Bush-whacker T-121, Operator'S Manual And Partsbook, Page: 18 / 60

18
2009 T-121
Gearbox Assembly Procedure
1. The output assembly goes into the housing first. If the upper bearing race has been pulled
out it must be pressed in. After the bearings are pressed onto the output shaft, the shaft can
be inserted into the housing.
2. The lower bearing race will have to be pressed into the housing until it is flush with the bot-
tom surface of the housing. Using the same number and thickness of gaskets replace the
output cap. The 1/2” bolts are torqued to 60 foot pounds.
3. The bearing preload is measured by rolling torque. The rolling torque should be between 6-
15 inch pounds. If the rolling torque is too high the output cap will need to be removed and
an additional gasket added. When a gasket is added the lower race will need to be pulled out
slightly. If the rolling torque is too low or there is any movement of the output shaft, a gas-
ket will need to be removed.
4. Once the preload is set, remove the output cap. Install the seal into the cap and apply sealant
to the gaskets. Replace the output cap, making sure the torque is correct.
5. Slide the output gear onto the output shaft in the housing.
6. The bearing race for the rear bearing on the input shaft must be pressed in.
7. Slide the input gear onto the shaft to the retaining ring. Then place the spacer above the
gear. Press the bearing on the front of the input shaft. Lastly, press the bearing onto the rear
of the shaft.
8. Place the input shaft assembly in the housing and check the gear mesh and black lash. The
gear mesh is correct when the back surface of the gear teeth are level. The back lash should
be between 0.006” and 0.014” when measured at the pitch diameter of the gear set. If the
gear mesh or back lash are incorrect use shims to correct.
9. Press the bearing race into the input cap. Using the same number and thickness of gaskets,
place the input cap on the housing. Torque the 3/8” bolts to 25 foot pounds.
10. The bearing preload is measured in the same manner as for the output shaft. The rolling
torque should be between 11-25 inch pounds. Refer to step 3 for correction of the preload.
11. Once the preload is set, remove the input cap. Install the seal into the input cap and apply a
sealant to the gaskets. Replace the input cap taking care not to damage the seal. Check the
position of the oil plugs on the input cap. The oil level check plug should be just below and
to the right of the input shaft, with the fill plug directly under the input shaft. Torque the
bolts back to 25 foot pounds.
12. Fill the gear box with the recommended lubricant in an upright position similar to the
mounting position. Fill the gearbox to the level plug (1/8” pipe plug). Check the lubricant
with a dipstick (a small piece of wood works well as a dipstick).