Specifications, Service and Repair of Farm and Lawn Tractors

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Kubota BX23, BX23S, BX24, BX25, BX25D hydrostatic transmission - Checking and service

Kubota BX23, BX23S, BX24, BX25, BX25D HST - Basic components

Removing levers and mower lift arm

Tap out the spring pin from the range gear shift lever and front wheel drive lever, then remove the both levers. Remove the hydraulic control lever. Remove the PTO select lever and PTO clutch control lever. Apply grease to inside of the front coupling and rear mounting. Hydraulic control lever mounting bolt and nut - 18 to 20 Nm / 13 to 15 lbf-ft. Removing PTO clutch valve - Remove the stopper. Draw out the PTO clutch valve from the transaxle assembly. Clean the oil passages. Apply the transmission fluid to the O-rings.

Removing 4WD detent ball

Remove the 4WD detent bolt, the detent spring and the detent ball before removing the transaxle front case, not to drop the detent ball into the transaxle case. Removing neutral arm and trunnion arm - Disconnect the neutral spring from the HST front cover. Loosen the neutral adjuster. Remove the external circlip. Remove the bolts. Remove the neutral adjuster and the neutral arm. Remove the trunnion arm. Adjust the HST neutral position.

Removing oil cooler cover

Remove the HST front cover not to damage the oil seal. Remove the center section. Tighten hydrostatic transmission mounting bolts and the nut to the factory specifications. Oil cooler cover mounting bolt (M8) - 18 to 20 Nm / 13 to 15 lbf-ft. Oil cooler cover mounting nut (M8) - 18 to 20 Nm / 13 to 15 lbf-ft. Removing center section and valve plates - Remove the valve plates. Check the direction of the groove. Install the valve plates to the anchor pins securely. Install the groove of the valve plate (pump plate) to the engine side.

Removing check and high pressure relief valve plug

Remove the check and high pressure relief plug (G 1/2). Check and high pressure relief valve plug (G 1/2) - 59 to 78 Nm / 44 to 57 lbf-ft. Checking check and high pressure relief valve (Kubota BX23, BX23S, BX24, BX25, BX25D) - After removing the plug, draw out the spring and the check and high pressure relief valve assembly. Since there is an orifice in the check and relief valve body (reverse), re-install the check and relief valve to their original positions. Orifice Factory specification - 1.5 mm / 0.059 in.

Removing cylinder block

Remove the gasket. Remove the O-ring. Remove the cylinder block assembly from the transaxle. Turn the disassembling and the assembling stand vertically. Install the cylinder block assembly to the shafts not to drop the pistons from the cylinder block assembly carefully.

Removing cylinder block and piston

Remove the piston and the spring from the cylinder block. Apply clean transmission oil to the cylinder block and the piston. Remove the circlip from the pump shaft and the motor shaft. Remove the thrust bearing. Remove the swashplate and the thrust roller bearing. Apply clean transmission oil to the cradle bearing and the trunnion arm. Hold the slot guide with a minus screw driver. Apply clean transmission oil to the thrust roller bearing. Removing hydraulic cylinder - Disconnect the delivery pipe. Remove the hydraulic cylinder mounting bolts. Remove the hydraulic cylinder. Hydraulic cylinder mounting bolt - 40 to 44 Nm / 29 to 32 lbf-ft.

Kubota BX23, BX23S, BX24, BX25, BX25D - Transaxle shafts

Removing transaxle case front cover

Before removing the transaxle case front cover, remove the 4WD detent bolt, the detent spring and the detent ball from the transaxle case front cover. Remove the circlip from the HST pump shaft (PTO shaft) and the HST motor shaft securely. Remove the transaxle case front cover mounting bolts. Remove the transaxle case front cover as an unit. Transaxle case front cover mounting bolt (M10) - 39 to 44 Nm / 29 to 32 lbf-ft. Removing hydraulic pump assembly - Remove the hydraulic pump assembly mounting bolt. Remove the hydraulic pump assembly as an unit from the transaxle case. Apply transmission oil to the O-rings. Since the mounting bolt is installed through the hydraulic pump to the transaxle case, bind the sealing tape to the mounting bolt securely. Hydraulic pump assembly mounting bolt (M6) - 7.9 to 8.8 Nm / 5.8 to 6.5 lbf-ft. Hydraulic pump assembly mounting bolt (M8) - 18 to 20 Nm / 13 to 15 lbf-ft.

Removing rear PTO cover assembly

Remove the rear PTO cover mounting bolts. Remove the rear PTO cover. Remove the rear PTO shaft from the rear PTO cover. Pull the 11T PTO select shaft with the bearing approximately the bearing thickness. Apply liquid gasket to the joint surface of transaxle case to the rear PTO cover. Bind the vinyl tape to the rear PTO shaft not to damage the oil seal. Rear PTO cover mounting bolt (M8) - 18 to 20 Nm/13 to 15 lbf-ft. Removing PTO clutch assembly - Remove the bearing. Remove the external circlip and the clutch gear. Remove the seal rings. Remove the bearing. Remove the external circlip using a clutch spring compressor. Disassembling the clutch pack inner parts. Draw out the oil seal with a screw driver. Remove the internal circlip from the rear axle case. Draw out the rear axle from the rear axle case.

Removing rear axle case

Remove the rear axle case (R.H.) mounting bolts. Remove the rear axle case (R.H.) as an assembly from the transaxle case. Remove the 37T spiral bevel gear. Since the adjusting shims are installed behind the 37T spiral bevel gear, check the shims. Remove the 10T final gear shaft. Remove the 66T final gear with the differential lock shift fork. Rear axle case mounting bolt (M8) - 18 to 20 Nm / 13 to 15 lbf-ft.

Removing 66T final gear

Remove the bearing with a puller. Remove the bearing with a puller. Remove the differential lock shifter and 66T final gear. Put parting marks on the differential pinions and the differential side gears. Tap out the differential pinion shaft. Remove the differential pinions, the differential pinion washers, differential side gears and the differential side gear washers. 66T final gear mounting bolt (Kubota BX23, BX23S, BX24, BX25, BX25D) - 61 to 70 Nm / 45 to 52 lbf-ft. Removing rear axle case and brake - Remove the internal circlip. Remove the shim, the bearing holder and the other brake parts from the brake case. Apply grease to the steel balls. Check that the brake cam lever moves smoothly.

Kubota BX23, BX23S, BX24, BX25, BX25D HST - Assembling shafts

Assembling select arms and HST pump shaft

Install the PTO select arm. Install the range shift arm and the front wheel drive shift arm. Install the idle gear shaft. Install the rear PTO cover and the PTO select gear shaft before installing HST pump shaft assembly. After installing the rear PTO cover to the transaxle case, install the PTO select gear shaft. Install hydrostatic transmission pump shaft (PTO clutch shaft). Assembling front wheel drive shaft, shifter, spiral bevel pinion shaft and mid-PTO shaft - Install the front wheel drive shaft. Install the shifter and the spiral bevel pinion shaft together. Install the mid-PTO idle gear shaft and the mid- PTO shaft and the HST motor shaft together. Checking pump shaft - Check the seal surface and the bearing surface. If the pump shaft is rough or grooved, replace it. If the ball bearing or the needle bearing is worn, replace it.

Checking center section

Check the center section surface for scratches or wear. If deep scratch or excessive wear is found, replace the hydrostatic transmission assembly. Checking charge relief valve - Check the charge relief valve and the spring. If damages are found, replace it. Checking check and high pressure relief valve - Check and high pressure relief valve (reverse) has a pin hole. Pin hole (Kubota BX23, BX23S, BX24, BX25, BX25D) - 1.5 mm / 0.059 in. Check the check and high pressure relief valve for scratches and damage. Check the spring for breakage and wear. If anything are unusual, replace the check and high pressure relief valve as complete assembly.

Checking cylinder block assembly

Check the cylinder blocks and the pistons for scratches and wear. If there are scratch or worn, replace the cylinder block assembly. Check the pistons for their free movement in the cylinder block bores. If the piston or the cylinder block is scored, replace the cylinder block assembly. Check the polished face of the cylinder block for scoring. If it is scored, replace the cylinder block assembly. Checking thrust washer, thrust roller bearing, thrust plate and cradle bearing - Check the thrust bearing for scratches and excessive wear. If it is worn, replace it. Check the thrust plate for scratches and excessive wear. If it is worn or scored, replace it. Check the cradle bearing for excessive wear. If it is worn, replace it. Checking needle bearing - Check the needle bearing for wear. If the needle bearing are worn, replace them.

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