Caterpillar SR121
Maintenance schedule, common problems & OEM parts breakdown
The Cat SR121 is a two-stage hydraulic snow blower attachment, not a self-propelled machine. It has no onboard engine, ECM, or transmission - the auger and impeller run entirely off the carrier's auxiliary hydraulic circuit, with optimal flow around 80 L/min (21.1 gpm) at roughly 230 bar (3336 psi). It mounts through a universal quick-attach coupler to compact wheel loaders, skid steer loaders, and compact track loaders in the 226D3 through 299D3 range and the 906-908 series. Operating weight is 501 kg (974.4 lb), with an intake width of 1942 mm (76.5 in), cutting height of 867 mm (34.1 in), and a 457 mm (18 in) auger feeding a 635 mm (25 in) impeller. Maximum throw is 12.2 m (40 ft) with 270 degrees of hydraulic chute rotation. Overload protection comes from a reversible auger and impeller drive rather than mechanical shear pins.
The SR121 sits at the top of the compact single-auger SR-family, above the smaller SR115 and mid-size SR118 and sharing its platform and SNB serial prefix with siblings SR115, SR117, SR118, SR318, and SR321. Larger-volume clearing moves up to the high-flow SR318/SR321 line rather than a distinct successor to the SR121 itself; no separate generational split is documented for this model, and Cat has kept it as a single continuous configuration across its production run. In the used and parts market, value comes down to attachment condition rather than model year: gearbox oil condition and shaft play, auger and impeller wear, coupler wedge and pin wear, and hydraulic hose integrity all matter more than cosmetic wear. Demand is seasonal and spikes ahead of winter, so buyers checking carrier fit, coupler lock-up, and chute rotation before the season starts get the most reliable use out of a used unit.
Below: full specifications, fluids & capacities, the factory service schedule, common service parts, verified fault codes, what owners discuss, attachment guidance, the complete assembly directory, and a serial-number reference. Complete parts lists with full OEM part numbers, exploded diagrams, quantities, and fitment data are available free in Heavy Parts AI.
Caterpillar SR121 specifications
Engine
| Power source | No onboard engine. The SR121 is a passive hydraulically driven attachment powered off the carrier machine's auxiliary hydraulic circuit. |
| Carrier compatibility | Fits Cat compact wheel loaders (906/906K/906M, 907/907K/907M, 908/908K/908M) and compatible skid steer / multi terrain loader carriers rated for the required hydraulic flow class; shares a compatibility chart with siblings SR115 and SR118. |
| Emissions tier | Not applicable — no engine on the attachment itself. |
Weights
| Operating weight | 974.4 lb (501 kg) |
| Shipping weight | Not separately published — matches operating weight for this attachment class |
| Ground pressure | Not published — not applicable to a mounted attachment |
Dimensions
| Overall length | 37.4 in (951 mm) |
| Overall width | 85.9 in (2181 mm) |
| Overall height | 72.6 in (1843 mm) |
| Intake width | 76.5 in (1942 mm) |
| Cutting height | 34.1 in (867 mm) |
| Auger diameter | 18 in (457 mm) |
| Impeller fan diameter | 25 in (635 mm) |
| Impeller fan width | 8.7 in (222 mm) |
Performance
| Maximum throw distance | 40 ft (12.2 m) |
| Chute rotation | 270 degrees, allowing discharge to front or either side |
| Required hydraulic flow class | Standard flow |
| Optimal hydraulic flow | 80 L/min (21.1 gpm) |
| Optimal hydraulic pressure | 230 bar (3336 psi) |
| Travel speed / gradeability | Not applicable — attachment has no self-propulsion; performance depends entirely on carrier machine |
Service capacities (summary)
| Fuel tank | Not applicable — no onboard engine or fuel system |
| Hydraulic system | No dedicated onboard reservoir; draws hydraulic oil from the carrier machine's auxiliary circuit |
| Engine oil | Not applicable — no onboard engine |
| Cooling system | Not applicable — no onboard engine |
Values vary by configuration, region, and serial range — confirm against your machine before planning transport or lifts.
SR121 fluids & capacities
| System | Capacity | Recommended fluid |
|---|---|---|
| Engine crankcase (with filter) | Not applicable | SR121 has no onboard engine. It is a passive two-stage snow blower work tool driven entirely by the host carrier's hydraulic system, so there is no engine oil or filter to service on the attachment itself. |
| Cooling system | Not applicable | No engine, radiator, or coolant circuit on this attachment. Cooling of the drive circuit is handled by the host machine's hydraulic oil cooler. |
| Fuel tank | Not applicable | No onboard fuel system. The attachment carries no fuel tank of its own. |
| Transmission / powertrain compartment | Not applicable | No powershift transmission, torque converter, or final drive housings onboard. Auger and impeller are turned directly off hydraulic motors, not through an onboard vehicle transmission. |
| Auger/impeller drive gear case | Not documented for this model in available sourcing | Cat literature confirms a gear-driven auger/impeller train inside the housing, but the OMM fill quantity and gear-oil grade for that internal gear case could not be confirmed from available sourcing for the SR121 specifically. Verify with your dealer or the machine's data plate before servicing. |
| Final drives (each) | Not applicable | SR121 is a mounted work tool, not a self-propelled unit — it has no final drive housings of its own. |
| Hydraulic system (host-supplied) and tank | No separate onboard hydraulic tank; draws from the host carrier's hydraulic system. Operating flow 76-87 L/min (20-23 US gpm); operating pressure 200-230 bar (2,900-3,300 psi) | Uses whatever hydraulic oil the host carrier's OMM specifies for its own hydraulic system (typically Cat HYDO Advanced or equivalent multigrade hydraulic oil, viscosity selected per the carrier's ambient-temperature chart). The attachment itself carries no separate hydraulic reservoir or fluid spec. |
| Axles / differentials | Not applicable | Not a wheeled or tracked unit; no axle or differential compartments exist on this attachment. |
| Grease (chute rotation, auger/impeller pivots and bearings) | Spec only — grease points per zerk fitting, no bulk fill quantity applies | General Cat attachment practice calls for a lithium-complex, multipurpose chassis grease (Cat Multipurpose Grease or equivalent NLGI grade 2, cold-weather rated) at chute-rotation and pivot zerks. The exact grade called out in the SR121 OMM could not be confirmed from available sourcing — confirm the specific grease and interval against the machine's own maintenance chart before servicing. |
Capacities are refill values from factory literature — always fill to the dipstick/sight gauge, not the number.
Caterpillar SR121 maintenance schedule
| Service interval | Tasks |
|---|---|
| Every 10 h |
|
| Every 250 h |
|
| Every 500 h |
|
| Every 1,000 h |
|
| Every 2,000 h |
|
| Every 4,000 h |
|
Servicing the SR121 beyond the schedule
Predictive Maintenance & Fluid Analysis
The SR121 has no engine oil or coolant to sample - the fluids that matter are the host carrier's hydraulic oil and the attachment's own gearbox lube. Pull periodic hydraulic oil samples from the carrier circuit driving the attachment to catch contamination or wear metal before it damages the drive motor. Check gearbox oil condition at each interval for metal fines or discoloration. Keep chute rotation bearings and pivot pins on a strict grease schedule since they see the most motion and show play first.
Corrective & Common Repairs
Common SR121 repairs center on the drivetrain and coupler, not an engine. Chewed or cracked auger flighting and impeller blades from ice and debris are the most frequent fix. Gearbox oil leaks or gear noise usually trace to worn shaft seals or bearings. Chute rotation lag or binding points to a sticking hydraulic control valve or worn rotation drive. Loose, rattling attachment fit on the carrier almost always comes down to worn coupler wedge pins or bushings rather than the coupler frame itself.
Overhaul & Rebuild Points
A full SR121 overhaul centers on three assemblies: the gearbox, the auger/impeller shafts, and the hydraulic drive motor. Gearbox rebuilds replace the gear set, bearings, and seals once internal play or metal contamination shows up in oil checks. Auger and impeller shafts wear at their bearing and seal locations from constant torque reversal during overload protection cycling. The hydraulic motor is a rebuild-or-replace decision once flow output or torque drops below spec. Coupler wedge and pin wear also gets addressed at major overhaul rather than left for field replacement.
Seasonal & Environment Servicing
Cold-weather performance depends on the host carrier's hydraulic fluid viscosity grade matching ambient temperature, since the SR121 has no fluid system of its own to condition. Before storage, clear all packed snow and moisture from the auger housing and chute to prevent freeze-lock and corrosion over the off-season. Grease every pivot and rotation point heavily before storing to displace moisture from the joints. Touch up paint and coatings on the auger, impeller, and chute at the start of each season to slow rust from salt and road grit exposure.
SR121 attachments & work tools
Two-stage snow blower work tool (SR115/SR118/SR121 size class)
SR121 is a two-stage auger-impeller snow blower work tool, not a host machine that takes attachments. It sits at the top of the compact SR115/SR118/SR121 sub-family sized for skid steer loaders, compact track loaders, and compact wheel loaders; a separate, larger SR3xx/SR4xx snow blower line exists for bigger wheel loaders and is not interchangeable with this class.
Sizing / capacity for this class
Intake width is about 1942 mm (76.5 in), overall width about 2181 mm (85.9 in), auger diameter 457 mm (18 in), impeller diameter 635 mm (25 in), and maximum throw distance up to 12.2 m (40 ft). Operating weight is roughly 500 kg (974 lb), making the SR121 the largest and heaviest of the SR115/SR118/SR121 trio.
Coupler / mounting system
Mounts to the carrier's universal skid steer-style hydraulic quick-attach coupler, shared across compatible skid steer loaders, compact track loaders, and compact wheel loaders. Hydraulic and joystick-control connections are plug-n-play at hookup, with no extra wiring needed.
Hydraulic kit / flow requirements
Runs off the carrier's auxiliary hydraulic circuit; optimal flow and pressure for the SR121 is about 80 L/min (21 gpm) at roughly 230 bar (3336 psi). The carrier needs a compatible auxiliary hydraulic kit sized for this flow, and actual delivered flow/pressure varies by host machine and hydraulic configuration.
Obstruction protection / drivetrain guarding
Auger and impeller are hydraulically reversible to clear packed snow or expel obstructions, eliminating the mechanical shear pins used on older-style blowers. A bolt-on, reversible cutting edge extends wear life and simplifies field replacement.
Chute and deflector control
Chute rotates up to 270 degrees to direct discharge to the front or either side, keeping snow off the operator. A hydraulically actuated deflector, controlled from the cab joystick, sets throw distance and trajectory.
Cutting-height adjustment / skid shoes
Adjustable skid shoes set auger cutting height above the surface, letting the operator tune ground clearance for pavement versus gravel or uneven surfaces.
Drift cutters (standard)
Side-mounted drift cutters are fitted ahead of the intake to help the blower cut into and push through high, dense snowbanks.
Operator access / safety guarding
Grated access steps with serrated, slip-resistant surfaces and chute-mounted grab handles are built in for safer mounting, dismounting, and service access around the unit.
Host machine compatibility class
Factory-listed for Cat skid steer loaders and compact track loaders in the mid-to-large frame range and Cat compact wheel loaders (900-series, including 906-908 and their M-series equivalents). Exact approved carrier list varies by region and dealer; confirm current fitment against a dealer compatibility chart before ordering.
All SR121 assemblies by section
Every catalogued assembly group for the Caterpillar SR121. Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.
Electrical System
281-3790 Wiring Gp-Work Tool
| 10***67 | Washer-Hard; (7.2x25x2-mm Thk) | 2 |
| 11***15 | Relay As; (12-Volt)(Junction Box) | 2 |
| 12***78 | Locknut; (M6x1-Thd) | 4 |
261-4419 Wiring Gp-Work Tool
| 10***67 | Washer-Hard; (7.2x25x2-mm Thk) | 2 |
| 10***02 | Kit-Receptacle; (2-Pin)(Engine Sensor Wiring Harness) | 3 |
| 11***15 | Relay As; (12-Volt)(Junction Box) | 2 |
Frame And Body
290-8925 Deflector Gp-Snowblower
| 03***55 | Locknut; (5/16-18-Thd)(Marked X) | 6 |
| 12***78 | Locknut; (M6x1-Thd) | 2 |
| 13***85 | Rivet-Pop | 7 |
290-8888 Deflector Gp-Snowblower
| 03***55 | Locknut; (5/16-18-Thd)(Marked X) | 6 |
| 12***78 | Locknut; (M6x1-Thd) | 2 |
| 13***85 | Rivet-Pop | 7 |
290-8915 Frame Gp-Snowblower
| 1K***72 | Locknut Horn To Guard | 8 |
| 21***22 | Support Group-Work Tool | 2 |
| 21***23 | Frame As | 1 |
290-8919 Frame Gp-Snowblower
| 1K***72 | Locknut Horn To Guard | 9 |
| 21***75 | Frame As | 1 |
| 21***80 | Impeller As | 1 |
290-8924 Frame Gp-Snowblower
| 1K***72 | Locknut Horn To Guard | 7 |
| 21***82 | Impeller As | 1 |
| 21***83 | Guard As | 1 |
213-7222 Support Gp-Work Tool
| 21***22 | Support Group-Work Tool | 1 |
| 28***93 | Tube As | 1 |
| 28***97 | Pad As; (Stabilizer) | 1 |
Hydraulic System
283-9595 Cylinder Gp-Hydraulic
| 28***95 | Cylinder Group-Hydraulic | 1 |
| 4K***77 | Nut-Self Locking | 1 |
| 7J***04 | Seal-O-Ring (Id=7.65mm) | 2 |
290-8926 Hydraulic Ar-Snowblower
| 28***95 | Cylinder Group-Hydraulic | 1 |
| 29***26 | Hydraulic Ar-Snowblower | 1 |
| 29***97 | Manifold Group-Control | 1 |
295-4866 Hydraulic Ar-Snowblower
| 28***95 | Cylinder Group-Hydraulic | 1 |
| 29***97 | Manifold Group-Control | 1 |
| 29***66 | Hydraulic Ar-Snowblower | 1 |
295-4867 Hydraulic Ar-Snowblower
| 28***95 | Cylinder Group-Hydraulic | 1 |
| 29***97 | Manifold Group-Control | 1 |
| 29***67 | Hydraulic Ar-Snowblower | 1 |
290-8916 Hydraulic Ar-Snowblower
| 28***95 | Cylinder Group-Hydraulic | 1 |
| 29***16 | Hydraulic Ar-Snowblower | 1 |
| 29***97 | Manifold Group-Control | 1 |
290-8920 Hydraulic Ar-Snowblower
| 28***95 | Cylinder Group-Hydraulic | 1 |
| 29***20 | Hydraulic Ar-Snowblower | 1 |
| 29***97 | Manifold Group-Control | 1 |
295-4870 Lines Gp-Connecting
| 10***03 | Plate-Cover | 1 |
| 14***15 | Connector As | 4 |
| 14***36 | Adapter; (Straight) (-6 Orb X -6 Orfs) | 2 |
295-4871 Lines Gp-Connecting
| 10***03 | Plate-Cover | 1 |
| 14***48 | Fitting As; (Quick Disconnect, Male) | 1 |
| 14***49 | Fitting As; (Quick Disconnect, Female) | 1 |
295-4869 Lines Gp-Connecting
| 10***03 | Plate-Cover | 1 |
| 14***15 | Connector As | 4 |
| 14***36 | Adapter; (Straight) (-6 Orb X -6 Orfs) | 2 |
295-4868 Lines Gp-Connecting
| 10***03 | Plate-Cover | 1 |
| 14***15 | Connector As | 4 |
| 14***36 | Adapter; (Straight) (-6 Orb X -6 Orfs) | 2 |
295-4872 Lines Gp-Connecting
| 10***03 | Plate-Cover | 1 |
| 14***48 | Fitting As; (Quick Disconnect, Male) | 1 |
| 14***49 | Fitting As; (Quick Disconnect, Female) | 1 |
295-2597 Manifold Gp-Control
| 10***08 | Kit-Seal; (Solenoid Valve, Quick Steer) | 1 |
| 19***27 | Kit-Seal; (Pressure Reducing Valve) | 1 |
| 19***95 | Valve Group-Solenoid; (Swing/Extension) | 2 |
212-4588 Motor Gp-Gerotor -Auger, 67-In
| 17***46 | Kit-Seal | 1 |
| 21***88 | Motor Group-Gerotor; -Auger, 67-In | 1 |
227-5496 Motor Gp-Gerotor
| 17***46 | Kit-Seal | 1 |
| 22***96 | Motor Group-Gerotor | 1 |
| 3J***54 | Packing,Preformed Part Of Kit P/N 5r***27 | 1 |
216-0795 Motor Gp-Gerotor
| 17***46 | Kit-Seal | 1 |
| 21***95 | Motor Group-Gerotor | 1 |
| 22***72 | Key | 1 |
227-5510 Motor Gp-Gerotor
| 17***46 | Kit-Seal | 1 |
| 22***10 | Motor Group-Gerotor | 1 |
213-7192 Motor Gp-Gerotor
| 17***46 | Kit-Seal | 1 |
| 21***92 | Motor Group-Gerotor | 1 |
| 22***72 | Key | 1 |
212-4589 Motor Gp-Gerotor
| 17***46 | Kit-Seal | 1 |
| 21***89 | Motor Group-Gerotor | 1 |
| 22***72 | Key | 1 |
212-4587 Motor Gp-Gerotor -Deflector
| 1B***14 | Key-Woodruff | 1 |
| 1G***32 | Kit-Seal | 1 |
| 21***87 | Motor Group-Gerotor; -Deflector | 1 |
179-9223 Valve Gp-Check
| 17***23 | Valve Group-Check; -Steering Pump | 1 |
| 3J***07 | Seal Valve Assembly To; Seal- Tube Assembly To Logic Valve | 1 |
| 4J***77 | Seal - O - Ring (11.23mm Od) | 1 |
Service Equipment And Supplies
261-4426 Plate & Film Gp
| 12***56 | Film; (Warning) (No Step) (On Top Of Hood Behind Cab On Each Side) (On Each Fender Flare) | 1 |
| 15***62 | Film-Information; (Tie-Down Location) | 2 |
| 22***45 | Film-Warning; (Crush Hazard, Stay Back) | 2 |
290-8927 Plate & Film Gp
| 12***56 | Film; (Warning) (No Step) (On Top Of Hood Behind Cab On Each Side) (On Each Fender Flare) | 1 |
| 15***62 | Film-Information; (Tie-Down Location) | 2 |
| 22***45 | Film-Warning; (Crush Hazard, Stay Back) | 2 |
290-8921 Plate & Film Gp
| 12***56 | Film; (Warning) (No Step) (On Top Of Hood Behind Cab On Each Side) (On Each Fender Flare) | 1 |
| 15***62 | Film-Information; (Tie-Down Location) | 2 |
| 22***45 | Film-Warning; (Crush Hazard, Stay Back) | 2 |
261-4423 Plate & Film Gp
| 12***56 | Film; (Warning) (No Step) (On Top Of Hood Behind Cab On Each Side) (On Each Fender Flare) | 1 |
| 15***62 | Film-Information; (Tie-Down Location) | 2 |
| 22***45 | Film-Warning; (Crush Hazard, Stay Back) | 2 |
290-8917 Plate & Film Gp
| 12***56 | Film; (Warning) (No Step) (On Top Of Hood Behind Cab On Each Side) (On Each Fender Flare) | 1 |
| 15***62 | Film-Information; (Tie-Down Location) | 2 |
| 22***45 | Film-Warning; (Crush Hazard, Stay Back) | 2 |
Work Tool Arrangement
286-0725 Snowblower Ar -73-In
| 28***90 | Bracket, Wiring Group-Work Tool | 1 |
| 28***25 | Snowblower Ar; -73-In | 1 |
| 29***14 | Drive Group-Snowblower | 1 |
286-0727 Snowblower Ar -73-In
| 26***19 | Wiring Group-Work Tool | 1 |
| 26***23 | Plate & Film Group | 1 |
| 28***27 | Snowblower Ar; -73-In | 1 |
286-0728 Snowblower Ar -85-In
| 26***19 | Wiring Group-Work Tool | 1 |
| 26***26 | Plate & Film Group | 1 |
| 28***28 | Snowblower Ar; -85-In | 1 |
286-0724 Snowblower Ar -67-In
| 28***90 | Bracket, Wiring Group-Work Tool | 1 |
| 28***24 | Snowblower Ar; -67-In | 1 |
| 29***23 | Drive Group-Snowblower | 1 |
286-0726 Snowblower Ar -85-In
| 28***90 | Bracket, Wiring Group-Work Tool | 1 |
| 28***26 | Snowblower Ar; -85-In | 1 |
| 29***18 | Drive Group-Snowblower | 1 |
Work Tools
290-8923 Drive Gp-Snowblower
| 01***41 | Setscrew-Socket | 2 |
| 02***87 | Fitting-Grease; (Universal Joint) | 2 |
| 21***44 | Sprocket Group; (16-Teeth, Impeller) | 1 |
290-8914 Drive Gp-Snowblower
| 01***41 | Setscrew-Socket | 2 |
| 02***87 | Fitting-Grease; (Universal Joint) | 2 |
| 21***44 | Sprocket Group; (16-Teeth, Impeller) | 1 |
294-7388 Drive Gp-Snowblower
| 01***41 | Setscrew-Socket | 2 |
| 02***87 | Fitting-Grease; (Universal Joint) | 2 |
| 21***44 | Sprocket Group; (16-Teeth, Impeller) | 1 |
290-8918 Drive Gp-Snowblower
| 01***41 | Setscrew-Socket | 2 |
| 02***87 | Fitting-Grease; (Universal Joint) | 2 |
| 21***44 | Sprocket Group; (16-Teeth, Impeller) | 1 |
SR121 serial number reference
The PIN plate is riveted to the SR121 mainframe near the mount plate/coupler end of the attachment, not on the auger housing. Read it as a 3-letter prefix (SNB for this platform) followed by a sequential unit number; the prefix identifies the snow blower product family and manual set, not a specific model within that family, so use the model nameplate together with the PIN to confirm SR121 versus a sibling.
| Prefix | Identifies | Notes |
|---|---|---|
| SNB | SR121 snow blower (shared platform prefix across SR117/SR118/SR121/SR318/SR321, later SR115/SR118/SR121/SR318/SR321) | SNB00001-UP covers the whole snow blower platform family under one electrical system manual and one parts manual set. An earlier document scope lists SR117, SR118, SR121, SR318 & SR321; a later parts manual edition drops SR117 and adds SR115 as its successor, keeping the same SNB range for the rest of the family including SR121. No SR121-specific split of the SNB range is documented. Passive hydraulic work tool, driven off the host carrier's auxiliary circuit; no onboard engine, ECM, or reservoir, so there is no separate engine-serial scheme to cross-check against. Confirm the exact cut-in number for a specific unit with your dealer. |
Frequently asked questions
What powers the Cat SR121 snow blower?
The SR121 has no onboard engine. It runs entirely off the host carrier's auxiliary hydraulic circuit, with an optimal flow around 80 L/min (21.1 gpm) at about 230 bar (3336 psi). It attaches to compact wheel loaders, skid steer loaders, and compact track loaders in the 226D3-299D3 and 906-908 ranges.
What is the operating weight of the SR121?
501 kg (974.4 lb). Listed weight can vary slightly by source depending on configuration, so treat this as the standard published figure.
What replaced the SR121, or how does it fit the lineup?
No dedicated successor is documented. The SR121 is the largest single-auger size in the compact SR115/SR118/SR121 tier and shares its platform and SNB serial prefix with siblings SR115, SR117, SR118, SR318, and SR321. Higher-volume clearing needs move up to the high-flow SR318/SR321 models rather than a direct replacement for the SR121.
What SR121 owners discuss
What hydraulic flow and pressure does the SR121 actually need from the carrier, and what happens if it's mismatched?
How does the SR121 protect its auger and impeller from ice chunks and buried debris since there's no shear pin?
Is the hydraulic chute rotation and deflector control reliable, and what commonly goes wrong with it?
What wears on the quick-attach coupler and mounting interface, and how do owners catch it early?
How should skid shoes be set, and does it matter for a hydraulic blower like the SR121?
What should I check when buying a used SR121, since there's no engine or ECM to worry about?
Does cold weather affect how the SR121 performs, given it runs entirely on the host machine's hydraulics?
Compiled from owner and technician discussions across the industry — experiences vary by serial range and machine history.
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