Specifications, Service and Repair of Farm and Lawn Tractors

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Kubota B6100, B7100 - HST Transmission


Kubota B6100HST, B7100HST tractors are equipped with a hydrostatic transmission.

Kubota B6100, B7100 Hydrostatic Transmission - Operation



Engine power is transferred to the input shaft (7) which drives the trochoid rotor assembly (5) and variable displacement piston pump (24). Trochoid rotor assembly (5) is located in charge pump case (6) and is used to supply low pressure oil to the charge system. Cylinder block (27) within the variable displacement piston pump (24) is rotated against variable swashplate (29) surface. If the swashplate is moved in the forward or reverse direction, oil will be pumped to the fixed displacement piston motor (21) to turn the output shaft (19). The higher the volume of oil the faster the output shaft will turn. Volume of oil is controlled by the variable swashplate degree of tilt. Fluid direction and pressure regulation is governed by valves contained within the circuits.

Pressure Test

Pressure tests may be performed after removing hydrostatic transmission protective cover as follows: Remove speed control knob, left and right hood latch, front and rear mounting cap screws, then withdraw cover.

Case Pressure

Remove plug from port and install a low pressure gage. Position high-low gear shift and speed control pedal in neutral. Engage parking brake, then .run engine at 2800 rpm. Recommended reading is 165.6-220.8 kPa (24-32 psi) with an allowable limit of 144.9-248.4 kPa (21-36 psi). Low case pressure could cause transmission overheating, resulting from oil not being circulated to oil cooler. A high pressure reading could indicate that the pipe to the oil cooler or the oil cooler itself is clogged, which could cause oil seal damage.

Charge Pressure

Prior to charge pressure testing, check case pressure as outlined in previous section. To check charge pressure, remove plug from port and install a low pressure gage. Position high-low gear shift and speed control pedal in neutral. Engage parking brake, then run engine at 2800 rpm. To calculate correct charge pressure, deduct case pressure reading from measured charge pressure. Recommended reading is 441.6-579.6 kPa (64-84 psi) with an allowable limit of 414-607.2 kPa (60-88 psi). Low pressure could cause a lack of power or noise and vibration.

High Relief Pressure (Forward or Reverse)

Remove plug from port to test forward circuit or port to test reverse circuit. Install a high pressure gage that will read at least 27.6 MPa (4000 psi). Start engine and allow transmission fluid to warm up to operating temperature. Engage parking brake, then set engine speed at 2800 rpm. Depress speed control pedal approximately 10 mm (25/64-inch) in direction of circuit being tested (forward or reverse). Record gage reading as quickly as possible. Depressing speed control pedal more than 10 mm (25/64-inch) will give an incorrect high reading. DO NOT hold speed control pedal down longer than 10 seconds. Recommended high relief pressure is 21.6-25.5 MPa (3130-3700 psi).

Vacuum

Remove plug from port and install a vacuum gage with maximum capability of 762 mm Hg (30 in. Hg). Engage parking brake, then run engine at 2800 rpm. Recommended maximum vacuum gage readings are as follows; readings will vary according to oil temperature: Oil Temperature / Gage Reading - 30C (86F) / 120 mm Hg (4.7 in. Hg), 50C (122F) / 60 mm Hg (2.4 in. Hg), 80C (176F) / 35 mm Hg (1.4 in. Hg). A high vacuum reading indicates incorrect oil type or a clogged strainer. A fluctuating reading indicates a faulty or loose connection on the suction side.

Kubota B6100, B7100 Tractor - HST Linkage

Operation



Neutral holder (5) is connected to transmission trunnion shaft which controls the angle of variable swashplate. Neutral holder (5) is connected to rod guide (3) via speed control rod (4). Depressing pedal (9) causes rod guide (3) to rotate. Forward travel speed may be set by engaging speed control linkage (1, 2 and 11 through 15). Speed control linkage must be disengaged manually. Neutral adjuster (6) is used to correctly position needle bearing (7) in center position of neutral holder (5) when pedal (9) or speed control linkage is released, thus placing transmission in neutral position. Spring (25) is used to return neutral holder arm (8). Damper (10) slows pedal return rate to prevent tractor from stopping too quickly and to prevent transmission damage due to fast pedal direction change over.

Adjustment

Before performing adjustments, be sure mechanism moves freely without binding. Dirt, grit or other foreign material may cause false adjustment settings. To adjust neutral position proceed as follows: Place selector lever in two-wheel drive, raise rear wheels off the ground, then start engine and set engine speed at low idle. Loosen cap screw and turn slot (18) counterclockwise so the rear wheels rotate in forward direction. Turn slot (18) clockwise until the rear wheels completely stop.



Mark position (X) of slot (18) on clutch housing (17) where rear wheel rotation stopped. Continue to turn slot (18) clockwise until the rear wheels rotate in the reverse direction, then turn slot (18) in counterclockwise direction until rear wheels completely stop. Mark position (Y) of slot (18) on clutch housing (17) where rear wheel rotation stopped. Position neutral adjuster (6) so slot (18) is centered between marks X and Y, then tighten cap screw (16) to 19-32 Nm (14-24 ft-lbs.) torque while securely holding slot (18) in position. After lowering rear wheels, check that wheels stop automatically after forward-reverse pedal is released from either direction. If the wheels continue to turn in the forward direction, turn slot (18) clockwise in small increments. If the wheels continue to turn in the reverse direction, turn slot (18) counterclockwise in small increments. Continue adjustment procedure until neutral position is obtained when pedal is released from both directions. If true neutral position cannot be found by adjustment procedure, move neutral holder arm by hand to determine if true neutral position can be obtained. If neutral cannot be found, problem may be located in the neutral valve.



To adjust forward speed control components proceed as follows: Loosen locknut (12) and turn turn-buckle (13) until dimension (D) is 6-8 mm (15/64-5/16 inch), then retighten locknut (12). Loosen locknut (37) and turn adjuster nut (39) to adjust tension on spring (38) until force required to operate lever (1) in R direction is 25-30 N (5.5-6.6 lbs.), then retighten locknut (37).



If excessive play is noted in lever, adjust as follows: Loosen screw (34) and reposition retainer plate (33) until play is reduced and head of bolt (32) does not rotate when lever (1) is operated. After installing cover (35), place lever (1) in position L, then depress reverse side of speed control pedal. Observe linkage to make sure that cam (15) does not contact lever (1).

Clutch Housing/Transmission Case Split

Drain transmission/hydraulic system fluid into a suitable container. Remove hydrostatic transmission protective cover as follows: Remove speed control knob, left and right hood latch, front and rear mounting cap screws, then withdraw cover. Remove hydrostatic transmission oil filter and joint. Raise hood and disconnect negative battery cable from battery post. Detach hydraulic lines as needed. Disconnect speed control rod from rod guide. Remove right and left brake pedal rods. Remove differential lock shaft. On four-wheel drive models, loosen drive shaft protective cover band at joint case, then withdraw drive shaft from joint case.

Remove bolts and nuts securing step plates to fenders. Remove clutch housing and transmission case connecting plate from underneath side. Support rear of tractor. Attach a hoist with suitable holding fixtures to clutch housing. Remove bolts and nuts securing clutch housing to transmission case, then separate components. Reassembly is reverse order of splitting procedure. Tighten bolts and nuts securing clutch housing to transmission case to 61-107 Nm (45-79 ft-lbs.) torque. Refill transmission/hydraulic system with 13.5 liters (3.6 gal.) of the following hydrostatic transmission fluid or a suitable equivalent.

Kubota B6100HST, B7100HST Transmission - Remove and Overhaul

Split clutch housing from transmission case. Remove pin, then separate propeller shaft from transmission. On Kubota B6100HST, B7100HST tractors equipped with 4WD, remove pin, then separate drive shaft from transmission. Remove nuts and cap screw from each side of hydrostatic transmission, then separate hydrostatic transmission from range transmission case. Installation procedure is reverse order of removal. Tighten nuts and cap screw to 48-56 Nm (35-41 ft-lbs.) torque.



Disassemble neutral holder assembly. Place alignment marks on neutral adjuster (6) and neutral holder arm (8), so neutral position can be determined after reassembly. Remove snap ring (3), then withdraw gear (2) and bearing (4). Remove snap ring (7), then withdraw gear (6). On models so equipped, extract front-wheel drive shaft (5) out front of transmission. Remove nipple fitting (1) and gasket (8). Remove screws (1 and 3) from port block (4), then separate port block (4) from case (2). Note that valve plates may remain with port block during separation, be careful not to allow plates to fall free. Remove valve plates. Note that valve plate with two notches is located on pump side, while valve plate with no notches is located on motor side.



Remove screws securing charge pump case to transmission case. Tap on rear of input shaft with a suitable mallet to break charge pump case loose from transmission case, then withdraw charge pump assembly along with the two dowel pins. Withdraw pump cylinder block from case. Remove circlip, then extract pistons and retainer plate. Remove thrust plate which is attached to variable swashplate. Remove stop bolt, hold output shaft and tap case with a soft mallet to extract motor cylinder block assembly. Remove screws securing left and right trunnion shaft covers and remove covers, then remove variable swashplate.



Separate input shaft from charge pump case, then inspect shaft for excessive wear and any other damage. Check pistons for smooth movement through cylinder block bores. Examine piston barrel and cylinder block bores for scratches, burrs, excessive wear and any other damage. Inspect slipper for excessive wear; minimum allowable thickness is 2.90 mm (0.114 inch). If clogged, blow lubricant hole clear with compressed air. Inspect polished face of cylinder block for scratches and any other damage. Examine internal spring of cylinder block for cracks and broken coils. Inspect valve plates for scratches, corrosion, excessive wear and any other damage. Inspect charge pump case (10) and trochoid rotor assembly (24) for scratches, excessive wear and any other damage. Examine needle bearing (25) for cracked and missing rollers, excessive wear and any other damage. Except for seals, charge pump must be renewed as a complete unit.

Recommended side clearance between trochoid rotor and straightedge measured should be 0.030-0.045 mm (0.0012- 0.0018 inch). Remove forward and reverse neutral and check valves. Be sure that check valve moves unrestricted along valve body. Inspect all components for heavy scratches, burrs, corrosion, excessive wear and any other damage. If clogged, blow passages of neutral valve and valve body clear with compressed air. Inspect springs for any deformities and broken coils. Remove high pressure relief valve.

Note that to maintain set pressure of relief valve, height of plug (44) must be measured and alignment marks placed on plug (44) and port block (4) before plug (44) is removed. To remove seat (51), special tool or a suitable equivalent must be used. Inspect all components for heavy scratches, burrs, corrosion, excessive wear and any other damage. If clogged, blow valve passages clear with compressed air. Inspect spring (45) for any deformities and broken coils. Remove charge relief valve. Inspect valve for heavy scratches, burrs, corrosion, excessive wear and any other damage. Inspect spring for any deformities and broken coils.



Inspect trunnion shaft covers and bushings for excessive wear and any other damage. Inspect pump side needle bearing (59) and motor side needle bearing (60) located in port block (4) for cracked or missing rollers, excessive wear and any other damage. Renew all parts as needed. Renew all seals, gaskets and O-rings. Oil seals must be installed using suitable tools to prevent seal damage and ensure proper seating. Lubricate all working components with the following hydrostatic transmission fluid or a suitable equivalent during reassembly. Reassembly is reverse order of disassembly. Observe the following during reassembly. Needle bearings should be installed with marked side protruding 3.5 mm (9/64 inch) above port block (4) machined surface.



Install pump side oil seal in port block (4) so top of seal surface is 3 mm (1/8-inch) below machined surface. Install motor side oil seal in port block (4) so top of seal surface is 0.5 mm (1/64-inch) above machined surface. Apply a thin coat of suitable grease to lip surface of oil seals. Install trunnion shaft oil seal in cover so top of seal surface is 1 mm (3/64-inch) below outside surface. Apply a thin coat of suitable grease to lip surface of oil seal. Install snap ring with its square edge (opposite edge is rounded) facing out. Cap nut should be tightened to 59-69 Nm (43-51 ft-lbs.) torque. Tighten screws securing trunnion shaft covers to 2-2.5 Nm (17-23 in-lbs.) torque.

Install charge pump oil seal in case so end of seal is 4 mm (5/32-inch) below outside surface. Install snap ring retaining oil seal so square edge of snap ring faces out. Tighten screws securing case to 11-14 Nm (8-10 ft-lbs.) torque. Cylinder block and pistons are assembled in reverse order of disassembly. Be sure to lubricate entire unit with clean hydrostatic fluid. Pump side circlip is installed with flat side or undistorted side towards retainer plate. Observe the following during installation of output shaft and motor cylinder block assembly in case. Install stop bolt and tighten to 16-21 Nm (12-15 ft-lbs.) torque.

Align hole of fixed swashplate with dowel pin in case. Install pump side valve plate and motor side valve plate. During assembly of case components to port block assembly a protective cover should be used over input shaft and output shaft to protect seal lips. Note that port block floats over case assembly and should separate from case when holding hand pressure is released. Tighten screws securing port block to case to 23-27 Nm (17-20 ft-lbs.) torque. Be sure input shaft and output shaft rotate smoothly. Note that square edge of snap rings securing gears and/or bearings should face towards the component it is retaining.

Kubota B6100, B7100 Tractor - Power Take-Off

Two rear PTO speeds and one mid-PTO speed are available by altering the gear combinations through positioning of PTO select lever. When power take-off select lever is placed in low speed range, power is transmitted to rear PTO. Rear PTO shaft will rotate at a speed of 540 rpm when engine speed is set at 2800 rpm. When PTO select lever is placed in high speed range, power is transmitted to rear PTO and mid-PTO. Rear PTO shaft will rotate at a speed of 850 rpm and mid-PTO shaft will rotate at a speed of 2450 rpm when engine speed is set at 2800 rpm. A one-way clutch is used to prohibit reverse drive when rear PTO speed exceeds engine speed.

Rear PTO

To remove PTO components located in center housing, first remove the six cap screws securing rear cover (54) to center housing (2). Using a suitable mallet, lightly tap rear cover (54) to separate components, then withdraw rear cover with components (43 through 57). Using a suitable puller, extract bearing (42) from shaft end (38). Remove snap ring (41), then withdraw gear (40). To service one-way clutch (34) or extract power take-off drive shaft (38), first remove hydraulic lift cover. Remove all components as needed that will obstruct in center housing and transmission case split. Using suitable holding fixtures, support center housing and transmission case, then split units apart. Remove snap ring (35) and withdraw one-way clutch half (34) and spring (36). Lightly tap front end of shaft (38) to break bearing (39) loose from center housing bore, then extract shaft.



1.Transmission case, 2.Center housing, 3.Shift rail, 4.Shift fork, 5.Ball, 6.Spring, 7.Rod, 8.Thrust washer, 9.Needle bearings, 10.Gear, 11.Thrust washer, 12.Gasket, 13.Lock screw, 14.Tab washer, 15.Shaft, 16.Cap, 17.Oil seal, 18.Cover plate, 19.Gasket, 20.Bearing, 21.Shaft and gear, 22.Bearing, 23.Mid-PTO case, 24.Gasket, 25.Drain plug, 26.Dowel pin, 27.Lever, 28.O-ring, 29.Plate, 30.Select plate, 31.Select lever, 32.Pin, 33.Grip, 34.One-way clutch, 35.Snap ring, 36.Spring, 37.Bushing, 38.PTO drive shaft, 39.Bearing, 40.PTO drive gear, 41.Snap ring, 42.Bearing, 43.Cap screw, 44.Washer, 45.Washer, 46.Washer, 47.Bearing, 48.PTO gear, 49.Spacer, 50.Bearing, 51.Spacer, 52.Bushing, 53.Shim, 54.Rear cover, 55.Seal, 56.PTO output shaft, 57.Cap

Inspect all components for damage and excessive wear. Renew all components as needed. Renew seal and gaskets during reassembly. Installation is reverse of removal. Tighten cap screws securing center housing to transmission case to 19-32 Nm (14-24 ft-lbs.) torque and nuts to 25-39 Nm (18-29 ft-lbs.) torque.

Mid-PTO

Raise hood and disconnect battery cable from negative battery post. Remove the four cap screws securing case (23) to bottom side of transmission case (1), then withdraw mid-PTO unit. Disassemble Mid-PTO unit. Inspect components and renew any which are damaged or excessively worn. Installation is reverse order of removal. Install new gasket (12). Tighten cap screws securing case (23) to transmission case (1) to 48-56 Nm (35-41 ft-lbs.) torque.

Kubota B6100HST, B7100HST Tractor - Engine Clutch

Adjustment

Clutch pedal free play should be 2-4 mm (5/64-5/32 inch). Clutch pedal travel should not exceed 8 mm (5/16-inch). Safety switch should not be engaged until clutch pedal is depressed past the recommended free play setting, placing clutch in disengaged position. If clutch pedal free play is too little, then shorten intermediate rod. If clutch is difficult to disengage, then lengthen intermediate rod. To adjust intermediate rod length, unhook spring, remove cotter key, withdraw pin, loosen locknut and turn clevis until desired setting is attained, then retighten locknut. Reassemble using a new cotter key. Adjust clutch pedal travel by loosening locknut and turning adjusting screw until correct travel distance is attained, then retighten locknut. Safety switch is adjusted on some models by loosening locknuts, then screwing switch in or out of mounting bracket. On other models, an adjusting screw positioned in lever arm is used.

Engine/Clutch Housing Split

Drain engine oil and transmission/hydraulic system fluid into suitable containers. Detach negative battery terminal from battery post. Remove air cleaner assembly, muffler and left and right side covers. Detach drag link from steering arm. Disconnect positive battery terminal from battery post. Disconnect electrical wiring at engine starter, oil pressure sending unit, headlights, glow plugs, alternator and safety switch. If needed, loosen front-wheel drive shaft protective cover band at joint case, then withdraw drive shaft from joint case. Disconnect throttle linkage and compression release cable. Disconnect fuel leak-off line from rear injector. Remove heat insulator plate located at rear of engine. Close fuel shut-off valve at fuel filter, then disconnect fuel supply line from fuel pump.

Remove line connecting fuel tank to fuel filter at filter port and plug openings to prevent fuel spillage. Remove fuel filter assembly and fuel tank. Remove hydraulic fluid supply lines. Note copper washers and O-rings when disassembling. Attach a suitable hoist or holding fixture to engine assembly and support rear of tractor with a suitable jack. Remove the eight cap screws connecting engine to clutch housing. Pull engine and front end assembly along with clutch assembly straight forward to separate engine from clutch housing. Reinstall in reverse order of removal. Tighten the eight cap screws securing engine to clutch housing to 19.7-29.5 Nm (15-22 ft-lbs) torque. Replenish engine oil and transmission/hydraulic fluid with quantity and grade of lubricant. Bleed fuel system.

Kubota B6100, B7100 Clutch - Remove and Reinstall



1. Clutch disc, 2. Pressure plate, 3. Cap, 4. Spring, 5. Pin, 6. Cover, 7. Lever seat, 8. Release lever, 9. Washer, 10. Castle nut, 11. Cotter key, 12. Return spring

To remove clutch assembly for service, first split tractor between engine and clutch housing. Insert clutch centering tool into clutch disc. Remove cap screws securing cover (6) and pressure plate (2) assembly to flywheel, then withdraw pressure plate assembly. Remove clutch centering tool along with clutch disc (1). Reinstall clutch assembly in reverse order of removal. Align clutch disc to engine crankshaft pilot bearing hole using clutch centering tool, then securely tighten cap screws mounting pressure plate assembly to flywheel. Height of release levers should be 44.8-46.2 mm (1.764-1.819 inches) measured from flywheel to surface.



Allowable difference between release lever heights is 0-0.3 mm (0-0.012 inch). Check lever heights by installing clutch centering tool (2) along with measuring tool (3), then using feeler gage (G), measure clearance between release lever (1) and measuring tool (3). Adjust release lever height by removing cotter key (11) and turning castle nut (10).

Kubota B6100HST, B7100HST Clutch - Overhaul

Remove clutch assembly. Remove cotter keys (11), then exercising caution, remove castle nuts (10). Cover (6) and pressure plate (2) are renewable only as parts of the complete assembly. Measure clutch disc wear using a suitable depth gage. Renew clutch disc if distance from clutch disc surface to top of rivet head is not at least 0.1 mm (0.004 inch). Inspect pressure plate (2) surface for cracks, scoring, heat discoloration and excessive wear. Surface grind or renew as needed. Inspect springs (4) for cracks, weakness, warpage and any other damage. Inspect all other parts for excessive wear or any other damage. Renew all parts as needed. Reassembly is reverse order of disassembly.

Release Bearing

Release bearing may be serviced after separation of engine from clutch housing. Renew bearing if outer race does not turn smoothly without noise or excessive play is noticed when outer race is tilted forward or backward. Extract release bearing from holder to renew.

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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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L3301 L35 L3710 L3901 L4310
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M8200 M8540 M9000 MX5100 MX5200