How to Replace the Gearbox on a Bolens String Trimmer

Grinding sound coming from the trimmer head area of your trimmer? You might need a new gearbox. The gearbox assembly consists of a new gearbox, a new trimmer head, and the screws needed to attach it. The gearbox adjusts the angle of the shaft by about 45-degrees, so the trimmer head can be attached parallel to the ground when you use the trimmer. There are two gears inside the gearbox that make this angle change possible. The gears also provide extra torque for the trimmer head. After years of use, the gears can become worn, and eventually fail. When this happens, the trimmer head will stop spinning or will start and stop erratically. There will often be a grinding sound from the gear box.

Let's get started.

REMOVING THE GEARBOX   1. Remove the gearbox.

a. Remove the center retaining screw from the gearbox assembly.

b. Loosen the two (side) clamping screws.

c. Remove the gearbox from the shaft. (Use a rubber mallet as-needed to tap the gearbox away from the shaft).

INSTALLING THE NEW GEARBOX
2. Install the gearbox.

a. Install the new gearbox onto the lower shaft, aligning the square drive shaft with the squared opening in the gearbox.

b. Align the center hole on the gearbox with the hole on the lower shaft.

c. Install and tighten the center retaining screw.

d. Install and tighten the two (side) clamping screws to secure the gearbox to the shaft.