Modern Automotive Technology PowerPoint for by Russell Krick Publisher The Goodheart-Willcox Co., Inc. Tinley Park, Illinois

Chapter 55 Manual Transmission Fundamentals

Contents Basic transmission parts Purpose of a manual transmission Gear fundamentals Manual transmission construction Transmission types Transmission power flow Other transmission designs Speedometer drive Manual transmission switches

Basic Transmission Parts Input shaft Gears Synchronizers Shift forks Shift linkage Gear shift lever Output shaft Transmission case

Basic Transmission Parts

Purpose of a Manual Transmission A manual transmission is designed to change the vehicle’s drive wheel speed and torque in relation to engine speed and torque

Transmission Features A manual transmission should: be able to increase torque to the drive wheels for quick acceleration supply different gear ratios to match load conditions provide a reverse gear provide an easy means of shifting gears operate quietly with minimal power loss

Gear Fundamentals Gears are discs with teeth machined on their perimeters (rims) They transmit turning effort from one shaft to another When gears are different sizes, output speed and torque change

Gear Drive A small gear driving a larger gear increases torque and decreases speed

Gear Drive A large gear driving a smaller gear decreases torque and increases speed

Gear Ratio The number of revolutions a drive gear must turn before the driven gear completes one revolution Calculated by dividing the number of teeth on the driven gear by the number of teeth on the drive gear Gear Ratio = # of driven gear teeth # of drive gear teeth

Gear Ratio If the drive gear has 12 teeth and the driven gear has 24 teeth, the gear ratio is two-to-one Gear Ratio = # of driven gear teeth # of drive gear teeth = 24 12 = 2, written 2:1

Gear Ratio

Transmission Gear Ratios First gear approximately 3:1 Second gear approximately 2:1 Third (high) gear approximately 1:1 Reverse gear approximately 3:1

Gear Reduction Occurs when a small gear drives a larger gear Increases turning force (torque) Used in lower transmission gears

Overdrive Ratio Results when a larger gear drives a smaller gear Output gear speed increases Output torque is reduced

Gear Types Two gear types are commonly used in automotive transmissions spur gears helical gears

Spur Gears Somewhat noisy The teeth are cut parallel to the centerline of the gear shaft Used for sliding gears such as reverse gear

Helical Gears The teeth are machined at an angle to the centerline Quieter and stronger than spur gears Used for main drive gears that are in constant mesh

Gear Types

Gear Backlash Distance between the meshing gear teeth Allows lubricating oil to enter the high-friction area between the gear teeth Allows the gears to expand during operation

Manual Transmission Lubrication Bearings, shafts, and gears are lubricated by oil splash lubrication As the gears rotate, they sling oil around inside the transmission Typically, 80W or 90W gear oil is used

Transmission Bearings Bearings reduce the friction between the surfaces of rotating parts Three basic types are used: ball bearings roller bearings needle bearings Used between shafts and housing, or between gears and shafts

Transmission Bearings Three types of antifriction bearings are used

Manual Transmission Construction

Transmission Case Supports the bearings and shafts Provides an enclosure for gear oil Made of cast iron or aluminum A drain plug and fill plug are provided typically, the oil level should be level with the bottom of the fill plug hole at operating temperature

Extension Housing Bolts to the rear of the transmission case Encloses the output shaft Holds the rear oil seal

Front Bearing Hub Covers the front transmission bearing Acts as a sleeve for the release bearing

Manual Transmission

Transmission Shafts At least four shafts are commonly used: input shaft (clutch shaft) countershaft (cluster gear shaft) reverse idler shaft output shaft (main shaft)

Input Shaft Transfers rotation from the clutch disc to the countershaft gears Any time the clutch disc turns, the input shaft gear turns

Countershaft Holds the countershaft gears into mesh with the input gear and other gears Located slightly below and to one side of the input shaft Normally, it is locked in the case and does not turn

Reverse Idler Shaft Supports the reverse idler gear Allows the reverse idler gear to mesh with gears on both the countershaft and output shaft

Output Shaft Holds the output gears and synchronizers Connects to the drive shaft to turn the wheels Gears are free to revolve on the shaft, but the synchronizers are locked on the shaft by splines

Transmission Shafts

Transmission Gears The input shaft gear turns the countershaft gears, which then turn the output shaft gears

Output shaft rotation is reversed Gear Ranges Gear reduction Direct drive Output shaft rotation is reversed

A machined part of the steel input shaft Input Gear A machined part of the steel input shaft

Several gears machined from a single piece of steel Countershaft Gear Several gears machined from a single piece of steel

Reverse Idler Gear Assembly

Output Shaft Gears

Synchronizers Synchronizers have two functions: prevent the gears from clashing (grinding) during engagement lock the output gear to the output shaft

Synchronizer Theory When the synchronizer is away from an output gear, the gear freewheels (spins freely) on the output shaft When the synchronizer slides against the output gear, it locks the output gear to the output shaft Power flows through the output shaft to the drive wheels

Synchronizer Construction The hub is splined to the output shaft

Synchronizer Operation When the driver shifts gears, the synchronizer sleeve slides on its splined hub toward the output gear The blocking ring cone rubs on the side of the drive gear cone, causing friction between the two The output gear, synchronizer, and output shaft begin to spin at the same speed

Synchronizer Operation

Synchronizer Operation As soon as the speed is equalized, the sleeve can slide over the blocking ring and spur gear teeth on the output gear This locks the output gear to the synchronizer hub and to the shaft Power flows through that gear to the drive wheels

Synchronizer Operation

Fully Synchronized Transmission All the forward output gears use a synchronizer Allows the driver to downshift into any lower gear (except reverse) while the vehicle is moving

Transfer movement from the gear shift linkage to the sleeves Shift Forks Transfer movement from the gear shift linkage to the sleeves

Movement of the shift linkage moves the shift fork Shift Fork Assembly Movement of the shift linkage moves the shift fork

External Shift Rod Linkage

Internal Shift Rail Linkage

Internal Shift Rail Linkage

Column Shift Mechanism

Transmission Types There are several types: three-speed four-speed five-speed Some transmissions have an overdrive in high gear Extra gear ratios are needed for the small, low-horsepower engines

Transmission Power Flow

First Gear Linkage rods move the shift forks so that the first gear synchronizer is engaged to the first output gear The input shaft gear turns the countershaft gears First gear is locked to the output shaft A small gear on countershaft drives a larger gear on the output shaft The gear ratio is about 3:1

First Gear

Second Gear The first gear synchronizer is slid away from the first gear The second-third synchronizer is then engaged Power flow is through the second gear on the output shaft The gear ratio is about 2:1

Second Gear

Third Gear The synchronizer is slid over the small teeth on the input shaft gear The synchronizer locks the input shaft directly to the output shaft All the output shaft gears freewheel on the shaft Power flow is straight through the transmission The gear ratio is 1:1

Third Gear

Reverse The synchronizer is moved into the reverse gear on the output shaft, locking the gear to the output shaft Power flows through the countershaft, reverse idler gear, reverse gear, and to the output shaft

Reverse

Neutral All the synchronizer sleeves are located in the center of their hubs All the output shaft gears freewheel on the output shaft No power is transmitted to the output shaft

Neutral

Overdrive In many transmissions, high gear is an overdrive An overdrive gear ratio is less than 1:1 e.g. 0.87:1 Overdrive increases fuel economy

Five-Speed, Overdrive Transmission – Neutral

Five-Speed, Overdrive Transmission – 1st Gear

Five-Speed, Overdrive Transmission – 2nd Gear

Five-Speed, Overdrive Transmission – 3rd Gear

Five-Speed, Overdrive Transmission – 4th Gear

Five-Speed, Overdrive Transmission – 5th Gear

Five-Speed, Overdrive Transmission – Reverse

Other Transmission Designs Many transmission design variations are used by the numerous auto manufacturers Whether rear-wheel drive, front-wheel drive, or all-wheel drive, all transmissions use similar principles

Five-Speed Manual Transmission

Front-Engine, All- Wheel Drive Vehicle

Speedometer Drive A worm gear on the output shaft drives the speedometer gear and cable The gear on the output shaft turns a plastic gear on the end of the speedometer cable The cable runs through a housing up to the speedometer head

Manual Transmission Switches

Back-up Light Switch Closed by the action of the reverse gear shift linkage When shifted into reverse, the linkage closes the switch The switch carries current to the back-up lamps

Ignition Spark Switch Used on a few vehicles Allows distributor advance only when transmission in high gear Reduces pollution by retarding ignition timing in low gears Usually located on side of transmission