Question 60 MODE01 - Chief MODU Engineer

The Correct Answer is B ### Why Option B ("feeler gauge") is Correct Backlash in a gear drive is the clearance or distance between the non-driving flanks of adjacent teeth on mating gears. It is essentially the amount of free movement one gear has before engaging the other. The most common, accurate, and practical method for directly measuring this small physical gap, especially in applications like automotive differentials or transmissions (where an illustration like MO-0091, often showing a ring and pinion gear, is common), is by using a **feeler gauge**. The feeler gauge blades, which have precise thicknesses, are inserted into the gap between the meshing gear teeth to determine the maximum clearance. ### Why Other Options are Incorrect **A) lead wire:** Lead wire (or plastic gauge) is a deformation material used specifically to measure the clearance between two surfaces that are clamped tightly together, such as connecting rod bearings or main bearings. It is not suitable for measuring the dynamic, open clearance (backlash) between gear teeth. **C) lash indicator:** While a "lash indicator" (typically a dial indicator mounted on a magnetic base) is the preferred tool for precisely measuring the *runout* or *movement* of the gear (e.g., measuring the movement of the ring gear while holding the pinion stationary), it measures displacement. A feeler gauge is often used in conjunction with a dial indicator, but the feeler gauge directly measures the physical gap defined as backlash, making it a more fundamental and universally applicable answer for *determining* the gap itself. In many standard shop procedures, a feeler gauge is the primary method for checking backlash compliance against specifications. **D) red dye indicator:** Red dye penetrant is a non-destructive testing method used to find surface flaws, cracks, or porosity in materials. It is completely unrelated to the measurement of mechanical clearances or backlash.