Automobile & Light Truck Certification Test A5 BrakesMachiningMedium
A technician is setting up a bench-type brake lathe to machine a drum. After mounting the drum on the arbor, the technician uses a dial indicator on the drum's friction surface. The indicator shows excessive runout (more than 0.006 inches). What is the FIRST step the technician should take to correct this issue?
- ARe-position the drum on the arbor, ensuring proper seating.
- BIncrease the spindle speed of the lathe.
- CAdjust the setting of the cutting bits.
- DApply a heavier depth of cut for the first pass.
Show answer & explanationAnswer & explanation
Correct answer: A. Re-position the drum on the arbor, ensuring proper seating.
Excessive runout after mounting the drum indicates a problem with how the drum is seated on the arbor or the arbor itself. The first step is always to re-seat the drum and re-check, as improper mounting is a common cause of runout.
Why the other options are wrong
- B. Spindle speed affects cutting action, not the physical alignment of the mounted drum.
- C. Cutting bit adjustment is for the machining process itself, not for correcting initial mounting runout.
- D. A heavy depth of cut would not correct runout; it would simply cut the drum unevenly based on the existing runout.
Brake Drum Runout
The amount of lateral deviation or wobble in the friction surface of a brake drum as it rotates, which can cause pulsation, noise, and uneven pad wear if excessive.
- Measured with a dial indicator.
- Can be caused by improper mounting, warped drums, or worn bearings.
- Must be corrected before machining for a quality finish.
Memory trick: Is it seated right? If not, it's not straight!