Universal Joints and Rear Axle in Vehicle Transmission for SS 3

Class: SS 3
Term: First Term
Week: 5
Age: 16 years
Duration: 45 minutes
Subject: Auto Mechanic Work
Curriculum Theme: Vehicle Transmission System
Previous Lesson: Fluid Flywheel, Gearbox and Propeller Shaft
Topic: FLUID FLY WHEEL AND TRANSMISSION COMPONENTS – UNIVERSAL JOINTS, REAR AXLE.
Subject Matter: The teacher will dismantle, inspect and reassemble a rear axle. He will test the propeller shaft for straightness (using dial indication and vee-block). He will reassemble component parts of the gear box. The students will identify and examine types of rear axle assembly; semi- floating, three- quarter floating, fully floating; Resources; live vehicle, rear axle, tools, posters, charts, universal joints

Specific Objectives

By the end of the lesson, pupils/students should be able to:

Cognitive Domain

• Identify the components of a rear axle assembly.
• Explain the function of universal joints in vehicle transmission.
• Describe the different types of rear axle assemblies.

Psychomotor Domain

• Dismantle and inspect a rear axle.
• Reassemble a rear axle correctly.
• Test a propeller shaft for straightness using a dial indicator and vee-block.
• Identify and examine semi-floating, three-quarter floating, and fully floating rear axle assemblies.

Affective Domain

• Appreciate the importance of proper inspection and reassembly procedures in vehicle maintenance.
• Demonstrate safety precautions during practical work involving vehicle components.

Reference Materials

The following resources were used in planning this lesson:

• 2025 Revised 9 Years Basic Education Curriculum
• Relevant State Unified Scheme of Work
• Auto Mechanic Work for Senior Secondary Schools, Book 3
• The HeadTeacher Scheme of work

Instructional Materials

The teacher will teach this lesson with the aid of:

• A live vehicle (for demonstration purposes)
• A dismantled rear axle assembly
• Various auto mechanic tools (wrenches, sockets, screwdrivers, dial indicator, vee-block, etc.)
• Posters and charts illustrating universal joints and different rear axle types
• Universal joints (various types if available)

Rationale for the Lesson

This lesson provides students with essential practical skills and theoretical knowledge concerning universal joints and rear axle assemblies, which are critical components of a vehicle’s transmission system. Understanding their function, types, and maintenance procedures is fundamental for aspiring auto mechanics, ensuring safe and efficient vehicle operation.

Prerequisite/Previous Knowledge

Students should have basic knowledge of vehicle transmission systems, including the propeller shaft and gearbox, from previous lessons.

Lesson Content/Board Summary

Universal Joints and Rear Axle in Vehicle Transmission

Universal Joints

Universal joints (U-joints) are flexible couplings that connect two shafts, allowing them to transmit rotational motion at an angle to each other. They are essential in vehicle transmission systems to accommodate changes in angle and length between the gearbox output shaft and the rear axle input shaft (differential pinion shaft) as the vehicle moves over uneven terrain.

1. Function: To transmit power smoothly from the propeller shaft to the differential, despite the changing angles caused by suspension movement.
2. Location: Typically found at both ends of the propeller shaft.

Rear Axle

The rear axle is a crucial component of the vehicle’s drivetrain that transmits power from the differential to the driving wheels. It also supports the weight of the vehicle and maintains the wheel alignment.

1. Components: Includes the axle housing, axle shafts, differential unit, and wheel bearings.
2. Function: To transfer torque from the propeller shaft (via the differential) to the road wheels, allowing the vehicle to move.

Types of Rear Axle Assembly

Rear axle assemblies are classified based on how the axle shaft is supported and how it handles bending and shearing loads.

1. Semi-Floating Axle

   In a semi-floating axle, the axle shaft supports the vehicle’s weight and transmits driving torque. The outer end of the axle shaft is supported by a single bearing located inside the axle housing, close to the wheel hub. It is commonly used in passenger cars and light-duty trucks.

   1. Load Bearing: Carries both bending (vehicle weight) and shearing (driving torque) loads.
   2. Support: One bearing at the outer end.

2. Three-Quarter Floating Axle

   The three-quarter floating axle provides better support than the semi-floating type. It uses two bearings at the outer end of the axle shaft, which are mounted on the axle housing. This arrangement helps to relieve some of the bending stress on the axle shaft, allowing it to primarily transmit torque.

   1. Load Bearing: Primarily carries shearing loads, with some bending load.
   2. Support: Two bearings at the outer end, mounted on the axle housing.

3. Fully Floating Axle

   A fully floating axle is designed so that the axle shaft carries only the driving torque (shearing load). The vehicle’s weight and all bending loads are supported by the axle housing through two bearings located outside the axle shaft, at the wheel hub. This design is robust and commonly used in heavy-duty vehicles like trucks and buses.

   1. Load Bearing: Carries only shearing loads (driving torque).
   2. Support: Two bearings at the wheel hub, supporting the axle housing.

Propeller Shaft Straightness Test

The propeller shaft must be straight to ensure smooth power transmission and prevent vibrations. Straightness is tested using:

1. Dial Indicator: A precision measuring instrument used to detect small deviations.
2. Vee-Block: A V-shaped block used to support cylindrical workpieces (like the propeller shaft) horizontally for inspection.

The propeller shaft is placed on vee-blocks, and a dial indicator is used to measure run-out (deviation from straightness) as the shaft is rotated.

Teaching Methods/Instructional Techniques

Discussion, Demonstration, Guided Practice, Question and Answer, Explanation, Observation, Practical Activity

Instructional Procedures

Step 1: Introduction

Time: 5 minutes

Teaching Skill: Explaining/Questioning

Teacher’s Activity: The teacher greets the students and reviews the previous lesson on the propeller shaft and gearbox. The teacher then introduces the new topic by asking students about the components that connect the gearbox to the rear wheels and how power is transmitted despite suspension movement.

Pupils’ Activity: Students respond to questions and listen attentively to the introduction of the new topic.

Learning Point: Link to previous lesson

Step 2: Introduction to Universal Joints

Time: 7 minutes

Teaching Skill: Explanation/Demonstration

Teacher’s Activity: The teacher explains what universal joints are, their function, and where they are located in the transmission system. The teacher uses a universal joint component and charts/posters to demonstrate its structure and how it allows for angular movement.

Pupils’ Activity: Students observe the universal joint, ask questions, and take mental notes.

Learning Point: Universal joint function

Step 3: Introduction to Rear Axle

Time: 7 minutes

Teaching Skill: Explanation/Demonstration

Teacher’s Activity: The teacher explains the function of the rear axle and identifies its main components using a dismantled rear axle assembly. The teacher highlights how it transmits power to the wheels and supports vehicle weight.

Pupils’ Activity: Students observe the rear axle components and listen to the explanation.

Learning Point: Rear axle components

Step 4: Demonstrating Rear Axle Dismantling and Inspection

Time: 8 minutes

Teaching Skill: Practical Demonstration

Teacher’s Activity: The teacher demonstrates how to safely dismantle and inspect a rear axle assembly, pointing out key wear points and components that require attention during maintenance. The teacher also demonstrates reassembly briefly.

Pupils’ Activity: Students observe the dismantling, inspection, and reassembly process, asking questions about specific steps.

Learning Point: Rear axle practical steps

Step 5: Types of Rear Axle Assembly

Time: 7 minutes

Teaching Skill: Explanation/Identification

Teacher’s Activity: The teacher explains and differentiates between semi-floating, three-quarter floating, and fully floating rear axle assemblies, using charts and the dismantled rear axle to point out distinguishing features where possible. Students are guided to identify these types.

Pupils’ Activity: Students identify and examine the different types of rear axle assemblies based on the teacher’s explanation and visual aids.

Learning Point: Rear axle types

Step 6: Propeller Shaft Straightness Test

Time: 4 minutes

Teaching Skill: Demonstration

Teacher’s Activity: The teacher demonstrates how to test a propeller shaft for straightness using a dial indicator and vee-blocks, explaining the importance of this test for smooth vehicle operation.

Pupils’ Activity: Students observe the demonstration of the propeller shaft straightness test.

Learning Point: Propeller shaft testing

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

1. What is the primary function of a universal joint?
2. Mention two main components of a rear axle assembly.
3. Differentiate between a semi-floating and a fully floating rear axle assembly.
4. What tools are used to test a propeller shaft for straightness?

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Understanding transmission components

Step 8: Note-Taking

Time: 4 minutes

Teaching Skill: Guided Writing

Teacher’s Activity: The teacher guides pupils/students to copy the essential Board Summary notes on universal joints, rear axle components, and types of rear axle assemblies into their notebooks.

Pupils’ Activity: Pupils/students copy the notes carefully into their notebooks.

Learning Point: Recording lesson content

Step 9: Conclusion

Time: 3 minutes

Teaching Skill: Summarising

Teacher’s Activity: The teacher briefly summarises the key learning points about universal joints, rear axles, their types, and the importance of proper inspection and maintenance in vehicle transmission systems.

Pupils’ Activity: Students listen and ask any final questions.

Learning Point: Lesson consolidation

Continuous Assessment/Further Study

Type: Homework/Practical Exercise

Instruction: Research and draw the three types of rear axle assemblies, clearly labelling their distinguishing features. Additionally, identify common faults associated with worn universal joints and their symptoms in a vehicle.

1. Draw and label a semi-floating rear axle assembly.
2. Draw and label a three-quarter floating rear axle assembly.
3. Draw and label a fully floating rear axle assembly.
4. List three common symptoms of a faulty universal joint.

Lesson Keywords

• Universal joint – A flexible coupling that transmits power between shafts at an angle.
• Rear axle – A component that transmits power from the differential to the driving wheels.
• Propeller shaft – The shaft that connects the gearbox to the differential.
• Semi-floating axle – An axle that carries both vehicle weight and driving torque, with one outer bearing.
• Three-quarter floating axle – An axle that primarily carries torque, with two outer bearings on the housing.
• Fully floating axle – An axle that carries only driving torque, with vehicle weight supported by the housing on two outer bearings.
• Dial indicator – A precision tool used to measure small linear distances or deviations.
• Vee-block – A V-shaped block used to support cylindrical objects for inspection.

Differentiation

For struggling learners: Provide simplified diagrams of the axle types and universal joints. Focus on identifying the main function and location of each component. Allow them to work in pairs during practical observation.
For advanced learners: Challenge them to research the advantages and disadvantages of each rear axle type for different vehicle applications. Encourage them to explain the forces acting on each axle type in detail.

Suggested Lesson Videos

For further visual understanding, search on YouTube for:
universal joint function auto mechanics
types of rear axle assembly explained
propeller shaft runout test

Teacher Guide for Using This Lesson Plan

Before the lesson, ensure all instructional materials, especially the dismantled rear axle, universal joints, and tools (dial indicator, vee-blocks), are readily available and in good working condition. Arrange the classroom or workshop to facilitate clear demonstration and student observation. Begin by briefly reviewing prior knowledge of vehicle transmission to set the context. During the practical demonstrations of dismantling, inspection, and reassembly, emphasise safety procedures and the correct use of tools. Guide students to actively observe and identify the different components and axle types. For the propeller shaft straightness test, ensure students understand the purpose and how to interpret the dial indicator readings. Encourage questions throughout the practical activities. Students should copy the Board Summary notes during Step 8. Conclude by reinforcing the importance of these components for vehicle performance and safety, linking theoretical knowledge with practical application.