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 100 pages of step-by-step procedures span the engine, clutch, transmission, and steering. Another 10 pages of 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 |
|---|---|
| G General | 11-60 |
| 1 Engine | 61-143 |
| 2 Clutch | 144-161 |
| 3 Transmission | 162-212 |
| 4 Rear Axle | 213-223 |
| 5 Brakes | 224-238 |
| 6 Front Axle | 239-257 |
| 7 Steering | 258-277 |
| 8 Hydraulic System | 278-305 |
| 9 Electrical System | 306-350 |
| F Front Loader | 351-385 |
| B Backhoe | 386-437 |
Quick Reference Specifications
| Specification | Value | Page |
|---|---|---|
| TL421 | ||
| Loader side frame mounting screw, bolt and nut tightening torque | 150 to 160 N·m | p. 393 |
| BT751 | ||
| Troubleshooting for 'Individual Cylinder Circuit Weak or Inoperative' due to 'Piston seal ring worn or damaged' | Replace | p. 475 |
| 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.
How to reset Kubota B21 HST or transmission issue
A wandering HST neutral calls for a neutral adjustment. Lift the rear wheels clear of the ground, run the engine, then rotate the neutral adjuster until the wheels stop moving. The full procedure is detailed on page 205 of the manual.
What format is this Kubota B21, TL421, BT751 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 Kubota B21, TL421, BT751 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.
Document Quality
This is a scan of a physical workshop manual. The full text is searchable and copyable thanks to an accurate OCR layer. Text is clear and easy to read, while the diagrams and illustrations are raster images that are legible but may pixelate when zoomed in. The pages are clean with no distracting marks or scan artifacts, and you will find a few blank pages that serve as section dividers.
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