Descripción
PTO Shaft Overrunning Clutch – RA2 Series (with Yoke)
The PTO Shaft Overrunning Clutch – RA2 Series (with Yoke) is a premium-quality overrunning clutch specifically engineered for PTO (Power Take-Off) drive shaft systems used across agricultural, industrial, and forestry machinery. Also known as a PTO slip clutch, PTO safety clutch, or tractor PTO overload protector, this device safeguards your expensive equipment from damage caused by sudden torque overloads, obstructions, and operational jamming.
Available Models: 5RA2, 6RA2, 7NRA2, 6RA2, 8RA2
Torque Range: Torque: 3500 Nm (max)
Spline Options: 1 3/8″ Z6
Key Components: Circlip, Retaining washer, Push pin kit, Hub, Prong kit (Qty.=3), Housing with yoke, Grease nipple
Technical Specifications & Dimensions
| Series | Max Torque (Nm) | Spline | A (mm) | B (mm) |
|---|---|---|---|---|
| 5RA2 | 3500 | 1 3/8″Z6 | 172 | 21 |
| 6RA2 | 3500 | 1 3/8″Z6 | 178 | 21 |
| 7NRA2 | 3500 | 1 3/8″Z6 | 175 | 21 |
| 6RA2 | 3500 | 1 3/8″Z6 | 178 | 21 |
| 8RA2 | 3500 | 1 3/8″Z6 | 189 | 21 |
* All dimensions in millimeters. Torque values in Newton-meters (Nm). Spline specifications follow ISO/ASAE standards. Contact us for custom configurations.
Key Features & Advantages
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Multiple Output Configurations
Available in yoke, splined shaft, and flanged output variants to suit any installation requirement.
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Precision Overload Protection
Calibrated to disconnect at exact torque thresholds, preventing costly damage to gearboxes, bearings, and implement mechanisms.
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Rapid Response Time
Triggers within milliseconds of overload onset, minimizing the duration of damaging torque transfer to connected equipment.
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Easy Maintenance & Service
Simple modular design allows fast field service with standard tools. Replacement parts are readily available and affordable.
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Industrial-Grade Materials
Precision-machined from hardened alloy steel with heat-treated critical surfaces for maximum durability and service life.
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Universal PTO Compatibility
Standard 1 3/8″ Z6 spline interface fits all major tractor and implement PTO shafts without adapters or modification.
How It Works — Operating Principle
The overrunning clutch (also known as a freewheel clutch) allows the output shaft to rotate freely in one direction while transmitting full torque in the other. Inside the housing, spring-loaded prongs engage with a ratchet surface on the hub. When the input shaft drives the output shaft in the intended direction, the prongs lock into the ratchet teeth and transmit power. When the output shaft attempts to overdrive the input (such as when a tractor PTO is disengaged while a heavy flywheel implement is still spinning), the prongs disengage and the output freewheels. This prevents dangerous back-drive forces from traveling through the PTO shaft to the tractor transmission, protecting both equipment and the operator.
Reset Method: Automatic — continuous engagement/disengagement
Best Suited For: Implements with high rotational inertia (mowers, balers, flail choppers) requiring back-drive protection
Typical Agricultural Application Scenarios
Post Hole Diggers
Absorbs extreme torque shock when the auger bit strikes rock, buried concrete, or dense root masses, protecting both the auger drive and tractor PTO.
Snow Blowers & Snow Throwers
Guards against damage from ice chunks, frozen debris, and compacted snow banks that generate sudden, extreme torque loads on the impeller shaft.
Rotary Mowers & Flail Mowers
Protects the mower gearbox from damage when blades strike hidden rocks, stumps, or metal debris. The torque limiter absorbs the shock load and prevents it from reaching the tractor PTO.
Hay Balers & Round Balers
Prevents baler mechanism damage during slug feeding, twine wrapping failures, or foreign object ingestion by disconnecting the driveline before damaging torque levels are reached.
Rotary Tillers & Cultivators
Guards the tiller gearbox and tractor PTO when tines encounter buried rocks, roots, or compacted soil layers that can generate extreme torque spikes.
Torque Limiter Type Comparison
| Feature | Ball Detent | Friction Disc | Shear Pin/Bolt | Ratchet (Pawl) | Automatic (Cam) |
|---|---|---|---|---|---|
| Torque Range | Low–Medium | Medium–High | Low–Very High | Low–High | Medium–High |
| Speed Range | 540–1000 RPM | 540–1000 RPM | 540–1000 RPM | 540–1000 RPM | 540–1000 RPM |
| Reset Method | Automatic | Automatic (slip) | Manual (replace bolt) | Automatic (ratchet) | Automatic (cam) |
| Best Application | Light implements | Frequent moderate overloads | Infrequent severe overloads | Frequent transient overloads | High-utilization, no consumables |
| Consumable Parts | None | Friction linings (long life) | Shear bolts | None | None |
| Torque Precision | Moderate | Good (adjustable) | Excellent (bolt-grade calibrated) | Good | Very Good (adjustable) |
Installation & Usage Guide
Installation Steps
Step 1: Verify that the PTO shaft spline size matches the torque limiter spline specification (1 3/8″ Z6). Clean all spline surfaces thoroughly.
Step 2: Slide the torque limiter onto the PTO shaft spline, ensuring full engagement. Secure with the provided push pin kit or retaining hardware.
Step 3: Connect the output side (yoke or splined shaft) to the implement input shaft or gearbox. Ensure proper alignment and secure all fasteners to the recommended torque.
Step 4: Apply grease through the grease nipple to lubricate the spline interface and internal components. Use lithium-based EP grease (NLGI #2).
Step 5: Perform a low-speed test run to verify correct engagement and smooth operation before full-power operation.
Safety & Maintenance Tips
⚠ Always disengage the tractor PTO before inspecting or servicing the torque limiter.
⚠ Use only genuine replacement parts specified for your series to maintain the correct torque rating.
⚠ Re-grease spline connections every 8 operating hours or as specified in your equipment manual.
⚠ Inspect for wear, cracks, or damage before each season. Replace worn components immediately.
⚠ Never operate with damaged or missing PTO shaft safety shields.
Selection Guide — Choosing the Right Model
Selecting the correct torque limiter requires confirming the following parameters:
✓ Required Torque Rating (Nm): Match the implement’s maximum operating torque plus a 20–30% safety margin.
✓ PTO Shaft Spline Size: Commonly 1 3/8″ Z6 (6-spline) or 1 3/4″ Z6/Z20. Verify both input and output spline requirements.
✓ PTO Speed: Standard 540 RPM or economy 1000 RPM — confirm your implement’s requirement.
✓ Connection Type: Yoke output for standard shaft tubes, splined shaft for inline assemblies, or flanged output for direct gearbox mounting.
✓ Overload Frequency: Frequent overloads favor auto-reset types (ratchet, friction, automatic). Infrequent but severe overloads suit shear bolt types.
✓ Environmental Conditions: Consider dust, moisture, temperature extremes. Sealed automatic and friction types offer superior protection in harsh environments.
Need help choosing? Contact our engineering team for personalized selection assistance.
Quality Certification & Service Commitment
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ISO 9001:2015
Certified quality management system ensuring consistent product excellence
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CE Marked
Compliant with European safety, health, and environmental protection standards
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12-Month Warranty
Full warranty against manufacturing defects under normal operating conditions
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Global Shipping
Fast worldwide delivery with professional export packaging and documentation
Frequently Asked Questions (FAQ)
What Our Customers Say
🇦🇷 Miguel R. — Ranch manager, Buenos Aires Province, Argentina
“Outstanding durability in our dusty Pampas conditions. We’ve been using these for two years on grain augers and feed mixers with zero failures. The sealed design keeps the dust out.”
★★★★★
🇺🇸 David H. — Equipment dealer, Iowa, United States
“Our customers keep coming back for these. The quality matches or exceeds European OEM brands at a fraction of the cost. We stock the full range for combine, baler, and mower applications.”
★★★★★
🇳🇿 Craig W. — Dairy farmer, Waikato, New Zealand
“Using these on our pasture toppers and feed wagons. They’ve saved our PTO shafts from damage multiple times when hitting hidden stumps. Brilliant design — the auto-reset means we don’t lose any milking time.”
★★★★★
🇬🇧 William D. — Arable contractor, Yorkshire, United Kingdom
“Top-notch manufacturing quality. These drop straight onto standard UK PTO shafts and the torque ratings are spot-on. I’ve fitted them on cultivators, grain drills, and mowers — all performing perfectly.”
★★★★★
🇦🇺 James M. — Grain farmer, NSW, Australia
“We fitted these torque limiters on all our header drives after losing a gearbox last harvest. They’ve triggered twice on hidden rocks and saved us thousands in repairs each time. Absolutely essential equipment for Australian broadacre farming.”
★★★★★
Related PTO Shaft Products & Accessories
PTO Shaft Components
Complete range of PTO shaft yokes, cross bearings, tubes, shields, and adapters for all standard sizes.
Agricultural Gearboxes
Matched gearboxes designed to work seamlessly with our PTO shafts and torque limiters.
Available PTO Accessories:
• PTO shaft yokes (plain bore, splined, quick-release)
• Safety shields and guard tubes (EN 12965 compliant)
• Spline adapters (1 3/8″ to 1 3/4″ conversion)
• Cross bearing kits and U-joint repair kits
• Telescoping PTO shaft tubes (triangular and lemon profile)
• Push pin kits and retaining hardware
Ready to Protect Your Equipment?
Whether you need a single replacement unit or bulk OEM supply, our team is ready to help you select the perfect torque limiter for your application. We offer competitive B2B pricing, technical consultation, and fast global delivery.
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