Pulling the backhoe off your B21 this weekend? The job goes faster with the right book open. This 437-page Kubota B21, TL421, BT751 Shop Manual PDF (OEM #9Y011-12011) treats the tractor, TL421 front loader, and BT751 backhoe as one connected machine. Hydraulic schematics trace the HST circuit, wiring diagrams cover the full electrical system, and step-by-step procedures span the engine, clutch, transmission, and steering. Troubleshooting charts and a complete torque section pin down every fastener on the loader and backhoe. Fill the transmission case with 27.5 L of hydraulic fluid, set fan belt deflection at 7 to 9 mm, then torque the loader side frame bolts to 150 to 160 N·m. Every hour that backhoe sits idle costs you a paying job. Bookmarked and searchable, so you can jump straight to the backhoe section or pull any spec by keyword.
What's Inside This Kubota B21, TL421, BT751 Manual
| System | Pages | Key Topics |
|---|---|---|
| To the Reader | - | Kubota Tractor B21, Kubota Front Loader TL421, Kubota Backhoe BT751, PTO, Engine, Hydraulic, Clutch, Transmission |
| General | - | Tractor Identification, Electrical Parts and Wiring, Lubricants, Fuel and Cooling Water, Screws, Bolts and Nuts, Stud Bolts, Hydraulic Hoses Fitting |
| Engine | - | Cylinder Block, Cylinder Head, Crankshaft, Piston and Piston Rings, Connecting Rod, Camshaft, Fuel Camshaft, Rocker Arm |
| Clutch | - | Linkage Mechanism, Operation, Clutch Disc, Pressure Plate Assembly, Release Bearing, Release Hub, Release Fork |
| Transmission | - | Hydrostatic Transmission, PTO System, Differential Gear System, Clutch Housing, Transmission Case, Differential Case |
| Rear Axle | - | Differential Gear Shaft, Ball Bearing, Rear Axle Case, Spur Gear, Differential, Spiral Bevel Gear, Differential Lock Shift Fork |
| Brakes | - | Brake Pedal, Rear Axle Case, Differential Lock Shift Fork, Differential Lock Clutch, 57T Gear, Brake Assembly, Brake Discs, Friction Plate |
| Front Axle | - | Front Wheel Alignment, Propeller Shaft, Drag Link, Front Axle Assembly, Tie-Rod, Axle Bracket, Bevel Gear Case |
| Steering | - | Hydraulic Circuit, Power Steering Body, Drag Link, Pitman Arm, Power Steering Assembly, Ball Nut Assembly, Valve Housing, Sector Gear Shaft |
| Hydraulic System | - | Hydraulic Pump, Flow Priority Valve, Position Control Valve, Hydraulic Block, Hydraulic Cylinder, Relief Valve, Hydraulic Piston, Lowering Speed Adjusting Valve |
| Electrical System | - | Wiring Diagram and Electrical Circuit, Starting System, Engine Key Switch Shut-Off System, Charging System, Lighting System, Easy Checker, Gauge, Opc(operator Presence Control)system |
| Front Loader | - | Safety Decals, Front Loader Terminology, Operating Dimensions, Hydraulic System, Control Valve Assembly, Feedback Linkage, Boom Cylinder, Bucket Cylinder |
| Backhoe | - | Safety Decals, Backhoe Terminology, Operating Dimensions, Cycle Time, Hydraulic Cylinders, Lift Capacity, Hydraulic System, Hydraulic Cylinder |
Quick Reference Specifications
| Specification | Value | Page |
|---|---|---|
| TL421 | ||
| Loader side frame mounting screw, bolt and nut tightening torque | 150 to 160 N·m | p. 393 |
| B21 | ||
| Hydraulic oil filter for HST, efficiency | 10 µm | p. 26 |
| Transmission case (Hydraulic Fluid) Capacity | 27.5 L | p. 20 |
| Fan belt tension | 7 to 9 mm (0.28 to 0.34 in.) deflection | p. 35 |
| Battery Cold Cranking Amps | 433 A | p. 33 |
| Main Switch Continuity (ON Position, 30 terminal - AC terminal) | 0 ohm | p. 339 |
| Fuse Capacity (Head lights) | 10 A | p. 41 |
| Main Switch Connector 30 terminal voltage | Approx. battery voltage | p. 339 |
| Thermostat Valve Opening Temperature (At Beginning) | 80.5 to 83.5 °C | p. 134 |
| PTO Power | 10.0 kW (13.5 HP) | p. 8 |
| Engine Oil Capacity (with filter) | 3.0 L | p. 8 |
Kubota B21, TL421, BT751 Common Problems This Manual Covers
Kubota B21 loader arm raises slowly then suddenly jumps to full speed partway up p. 20
Check the hydraulic fluid level before anything else. Drain and refill the transmission case to its full 27.5 L capacity (page 20) with clean fluid, then replace the 10 micron HST filter (page 26). Air trapped in the system mimics this hesitation, so cycle the loader fully ten times to bleed it out.
Manual Section: Front Loader Troubleshooting3-point hitch lifts fine with no implement attached but stalls and drops under any real weight
Verify the hydraulic fluid is full and clean first. A hitch that lifts empty but stalls under load points straight to internal pressure loss. Inspect the relief valve for leak-down and check pump output against its 32 L/min rating. Worn pump gears and contaminated fluid both bleed off the pressure the hitch needs.
Manual Section: Hydraulic System TroubleshootingBackhoe hydraulics feel weak or erratic, one cylinder noticeably slower than the rest p. 431
Test each cylinder separately to isolate the weak circuit. Inspect that cylinder for a worn or damaged piston seal ring and replace it if scored (page 431). A healthy bucket circuit delivers 13820 N (3110 lbs) of digging force, so a soft one means internal bypass. Check fluid level and clean the suction strainer.
Manual Section: Backhoe TroubleshootingFuses blow repeatedly when the turn signals or other electrical accessories are switched on p. 41
Pull the blown fuse and confirm it matches the rated capacity; headlight circuits take a 10 A fuse (page 41). Trace the turn signal harness against the wiring diagram (page 307) for chafed insulation or a pinched ground. Clean every corroded connector and bench-test the switch. A repeat blow means a hard short to ground.
Manual Section: Electrical System TroubleshootingEngine cranks slowly or will not start at all, intermittent no-start that comes and goes p. 33
Load-test the battery; it should hold its 433 A cold cranking rating (page 33). Clean and tighten corroded terminals, then check the starter switch for continuity. With the key ON, the 30 to AC terminals must read 0 ohm (page 324). A switch failing that test, or showing no battery voltage at terminal 30, needs replacement.
Manual Section: Electrical System TroubleshootingEngine temperature climbs into the red under load and coolant pushes out the overflow p. 134
Clean the radiator fins thoroughly; packed chaff is the usual culprit. Check coolant level cold, then inspect the fan belt for 7 to 9 mm (0.28 to 0.34 in.) of deflection (page 35) and tighten it if loose. Test the thermostat: it should begin opening at 80.5 to 83.5 °C (page 134). Replace a stuck unit.
Manual Section: Engine TroubleshootingFrequently Asked Questions
How do you reset the Kubota B21 hydrostatic transmission?
To adjust the hydrostatic transmission's neutral position, lift the rear of the tractor so the wheels are off the ground. Run the engine at low idle. Rotate the neutral adjuster (2) clockwise until the wheels turn in reverse, then counterclockwise until they stop. Mark this position. Repeat for forward rotation and set the adjuster groove between the two marks. The full procedure is on page 205.
What are the torque specs for the Kubota B21 loader and backhoe mount bolts?
Loader side frame mounting hardware (screw, bolt, and nut) torques to 150 to 160 N·m (15.3 to 16.3 kgf·m, 110 to 118 ft-lbs). The main frame mounting screw uses the same figure. Check the detailed torque tables for the remaining components.
How do you bleed the fuel system on a Kubota B21?
Bleeding the fuel system starts at the tank: fill it, then open the fuel cock. Start the engine and let it run about 30 seconds before shutting it down. That clears trapped air, which you will need to do after running the tank dry or swapping the fuel filter.
What format is this manual in?
Instant PDF download. The full 437-page searchable Shop Manual lands in your hands right after payment, ready to open on a laptop, tablet, or phone out in the shop.
Am I able to print pages from this manual?
Absolutely. No DRM or copy protection. Print the whole manual or just the pages you need. Any home or office printer works.
Can I find hydraulic circuit diagrams in this Kubota B21, TL421, BT751 manual?
Yes. The manual includes full hydraulic schematics with flow diagrams, valve configurations, and pressure specifications.
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