Specifications, Service and Repair of Farm and Lawn Tractors

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Kubota BX1500, BX1800, BX1850 - Transmission


Kubota BX1500, BX1800, BX1850 - Transmission System and Oil Flow



1 - Hydrostatic Transmission, 2 - Mid-PTO Assembly, 3 - Rear PTO Assembly, 4 - Brake Assembly, 5 - Differential Gear Unit, 6 - Range Gear Shift Unit, 7 - Front Wheel Drive Gear Unit, 8 - Hydraulic Pump Drive Gear Unit

Oil Flow



1-Cylinder Block (Pump), 2-Swashplate, 3-Piston, 4-Cylinder Block (Motor), 5-Check and High Pressure Relief Valve (Reverse), 6-Check and High Pressure Relief Valve (Forward), 7-Power Take-Off Clutch Valve, 8-Charge Relief Valve, 9-Oil Filter Cartridge, 10-Power Take-Off Relief Valve, 11-Oil Strainer, 12-Hydraulic Pump, 13-Transmission Case, 14-Power Steering, 15-Flow Priority Valve (Hydraulic Control Valve)

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 hydrostatic transmission needs to be supplied a want. The oil from the power steering circuit flows into the HST for charging. The charge oil aids smooth operation of pistons for pump and motor. The charge oil passes through the oil filter cartridge to charge relief valve port. The rest of oil passes through the charge relief valve into the hydrostatic transmission housing. And overflow oil from HST housing return to the transmission case.

Hydraulic Pump Drive Gear



1 - 19T Gear Shaft, 2 - 29T Idle Gear, 3 - Front Cover, 4 - 13T Gear, 5 - Hydraulic Pump, 6 - Clutch Shaft

The hydraulic pump (5) is mounted to front cover (3) of the transmission case and driven by 13T gear (4) on the clutch shaft (6).

Kubota BX1500, BX1800, BX1850 - Brake Assembly



1-Brake Cam Lever LH, 2-Transmission Case, 3-Rear Axle LH, 4-Steel Ball, 5-Cam Plate LH, 6-Friction Plate, 7-Bearing Holder LH, 8-Rear Axle RH, 9-Axle Cover, 10-Brake Cam Lever RH, 11-Brake Disc, 12-Brake Pedal, 13-Parking Brake Lock Pedal, 14-Spring, 15-Brake Rod, 16-Turnbuckle

The mechanical wet disc brakes are used for right and left travelling brakes. They are operated by the brake pedal (12) through the mechanical linkages and provide stable braking and require little adjustment. The brake body is incorporated in the transmission case (2) and axle cover (9) filled with transmission oil. For greater braking force, four brake discs (11) are provided at the right and left sides respectively, and the friction plates (6) fixed to the transmission case (2) and axle cover (9) are arranged between the brake discs (11).

Travelling Brake - When the brake pedal (12) is depressed, the linkage causes the brake cam levers (1), (10) to turn into the direction of arrow shown in the above figure. Therefore, the cam plates also moves and rides on the steel balls set in the grooves of the transmission case (2) and axle cover (9) to press the brake disc, the rear axle (3), (8) are braked by the frictional force generated by the cam plate and brake disc.

Parking Brake - When the parking brake is applied, the brake pedal (12) locked by the parking brake lock pedal (13) to actuate the brake mechanism same as a travelling brake.

Kubota BX1500, BX1800, BX1850 Tractor - Mid and Rear PTO



1 - Clutch Shaft, 2 - 12T Gear Clutch, 3 - PTO Clutch Pack, 4 - Rear Cover, 5 - Rear PTO Shaft, 6 - 11T Gear Shaft, 7 - PTO Select Gear, 8 - 26T Idle Gear, 9 - Mid-PTO Shaft, 10 - Idle Shaft, 11 - 22T Gear

Three kinds of power flow are selected by operating the PTO select lever to shift the PTO select gear (7) on the 11T gear shaft (6).

Mid-PTO Position - PTO Clutch Pack (3) - 12T Gear Clutch - PTO Select Gear (7) - 22T Gear (11) - 26T Idle Gear (8) - Mid-PTO Shaft (9).

Rear PTO Position - PTO Clutch Pack (3) - 12T Gear Clutch (2) - PTO Select Gear (7) - 11T Gear Shaft (6) - Rear PTO Shaft (5).

Kubota BX1500, BX1800, BX1850 Transmission - Checking And Adjusting

Adjusting Maximum Speed



1-Stopper Bolt (Reverse), 2-Speed Control Pedal, 3-Stopper Bolt (Forward)

Depress the speed control pedal (2) all the way and lengthen the stopper bolt (3) until it touches the bottom surface of the speed control pedal (2). Release the speed control pedal (2) to the neutral, lengthen the stopper bolt (3) half turn and lock it. Adjust the stopper bolt (1) length “A” to 30 mm (1.18 in.) and lock it securely. Maximum Forward Speed - 13.0 to 14.0 km/h (8.1 to 8.8 mph). Maximum Reverse Speed - 10.0 to 11.0 km/h (6.3 to 6.9 mph).

Preparation before HST Adjustment



1-Front Wheel, 2-Wooden Block, 3-Hydraulic Jack, 4-Rear Wheel, 5-Brake Rod, 6-Speed Control Pedal, 7-Front Wheel Drive Lever, 8-4WD OFF Position, 9-4WD ON Position, 10-Seat Belt, 11-Speed Control Pedal Link, 12-Speed Control Rod, 13-Trunnion Arm, 14-Neutral Arm, 15-Neutral Spring, 16-Neutral Adjust Lever

Place the wooden blocks (2) at F and R side of wheels not to move the tractor. Measure the speed control pedal (6) control force with a pushpull gauge before starting the engine. Remove the brake rod (5) because improper brake rod adjustment will cause the HST neutral adjustment unexpectedly. Remove the neutral spring (15) from the neutral arm (14). Move the neutral arm (14) by hand. Check that the neutral arm (14) moves smoothly around the neutral adjust lever (16). If the neutral arm (14) does not move smoothly around neutral adjust lever (16), apply spray grease to neutral arm fulcrum contacted to the neutral arm (14). Check it again. If the neutral arm (14) still does not move smoothly, change the neutral arm (14) with a new one. Reinstall the neutral spring (15) to the original position. Lift up the rear wheels (4) with safely by the hydraulic jacks (3). Shift the front wheel drive lever (7) to “OFF” position (8). To avoid the engine stopping in adjusting neutral and to contact the operator’s seat switch, fasten firmly seat belt (10) on the operator’s seat as shown in the figure. Speed control pedal control force (forward side pedal) - 60 to 100 N (13.5 to 22.8 lbs). Speed control pedal control force (reverse side pedal) - 40 to 80 N (9.0 to 18.0 lbs).

Adjustment of HST Neutral Position



1-Range Gear Shift Lever, 2-Hi Position, 3-NEUTRAL Position, 4-Lo Position, 5-Neutral Adjust Lever, 6-Locking Screw, 7-Neutral Plate, 8-Rear Wheel, 9-Speed Control Pedal, 10-Neutral Spring, 11-Adjust Rod

Start the engine. Shift the range gear shift lever (1) to “Hi” position (2). Loosen the locking screw (6). And push the neutral adjust lever (5) toward the tractor rear side as shown in the figure until the rear wheels (4) begin to rotate forward. Push the neutral adjust lever (5) toward tractor front side until the rear wheels (4) stop rotating. When the rear wheels (4) stop rotating, lock the neutral adjust lever (5) with the locking screw (6). Depress the speed control pedal (9) forward to rotate the rear wheels (8), release the foot from the speed control pedal (9) and check that the rear wheels (8) stop rotating. Depress the speed control pedal (9) reverse to rotate the rear wheels (8), release the foot from the speed control pedal (9) and check that the rear wheels (8) stop rotating. If the rear wheels (8) do not stop rotating, repeat the above mentioned procedure 3 to 5 again and check that the rear wheels (8) stop rotating at the neutral position of the speed control pedal (9). Shift the range gear shift lever (1) to “LOW” position. Check that the rear wheels (8) stop rotating at the neutral position of the speed control pedal (9). Reinstall the brake rod to the original position. Remove the hydraulic jacks. Disconnect the safety belt to return the operator’s seat switch to the original condition (for only model equipped Operator’s Presence Control System). Check the HST proper operation on the usual jobs.

Kubota BX1500, BX1800, BX1850 Transmission - Servicing Specifications

Charge Relief Valve (Setting Pressure) - 294.2 to 490.4 kPa 3.0 to 5.0 kgf/cm2 42.7 to 71.1 psi
Check and High Pressure Relief Valve (Setting Pressure) - 13.73 MPa 140 kgf/cm2 1991.2 psi
PTO Clutch (Operating Pressure) - 961 kPa 9.8 kgf/cm2 139.4 psi
Shift Fork to Shifter Gear Groove (Clearance) - 0.03 to 0.48 mm / 0.0012 to 0.019 in.
13T-25T Gear to Front Wheel Drive Idle Shaft - 0.007 to 0.043 mm / 0.0003 to 0.0017 in.
22T Gear to 11T Gear Shaft - 0.007 to 0.039 mm / 0.0003 to 0.0015 in.
12T Gear Clutch to Clutch Shaft - 0.007 to 0.037 mm / 0.0003 to 0.0015 in.
PTO Clutch Disc - 1.70 to 1.90 mm / 0.067 to 0.075 in.
Pressure Plate - 1.95 to 2.05 mm / 0.077 to 0.081 in.
Steel Plate - 1.15 to 1.25 mm / 0.045 to 0.049 in.
Clutch Piston Flatness - 0.15 mm / 0.0059 in.
Pressure Plate and Steel Plate Flatness - 0.20 mm / 0.0079 in.
Clutch Spring Free - 37.3 to 37.7 mm / 1.47 to 1.48 in.
PTO Brake Disc - 3.20 to 3.40 mm / 0.126 to 0.134 in.
Differential Case to Differential Side Gear - 0.050 to 0.151 mm / 0.0020 to 0.0059 in.
Differential Pinion Shaft to Differential Pinion - 0.080 to 0.122 mm / 0.0031 to 0.0048 in.
Differential Pinion to Differential Side Gear (Backlash) - 0.15 to 0.30 mm / 0.0059 to 0.0118 in.
Spiral Bevel Pinion Shaft Side (Clearance) - 0.1 to 0.3 mm / 0.0039 to 0.0118 in.
Spiral Bevel Pinion Shaft to Spiral Bevel Gear (Backlash) - 0.1 to 0.3 mm / 0.0039 to 0.0118 in.
Actuator and Bearing Holder (Flatness) – 0.30 mm / 0.0118 in.
Cam Plate and Ball - 22.89 to 22.99 mm / 0.9012 to 0.9051 in.
Brake Disc (Thickness) - 3.3 to 3.5 mm / 0.130 to 0.138 in.
Friction Plate - 1.92 to 2.08 mm / 0.0756 to 0.0819 in.

Kubota BX1500, BX1800, BX1850 Tractor - Transaxle Separating

Draining Transmission Fluid

Place oil pan under the tractor. Remove the drain plugs at the bottom of the transmission case. Drain the transmission fluid and reinstall the drain plug. When refilling - 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 to prescribed level. Use only multi-grade transmission oil. Use of other oils may damage the hydrostatic transmission or hydraulic system. Never work the tractor immediately after changing the transmission oil. Keeping the engine at medium speed for a few minutes to prevents damage to the transmission. Do not mix different brands oil together.

Speed Control Pedal, Lever Guides and Step



1-Lowering Speed Adjusting Knob, 2-Cutting Height Adjusting Dial Knob, 3-Lever Guide LH, 4-Step, 5-Lever Guide RH, 6-Speed Control Pedal, 7-Step Plate

Remove the lowering speed adjusting knob (1) and cutting height adjusting dial knob (2). Remove the step plate (7), speed control pedal (6) and lever guides (3), (5). Remove the step (4).

Fenders and Fuel Tank

Disconnect the lead wires from the tail lights. Remove the fuel cap, then remove the fenders as a unit. Replace the fuel cap. Fuel Tank - Drain the fuel. Disconnect the lead wire from fuel level sensor and fuel hoses from the fuel tank. Remove the fuel tank stays and cushions, then remove the fuel tank.

Lift Rod and Lower Link



1-Lift Rod RH, 2-Lower Link RH, 3-Lower Link LH, 4-Lift Rod LH, 5-Stopper Plate

Remove the lift rods (1) and (4). Remove the stopper plate LH (5), then tap out the lower link pin to remove the lower links (2), (3) with check chains as a unit.

PTO Cover, Fender Bracket, Hitch Plate and Others



1-Upper PTO Cover, 2-PTO Cover RH, 3-Rear Support RH, 4-Hitch Plate, 5-Rear Support LH, 6-PTO Cover LH, 7-Fender Bracket RH, 8-Fender Center Stay, 9-Fender Bracket LH

Remove the PTO covers (1), (2) and (6). Remove the hitch plate (4) and rear supports (3), (5). Remove the fender brackets (7), (9), shim and fender center stay (8). Do not firmly tighten all screws, bolts and nuts until most components are attached. After the all screws, bolts and nuts are tighten to the specified torque, install and secure the shim with hexagonal socket head screw between fender brackets (7), (9) and fender center stay (8). When tightening the upper PTO cover (1) mounting bolts and nuts, adjust the operating force to 29.4 to 49.0 N (3.0 to 5.0 kgf, 6.6 to 11.0 lbs).

Kubota BX1500, BX1800, BX1850 - Transmission Disassembly and Assembly

Transaxle Assembly



1 - Return Hose, 2 - Speed Control Rod, 3 - Power Steering Delivery Hose, 4 - Differential Lock Rod, 5 - Pipe, 6 - Brake Rod LH, 7 - Nut, 8 - Brake Rod RH, 9 - Spring, 10 - Front Wheel Drive Shaft, 11 - Rear Coupling Mounting Bolt, 12 - Wire Harness

Disconnect the speed control rod (2), differential lock rod (4) and brake rod (6), (8). Remove the rear coupling mounting bolt (11) and spring (9). Remove the nuts from the lift link rear (7) and wire harness (12) clamps. Disconnect the power steering delivery hose (3). Disconnect the return hose (1) and remove the pipe (5). Hold the transaxle assembly with nylon strap and crane. Remove the transaxle assembly mounting screws and separate it. Tighten the smaller screws (M12) first.

Parking Pedal, Propeller Shaft Assembly and Tie-rod



1-Spring, 2-Parking Pedal, 3-Propeller Shaft Assembly, 4-Tie-rod, 5-Front Coupling, 6-Rear Coupling, 7-HST Fan

Unhook the spring (1) and remove the parking pedal (2). Disconnect the front coupling (5) and remove the propeller shaft assembly (3). Remove the HST fan (7) from propeller shaft assembly (3). Remove the tie-rod (4). Apply grease to inside of the front coupling and rear coupling.

Brake Pedal, Speed Change Rod and HST Damper



1-Brake Pedal, 2-HST Damper, 3-Speed Change Rod, 4-Brake Arm, 5-Bush, 6-Spring

Remove the cotter pin and clevis pin, then remove the brake arm (4). Remove the spring (6), brake pedal (1) and bushes (5). Remove the rue rings, then remove the HST damper (2) and speed change rod (3).

PTO Clutch Assembly

Remove the PTO clutch assembly from transmission case. Apply transmission oil to the seal ring on the clutch shaft.

Disassembling PTO Clutch Assembly



1 - Collar, 2 - Needle Bearing, 3 - 12T Gear Clutch, 4 - Bearing Collar, 5 - Clutch Spring, 6 - Spring Collar, 7 - External Snap Ring, 8 - Brake Pressure Plate, 9 - External Snap Ring, 10 - Shim, 11 - External Snap Ring, 12 - Brake Disc, 13 - Clutch Shaft, 14 - Clutch Case, 15 - Pressure Plate, 16 - Internal Snap Ring, 17 - Clutch Piston, 18 - Clutch Disc

Remove the collar (1), needle bearings (2) and 12T gear clutch. Remove the external snap ring (9), then remove the shims (10), brake pressure plate (8) and brake disc (12). Remove the external snap rings (11) and (7). Remove the spring collar (6), clutch spring (5) and bearing collar. Remove the internal snap ring (16), then draw out the pressure plates (15) and clutch discs (18). Tap out the clutch shaft (13) and remove the clutch piston (17) from clutch case (14). Apply transmission oil to the O-rings, D-ring and seal ring, and take care not to damage it.

Axle Cover

Remove the rear bracket and front bracket. Remove the axle cover from transmission case. Apply liquid gasket to joint face of the transmission case to axle cover. Align the mounting surface of the front bracket, rear bracket and axle cover to the transmission case before tightening the bracket mounting nut.

Kubota BX1500, BX1800, BX1850 - Transmission Service

Cylinder Block Assembly



1-Cylinder Block, 2-Piston, 3-Thrust Washer, 4-Spring, 5-Polished Face

Check the cylinder blocks (1) and pistons (2) for scratches and wear. If scratch or worn, replace the cylinder block assembly. Check that the piston (2), spring (4) and thrust washer (3) are in each cylinder bore. 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 (5) of cylinder block for scoring. If 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



1-Seal Surface, 2-Bearing Surface, 3-Ball Bearing

Check the seal surface (1), the bearing surface (2) and the ball bearing (3). If the shaft is rough or grooved, replace it. If the ball bearing is worn, replace it.

Needle Bearing and Oil Seal

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

Clearance between Shift Fork and Shifter Gear Groove (Range Gear Shift)

Insert the shift fork into the shifter gear groove and measure the clearance with a feeler gauge. If the clearance exceeds the allowable limit, replace it. Clearance between shift fork and shifter gear groove 0.03 to 0.48 mm (0.0012 to 0.019 in). Allowable limit - 0.7 mm (0.028 in).

Clearance between 13T-25T Gear and Front Wheel Drive Idle Shaft

Measure the 13T-25T gear I.D. with a cylinder gauge, and then front wheel drive idle 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-25T gear and front wheel drive idle shaft - 0.007 to 0.043 mm / 0.0003 to 0.0017 in. Allowable limit - 0.10 mm / 0.0039 in. 13T-25T gear I.D. - 19.007 to 19.020 mm / 0.7483 to 0.7488 in. Front wheel drive idle shaft O.D. - 13.989 to 14.000 mm / 0.5507 to 0.5512 in. Needle O.D. - 2.494 to 2.500 mm / 0.0982 to 0.0984 in.

Clearance between 22T Gear and 11T Gear Shaft

Measure the 22T gear I.D. with a cylinder gauge, and then 11T gear 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 22T gear and 11T gear shaft - 0.007 to 0.039 mm / 0.0003 to 0.0015 in. Allowable limit - 0.10 mm / 0.0039 in. 22T gear I.D. - 24.007 to 24.020 mm / 0.9452 to 0.9457 in. 11T gear shaft O.D. - 19.987 to 20.000 mm / 0.7869 to 0.7874 in.

Clearance between 12T Gear Clutch and Clutch Shaft



Measure the 12T gear clutch I.D. with a cylinder gauge, and then clutch 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 clutch 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 12T gear clutch and clutch shaft - 0.007 to 0.037 mm / 0.0003 to 0.0015 in. Allowable limit - 0.10 mm / 0.0039 in. 12T gear clutch I.D. - 22.007 to 22.020 mm / 0.8664 to 0.8669 in. Clutch shaft O.D. - 17.989 to 18.000 mm / 0.7082 to 0.7087 in. Needle O.D. - 1.997 to 2.000 mm / 0.0786 to 0.0787 in.

PTO Clutch Disc Wear

Measure the thickness of PTO clutch disc with vernier calipers. If the thickness is less than the allowable limit, replace it. Thickness of PTO clutch disc - 1.70 to 1.90 mm / 0.067 to 0.075 in. Allowable limit - 1.55 mm / 0.061 in.

Pressure Plate and Steel Plate Wear

Measure the thickness of pressure plate and steel plate with vernier calipers. If the thickness is less than the allowable limit, replace it. Thickness of pressure plate - 1.95 to 2.05 mm / 0.077 to 0.081 in. Allowable limit - 1.80 mm / 0.071 in. Thickness of steel plate - 1.15 to 1.25 mm / 0.045 to 0.049 in. Allowable limit - 1.10 mm / 0.043 in.

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KUBOTA TRACTORS SPECIFICATIONS

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KUBOTA ENGINES DATA AND SERVICE SPECS

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KUBOTA FRONT END LOADERS

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KUBOTA TRACTORS TROUBLESHOOTING
L235 L2501 L2550 L275 L3110
L3301 L35 L3710 L3901 L4310
L5030 M4700 M5700 M6040 M6800
M8200 M8540 M9000 MX5100 MX5200