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Kubota B2100, B21, B7300 - Hydrostatic Transmission

Kubota B21, B2100, B7300 Tractor - Transmission Components

1 - Charge Relief Valve, 2 - Check and High Pressure Relief Valve, 3 - Trunnion Shaft, 4 - Center Section, 5 - Variable Displacement Piston Pump, 6 - Charge Pump, 7 - Input Shaft (Pump Shaft), 8 - Housing, 9 - Fixed Displacement Piston Motor

The hydrostatic transmission consists of a variable displacement piston pump and a fixed displacement piston motor. Convenient single lever control permits simple operation of the vehicle, starting, stopping, increasing or decreasing speeds, changing direction of travel, and even going up or down hills.

Pump and Motor

Pump and motor cylinder, each containing pistons, are connected by lines. Cylinders and lines are filled with oil. Pistons ride against swashplates located in pump and motor. In the pump, as the cylinder rotates, pistons move across the sloping face of swashplate and slide in or out of their cylinder bores. The oil, forced out by the pump pistons, causes the motor pistons to slide out of their cylinder bores. In the motor, sliding out of the cylinder and moving across the sloping face of swashplate, the pistons rotate the cylinder.

Oil Flow and Valves

The pump and motor are joined in a closed hydraulic loop and most of oil circulates within the main oil circuit. A little oil lubricates and oozes out from the clearance between the moving parts of the case. Then oil in the main oil circuit of the HST needs to be supplied a want. The combined oil flow from the power steering circuit and HST charge pump are flows into the HST for charging. The charge oil aids smooth operation of piston pump and motor. The charge oil passes through the oil cooler and transmission oil filter to charge relief valve port. The rest of oil passes through the charge relief valve into the HST housing. Oil from the hydraulic cylinder and overflow oil from HST housing return to the transmission case.

Charge Relief Valve

While pumped and filtered oil flows into the main oil circuit through the check valves, excessive oil passes to the case through the charge relief valve.

Check and High Pressure Relief Valve

The check and high pressure relief valves monitor the oil pressure in each line of the main oil circuit. In neutral, both valves are open and charging oil enters into the main oil circuit through the valves. At normal operation, the check valve in the high pressure side is closed and it pushes and opens the another one. When excessively high pressure is built up in one line, the high pressure relief valve located in this line is open and the oil flows into another line.

Control Linkage

The speed control pedal and the trunnion shaft of variable swashplate are linked with the speed control rod and the trunnion control lever assembly. As the front footrest of the pedal is depressed, the swashplate rotates and forward travelling speed increases. Depressing the rear footrest increases reverse speed. The roller on the trunnion lever holder with spring seats the detent of the trunnion arm so that the trunnion lever returns to neutral. Then, the swashplate is returned to neutral with the trunnion control lever assembly, when the pedal is released. The damper connected to the speed control pedal restricts the movement of the linkage to prevent abrupt operation or reversing. The speed set lever linked to the speed control pedal enables the linkage not to return to neutral and to keep a certain forward speed while the speed control pedal is released.

Kubota B2100, B21, B7300 HST - PTO System

Rear-PTO Shift Section

Besides neutral, one kind of power flow are available by operating the PTO shift lever to shift positions of 17T shifter gear (2) for rear-PTO.

1 - HST Pump Shaft, 2 - 14T Gear, 3 - 27T Gear, 4 - 2nd Gear Shaft with 13T and 18T Gear, 5 - 17T Shifter Gear, 6 - 3rd Shaft, 7 - Coupling, 8 - 5th Shaft with 11T Gear, 9 - 24T Gear, 10 - Rear-PTO Shaft.

Rear-PTO Shift Lever ON position

HST Pump Shaft (1) - 14T Gear (2) - 27T Gear (3) - 2nd Gear Shaft with 13T Gear (4) - 17T Shifter Gear (5) - 3rd Shaft (6) - Coupling (7) - 5th Shaft with 11T Gear (8) - 24T Gear (9) - Rear-PTO Shaft (10).

Mid-PTO Section

Besides neutral, one kind of power flow are available by operating the PTO shift lever to shift positions of shifter (5) or 11T shifter gear (7) for mid-PTO.

1 - HST Pump Shaft, 2 - 14T Gear, 3 - 27T Gear, 4 - 2nd Gear Shaft with 13T and 18T Gear, 5 - 13T Gear, 6 - 19T Gear, 7 - 11T Shifter Gear, 8 - Mid-PTO Shaft.

Mid-PTO Shift Lever ON Position

HST Pump Shaft (1) - 14T Gear (2) - 27T Gear (3) - 2nd Gear Shaft with 18T Gear (4) - 13T Gear (5) - 19T Gear (6) - 11T Shifter Gear (7) - Mid-PTO Shaft (8).

Kubota B21, B2100, B7300 - Clutch

Separating the Clutch Assembly

Remove the clutch assembly from the flywheel. Direct the shorter end of the clutch disc boss toward the flywheel. Apply molybdenum disulphide to the splines of clutch disc boss. Install the pressure plate, noting the position of straight pins. Align the center of clutch disc and flywheel by inserting the clutch center tool.

Clutch Rod and Clutch Release Fork

Remove the clutch pedal rod. Remove the external snap ring at the end of clutch rod and remove the clutch release fork and release bearing with release hub. Set the clutch release fork and release hub with set spring in the correct direction.

Kubota B21, B2100, B7300 HST - Clutch Replacement Service

Backlash between Clutch Disc and Clutch Shaft

Mount the clutch disc onto the propeller shaft. Hold the propeller shaft so that it does not rotate. Slightly move the disc and measure the displacement around disc edge. If the measurement exceeds the allowable limit, replace clutch disc. Displacement around disc edge - 2.0 mm (0.079 in).

Clutch Disc Wear

Measure the depth from clutch disc surface to the top of rivet at least 10 points with a depth gauge. If the depth is less than the allowable limit, replace. If oil is sticking to the clutch disc, or disc surface is carbonized, replace clutch disc. Depth to river top - 0.3 mm (0.012 in).

Pressure Plate Flatness

Place a straightedge on the pressure plate and measure clearance with a feeler gauge at several points. If the clearance exceeds allowable limit, replace pressure plate. When the pressure plate is worn around its outside and its inside surface only is in contact with the straightedge, replace it even if the clearance is within the allowable limit. Clearance between pressure plate and straightedge - 0.2 mm (0.008 in).

Checking Pressure Plate and Diaphragm

Check the pressure plate and if scratched on its surface, correct with sandpaper or replace it. Check the diaphragm for cracks and scratches. If defects are found, replace it.

Checking Clutch Release Bearing

Check the clutch release bearing. If surface is worn excessively, or abnormal sounds occur, replace it.

Kubota B2100, B21, B7300 Transmission - Checking And Adjusting

Neutral

Disengage the front wheel drive lever (Drive only rear wheels). Lift the rear of the tractor so that the rear wheels are off the ground and run the engine at low idling and drive only rear wheels. Depress the one end of speed control pedal and release, and do the same at the other end. If the rear wheels do not stop turning, adjust as following procedure. Before loosen the neutral adjuster setting screw, be sure to insert the screw driver to hole of neutral adjuster. This mean prevent to comes out neutral adjuster at adjusting window.

Adjusting Neutral

Disconnect the brake rod RH. Remove the HST pedal damper. Loosen the neutral adjuster setting screw. When rear wheels tend to turn forward - Rotate the neutral adjusting lever clockwise so that the rear wheels turn reverse. Then rotate it counterclockwise until wheels stop completely. When rear wheels tend to turn reverse - Rotate the neutral adjusting lever counterclockwise so that the rear wheels turn forward. Then rotate it clockwise until wheels stop completely.

Oil Pressure in Hydrostatic Transmission

Clean and clear the work area and fully engage the parking brake. Measure the following oil pressures using HST adaptors.

Check and High Relief Pressure

Remove the 8 mm (0.31 in.) hex socket head plug from P1 or P2 port (P1 is for forward and P2 is for reverse). Assemble the HST adaptor and threaded joint with the gasket between them. Install the assembled HST adaptor and threaded joint to P1 (forward) or P2 (reverse) port. Install the cable threaded joint in relief valve set pressure tester and high pressure gauge to threaded joint in order. Run the engine at 2600 rpm. Place the high-low shift lever in high. Depress the speed control pedal approx. 10 mm (0.39 in.) which rotates the trunnion shaft 0.087 rad (5.0°).

Kubota B21, B2100, B7300 - Transmission Case Disassembly

Charge Pump Housing and Spacer

Remove the charge pump mounting hex. socket head screw, and remove the charge pump assembly from the HST housing. Remove the charge pump spacer from the charge pump assembly.

Center Section

Remove the external snap ring and 14T gear. Remove the center section mounting hex. socket head screw. Lift and remove the center section from the HST housing. Place a new gasket on the housing. Press the cylinder block (motor side) by hand then softly reinstall the counter section. Be careful the pistons for come off from the cylinder block. Install the snap ring with its rounded edge facing the gear so that its sharp edge in the groove keep itself in place against the face.

Check and High Pressure Relief Valve

Remove the hex. socket head plug and remove the spring and relief valve assembly. Take care not to damage the O-ring On the plug.

Cylinder Block Assembly and Thrust Ball Bearing

1.Cylinder Block Assembly (Pump Side), 2.Cylinder Block Assembly (Motor Side), 3.Motor Shaft, 4.Thrust Ball Bearing

Lay the housing on its side. Remove the cylinder block assembly (pump side) (1). Remove the cylinder block assembly (motor side) (2) with the motor shaft (3). Remove the thrust ball bearing (4). Apply clean hydrostatic transmission oil to thrust ball bearing, cylinder block and piston.

Swashplate

Remove the swashplate from the housing. Remove the thrust plate, thrust roller bearing and thrust washer from the swashplate. Apply clean hydrostatic transmission oil to the thrust roller bearing. Place the swashplate into the housing, align the groove of swashplate and slot guide by keeping the slot guide from moving with a screw driver.

Slot Guide, Cradle Bearing and Trunnion Arm

Remove the slot guide from the trunnion arm. Remove the cradle bearing from the housing. Remove the trunnion arm. Remove the oil seal with a screw driver. Apply clean hydrostatic transmission oil to journal bearing, trunnion arm and cradle bearing.

Pump Shaft

Remove the internal snap ring. Tap the pump shaft with a plastic hammer slightly to slide out it from the housing.

Charge Relief Valve

Remove the charge relief valve plug. Remove the spring and charge relief corn. If shims are placed at the bottom of the relief valve plug bore, place them as they are. Take care not to damage the a-ring on the relief plug.

Separating Hydraulic Cylinder and Rear Axle Case

1 - Aux. Speed Change Lever, 2 - Rear-PTO Shift Lever, 3 - Mid-PTO Shift Lever, 4 - Connecting Plate, 5 - Top Link Bracket, 6 - Hydraulic Cylinder Assembly, 7 - Differential Lock Pedal Support, 8 - Differential Lock Pedal, 9 - Drawbar Frame

Remove the external snap ring and remove the auxiliary speed change lever (1) with rod, rear-PTO shift lever (2) and mid-PTO shift lever (3). Remove the hook and connecting plate (4). Remove the top link bracket (5). Remove the hydraulic cylinder mounting screws and dismount the hydraulic cylinder assembly (6). Disconnect the differential lock rod and remove the differential lock pedal support (7) with differential lock pedal (8). Remove the drawbar frame mounting screws and remove the drawbar frame (9). Apply liquid gasket to joint face of the differential case and the rear axle case, differential case and the hydraulic cylinder.

Separating Mid-PTO Case and Transmission Case

Remove the mid-PTO case mounting screws and separate the mid-PTO case from transmission case. Remove the transmission case mounting screws and nuts and separate the transmission case from the differential case. Apply liquid gasket to joint face of the transmission case, differential case and mid-PTO case.

Bearing Holder

Remove the external snap ring and remove the 27T gear. Remove the bearing holder mounting screws and remove the bearing holder.

2nd Gear Shaft and 17T Shifter Gear

1 - 2nd Gear Shaft, 2 - Bearing, 3 - 17T Shifter Gear, 4 - Shift Fork, 5 - Shift Lever

Remove the 2nd gear shaft (1) with bearings. Remove the bearing (2), 17T shifter gear (3) and shift fork (4) with shift rod. Remove the shift lever (5).

Middle Shaft and 3rd Shaft

Tap out the middle shaft and remove the 19T gear with bearing. Draw out the 3rd shaft with 13T gear. When assembling the 19T gear, face the chamber side to the rear. When installing the needle bearings into the 13T gear, apply transmission oil to the needle bearings.

Mid-PTO Shaft

1 - Spring, 2 - Ball, 3 - Shift Arm, 4 - Shifter, 5 - Oil Seal, 6 - Internal Snap Ring, 7 - Mid-PTO Shaft, 8 - 11T Shifter Gear, 9 - Bearing

Remove the spring (1) and ball (2). Draw out the dowel pi n and remove the shift arm (3) with shifter (4). Remove the oil seal (5) and internal snap ring (6). Remove the mid-PTO shaft (7) with 11T shifter gear (8) and bearings (9). Apply grease to lip and outer of oil seal.

Front Wheel Drive Shaft

Remove the external snap ring and remove the 20T shifter gear. Draw out the front wheel drive shaft to the front.

4th Gear Shaft and Spiral Bevel Pinion Shaft

Remove the spiral bevel pinion shaft with 15T-29T shifter gear, 13T gear. Remove the 4th gear shaft with 18T gear. When installing the spiral bevel pinion shaft, be sure to install the shim.

Kubota B21, B2100, B7300 HST - Transmission Case Service

Charge Pump

1.Spacer, 2.Gerotor Assembly, 3.Charge Pump Housing

Check the charge pump housing (3), spacer (1) and the gerotor assembly (2) for scratches and wear. If scratch or worn, replace the charge pump complete assembly.

Center Section

Check the surface of center section for scratches or wear. If deep scratch or excessive wear is found, replace the center section.

Check and High Pressure Relief Valve

Check the valve for scratches and damage. Check the valve seat in the center section for damage. Check the spring for breakage and wear. If anything unusual, replace the high pressure relief valve complete assembly.

Cylinder Block Assembly

1.Cylinder Block, 2.Spring, 3.Spring Seat, 4.Piston

Check cylinder blocks (1) and pistons (4) for scratches and wear. If deep scratch or excessive wear is found, replace the cylinder block assembly. Check that the piston (4), spring (2) and spring seat (3) are in each cylinder bore. Check the pistons for their free movement in the cylinder block bores. If the piston or cylinder block bore is scored, replace the cylinder block assembly.

Thrust Washer, Thrust Roller Bearing and Thrust Plate

Check the thrust roller bearing for scratches and excessive wear. If worn, replace. Check the thrust plate for scratches and excessive wear. If worn or scored, replace.

Pump Shaft

Check the seal surface, the bearing surface and the bearing. If the shaft is rough or groove, replace. If the bearing is worn, replace.

Needle Bearing and Oil Seal

Check the oil seals for damage. Check the needle bearings for wear. If the oil seals and bearings are worn, replace them.

Charge Relief Valve

Check the charge relief cone and the seat in the housing for damage. If defects are found, replace them.

Bearing Check

While holding the inner race, push and pull the outer race in all directions to check for wear and roughness. Apply transmission oil to the bearing and hold the inner race. For needle bearing, lay the needle rollers to check for any damage and wear. Replace it if defects are found.

Clearance between Shift Fork and Shift Gear Groove

Insert the fork into the shift gear groove and measure the clearance with a feeler gauge. If the clearance exceeds the allowable limit, replace it. Clearance between shift fork and shift gear groove - 0.10 to 0.35 mm (0.004 to 0.014 in).

Clearance between 13T Gear and 3rd Shaft

Measure the 13T gear I.D. with an inside micrometer, and then 3rd shaft O.D. with an outside micrometer. Measure the O.D. of two needles in the needle bearing with an outside micrometer. Clearance is the difference between the gear I.D. and the sum of shaft O.D. and two needle O.D. If the clearance exceeds the allowable limit, replace. Clearance between 13T gear and 3rd shaft - 0.007 to 0.046 mm (0.0003 to 0.0018 in). 3rd shaft O.D. - 21.987 to 22.000 mm (0.8656 to 0.8661 in). 13T gear I.D. - 28.007 to 28.021 mm (1.1026 to 1.1032 in). Needle O.D. - 2.994 to 3.000 mm (0.1179 to 0.1181 in).

Kubota B21, B2100, B7300 - Differential Case Service

Clearance between Differential Case and Differential Side Gear

Measure the differential side gear boss O.D. with an outside micrometer. Measure the differential case I.D. and the spiral bevel gear I.D. with an inside micrometer. If the clearance exceeds the allowable limit, replace it. Clearance between differential case and differential side gear - 0.025 to 0.066 mm (0.0016 to 0.0029 in). Differential case I.D. - 32.000 to 32.025 mm (1.2598 to 1.2608 in). Differential side gear O.D. - 31.959 to 31.975 mm (1.2582 to 1.2589 in). Spiral bevel gear I.D. - 32.000 to 32.025 mm (1.2598 to 1.2608 in).

Clearance between Differential Pinion Shaft and Differential Pinion

Measure the differential pinion shaft O.D. with an outside micrometer. Measure the 'differential pinion I.D. with an inside micrometer. If the clearance exceeds the allowable limit, replace it. Clearance between differential pinion shaft and differential pinion 0.016 to 0.045 mm (0.0006 to 0.0018 in). Differential pinion shaft O.D. - 15.973 to 15.984 mm (0.6289 to 0.6293 in). Differential pinion I.D. - 16.000to 16.018 mm (0.6299 to 0.6306 in).

Backlash between Differential Pinion and Differential Side Gear

Secure the differential case with a vise. Set the dial indicator (lever type) with its finger on the tooth of the differential side gear. Press differential pinion and side gear against the differential case. Hold the differential pinion and move the differential side, gear to measure the backlash. If the backlash exceeds the allowable limit, adjust with differential side gear shims. Backlash between differential pinion and differential side (Allowable limit) - 0.4mm (0.016 in).

Backlash between Spiral Bevel Pinion and Spiral Bevel Gear

Set the dial indicator (lever type) with its finger on the end of spiral bevel pinion. Move the spiral bevel pinion back and forth to each end and measure the side clearance. If the side clearance exceeds the factory spec., adjust with the shims at front end of spiral bevel pinion. Set the dial indicator (lever type) with its finger on the tooth surface of bevel gear. Measure the backlash by fixing the spiral bevel pinion and moving bevel gear by hand. If the backlash exceeds the factory spec., adjust with the shims at bearing holder and differential case. Adjust the backlash properly by repeating the above procedures. Side clearance of spiral bevel pinion - Less than 0.15 mm (0.006 in). Backlash between spiral bevel pinion and spiral bevel gear - 0.10 to 0.20mm (0.0039 to 0.0080 in).

Kubota B21, B2100, B7300 Tractor - Rear Axle

The rear axles are the semi floating type with ball bearings (2) between the rear axle (4) and the rear axle case (3), which supports the rear wheel load as well as transmitting power to the rear wheels. The differential (7) automatically controls the revolution of right and left wheels when the rear wheels encounter unequal road resistance during turning.

1 - Differential Gear Shaft, 2 - Ball Bearing, 3 - Rear Axle Case, 4 - Rear Axle, 5 - Spur Gear, 6 - Spiral Bevel Gear, 7 - Differential

Separating Rear Axle Case from Differential Gear Case

Drain the Transmission Fluid

Place oil pans underneath the transmission case. Remove the four drain plug. Drain the transmission oil. Reinstall the four drain plugs. Fill up from filling port after removing plug until reaching the gauge. After running the engine for few minutes, stop it and check the oil level again. Add the oil to prescribed level if it is not correct level.

Rear Wheel

Place a jack under the transmission case. Loosen the rear wheel cotter setting bolt and nut. Take out the wheel hub pin. Take out the rear wheel. When refitting or adjusting a wheel, tighten the bolts to the following torques then recheck after driving the tractor 200 m (200 yards) and there after daily check service.

Rear Axle Case

Disconnect the differential lock rod. Disconnect the brake rod. Remove the rear axle case mounting screw. Separate the rear axle case from differential gear case. Apply liquid gasket to joint face of the rear axle case and differential gear case after eliminate the water, oil and stuck liquid gasket.

Separating Hydrostatic Transmission

Tap out the spring pins and remove the universal joint with front wheel propeller shaft. Remove the neutral adjuster setting screw and loosen the trunnion control lever mounting bolt and nut. Then remove the trunnion control lever assembly. Remove the hydrostatic transmission mounting screws and nuts, and separate the hydrostatic transmission from the transmission case. When assembling the neutral spring bracket, adjust the clearance between nut and bracket. Apply liquid gasket to joint face of the HST and transmission case. When inserting the spring pins, face their splits in the direction parallel to the universal joint

Differential Gear Case

5th Gear Shaft and Rear-PTO Shaft

Remove the ternal snap ring and one-way clutch cam (Manual Transmission Type). Remove the rear-PTO cover mounting screw and remove the rear-PTO cover assembly. Apply liquid gasket to joint face of differential case and rear-PTO cover. Do not tighten the rear-PTO cover mounting screws before reassembling the differential case and transmission case.

Removing Differential

Remove the bearing holder mounting screws and remove the differential bearing holder. Remove the differential assembly. Install the differential assembly, noting the number of shims in the differential case left side and differential bearing holder.

Differential Side Gear and Differential Pinion

Put parting marks on the differential pinion and the differential side gear. Tap out the dowel pin. Remove the differential pinion shaft. Remove the differential pinion, differential side gear and shim. Install the differential pinion aligning the parting marks.

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