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
Topic: FLUID FLY WHEEL AND TRANSMISSION COMPONENTS – UNIVERSAL JOINTS, REAR AXLE.
Subject Matter: He 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
Previous Lesson: Fluid Flywheel, Gearbox and Propeller Shaft

Specific Objectives

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

Cognitive Domain

• Identify and describe the function of universal joints.
• Identify and describe the function of the rear axle.
• Differentiate between semi-floating, three-quarter floating, and fully floating rear axle assemblies.

Psychomotor Domain

• Safely dismantle and reassemble a rear axle.
• Inspect a rear axle for faults.
• Test a propeller shaft for straightness using a dial indicator and vee-block.
• Reassemble component parts of a gearbox.

Affective Domain

• Appreciate the importance of proper inspection and maintenance of transmission components.
• Demonstrate careful handling of tools and vehicle parts during practical activities.

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 (or a chassis with transmission components)
• A dismantled rear axle assembly
• Universal joints
• Assorted hand tools (wrenches, sockets, screwdrivers)
• Dial indicator and vee-blocks
• Posters and charts illustrating transmission components and rear axle types
• Safety goggles and gloves

Rationale for the Lesson

This lesson provides students with essential practical skills and theoretical knowledge regarding universal joints and rear axle assemblies, which are critical components of vehicle transmission systems. Understanding their function, types, and maintenance procedures is fundamental for diagnosing and repairing common vehicle faults, preparing students for careers in auto mechanics.

Prerequisite/Previous Knowledge

Students should have a basic understanding of vehicle transmission systems, the purpose of a gearbox, and the general layout of a vehicle’s drivetrain.

Lesson Content/Board Summary

FLUID FLY WHEEL AND TRANSMISSION COMPONENTS – UNIVERSAL JOINTS, REAR AXLE.

Universal Joints

Universal joints (U-joints) are flexible couplings that allow a rotating shaft to transmit power at an angle. They are essential in vehicle drive shafts (propeller shafts) to accommodate changes in angle between the gearbox and the rear axle as the vehicle moves over uneven terrain.

Functions of Universal Joints:

1. Transmit torque between shafts that are not in a straight line.
2. Allow for angular movement and changes in distance between components.
3. Compensate for misalignment between the transmission and the differential.

Rear Axle Assembly

The rear axle assembly is a critical component of a vehicle’s drivetrain that transmits power from the propeller shaft to the wheels, allowing them to rotate. It also supports the weight of the vehicle and maintains the wheel alignment.

Types of Rear Axle Assembly

Rear axle assemblies are primarily classified by how the axle shaft is supported and how it carries the vehicle’s weight. The main types include:

1. Semi-Floating Axle:

   In a semi-floating axle, the axle shaft supports the weight of the vehicle and transmits driving torque. The outer end of the axle shaft is supported by a bearing inside the axle housing, and the wheel is bolted directly to the axle flange. This type is commonly found in passenger cars and light trucks.

   Characteristics:

   1. Carries both vehicle weight and driving torque.
   2. If an axle shaft breaks, the wheel can detach.
   3. Simpler and less expensive to manufacture.
2. Three-Quarter Floating Axle:

   The three-quarter floating axle is an improvement over the semi-floating type. It uses a single bearing between the axle housing and the wheel hub, which helps to support some of the vehicle’s weight. The axle shaft still transmits driving torque and some bending loads.

   Characteristics:

   1. Better at handling side thrust than semi-floating.
   2. Axle shaft primarily transmits torque, but still carries some weight.
   3. Wheel is bolted to the hub, which is supported by the bearing.
3. Fully Floating Axle:

   In a fully floating axle, the axle shaft only transmits driving torque. The vehicle’s weight is entirely supported by two bearings mounted on the outside of the axle housing, with the wheel hub attached to the housing. This design is robust and typically used in heavy-duty vehicles like trucks and buses.

   Characteristics:

   1. Axle shaft carries only driving torque, no vehicle weight.
   2. If an axle shaft breaks, the wheel remains attached to the vehicle.
   3. More complex and expensive, but highly durable.

Dismantling, Inspection, and Reassembly of a Rear Axle

The process involves:

1. Dismantling: Carefully removing components such as the differential cover, axle shafts, bearings, and gears, following manufacturer’s guidelines.
2. Inspection: Checking all parts for wear, damage, cracks, pitting, or scoring. This includes examining gears, bearings, seals, and the axle housing.
3. Reassembly: Replacing worn parts, lubricating components, and reassembling the axle in reverse order of dismantling, ensuring correct torque settings and proper sealing.

Testing Propeller Shaft for Straightness

A bent or unbalanced propeller shaft can cause severe vibrations. Straightness is tested using:

1. Vee-blocks: The propeller shaft is placed on two vee-blocks.
2. Dial Indicator: A dial indicator is set up to touch the shaft surface.
3. Rotation: The shaft is slowly rotated, and any deviation from straightness is indicated by the dial gauge. Excessive runout indicates a bent shaft that requires repair or replacement.

Reassembly of Gearbox Components

Reassembling a gearbox involves:

1. Cleaning all components thoroughly.
2. Inspecting gears, shafts, bearings, and synchronizers for wear or damage.
3. Replacing worn parts with new ones.
4. Lubricating all moving parts during assembly.
5. Carefully fitting gears, shafts, and bearings into the gearbox casing, ensuring correct alignment and clearances.
6. Sealing the gearbox casing to prevent oil leaks.

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: Engaging/Recalling

Teacher’s Activity: The teacher greets the students and asks them to recall previous knowledge about vehicle transmission systems and the components involved in transferring power from the engine to the wheels.

Pupils’ Activity: Students respond by mentioning components like the engine, clutch, gearbox, and propeller shaft.

Learning Point: Recalling transmission components

Step 2: Introduction to Universal Joints

Time: 5 minutes

Teaching Skill: Explanation/Demonstration

Teacher’s Activity: The teacher introduces universal joints, explains their function in accommodating angular movement, and shows a physical universal joint or a diagram. He explains why they are needed in the propeller shaft.

Pupils’ Activity: Students observe the universal joint and listen to the explanation, asking questions for clarity.

Learning Point: Universal joint function

Step 3: Introduction to Rear Axle and its Function

Time: 5 minutes

Teaching Skill: Explanation/Visual Aid

Teacher’s Activity: The teacher introduces the rear axle assembly, explaining its role in power transmission and vehicle support. He uses charts or a live vehicle to point out its location and main parts.

Pupils’ Activity: Students observe the rear axle on the vehicle/chart and understand its basic function.

Learning Point: Rear axle purpose

Step 4: Identifying Types of Rear Axle Assembly

Time: 10 minutes

Teaching Skill: Explanation/Classification

Teacher’s Activity: The teacher explains and differentiates between semi-floating, three-quarter floating, and fully floating rear axle assemblies, highlighting their construction and how they support vehicle weight and transmit torque. He uses diagrams or actual components to illustrate the differences.

Pupils’ Activity: Students identify and examine the different types of rear axle assemblies shown, noting their key characteristics.

Learning Point: Rear axle types

Step 5: Practical Demonstration – Rear Axle

Time: 8 minutes

Teaching Skill: Demonstration/Practical Guidance

Teacher’s Activity: The teacher demonstrates the safe dismantling, inspection (checking for wear on gears, bearings, seals), and reassembly of a rear axle assembly, emphasizing correct procedures and safety precautions.

Pupils’ Activity: Students observe the teacher’s demonstration carefully, noting the steps and safety measures.

Learning Point: Rear axle practical skills

Step 6: Practical Demonstration – Propeller Shaft and Gearbox

Time: 8 minutes

Teaching Skill: Demonstration/Technical Skill

Teacher’s Activity: The teacher demonstrates how to test a propeller shaft for straightness using a dial indicator and vee-blocks. He also briefly demonstrates the reassembly of some component parts of a gearbox, highlighting critical alignment points.

Pupils’ Activity: Students observe the testing procedure and gearbox reassembly, understanding the importance of precision.

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. Name three types of rear axle assemblies.
3. Describe one key difference between a semi-floating and a fully floating axle.
4. Why is it important 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 types, and practical procedures into their notebooks.

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

Learning Point: Recording key concepts

Step 9: Conclusion

Time: 5 minutes

Teaching Skill: Summarizing

Teacher’s Activity: The teacher briefly reiterates the importance of universal joints and rear axle assemblies in vehicle transmission and the necessity of proper inspection and maintenance for vehicle safety and performance. He encourages students to practice the practical skills learned.

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

Learning Point: Consolidating lesson importance

Continuous Assessment/Further Study

Type: Practical Exercise/Homework

Instruction: In groups, research and prepare a short presentation on the common faults associated with each type of rear axle assembly and how they are diagnosed.

1. Identify at least two common faults for each type of rear axle (semi-floating, three-quarter floating, fully floating).
2. Describe the symptoms a driver might notice for each fault.
3. Suggest initial diagnostic steps for each fault.
4. Present your findings to the class next week.

Lesson Keywords

• Universal Joint – A flexible coupling that allows a rotating shaft to transmit power at an angle.
• Rear Axle – A component that transmits power from the propeller shaft to the wheels and supports vehicle weight.
• Propeller Shaft – A shaft that transmits power from the gearbox to the rear axle.
• Semi-Floating Axle – An axle type where the shaft supports vehicle weight and transmits torque.
• Three-Quarter Floating Axle – An axle type with a single bearing supporting some weight, with the shaft primarily transmitting torque.
• Fully Floating Axle – An axle type where the shaft only transmits torque, and vehicle weight is supported by two bearings on the housing.
• Dial Indicator – A precision measuring instrument used to check for straightness or runout.
• Vee-blocks – Supports used to hold cylindrical objects for inspection or machining.

Differentiation

For weaker learners, the teacher will provide simplified diagrams and focus primarily on identifying the different types of rear axles and their basic functions, offering more guided observation during practicals. Faster learners will be encouraged to research specific maintenance schedules for different axle types and investigate the role of the differential within the rear axle assembly.

Suggested Lesson Videos

For further understanding, students can search YouTube for:

• “How universal joints work”
• “Types of rear axle assembly explained”
• “Propeller shaft inspection and balancing”
• “Rear axle differential overhaul”

Teacher Guide for Using This Lesson Plan

Before the lesson, ensure all instructional materials, especially the live vehicle (or chassis), a dismantled rear axle, universal joints, and specialized tools like the dial indicator and vee-blocks, are in good working condition and safely arranged. Emphasize safety protocols during all practical demonstrations, ensuring students maintain a safe distance and wear appropriate personal protective equipment. Begin by engaging students with questions about power transmission to activate prior knowledge. Proceed systematically through the types of rear axles, using visual aids to make the distinctions clear. The practical demonstrations are central to this lesson; ensure each step of dismantling, inspection, and reassembly is clearly visible and explained. When demonstrating the propeller shaft straightness test, highlight the importance of accuracy. Allow students to ask questions throughout the practical sessions. Students should copy the Board Summary notes after the practical demonstrations and evaluation. Conclude by reinforcing the practical relevance of the lesson for future auto mechanics.