How to Calculate the Diameters of the Input Shaft of a Gear Box

Transmissions are commonly called gearboxes, especially manual-shift transmissions, which operate using a clutch. Manual and automatic transmissions both use input shafts, which are used to transmit power from the clutch, or torque converter in automatic transmissions, to the gearbox. likewise, the output shaft transmits the power from the transmission to the differentials, powering the vehicle. Calculating input shaft diameter is accomplished by measuring the shaft at the location the measurement is required, and requires accessing the input shaft, if not already removed.

Instructions

1

Access the gearbox input shaft. If the gearbox is still installed on the vehicle it needs to be removed. If already out of the vehicle, the input shaft is easily accessed, as it sticks straight out of the transmission front.

2

Measure the input shaft end diameter with a machinist's ruler. The end of the input shaft enters the clutch towards the engine. Input shafts have splines on the ends and it is important to measure the diameter from spline-end to spline-end. Measure the diameter, and mark it down, being sure to count the splines as well. Spline count and diameter measurement are required when ordering gearbox parts.

3

Use an outside micrometer to measure shaft diameter at other locations. When measuring the diameter of shaft locations other than the end, place the outside micrometer around the center of the shaft. Outside micrometers are vise-like, so turn thimble on the micrometer handle until the vise is snug on the input shaft center.

4

Write down the two measurements, one on the sleeve, directly forward of the thimble, and the thimble measurement itself. Add both measurements to calculate shaft diameter.