transmissions.

sliding shaft to which shift yokes are clamped: When the bar is moved by the gearshift lever spade, the bar slides in bushing supports, moving the shift yoke to effect a gear change. Also known as a shift rail.

a test performed on vehicles with automatic transmissions to verify the performance of the engine and transmission, usually to determine if one is at fault.

a synthetic heavy-duty automatic transmission oil recommended by Allison, which states that it extends oil change intervals by 300 percent.

a special tool required to adjust the valve rings in Allison automatic transmissions.

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

Most 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.

Only lubricants recommended by the transmission OEM should be used in a transmission. These could be gear, engine, or synthetic oils.

When mineral oils are used, the first oil change should 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. This is not required with synthetics.

In general linehaul application, it is good practice to schedule a transmission oil change from 50,000 to 100,000 miles of service. Oil change intervals can be extended up to 500,000 miles when synthetics are used.

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

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.

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.

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.

The detent mechanism locates the transmission shift lever in the correct location in each range select position. It provides an element of gearshift feel to the driver when shifting from one gear to another.

The detent mechanism consists of a spring-loaded detent steel ball or poppet. The spring loads the steel ball into the recess in the shift bar. The detent ball holds the shift bar in position and prevents unwanted movement of the other bars. When drivers make a shift, they must overcome the spring pressure of the detent ball to move the shift bar.

Input torque * Ratio

Input speed / Ratio

They transmit speed and torque unchanged; They decrease speed and increase torque; They increase speed and decrease torque.

low:high ratio

a spur gear

rotates in the same direction as the driving gear

first and reverse gears in the main box

nonsynchronized

a synchronizer

twin countershaft

It divides input torque between two separate shafts; It allows the face width of each gear to be reduced; It allows the main shaft to float between the countershafts.

a slave valve

a splitter cylinder and a button-actuated shift lever valve

a detent ball

power take-off (PTO) unit

It transfers torque from the transmission to a front drive axle; It transfers torque from the transmission to the rear drive axle(s); It may provide an additional gear reduction in the drivetrain.

the main shaft

Install lower reverse gear.

Place lower countershaft in case and install bearings.

Place upper countershaft in case - DO NOT install bearings.

Install input shaft and main drivegear. Time main drive gear to lower countershaft.

Install main shaft & countershaft. Leave reverse gear against 1st gear.

Temporarily install rear mainshaft bearing or use timing tool.

Time upper countershaft to drive gear.

Install upper reverse idler. (Has to happen before you slide rear gear to gear.)

Reverse mainshaft bearing/timing tool.

Slide rear gear to gear.

Install retainer washer and snap ring. (13 and 18 speed units. Star washer has internal taper. This must be torward rear or bearing will not fit correctly.)

Install rear bearing and retainer.

Install auxiliary driving gear and snap ring.

Turn 10 times left and 10 times right.

Roadranger

Twin Countershaft

Low-Inertia

Overdrive w/ Direct Shift Pattern

Convertible

Forward Opening Shift Housing

This (x) 100 = Nominal Torque Capacity

Forward Speeds

Ratio set

Multi-Mesh Gearing

Helical Auxiliary Gearing and Multi-Mesh Front Section Gearing

Improved Seal System

The Serial Number is the sequential identification number of the Transmission.

Multi-Torque

Top Speed

Autoshift

Fuller RoadRanger Overdrive

At the regulator.

Roadranger Twin countershaft Overdrive

Roadranger Twin countershaft Automated Overdrive

Roadranger Twin countershaft Low inertia Overdrive

synthetic E-500 gear lube

after 500,000 miles of linehaul service

Oil is level with the filler hole.

A damaged speedometer sleeve O-ring or gasket and a cracked bearing cover.

By installing a yoke sleeve kit or replacing the yoke.

Removal of the transmission from the chassis.

A shift rail assembly cannot be removed and repaired without first removing the transmission from the vehicle.

Driveline vibrations are caused by loose yokes, excessive drive shaft radial runout, slip spline joint radial play, bent drive shaft tubing, and failing U-joints.

Worn detent notches in the shift rail and worn gear clutch teeth.

Lack of lubricant in remote shift linkage.

They are not compatible with all other gear lubes.

Aeration and result in lubrication failures.

sliding clutch

When towing a truck from the front, the axle shafts should be pulled.

A safety interlock.

A shock load to the output shaft of the transmission.

On the front of the valve.

At the upper right corner on the rear section.