Tags

Lesson Plan Industry Sector
Transportation

Lesson Plan Originally Created By: Eli Jaramillo

**Turning Brake Drums (updated) By Eli Jaramillo

Part of Unit: Brake Systems

Lesson Plan Overview / Details

Overview:  At the end of this lesson, students will know how to determine if a vehicle brake drum should be turned or replaced and the steps necessry to safely and accurately turn (resurface) brake drums as needed.

Details:  This is a two-hour lesson in which students will learn how to use a brake drum lathe to turn brake drums.  The goal:  Instruct students on the importance of proper diagnostics, measurements, and equipment usage for fixed-right first-time and best customer satisfaction.

Understanding the proper use of a brake drum lathe is still a viable skill set needed by the professional technician.  This lesson will cover all aspects of this task.   Additionally, ASE test-preparation tasks will be emphasized during this lesson.

Lesson Time

Classroom: Hook activity
30 Minutes
Lab: Instructor demo
30 Minutes
Lab: Student practice
45 Minutes
Classroom: Wrap-up
15 Minutes

Objectives and Goals

  • Students will use the brake drum micrometer and critical thinking skills on a brake drum to interpret the results of their findings: "go" or "no-go".
  • Students will use both metric and US standard measuring systems when performing measurements on brake drums.
  • Students will understand how to find brake drum limit specifications using the following sources: 1) Specifications cast or imprinted on the brake drum. 2) Online or printed service and repair information.
  • Students will follow proper procedures when setting up and adjusting a brake drum lathe.
  • Students will use the brake drum lathe to accurately turn and create a proper finish in a brake drum.
  • Students will be taught the advantages and importance of ASE certification for brake technicians.

Activities in this Lesson

  • Materials needed:

    • Whiteboard: (Write the following) Unit:  Brakes.  Lesson today:  "Turning Brake Drums"
    • Worksheet:  Brakes and a Close Call!

    Instructor Note:  As students walk in, have them pick up the worksheet Brakes and a Close Call!  and start working on it while you're taking roll.  This is an ungraded worksheet that will be used for discussion.  It will help get the students settled and in tune with the topic for the lesson.

    Instructor:  "Here's the scenario:  You're driving out of the mountains in a clean 1950's vintage pickup truck. Most late-model vehicles have disk brakes, however your truck sports drum brakes all around, as it came from the factory.  It's a collector vehicle once owned by a relative, so you want to keep it all original.  And you also keep it well maintained.  This includes the brake job you had done on it about a month ago.  So you feel confident as you negotiate the narrow road and brake for the curves.  Suddenly coming around a blind curve, you encounter a rock slide that covers the road ahead.  You press on the brake pedal hard, only to find that the brakes aren't responding a quickly as you need.  You're heading straight for the rock slide, slowing down, but maybe not quickly enough..."

    Instructor:  "Fast forward to today and this class.  Most of you have either had experience or heard from someone in which brakes had an affect on either a vehicle accident or a close call."

    Instructor Note:  Call on a few students to share some of their 'close call' experiences.  You're looking for one that shared a scenario involving brake fade.

    Instructor:  "A few of you have shared close call experiences pertaining to vehicle brakes.  All of them shared the same braking requirement:  Stop the vehicle as quickly as possible.   What specific brake problems might have caused the brakes not to have the frictional 'grab' necessary to stop the vehicle on time?"

    Instructor Note:  You may get answers such as worn out brakes, low brake fluid, leak in the hydraulic system.  Those are all correct.  For our purposes, what you're looking for are the key words 'excessive heat' which can cause brake fade.  If students don't target in on that, 'lead' them into a discussion about metal thickness and the ability to absorb or store heat (i.e. brake drums turned too far causing a 'thin metal' condition, so they can't absorb the heat as readily, resulting in brake fade).

    Instructor:  "Excessive heat could be caused by many things.  Dragging brakes, misadjustment, weak brake shoe return springs, these could all cause this issue.  Another factor is metal thickness on the brake drum itself."

    Instructor:  "The other part of your worksheet asked you to list three important requirements of a brake system.  What do you feel these requirements are? (You're after Basics:  Stop quick, straight, every time.) (Call on students vs. asking for raise of hands.)

    Instructor:  "Today's lesson will cover the very important operation of turning a brake drum to ensure that the vehicle stops quick, straight, and every time."

    Instructor:  "Any questions on what we've covered so far?"

    Resources and Materials

    • Brakes and a close call!_worksheet.doc [ Download ] Worksheet used by students during the lecture.
  • Materials needed:

    • PowerPoint Presentation "Turning a brake drum" slides 1 through 7
    • Student lab worksheet " Turning a brake drum"
    • "Instructor Answer Key" version of the above worksheet
    • Brake shoes which have been worn down to metal
    • Brake drum which has been damaged due to 'metal-to-metal' contact from worn brake shoes
    • Brake drum which was turned too far (over factory spec or .060" limit)
    • Brake drum micrometer
    • # -grit sndpaper

    Instructor Note:  Hand out worksheet "Turning a Brake Drum".

    Instructor:  "You'll complete #1 on the worksheet in the classroom and the rest in the lab."  I'll be providing key words that you'll use to fill in the correct answer on the worksheet, so listen carefully."

    Instructor:  "For starters, here's the most important rule:  Not all brake jobs require the turning of a brake drum."

    Instructor:  " Back in 'the day', when technicians performed brake jobs, there was a more relaxed attitude about turning brake drums.  Technicians often put the drum back on the vehicle even if there was scoring or gouges in the drum inner surface.  Today, many technicians feel they need to turn the brake drum any time they do a brake job even if the surface is free of imperfections.  The rule of thumb is:  Drums should be turned only if there are major imperfections or an out-of-round condition.  Any questions so far?"

    Instructor:  "Minor scoring or glazing may be removed using the brake drum lathe and  -grit sandpaper vs. removing metal by lurning the drums.

      Instructor Note:  Hold up a brake drum that is a good candidate for this process.

    Instructor:   "If the drum needs to be turned, the technician should only turn the drum enough to remove the imperfection.  Turning removes metal.  Less brake drum metal equals less ability to absorb heat.  More heat in the brake drum can lead to brake fade."

    Instructor:  "Any questions on what we've covered so far?"

    Instructor:  "Another basic rule:  If you turn the drum on one side of the vehicle, you should turn the drum on the other side to the same diameter.  This will maintain 'same thickness' condition on both sides for even stopping."

    Instructor:  "As we mentioned, there may be some wear or frictional surface problems that require a drum to be turned or replaced.  Here are some examples."

    (Begin powerpoint presentation here)

    (Slide #1):   Instructor:  "OK, let's get started on the slide show.  First thing, as with any vehicle repair, we need to have a plan.  So here's our plan for this lesson.  First, a discussion of pre-checks we always follow before turning any drum.  This will include demonstrations of these pre-checks, followed with a demo in the lab of actually mounting and turning a brake drum.  Then we'll give you the chance to practice turning a brake drum.  Finally we'll have a wrap-up session to discuss what we've learned."

    Instructor:  "Any questions so far?  Okay, let's get started with some pre-checks before making a go-no go decision for turning a drum.  For starters, let's look at some examples of brake drum problems."

    (Slide #2):   Instructor:  "Here's a cracked brake drum.  Notice the deep cracks in the drum frictional surface.  This is dangerous, it cannot be machined out, and requires drum replacement. However, major cracks in the surface shouldn't be confused with heat checking.  This is a normal condition in which small hairline cracks appear on the frictional surface due to temperature changes on the drum surface.  Generally, these are superficial and do not affect brake performance."

    Instructor:  (Hold up a brake drum with slight scoring):   "Here's a brake drum with scoring, probably due to metal-to-metal contact with a worn brake shoe.  Slight scoring is probably OK and can be 'dressed' using some 80 -grit sandpaper."

    Instructor Note:  Show the sandpaper.

    (Slide #3):  Instructor:  "Next, we have an example of a drum with scoring due to metal-to-metal contact with worn-out brake shoes.  Deep scoring requires the drum to be turned.  Or if it's severe enough, the drum should be replaced."  

    (Slide #4):  Instructor:  "Drums with hard, raised, dark colored spots on the braking surface are “martensite spotted” which is caused by very high temperatures. If you try to turn the drums, these hard spots will leave a raised surface on the drum finish.  The drum should be replaced and the cause of excessive heat should be corrected."

    (Slide #5):  Instructor:  "Drums that are grease-stained do not require turning provided they are within measurment specifications.  They may be cleaned thoroughly with brake cleaner and hand-sanded with 80 -grit sandpaper."

    (Slide #6):  Instructor:  "The same with drums that have a blue suirface due to high heat conditions.  They may be sanded and returned to service.  However, the condition causing the heat should be determined and corrected."

    Instructor:  "Question:  What could cause a high heat situation?"   (Dragging brakes possibly due to misadjustment or wrong assembly process.)

    (Slide #7):  Instructor:  "Here we have a condition known as heat checking.  This could be caused by brake drums that don't have enough metal.  Metal absorbs heat.  If the brake drums are too thin because they've been turned too far, this may be causing a high heat condition.  Heat is the enemy of the brake system.  Too much heat can cause what to happen when braking?"  (Brake fade)

    Instructor:  "Any questions on what we've covered so far?"

    Instructor Note:  Hold up a brake drum which has been turned too far.

    Instructor:  "Here's an example of a drum which was turned too far, meaning that too much metal was removed." 

    Instructor Note:  Use the brake drum micrometer on this drum and show the reading on the scale.


    Instructor:  "Question:  What can happen if the drum is too thin, too much metal removed?"  (brake fade).

    Resources and Materials

    • Worksheet: Turning a brake drum [ Download ] Used by students during lecture.
    • PowerPoint: Turning a Brake Drum [ Download ] PowerPoint presentation used for lecture activity.
  • Pre checks continued Demo / Modeling

    Materials needed:

    • PowerPoint Presentation "Turning a brake drum" slides 8 and 9
    • Four or more brake drums (Will be used by students for measuring)
    • Four or more brake drum micrometers (Also to be used by students)
    • Safety glasses for all students observing this demonstration

    Instructor Note:  Use a brake drum and a brake drum micrometer to demonstrate the following:

    (Slide #8):  Instructor:  "Another condition called out-of-round may cause the brake pedal to 'pulsate' .  The drums should be machined to restore roundness of the drum frictional surface.  In this slide, we see a drum being checked for this out-of-round condition."

    Instructor Note:  Show a brake drum with an out-of-round condition.  Use the brake drum micrometer on this drum and show the reading on the scale.

    Instructor:  "Now we'll measure the drum inner diameter with an accurate brake drum micrometer. Notice the dial and how I fit it to the brake drum. When we measure, there should be no variation in the drum inner diameter greater than .002 inch."

    Instructor:  "Any questions on what we've covered so far?"

    (Slide #9):  Instructor:  " What's a 'rule of thumb' to follow about turning brake drums?"   (   Drums should be turned only if there are major imperfections or an out-of-round condition).

    Instructor:  "What's another important rule of thumb when turning the brake drum on one side of the vehicle?  (Turn the brake drum on the other side to the same diameter).

    Resources and Materials

    • PowerPoint: Turning a Brake DrumowerPoint: Turning a Brake Drum [ Download ] PowerPoint presentation used by the instructor for the lecture.
  • Materials needed:

    • Student worksheet:  "Turning a Brake Drum"
    • "Instructor Answer Key" version of the above worksheet
    • Four or more brake drums (Will be used by students for measuring)
    • Brake drum lathe
    • Four or more brake drum micrometers (Also to be used by students)
    • Four or more brake drum measuring calipers (Used by students)
    • 80-grit sandpaper
    • Safety glasses for all students

    Instructor:  "Based on our checks, we have determined that the drum is OK to turn or resurface.  The first thing to be aware of is safety:  Eye protection is a must.  And you must not wear loose clothing.  Also, if you have hanging jewelry or long hair, it should be tied or secured out of the way."

    Instructor:  "A few more 'rules of thumb' when turning brake drums:

    • Remove only enough material to take out imperfections and to provide a smooth surface.
    • Do not remove more than .060 inch over the standard drum diameter specification.
    • The amount of material removed during a single cut should be limited to .005 inch.
    • Do a final cut of .001"
    • After your final cut, use some # 80-grit sandpaper to give a final finish to your work.
    • "When turning the brake drum on one side of the vehicle, turn the brake drum on the other side to the same diameter."  

    Instructor:  "Any questions on what we've covered so far?"

    Instructor Note:   Use the Turning a brake drum worksheet Instructor Answer Key version as a guide when you demonstrate the brake lathe usage.  Students will follow along and fill in answers needed on their worksheets.

    Instructor Note:  After demonstrating the brake lathe, have students work in groups to service a brake drum:  Or if you only have one brake lathe you may need to spread this activity out over a few lab days.  Either way, the students should be instructed to follow their worksheets which will guide them through the pre-checks, measurements, then through turning the drum if needed. And you'll be initialling the "Instructor Check-off' line on their worksheets when they've completed the exercise.  

    For this activity, it's helpful to have some spare drums handy that the students can turn for practice in case their assigned drum meets specs.

    Resources and Materials

    • Worksheet: Turning a brake drum [ Download ] Worksheet: Turning a brake drum
  • Materials needed:

    • Student Worksheet:  "Turning a Brake Drum"
    • PowerPoint presentation slides 10 through 25

    Instructor:  "Now let's wrap up the lesson, and discuss what we've learned."

    NOTE:  Lead the students through the following PowerPoint slides by calling students out with questions pertaining to each slide vs. asking for a raise of hands to answer the questions. 

    (Slide 10 thru 14):  Instructor:  "What are the four prechecks we perform before turning a drum?"

    (Slide 15 thru 18):  Instructor:  "What are some important parts of the brake drum lathe and what do they do?"

    (Slide 19 thru 21):  Instructor:  "What are the main steps to mounting the drum on the lathe?

    (Slide 22 thru 25):  Instructor:  "What are some key points to remember when actually surfacing the brake drum?

    Instructor:  "Any questions on what we've covered?"

    NOTE:  Remind students of this final key point:  W hen turning the brake drum on one side of the vehicle, turn the brake drum on the other side to the same diameter.  

    Brake drums:  What's next?

    (Slide 26):  Instructor:  "In the next few days we'll continue discussion on brakes, emphasizing technology and information which will support the all-important ASE-Brakes certification process."

    Resources and Materials

    • PowerPoint: Turning a Brake Drum [ Download ] PowerPoint presentation used during lesson review.

Assessment

Assessment Types:
Projects, Interviews, Observations,

1.  Interviews:  (questions to students):  Instructor will ask key questions to guide students through the learning process.  (Calling students out vs. asking for hands).

2.  Observations:  The instructor will monitor student activities by observing students measuring, performing brake lathe set-up, and turning brake drums.  The Instructor will assist as needed and answer any questions that the students might have.

3.  Projects:  Students will use all necessary tools and equipment to accurately and safely turn a brake drum.