Manual Transmission Components and Operation

This presentation will explore: Gears and Gear Ratios Manual Transmission Construction Manual Transmission Operation

Gear Types

Three main types of gearing are used in a manual transmission system.

Spur gearing has teeth that are cut parallel to the rotating axis. These are noisy when operating at high speeds.

Helical gearing has teeth cut at an angle to the rotating axis. This provides more tooth surface area, allowing the gearing to run quieter.

Double helical gearing incorporates two sets of helical teeth on one gear. Very quiet operation, although expensive to manufacture.

Spur (straight cut)

Helical

Double helical

If the driver gear is smaller than the driven gear, this is known as an underdrive gear arrangement.

If the driver gear is larger than the driven gear, this is known as an overdrive gear arrangement.

Underdrive gears are the lower transmission range on a vehicle and are used for low speed and high torque (1st , 2nd or 3rd ).

An overdrive gear is normally the high gear (5th or 6th). It is used for high vehicle speeds and improved fuel economy.

Gear Ratios

Driven gear

Driver gear

Driven gear

Driver gear

Manual Transmission Layout

The picture shows a typical manual gearbox that incorporates the differential. This is known as a transaxle gearbox. It can be found on front wheel drive, rear wheel drive or four wheel drive vehicles.

Input shaft

Output shaft

Transmissioncase

Axle shaft (Output to wheels)

Differential

Manual Transmission Casing

The transmission housing must be able to support and secure the various shafts and components in the transmission system. Precision bores, faces and grooves are used to house the bearings, washers, gaskets and mounts.

Manufactured from either cast iron or aluminium, the casing must be strong towithstand the lateral forces generated, as power flows between gear clusters.

Manual Transmission Casing

The transmission casing, used in conjunction with seals, contains the lubrication required for the gearing. A filler plug in the side and a drain plug underneath, enable the oil to be topped up and changed.

Because manual transmissions operate at high speeds, gears can easily overheat. Lubrication is needed to ensure smooth and durable operation.

Filler plug

Drain plug

Typical oil level

Input Shaft Construction

The input shaft is supported by a bearing fitted to a shoulder and pressed into the transmission casing. There may also be a pilot bearing in the crankshaft.

The input shaft, also known as the clutch shaft, has a splined end that is directly connected to the clutch plate. Clutch rotation is directly transferred to the input shaft.

A single gear is used to drive the counter shaft. Cone and synchronizer teeth may be incorporated for engaging the output shaft to the input shaft, producing a ratio of 1:1 (direct drive).

Splines

Helical gear

Synchronizer teeth

Cone

Bearing shoulder

Counter (Lay) Shaft Construction

The counter shaft gear consists of a cluster of various gears, all rotating at the same speed, and continuously meshed with the gears on the input and output shafts.

Input shaft Output

shaft

Counter shaft

Thrust washer

Thrust washer

The counter shaft always turns in the opposite direction from the input shaft. It often runs the length of the transmission case and uses thrust washers to limit sideways motion of the gear.

Reverse Shaft Construction

The idler gear is meshed between a counter shaft gear and an output shaft gear.

When selecting reverse, the direction of drive is changed. This is achieved by using an idler gear.

Construction is generally a gear on a fixed shaft, which is supported by bushes or roller/needle bearings.

Input shaft Output shaft

Reverse idler gear

Counter shaft

Reverse idler gear

Reverse shaft (fixed)

Output Shaft Construction

Different sized gears are mounted on the output shaft.

The output shaft, also called the main shaft, is connected to the drive shaft. Casing supports, used in conjunction with bearings, hold the shaft in place.

These gears rotate freely on the output shaft, and are meshed with the gears of the counter shaft.

Outputshaft

1stgearBush

2nd & 1stsynchronizer

2nd gearblocking ring

2nd gear

Bush

3rd gear

4th and 3rd gearsynchronizer

4th gearblocking

ring

Output Shaft Construction

Outputshaft

1stgearBush

2nd & 1stsynchronizer

2nd gearblocking ring

2nd gear

Bush

3rd gear

4th and 3rd gearsynchronizer

4th gearblocking

ring

The synchronizers are held in place by splines on the output shaft, so they rotate with the shaft.

Smooth and precise gear selection is carried out using synchronizers. These prevent the clashing or crunching of gears.

Each synchronizer is normally used to select one of two different gears.

Synchronizer Components

Close-up view of synchronizer and blocking rings:

Blocking ring

Insert

Spring forinserts

Outer sleeve (Teeth lock hub, blocking ring and gear together)

Shift forkgroove

Blocking ring

Hub

Spring forinserts

Insert

Synchronizers

In doing so, it pushes a blocking ring against the gear’s cone, producing friction between the two.

When the synchronizer, blocking ring and gear are all rotating at the same speed, the gear is said to be synchronized.

As the driver selects a gear, the outer sleeve of a synchronizer slides over its hub and toward the required gear on the output shaft.

GearShift forkgroove

Gear cone

Synchronizer

Blocking ring

Outer sleeve

Hub

Synchronizers

The synchronizer sleeve now slides over the gear, the inner teeth of the sleeve engaging with teeth on the gear.

Power is now transferred from the counter shaft to the output shaft.

This locks the gear to the synchronizer hub, and therefore to the output shaft.

GearShift forkgroove

Gear cone

Synchronizer

Blocking ring

Outer sleeve

Hub

Selector Forks

Selector forks are used to move the synchronizer sleeves into the required positions. The number of forks varies with the number of gears.

The selector forks are moved by selector rods (rails). The driver’s gear lever controls the selector rods. When the driver selects a lever position, this transfers the movement to the selector forks, which in turn move the synchronizer sleeves.

Selector rods

Selector fork

Selector fork

Gear Lever

The gear lever is what the driver uses to manually change gear.

Gear levers are typically located on the steering wheel column or between the two front seats.

Modern variations of gear levers include finger tip buttons on the steering wheel, short shift and Tiptronic levers on the dashboard.

Gear Linkages

There are two main types of linkages: external and internal. These connect the driver’s gear lever to the selector rods and forks. Various configurations of linkage are used depending on the position of the transmission in relation to the lever (for example, rear wheel drive or front wheel drive vehicles).The diagram above shows a single rail selector that uses one selector rod. The rod has fixed pins to move the selector forks. The gate is formed by extensions of the selector forks. To select a gear, the rail is rotated until the selector pin aligns with the required selector fork and then moved backwards or forwards.

Selectorrod

Detents

Selector forks

Selectorpins

Fork

Pivot

Multi-Rail Selector

Multi-rail selection uses selector rods sliding in the gearbox housing. Sliding with these rods are the selector forks, which fit onto the synchronizer sleeves.

Pushing a selector fork will move the outer sleeve of the synchronizer hub to engage the selected gear.

Shift lever

Selector gates

Selector rods

Selector forks

The lower end of the gear lever moves between the three selector gates to align with one rod. When the gear lever is moved forward or backward, the selector rod and fork move laterally.

Retainers are spring-loaded balls or plungers, which locate in grooves in the selector rods to hold the rods in their selected position.

Retainers

Neutral Position Gear Engaged

Selector rod

Spring loaded ball

When a rod is shifted it must be retained in the gear position, or neutral, to give a positive feel and help prevent it jumping in or out of gear.

If two selector rods were moved at the same time by the gear lever, two gears would be engaged and cause the gearbox to lock up. To prevent this, an interlocking device may be used.

Interlock

A Ball and Plunger interlock (as shown in the diagrams) uses a pin sliding in a hole drilled through the central rod. The rods on each side have single grooves facing the middle. Holes in the casing hold two balls.

When an outer rod is moved, the ball is forced out of the groove and pushes the plunger across to hold the other two rods. When the centre rod is moved, both balls will drop into the grooves of the outer rods to lock them.

BallPlunger

Transmission Power Flow - Neutral

Neutral

When the shift lever is in the neutral position, the gears on the input shaft, countershaft and output shaft spin at engine speed, however, none of the gears are engaged to the output shaft, so there is no drive.

Input Output

Transmission Power Flow - First Gear

1st Gear

The diagram shows the power flow from input to output when 1st gear is selected.

Input Output

Transmission Power Flow - Second Gear

2nd Gear

The diagram shows the power flow from input to output when 2nd gear is selected.

Input Output

Transmission Power Flow - Third Gear

3rd Gear

The diagram shows the power flow from input to output when 3rd gear is selected.

Input Output

Transmission Power Flow - Fourth Gear

4th Gear

The diagram shows the power flow from input to output when 4th gear is selected. Connects the input shaft to the main shaft, giving direct drive (1:1).

Input Output

Transmission Power Flow - Fifth Gear

5th Gear

The diagram shows the power flow from input to output when 5th gear is selected, giving overdrive.

Input Output

Transmission Power Flow - Reverse Gear

The diagram shows the power flow from input to output when reverse idler gear is selected, changing the direction of rotation of the output shaft.

Reverse Gear

Input Output