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Kubota B2410, B2710, B2910, B7800 - HST Transmission

Kubota B2410, B2710, B2910, B7800 - Hydrostatic Transmission System

1 - Charge Relief Valve, 2 - Charge Pump, 3 - Charge Pump Case, 4 - Pump Shaft, 5 - Variable Swashplate, 6 - Thrust Collar, 7 - Retainer Plate, 8 - Piston, 9 - Cylinder Block (Motor), 10 - Needle Bearing, 11 - Motor Shaft, 12 - Valve Plate (Motor), 13 - Cylinder Block (Pump), 14 - Valve Plate (Pump), 15 - Neutral Valve, 16 - Check and High Pressure Relief Valve

Check and High Pressure Relief Valve

The check and high-pressure relief valve consists of pressure poppet, check valve seat, relief valve spring, spring guide and check valve spring. The valve is used to prevent an overload that would happen at a quick start, sudden stop or even during usual running. This valve doubles as a check valve. The check and high-pressure relief valves are laid out facing each other as shown in the figure.

In neutral, both valves are open and charging oil enters into the main oil circuit through the valves.

A - In Neutral (Stop): 1 - Check Valve Seat, 2 - Pressure Poppet, 3 - Relief Valve Spring, 4 - Spring Guide, 5 - Check Valve Spring, 6 - Valve Plug

At normal operation, the check valve in the high pressure side is closed and it pushes and opens the another one. An excessive charge flow goes through the charge relief valve into HST housing (B).

B - When Check Valve Activating (Normal Operation)

The check and high-pressure relief valve along the high-pressure line serves as a high-pressure relief valve. If the pressure exceeds a high-pressure limit level, the pressure poppet opens itself against the relief valve spring (3) force and opens the valve seat that is located between the check valve seat (1) and the pressure poppet (2). Now the flow goes from P1 to P2 and P3 (C).

C - When High Pressure Relief Valve Activating

If the P1 pressure drops, the relief valve spring forces the valve seat closed against the pressure. The high pressure oil at P1 does not flow to P2 any longer. As discussed above, the check and high-pressure relief valve protects engines, pumps, motors, gears and even the machine itself from overload.

Front Wheel Drive System

B2410: 1 - Front Wheel Drive Shaft, 2 - Shifter Gear 20T, 3 - Spiral Bevel Pinion Shaft, 4 - Gear 13T

B2710, B2910, B7800: 1 - Front Wheel Drive Shaft, 2 - Shifter Gear 19T, 3 - Spiral Bevel Pinion Shaft, 4 - Gear 14T

2-wheel drive or 4-wheel drive is selected by changing the position of shifter gear (2) with the front wheel drive lever. When the front wheel drive lever is set to “Disengaged”, the shifter gear (2) is neutral and power is not transmitted to the front wheel drive shaft (1). When the front wheel drive lever is set to “Engaged”, the shifter gear (2) slides to the right to engage with gear (4) on the spiral bevel pinion shaft (3). Therefore, the front drive shaft is actuated to drive the front wheels.

Kubota B2910, B7800 Hydrostatic Transmission - Cruise Control

Cruise Control Linkage

1 - Grip, 2 - Cruise Control Lever, 3 - Lever Pin, 4 - Cruise Control Arm, 5 - Cruise Control Rod, 6 - HST Pedal, 7 - HST Pedal Lever, 8 - HST Release Rod, 9 - Release Lever 1, 10 - Release Lever 2, 11 - Release Arm, 12 - Cruise Control Shaft, 13 - Spring

Tilt the cruise control lever (2) to the right, and the lever pin (3) is activated to lift the cruise control arm (4). Move the above lever forward, and the HST pedal lever (7) rises by the cruise control rod (5) that is coupled with the cruise control arm (4) (The HST pedal (6) is now in the depressed position). Now the cruise control lever (2) can be fixed (set) to a desired position through the disc (friction) and the plate under spring (13) force. With the cruise control lever (2) set at the center on the lever guide, the HST pedal (6) is given an allowance by the oval hole of the HST pedal lever (7). This pedal can be stepped further down by this allowance (This means that the machine speed can be accelerated from a setting and that when the HST pedal is released, the machine speed comes down to the setting).

Cruise Control Release System

This is release system of the cruise the cruise control back to neutral automatically when brake pedals are depressed. Cruise control lever is set with plate, friction disc by the cruise control shaft, release arm and spring. When brake pedals are depressed, brake link pull the HST release rod, release lever 1 and release lever 2. Afterwards, cruise control shaft is pulled though release arm. As a result, the holding force of cruise control lever is lost. And, cruise control lever returns to neutrality by force of the spring and the return force of HST.

Kubota B2410, B2710, B2910, B7800 - Differential Gear

1 - Spiral Bevel Gear, 2 - Spiral Bevel Pinion, 3 - Differential Gear Case, 4 - Differential Side Gear, 5 - Differential Pinion, 6 - Differential Pinion Shaft

The differential gear assembly is a mechanism to provide smooth steering. It automatically provides different optimum torques to the right and left wheels according to road resistance and braking friction at the wheels. The differential gear assembly is composed of the differential case, differential pinions, differential side gears, differential pinion shaft, spiral bevel gear, etc.

Differential Lock: 1 - Differential Pinion, 2 - Shift Fork, 3 - Differential Lock Lever, 4 - Differential Gear Shaft, 5 - Differential Lock Clutch, 6 - Differential Case, 7 - Differential Pinion Shaft, 8 - Spiral Bevel Gear, 9 - Differential Gear Shaft

Kubota B2410, B2710, B2910, B7800 Differential Troubleshooting

Problem - Excessive or Unusual Noise at All Time

Improper backlash between spiral bevel pinion and bevel gear - Adjust.
Improper backlash between differential pinion and differential side gear - Adjust.
Bearing worn - Replace.
Insufficient or improper type of transmission fluid used - Replenish or replace.

Problem - Noise while Turning

Differential pinions or differential side gears worn or damaged - Replace.
Differential lock binding (does not disengage) - Replace.
Bearing worn - Replace.

Problem - Differential Lock Can Not Be Set

Differential lock shift fork damaged - Replace.
Differential lock shifter mounting pin damaged - Replace.
Differential lock clutch damaged - Replace.

Problem - Differential Lock Pedal Does Not Return

Differential lock pedal return spring weaken or damaged - Replace.
Differential lock fork shaft rusted - Repair.

Kubota B2410, B2710, B2910, B7800 Tractor - Separating Engine from Clutch Housing

Draining Transmission Fluid

Place oil pan underneath the transmission case, and remove the drain plugs. Drain the transmission fluid. Reinstall the drain plug. Fill new oil from filling port after removing the filling plug up to the upper notch on the dipstick. After running the engine for few minutes, stop it and check the oil level again, if low, add oil prescribed level. Transmission fluid capacity: B2410 - 12.5 L, B2710 - 15.5 L, B2910, B7800 - 14.5 L.

Hood, Side Cover and Battery Cord

Open the hood and remove the front grille. Disconnect the battery grounding cord. Disconnect the head light connectors and remove the hood and side covers. When disconnecting the battery cords, disconnect the grounding cord first. When connecting, positive cord first.

Steering Wheel

Remove the steering wheel cap. Remove the steering wheel mounting nut and remove the steering wheel with a steering wheel puller

Meter Panel and Panel Under Cover

Open the meter panel and disconnect the meter panel connector and hour-meter cable. Then remove the meter panel. Disconnect the combination switch connector, main switch connector, hazard switch connector and position light switch connector. Tap out the spring pin and remove the hand accelerator lever. Remove the panel under cover.

Fuel Tank

Disconnect the fuel hose at the fuel filter side, then drain fuel completely. Remove the fuel tank frame stay. Disconnect the hazard unit, starter relay and regulator connectors and remove the lead wire for fuel gauge. Remove the fuse box. Disconnect the overflow hoses of fuel line. Remove the tank frame with fuel tank. Disconnect the hydraulic pipes and remove the battery stay with oil cooler. Disconnect the 2P connector and remove the engine stop solenoid. Apply a thin coat of liquid gasket to both surface of the engine stop solenoid.

Bi-speed Turn Cable (Bi-speed Model)

Remove the spring lock pin and loosen the lock nuts and then remove the bi-speed turn cable.

Propeller Shaft Cover and Coupling

Loosen the clamp and slide the propeller shaft cover to the rear. Tap out the spring pin and then slide the coupling to the rear. Apply grease to the splines of the propeller shaft and coupling.

Universal Joint and Bearing Holder

Loosen the clamp and slide the universal joint cover to the rear. Tap out the spring pins and then slide the universal joint to the rear. Remove the bearing holder with propeller shaft and universal joint. Apply grease to the splines of the propeller shaft and universal joint.

Drag Link

Remove the cotter pin and loosen the slotted nut. Disconnect the drag link with a tie-rod end lifter from the knuckle arm.

Separating the Engine from Clutch Housing

Remove the power steering delivery pipe. Disconnect the accelerator rod. Disconnect the three point hitch delivery pipe and suction hose at the hydraulic pump. Disconnect the glow plug lead wire and thermo sensor lead wire. And then disconnect the connector for alternator and starter motor lead wire. Place the jack under the center frame. Hoist the engine by the chain at the engine hook. Remove the engine mounting screws and separate the engine from the clutch housing.

Kubota B2410, B2710, B2910, B7800 - Hydrostatic Transmission Adjusting

Adjusting Maximum Speed

Shorten the stopper bolt front to the position where the length of the bolt is not touched to the HST pedal (1) even if the HST pedal is fully depressed forward. Lengthen the length of the stopper bolt front gradually with the HST pedal fully depressed and lengthen the one turn from the position where the head of the stopper bolt touches the HST pedal. Tighten the lock nut. Adjust the length of stopper bolt rear to 27 to 28 mm (1.06 to 1.10 in.).

Maximum speed with turf tire (Forward)

B2410 - 21.1 to 22.1 km/h (13.2 to 13.8 mph).
B2710, B2910, B7800 - 23.5 to 24.5 km/h (14.7 to 15.3 mph).

Maximum speed with turf tire (Reverse)

B2410 - 16.8 to 17.8 km/h (10.5 to 11.1 mph).
B2710, B2910, B7800 - 18.7 to 19.7 km/h (11.7 to 12.3 mph).

Adjusting Cruise Control Linkage

With the cruise control lever at the N position on the lever guide, check for a gap between the lever pin and the cruise control arm. Adjust the cruise control rod, when required, to leave no gap between them. At the same time, make sure that there is no gap between the rear end of the oval hole of the HST pedal lever and the pin of the HST pedal. Finally step down the HST pedal all the way to make sure that the cruise control lever can hold the HST pedal in place.

Adjusting Cruise Control Release Linkage

Adjust the brake pedals play first. Then adjust the HST release rod turnbuckle to allow no gap between the release levers 1 and 2 as well as between the release lever 2 and the release rod. Now step on one of the brake pedals to make sure the cruise control is not released. Also step on both the brake pedals coupled together to make sure that the cruise control is released.

Cruise Control Lever

After adjusting the cruise control linkage, measure the force to move the cruise control lever forward at its top (grip). If the force is not within the factory specifications, loosen the lock nut and turn the nut to adjust. Retighten the lock nut securely.

Kubota B2410, B2710, B2910, B7800 Tractor - Transmission Case

Neutral Holder and Neutral Holder Arm

Place parting marks on the neutral adjuster and the neutral holder arm. Remove the neutral holder arm with neutral adjuster. Remove the screw and pull out the neutral holder. Align the parting marks and install the neutral adjuster and the neutral holder arm.

Charge Pump

Remove the charge pump mounting screws, and remove the charge pump assembly from the HST housing. Take care not to damage the O-ring. 14T Gear - Remove the external snap ring and draw out the 14T gear.

Center Section

Remove the center section mounting hex. socket head screws. Tap the front of center section flange with a soft hammer and separate the center section from HST housing. Cover the splines of each shaft with thin tape to protect sealing lip. Install center section with gasket, O-ring and valve plates in place. Valve plates may stick to the center section but they are not fixed. Take care not to drop them. Valve plates are not interchangeable. Valve plate of pump has two notches and the one of motor has no.

Motor Cylinder Block and Pump Cylinder Block

Pull out the output shaft and motor cylinder block with pistons as a unit. Slide out the pump cylinder block with pistons.

4th Gear Shaft and Spiral Bevel Pinion Shaft

Remove the spiral bevel pinion shaft with 15T-29T (B2410) or 16T-27T-32T shifter gear, 13T (B2410) or 14T gear and shift fork. Remove the 4th gear shaft. When installing the spiral bevel pinion shaft, be sure to install the shims. When disassembling the spiral bevel pinion shaft, be sure to replace the external snap ring with new one.

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 Middle Shaft

Remove the 2nd gear shaft with bearings. Remove the 3rd shaft assembly and shift fork with shift rod. Remove the middle shaft and 19T gear with bearing. When assembling the 19T gear, face the chamfer side to the rear. 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.

Mid-PTO Shaft

Remove the spring and ball. Draw out the dowel pin and remove the shift arm with shifter. Remove the oil seal and internal snap ring. Remove the mid-PTO shaft with 11T shifter gear and bearings. Apply grease to lip and outer of oil seal.

Kubota B2410, B2710, B2910, B7800 - Hydrostatic Transmission Service

Charge Pump

Check the charge pump housing and the gerotor assembly for scratches and wear. If scratch or worn, replace the charge pump complete assembly.

Input Shaft

Pull out the input shaft from the case. Check the seal surface, the bearing surface and the bearing. If the shaft is rough or grooved, replace. If the bearing is worn, replace.

Cylinder Block Bore and Pistons

Lift all the pistons gently with the retainer plate. Check the pistons for their free movement in the cylinder block bores. If the piston or the cylinder block bore is scored, replace cylinder block assembly. Do not interchange pistons between pump and motor cylinder block. Pistons and cylinder blocks are matched. Clearance between piston and bore - 0.02 mm (0.0008 in).

Piston Slipper and Retainer Plate

Check the slipper for flatness. If rounded, replace Measure the thickness of piston slipper. If the measurement is less than the allowable limit, replace. Check the lubricant hole for clogging. Thickness of slipper - 3.00 mm (0.118 in).

Cylinder Block Face

Check the polished face of cylinder block for scoring. If scored, replace cylinder block assembly. Check the spring for breakage. If broken, replace cylinder block assembly.

Transmission Case

Checking Bearing

Hold the inner race, and push and pull the outer race in all directions to check for wear and roughness. Apply transmission fluid to the bearing, and hold the inner race. Then, turn the outer race to check rotation. If there is any defect, replace it.

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 it. Clearance between 13T gear and 3rd shaft - 0.007 to 0.046 mm (0.00028 to 0.00181 in). 3rd shaft O.D. - 21.987 to 22.000 mm (0.86562 to 0.86614 in). 13T gear I.D. - 30.007 to 30.021 mm (1.18138 to 1.18193 in). Needle O.D. - 3.994 to 4.000 mm (0.15724 to 0.15748 in).

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