How To Use a Drum Micrometer

Do you need to find out the exact measurement of your brake drum’s inside diameter? Then, learn how to properly use a drum micrometer.  Once you have become more familiar with the tool, you can readily work on your car’s drum braking systems, especially if you have a four-wheel antique. You can use it in taking care of your car’s rear brakes, too.

Understand that your brake drum’s inside diameter begins to wear off during the brake shoe replacement process. Watch out for your brake drum when you machine it on a lathe. After a while, your brake drum’s inside diameter changes. When it becomes too thin or too wide, it is going to become less effective.

Don’t forget that all vehicle types have a so-called “discard” measurement for brake drums. The “discard” measurement sets the limit on how far you can reach your brake drum’s inside diameter. A drum micrometer can aid in letting you determine how far is your brake drum to the “discard” measurement.

Here are some guidelines for you:

  • Lay your brake drum upside down on a working table. See to it that the surface is leveled. You should also check your brake drum’s inside diameter. Is it facing upward? If not, adjust it accordingly.
  • Inspect your brake drum’s inside diameter. Do you notice any heat cracks? Are scorings already present? Scorings lead to uneven surfaces. Uneven surfaces can cut deeply into your brake drum’s interior surface. Why?  It is where you place your shoes.
  • If scorings are already present, examine them further. Which score line is the deepest?  Bring out your drum micrometer to measure it. That should let you know if you can machine your brake drum.
  • Check out the indicators of your drum micrometer. Are they properly positioned? Are they evenly distributed inside your brake drum? If not, exert pressure on them. Keep the pressure light and even. The pressure is going to let the misplaced indicators to fit or line up with the scorings in your brake drum’s inside diameter.
  • Hold you brake drum. You can ask someone to help you, if necessary. Otherwise, you can simply position your hands right at each end of your drum micrometer. Continue by turning your drum micrometer.
  • Let your brake drum’s inside circumference follow a clockwise direction. Focus on your drum micrometer’s dial indicator. Is there any variance? Measure it. A measurement anomaly clearly indicates that your brake drum has started warping. In other words, it is already useless.
  • Record the exact measurement indicated in your drum micrometer’s reading. Compare your reading and the circumference measurement? Is there any variance?  
  • Generally, you can find a measurement stamp on your brake drum. It is right on the outside face. The measurement stamp reads: “machine to”. This should be your last consideration. Once you have checked its measurement, you can tell if your brake drum has to be replaced. Realize that reading the measurement may be challenging because the part has been exposed. 

The entire process may turn out to be tedious.  So, be patient. You may have to remove any dust or rust, if needed.


Share this article!

Follow us!

Find more helpful articles: