Lawn Tractor: Drive Jumps or Jerks

Bearings are located between stationary objects and rotating shafts. A seized bearing can limit or stop the movement of a shaft. To check for a bad bearing you will need to disconnect the battery and remove mower deck. Next, remove the drive belt (to determine how to remove the belt, follow our instructions under the “Belt” heading above). Spin all the pulleys and look for a seized bearing. Check for any grinding noise as well as any play, which can indicate a worn bearing. Next, remove the hold-down bolt on the pulley. You may need an open-ended box end wrench to hold on to the nut on the back side of the pulley as you loosen the hold-down bolt. Remove the old bearing and replace it with a new one inside the pulley. You will require a press to do this procedure. With the old bearing replaced, you can re-install the pulley, the drive belt, the mower deck, and the battery.

The drive belt transfers power from the crankshaft pulley to the transmission. As the sides of the belt wear off, it makes the belt narrower, which can end up stretching the belt longer. This can make the belt too long to work properly with the variable speed pulleys. To replace this belt, first remove the cutting deck and battery. Locate the instructions for removing the cutting deck in your owner’s manual to determine the correct process for your model. Next, lift the seat to access the battery. When disconnecting the battery, always disconnect the black negative battery cable first, then disconnect the red positive battery cable. Under the battery compartment you will see a large transaxle pulley. Loosen the large nut holding the pulley to the input shaft, and disconnect the spring from the anchor bolt on the left side of the tractor. Use a spring puller or a small piece of rope to relieve tension on the upper drive belt. It is worth noting that the orientation of left and right is determined from the operator's position in the seat. Remove the upper (rear) belt from the transaxle pulley and remove the belt from the mower. Next, remove the belt guide from the variable speed pulley bracket (these are all accessed through the battery compartment). Lift the middle sheave slightly so the belt will clear the belt guide, and remove the belt from the variable speed pulley. Next, remove the belt keeper that surrounds the engine pulley. Then, remove the bolt securing the crank shaft pulley (an air impact gun is recommended for this procedure). Pull the lower drive belt towards the engine for removal. Install the new lower drive belt and check your owner’s manual for correct routing. Re-install the crankshaft pulley and apply anti-seize lubricant to the crankshaft. Re-install the spacer with the rounded shoulder towards the engine. Next, re-install the pulley and torque the hold-down bolt to 38-50 foot-pounds. Replace the lower transmission belt and re-install the mower keeper and belt guide. Re-install the tension spring and tighten the transmission pulley to 10-15 foot-pounds. Next, you need to check the speed control linkage on the variable speed belt drive. With the parking brake engaged, remove the cotter pin from the ferrule on the top side of the variable speed pulley bracket and disconnect the ferrule from the bracket. If you need to make an adjustment, there will be tension on the linkage and the resulting friction will cause resistance as you slide out the ferrule. Thread the ferrule up or down the rod until the post fits in the hole without any resistance. Reinstall the cotter pin back in the ferrule on the top side of the variable speed pulley bracket. At this point, check the cruise control/parking brake adjustment on the variable speed belt drive with the parking brake engaged. Remove the cotter pin that secures the ferrule in the latch assembly and disconnect the linkage from the latch assembly. Adjust the ferrule with a new cotter pin as you did when adjusting the speed control linkage. Then, secure the ferrule with a new cotter pin and test the operation of the linkage. Finally, re-install the mower deck and battery.

Your transaxle houses both the transmission and the differential in the same unit. It is designed to transmit power in forward and reverse, and transmit power to the drive wheels. A worn gear in this unit can cause your lawn tractor to jump in gear. If your tractor is experiencing this problem, you will hear a noise coming from the unit during operation. The best thing to do is to replace the transaxle assembly entirely, as rebuilding the inside requires great skill. To replace the transaxle, first jack the tractor up off the ground and set the parking brake to release tension on the belt. Next, maneuver the drive belt off the transmission pulley. Now you can pull the cotter pin out on the brake lever and remove the lever itself. Remove the bolts on each side holding the axle onto the frame and the front mounting bolts, and pull the transaxle out from lawn tractor. Before installing a new transaxle make sure the breather cap is installed. Then, slide the new transaxle into place and re-install the mounting bolts. Finally, re-connect the brake lever and cotter pin, and re-attach the belt.

Pulleys transfer power from the belt to other shafts. A pulley that is binding will cause the lawn tractor to jerk forward. To check for a binding pulley, start by disconnecting your battery, and remember to start with the negative cable first. Now you can remove your mower deck. Remove your drive belt and check the inside condition of the pulleys. If any pulley is concaved, has deep grooves on the inside, or is bent, it will need to be replaced. Remove any hold-down bolts. You may need an open-ended box end wrench to hold the nut on the back side of the pulley as you loosen the hold-down bolt. Next, replace the pulley and re-install the new one. Re-install the drive belt and the mower deck.