Manual and Automatic Drivetrain Systems

Manual and Automatic Transmission Systems

Chapter Introduction

This chapter covers all the knowledge required for the Red Seal exam concerning transmission systems, both manual and automatic. You must master not only the operating principles, but also diagnostic procedures, ratio calculations, wear tolerances, and applicable safety standards. The transmission is the bridge between the engine and the wheels; any diagnostic or repair error can lead to catastrophic failures and risks of serious injury.

Fundamental Principles of Transmissions

Role and Function of the Transmission

The transmission's function is to modify the torque and speed transmitted from the engine to the drive wheels. It allows the vehicle to start from a standstill, climb hills, accelerate, and maintain economical cruising speed. Without a transmission, the engine would stall at a stop and could not operate within its useful RPM range.

The gear ratio is the relationship between input speed and output speed. A ratio lower than 1:1 is an overdrive ratio, while a ratio higher than 1:1 is a reduction ratio. Torque is multiplied by the gear ratio, while speed is divided by that same ratio.

Calculating Gear Ratio

The gear ratio is calculated as follows:

Ratio = Number of teeth on driven gear ÷ Number of teeth on driving gear

Example: a driving pinion with 20 teeth drives a driven gear with 60 teeth. The ratio is 60 ÷ 20 = 3.0:1. Torque is multiplied by 3 and speed is divided by 3.

For a complete drivetrain, the overall ratio is the product of the transmission ratio, the differential ratio, and the transfer case ratio (if applicable):

Overall ratio = Transmission ratio × Differential ratio × Transfer case ratio

Mechanical Efficiency and Losses

No transmission is perfectly efficient. Losses come from gear friction, bearings, seals, and the hydraulic pump (for automatics). Typical efficiency of a manual transmission is 94 to 97%, while a conventional automatic transmission achieves 85 to 92%. Dual-clutch transmissions (DCT) fall in between, at 92 to 95%.

Manual Transmission

Main Components

The manual transmission includes the following components:

Input shaft (clutch shaft): receives torque from the engine via the clutch.

Output shaft: transmits torque to the differential.

Countershaft (intermediate shaft): transmits motion between the input shaft and the output shaft.

Idler gears: mounted on bearings on the output shaft, they spin freely until locked by the synchronizer.

Synchronizers: devices that equalize gear speeds before engagement.

Shift forks: move the synchronizers.

Shift mechanism: controlled by the gear shift lever.

Synchronizers: Principle and Operation

The synchronizer is a critical component. It uses a friction cone to equalize speed between the idler gear and the shaft before tooth engagement. Operation occurs in three phases:

29.Travel phase: the fork pushes the synchronizer hub toward the gear.

30.Synchronization phase: the friction cone makes contact, creating a friction torque that equalizes speeds.

31.Engagement phase: once speeds are equalized, the locking teeth engage without shock.

End play: most synchronizers have an end play of 0.05 to 0.15 mm. Excessive play indicates wear and can cause gear grinding when shifting.

Disassembly and Inspection Procedure

For the exam, you must know the logical disassembly sequence:

35.Drain the transmission oil (respect environmental standards).

36.Remove the transmission case.

37.Measure shaft end play and radial play using a dial indicator.

38.Inspect gear teeth for wear, pitting, or cracking.

39.Check bearings for noise, play, or brinelling marks.

40.Inspect synchronizers: measure the clearance between the hub and the ring.

41.Check fork condition: wear on contact surfaces.

42.Verify shaft alignment.

Typical specification: the clearance between the synchronizer hub and the locking ring must not exceed 0.10 mm. Beyond that, replace the assembly.

Manual Transmission Oils

Manual transmission oils are classified according to SAE J306 standard. Common grades are 75W-90, 80W-90, and 75W-140. The API GL-4 classification is suitable for copper-alloy synchronized transmissions, while API GL-5 is recommended for axles and certain high-pressure transmissions. Caution: using GL-5 oil in a transmission with brass synchronizers can cause brass corrosion.

SAE Grade	Viscosity at 100°C (cSt)	Typical Use
75W-90	13.5 – 24.0	Modern transmissions
80W-90	13.5 – 24.0	Older transmissions
75W-140	24.0 – 41.0	Heavy-duty applications

Clutch

Clutch Types

The manual clutch is of the dry friction type in the vast majority of light vehicles. It includes:

The pressure plate (or clutch mechanism).

The clutch disc (friction disc).

The release bearing (throwout bearing).

The flywheel.

Pedal Adjustment and Free Play

The clutch pedal free play must conform to manufacturer specifications, generally between 10 and 25 mm. Insufficient free play causes clutch slippage; excessive free play causes incomplete disengagement and gear grinding.

Replacement Procedure

57.Remove the transmission.

58.Measure the clutch disc thickness (typical minimum: 6.0 mm for a new disc of 8.0 mm).

59.Check flywheel runout (maximum 0.05 mm).

60.Check pressure plate parallelism (maximum 0.10 mm).

61.Align the disc using an alignment tool.

62.Tighten pressure plate bolts in a crisscross pattern, to the specified torque.

63.Adjust pedal free play.

Typical torque specification: pressure plate bolts are tightened to 25-35 N·m depending on the manufacturer. Always consult the manufacturer's specifications.

Automatic Transmission

Components and Hydraulic Circuits

The conventional automatic transmission includes:

Torque converter: replaces the clutch.

Planetary gear set: provides the gear ratios.

Clutches and brakes: control the planetary gear set elements.

Valve body: distributes hydraulic pressure.

Oil pump: generates pressure.

Transmission Control Module (TCM): controls the solenoids.

Torque Converter

The torque converter consists of three main elements:

Pump (impeller): driven by the engine.

Turbine: drives the transmission input shaft.

Stator: redirects oil flow to multiply torque.

The torque multiplication ratio (output torque ÷ input torque) can reach 2.5:1 at a complete standstill. This ratio decreases as the turbine accelerates, until it reaches approximately 1:1.

Lock-up clutch: at stabilized speed, the lock-up clutch mechanically couples the pump and turbine, eliminating slippage and improving fuel efficiency. The operating temperature of the converter should remain between 80°C and 100°C.

Planetary Gear Set: Ratio Calculations

The simple planetary gear set consists of a sun gear, a ring gear, and planet gears mounted on a planet carrier. The general formula is:

N_ring = N_sun × (Z_sun ÷ Z_ring)

Where Z represents the number of teeth. For a simple planetary gear set with a 30-tooth sun gear and a 75-tooth ring gear:

Sun gear fixed, ring gear driving, planet carrier driven: ratio = 1 + (Z_ring ÷ Z_sun) = 1 + (75 ÷ 30) = 3.5:1

Ring gear fixed, sun gear driving, planet carrier driven: ratio = 1 + (Z_sun ÷ Z_ring) = 1 + (30 ÷ 75) = 1.4:1

Planet carrier fixed, sun gear driving, ring gear driven: ratio = Z_ring ÷ Z_sun = 75 ÷ 30 = 2.5:1 (reverse rotation)

Electronic Diagnostics and Trouble Codes

Modern automatic transmissions are controlled by the Transmission Control Module (TCM). OBD-II trouble codes are standardized according to the SAE J2012 standard. Transmission-specific codes begin with P0700 to P0999 for generic codes and P2700 to P2799 for manufacturer-specific codes.

Code	Description	Typical Action
P0715	Input speed sensor circuit	Check sensor and wiring
P0730	Incorrect gear ratio	Check internal clutch and solenoids
P0741	Torque converter clutch stuck off	Check solenoid and converter
P0750	Shift solenoid A	Test solenoid and its circuit

Pressure Testing Procedure

Pressure testing the automatic transmission is essential for diagnosis. Typical line pressure is:

At idle: 400 to 600 kPa (4 to 6 bar)

Under load (stall test): 1,200 to 1,800 kPa (12 to 18 bar)

Stall test: hold the service brake firmly, place the selector in D, and accelerate to full throttle for a maximum of 5 seconds. The maximum RPM reached must conform to specifications (generally 1,800 to 2,500 RPM). RPM that is too high indicates converter or clutch slippage; RPM that is too low indicates an engine restriction or a faulty converter.

Drive Shafts and CV Joints

Drive Shaft (Propeller Shaft)

The drive shaft transmits torque from the transmission to the differential. It must be dynamically balanced. An imbalance causes vibrations at high speed. The angular play of U-joints must not exceed 0.10 mm measured with a dial indicator.

CV Joints (Constant Velocity Joints)

CV joints transmit torque at a constant angle. Two main types:

Tripod joint: used on the transmission side, allows axial movement.

Ball-type joint (Rzeppa): used on the wheel side, allows a large steering angle.

Inspection: check the condition of the boots. A torn boot causes grease loss and contamination by water and dirt. A damaged joint produces a clicking noise when turning or a humming noise during acceleration.

Differential

Function and Types

The differential allows the drive wheels to rotate at different speeds when cornering. The main types are:

Open differential: distributes torque equally, but sends all power to the wheel that is spinning.

Limited-slip differential (LSD): uses clutches or a viscous coupling to limit speed difference.

Locking differential: locks both wheels together for maximum traction.

Axle Ratio

The axle ratio (final drive ratio) is calculated as follows:

Axle ratio = Number of teeth on ring gear ÷ Number of teeth on drive pinion

Example: ring gear with 41 teeth, pinion with 10 teeth → ratio = 41 ÷ 10 = 4.10:1.

Backlash Adjustment

The backlash between the ring gear and drive pinion must be between 0.10 and 0.20 mm for most vehicles. This clearance is measured with a dial indicator placed on a ring gear tooth. Excessive backlash causes noise; insufficient backlash causes overheating and rapid wear.

Bearing preload: the drive pinion preload is adjusted using shims or a collapsible spacer. The rotating torque resistance of the pinion should be 1.5 to 3.5 N·m for new bearings.

Canadian Standards and Codes

Canadian Electrical Code

Although vehicles are not directly covered by the Canadian Electrical Code, Part I, repair shops must comply with the rules regarding electrical installations. Rule 8-200 concerns conductor ampacity and overcurrent protection. Lifting equipment and power tools must comply with CSA C22.2 for safety.

CSA B149.1

CSA B149.1 (Natural Gas and Propane Installation Code) applies to vehicles running on compressed natural gas (CNG) or propane. Alternative fuel systems installed on vehicles must comply with this standard. Technicians working on these systems must know the purging and depressurization procedures before any intervention.

Occupational Health and Safety Standards

Provincial occupational health and safety standards apply in all workshops. Key points:

Use of safety glasses and oil-resistant gloves.

Lifting vehicles with hoists compliant with CSA Z271 (standard for vehicle hoists).

Adequate ventilation during engine testing (carbon monoxide).

Management of waste oils in accordance with Canadian environmental regulations.

Systematic Diagnostic Procedures

Decision Tree for a Transmission That Won't Shift

131.Check oil level and condition.

132.Check trouble codes with a diagnostic tool.

133.Check electrical connections and solenoids.

134.Perform a hydraulic pressure test.

135.Check the shift cable or linkage.

136.If everything is normal, remove the transmission for internal inspection.

Measuring Clearances: Tools and Tolerances

Component	Measuring Tool	Typical Tolerance
Shaft end play	Dial indicator	0.05 – 0.15 mm
Bearing radial play	Dial indicator	0.02 – 0.08 mm
Backlash	Dial indicator	0.10 – 0.20 mm
Flywheel runout	Dial indicator	0.05 mm max
Clutch disc thickness	Caliper	6.0 mm min

Calculating Engine RPM Based on Vehicle Speed

To calculate engine RPM at a given speed:

RPM = (Speed (km/h) × Axle ratio × Transmission ratio × 1,000) ÷ (Tire circumference (m) × 60)

Example: vehicle at 100 km/h, axle ratio 3.73, transmission ratio 0.70 (overdrive), tire circumference 2.0 m:

RPM = (100 × 3.73 × 0.70 × 1,000) ÷ (2.0 × 60) = 261,100 ÷ 120 = 2,176 RPM

Preventive Maintenance

Oil Change Intervals

Transmission oil change intervals vary by manufacturer. In general:

Manual transmission: every 60,000 to 100,000 km.

Automatic transmission: every 60,000 km for severe service, 100,000 km for normal service.

Differential: every 80,000 to 120,000 km.

Safe Drain Procedure

151.Wear oil-resistant gloves and safety glasses.

152.Place a catch pan under the drain plug.

153.Remove the drain plug carefully (oil may be hot).

154.Allow to drain completely.

155.Replace the plug gasket.

156.Fill with the manufacturer-specified oil.

157.Check the level according to procedure (engine running for automatics).

Pitfalls to Avoid

Confusing API GL-4 and GL-5 classifications: using GL-5 in a transmission with brass synchronizers causes corrosion. Always check the manufacturer's specification.

Neglecting clutch pedal free play adjustment: incorrect free play is a common cause of premature failure.

Forgetting to purge the hydraulic circuit after a converter replacement: trapped air causes erratic operation.

Measuring backlash without proper preload: the measurements will be inaccurate.

Using a diagnostic tool without checking the oil level: many trouble codes are caused by low fluid level.

Confusing transmission ratio and axle ratio in engine RPM calculations.

Over-tightening pressure plate bolts: deforms the plate and causes slippage.

Ignoring high-speed vibrations: they often indicate an unbalanced drive shaft or worn joints.

Not respecting torque specifications: always consult the manufacturer's specifications.

Reusing gaskets and O-rings: they must be replaced systematically.

Summary

The transmission modifies torque and speed between the engine and the wheels. Gear ratio = driven teeth ÷ driving teeth.

The manual transmission uses synchronizers to equalize speeds before engagement. Synchronizer end play must not exceed 0.10 mm.

The dry friction clutch requires precise pedal free play adjustment (10 to 25 mm).

The automatic transmission uses a torque converter with a maximum torque multiplication ratio of approximately 2.5:1. Pressure testing and the stall test are essential diagnostic tools.

The planetary gear set follows the formula: ratio = 1 + (Z_ring ÷ Z_sun) for the fixed sun gear case.

The differential allows speed difference between the wheels. Backlash must be 0.10 to 0.20 mm.

Applicable Canadian standards include the Canadian Electrical Code, Part I (Rule 8-200) for shop installations and CSA B149.1 for gas vehicles.

Engine RPM calculations require knowing the axle ratio, transmission ratio, and tire circumference.

Typical maintenance intervals are 60,000 to 100,000 km for transmission oils.

Safety requires glasses, gloves, adequate ventilation, and compliance with lifting standards (CSA Z271).

This chapter has provided you with the essential knowledge to approach Red Seal exam questions on transmission systems. Review the formulas, tolerances, and diagnostic procedures. Practicing calculations and memorizing typical specifications will give you a decisive advantage on exam day.