Part of the Yanmar Parts Manuals.
A split fuel hose on a 1986 Yanmar crawler backhoe is a ten-minute swap, once you know which part number to order. This parts catalog for the YB121U and YB151U, including the -2, R, canopy, and cabin versions, walks the machine end to end: fuel tank and lines, battery and electrics, hydraulic piping, pump and cylinders, travel motor, track rollers and crawler, turning frame, and the operator station.
Guessing at parts is how a small backhoe ends up parked for a week waiting on the wrong seal kit. Here every assembly is broken out with Yanmar part numbers, so you can match what is on your machine (serial numbers 10501 onward and 20501 onward, 3TNA72L-UBVM diesel) before you spend anything.
The PDF runs 178 pages with 77 bookmarks, so jumping from the wiring diagram to the bucket cylinder takes seconds. Buy it once, download it, and it stays on your drive for as long as you own the machine.
What's Inside This Yanmar YB121U / YB151U Series Parts Manual
| System | Pages | Key Topics |
|---|---|---|
| Electrical System | Wiring Diagram, Battery, Electric Part | |
| Undercarriage & Travel | Travel Motor | |
| Rear Axle, Differential & Brakes | Brake Valve | |
| Hydraulics & 3-Point Hitch | Hyd. Oil Piping, Hyd. Oil Tank, Control Valve, Bucket Cylinder, Turning Motor, 3rd Valve Piping | |
| Loader, Backhoe & Attachments | Boom & Bucket, Bucket 250, Bucket 300, Bucket 350, Bucket 450, Bucket 250W, Bucket 300W, Bucket 350W, Bucket 450W | |
| Body & Operator Station | Turning Frame, Bonnet, Seat & Step, Canopy, Cabin, Heater & Defroster, Wind Washer | |
| Decals & Accessories | Tool | |
| Other Components | Specifications, Inlet House & Exhaust Pipe, Control Equipment |
Quick Reference Specifications
| Specification | Value | Page |
|---|---|---|
| FUSE | 5A | p. 28 |
Yanmar YB121U / YB151U Series Common Problems This Manual Covers
Engine stalls when digging gets hard
Power fades under load and the engine dies, usually a starved fuel supply from a clogged filter or debris in a forty-year-old tank. The Fuel Line section identifies every filter, hose, and fitting in the supply run so you can renew the lot in one order.
Manual Section: Fuel Line p. 9Intermittent no-start and electrical gremlins
A 1986 machine that starts one day and not the next usually has corroded battery terminals, chafed wiring, or a blown fuse. The Electric Part listings let you order switches, cables, and the correct 5A, 10A, and 15A fuses by part number.
Manual Section: Electric Part p. 12Weak or leaking hydraulics
Hoses harden and joints seep, and digging power drops as oil escapes or picks up contamination. The Hyd. Oil Piping breakdown names each hose, joint, and seal so you replace the exact line that is weeping instead of guessing.
Manual Section: Hyd. Oil Piping p. 34Bucket cylinder drift and leaking seals
A bucket that will not hold its curl, or a rod wearing a film of oil, means the cylinder needs seals, and pins and bushings usually wear at the same rate. The Bucket Cylinder section lists the components you need to rebuild it.
Manual Section: Bucket Cylinder p. 54Worn track rollers and loose tracks
Bad track tension and packed mud chew through rollers and idlers faster than anything else on a crawler machine. The Track Roller pages, alongside the track frame and crawler listings, identify each undercarriage wear part for both models.
Manual Section: Track Roller p. 15Noisy or weak travel motor
Growling, vibration, or one track pulling slower than the other points to trouble in the travel drive. The Travel Motor section breaks the assembly into orderable parts so you are not stuck sourcing a complete used unit.
Manual Section: Travel Motor p. 60Overheating under sustained load
A clogged radiator or perished engine mounts show up as creeping temperature and falling power on long digs. The Engine Mount & Radiator section covers the cooling hardware and mountings so you can replace them before the engine pays the price.
Manual Section: Engine Mount & Radiator p. 7Frequently Asked Questions
Which machines does this parts catalog cover?
It covers the Yanmar YB121U and YB151U crawler backhoes, including the -2 and R variants in canopy and cabin form, from serial numbers 10501 onward and 20501 onward, along with the 3TNA72L-UBVM diesel engine fitted to them. It is Yanmar publication 000Y00K2103.
Does it include machine specifications?
Yes, the Specifications section on page 3 covers the YB121U and YB151U range, and the catalog identifies the engine as the Yanmar 3TNA72L-UBVM diesel. p. 3
Are the different bucket sizes listed?
Yes. The Boom & Bucket section starting on page 42 covers the boom and bucket assemblies, with listings for the 250, 300, 350, and 450 buckets and their W versions, and separate sections follow for the blade and each cylinder. p. 42
Is there a wiring diagram?
Yes, a dedicated Wiring Diagram section starts on page 5, and the Electric Part listings cover the battery, switches, and the 5A, 10A, and 15A fuses used on both models. p. 5
Is this Yanmar YB121U manual a download or a disc?
This is a 178-page scanned PDF (4 MB) 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 this Yanmar YB121U manual?
Absolutely. No DRM or copy protection. Print the whole manual or just the pages you need. Any home or office printer works.
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