Part of the Yanmar Repair Manuals.
Chase a weak boom on a Yanmar YB401W long enough and you end up at the control valve, and this service manual supplement is where Yanmar documented it. Written for the YB401W wheel backhoe from serial number 50001 onward with the 4TNA78TL-DBW or 4TNA78TL-RBW engine, it walks the machine system by system: electrical components, engine, control valve, clutch valve, shut off valve (suspension lock valve), and steering.
Alongside maintenance procedures for each part, it carries technical data (specifications, engine maintenance standards, tightening torques), adjustment procedures including toe-in and steering angle, fuel oil and power transmission system diagrams, and a periodic replacement schedule for vital aging parts. When a steering cylinder starts weeping, that schedule tells you it takes a complete seal set, so you order the right parts the first time.
The file is a 64 page English PDF, 4.8 MB, with 65 bookmarks for quick navigation. Download it instantly and print the pages you need for the bench.
What's Inside This Yanmar YB401W Manual
| System | Pages | Key Topics |
|---|---|---|
| Technical Data | - | Engine Maintenance Standards, Tightening Torque Of Main Parts |
| Maintenance Procedure for Each Part | - | Electrical Components, Engine, Control Valve, Clutch Valve, Shut Off Valve (Suspension Lock Valve), Steering System, Revolving System, Work Equipment |
| Adjustment Procedure for Each Part | - | Toe-in Adjustment, Fuel Oil System Diagram, Power Transmission System Diagram, Periodic Replacement Of Vital Aging Parts |
| Reference | - | Assembly Procedure Of Collet Joint, Disassembly/Assembly Of Front Open Type Cab |
Quick Reference Specifications
| Specification | Value | Page |
|---|---|---|
| Cylinder head main bolt tightening torque | 750~850 Kg-cm (74~83 N-m) | p. 16 |
| OK monitor buzzer behavior for multiple abnormal sensors | When several sensors become abnormal simultaneously, the buzzer sounds intermittently for 10 seconds from the time when the first sensor become abnormal. | p. 22 |
| Hydraulic oil intake filter type | Wire mesh type SFB-16 | p. 10 |
| Hydraulic hose for steering replacement period | Every 2 years | p. 54 |
| Steering cylinder packing, dust seal, O-ring replacement period | Every 2 years | p. 54 |
| Permissible clearance between pin and bushing | 1.0 mm | p. 48 |
| Fan belt tension | 10 ~ 15 kg | p. 14 |
| Engine Plunger Diameter | 8.0 mm | p. 5 |
| Battery Voltage-Capacity | 12V 80AH | p. 6 |
| Overall Length (transporting posture) | 5,430 mm | p. 7 |
| Maximum Digging Depth | 3,230 mm | p. 7 |
Yanmar YB401W Common Problems This Manual Covers
Hydraulic power fades once warm
Weak or slow boom and bucket movement that gets worse as the oil heats up often traces to internal leakage past worn valve spools. The Control Valve procedure in this supplement lets you open, inspect, and reassemble the valve instead of guessing at the leak path.
Manual Section: Control ValveEngine stalls soon after starting
On a machine of this age, stalling shortly after startup usually points to fuel delivery restriction or air in the fuel lines. The Engine maintenance procedures, together with the Fuel Oil System Diagram, let you trace the circuit from tank to injection pump.
Manual Section: EngineWarning buzzer and sensor faults
Aging senders and wiring set off the OK monitor and leave you wondering which alarm is real. The Electrical Components section documents monitor behavior, including how the buzzer sounds intermittently for 10 seconds when several sensors go abnormal at once, so you can read the warning correctly.
Manual Section: Electrical ComponentsSteering wanders or feels loose
Loose, wandering steering on the YB401W is often a mix of worn geometry and aging hydraulics. The Steering System section covers the maintenance procedure, toe-in and steering angle adjustments have their own procedures, and the replacement schedule calls for the steering hydraulic hose and cylinder seal set every 2 years.
Manual Section: Steering SystemFront end rocks while digging
The suspension lock should hold the front axle rigid when you dig; if it feels spongy, air in the lock cylinder is a common cause. This supplement covers the shut off valve itself and includes an air bleeding method for the suspension lock cylinder.
Manual Section: Shut Off Valve (Suspension Lock Valve)Harsh or slipping travel engagement
Jerky takeup when shuttling between digging and travel points at the clutch valve. The Clutch Valve maintenance procedure covers the valve, and the Power Transmission System Diagram shows where it sits in the driveline.
Manual Section: Clutch ValveSlop in work equipment pins
Long days and thin grease wear the boom and bucket pivots until the bucket edge chatters. The manual sets the permissible clearance between pin and bushing at 1.0 mm, so you replace on measurement instead of eyeballing it.
Manual Section: Work EquipmentFrequently Asked Questions
Which machines and engines does this manual cover?
It covers the Yanmar YB401W wheel backhoe, serial number 50001 and after, fitted with the 4TNA78TL-DBW or 4TNA78TL-RBW engine. It is a service manual supplement for machines from that serial break.
Does it include torque specifications?
Yes. The Technical Data section includes Tightening Torque Of Main Parts. The cylinder head main bolts, for example, are listed at 750~850 Kg-cm (74~83 N-m). p. 16
Does it cover steering repairs and service intervals?
Yes. The Steering System section covers maintenance, with separate toe-in and steering angle adjustment procedures. The periodic replacement table calls for the steering hydraulic hose every 2 years, and the steering cylinder packing, dust seal, and O-ring every 2 years, replaced as a seal set. p. 54
Will it help me troubleshoot electrical and warning problems?
The Electrical Components section covers the machine's electrical system, including OK monitor behavior. For instance, when several sensors become abnormal at the same time, the buzzer sounds intermittently for 10 seconds from the first abnormal sensor, which tells you how to interpret the alarm. p. 22
How will I receive this Service Manual Supplement?
This is a 64-page searchable PDF ready for immediate download. Works on any device, so pull it up on your phone while you're under the hood. No shipping, no waiting.
Can I print specific sections of this manual?
Yes. The PDF has no DRM restrictions, so print any page or section you need for your shop. Works with any standard printer.
Does this manual have electrical diagrams?
Yes. This manual includes wiring diagrams for the electrical system.
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