Overrunning Clutch for PTO Shaft
The Overrunning Clutch (also called a freewheel clutch or one-way clutch) is a uni-directional torque transmission device for PTO shaft systems. It allows the implement to continue spinning freely after the tractor PTO is disengaged, preventing dangerous kickback forces from travelling back up the driveline. This protects both the operator and the PTO shaft components from shock loads caused by implement inertia. With a maximum torque capacity of 2400 Nm (RA1 series) to 3500 Nm (RA2 series) and standard 1 3/8″ Z6 spline, the overrunning clutch is essential for high-inertia implements such as flail mowers, cutter bars and rotary harrows. GBC supplies both housing-with-yoke (RA) and housing-with-splined-shaft (RAS) configurations for full compatibility.
PTO Overrunning Clutch – Freewheel Protection Against Implement Kickback
An overrunning clutch (freewheel clutch, one-way bearing clutch, or anti-kickback coupling) is a critical safety component mounted on the PTO driveline. It transmits torque in one direction only – from the tractor to the implement – while allowing the implement to freewheel when it spins faster than the input or when the PTO is disengaged. This prevents the stored rotational energy (inertia) of heavy implements from back-driving the PTO shaft, which can cause severe driveline damage or dangerous whipping. GBC provides overrunning clutches in the RA1 series (2400 Nm) and RA2 series (3500 Nm).
Technical Specifications
| Series | Max Torque (Nm) | Spline | A (mm) | B (mm) |
|---|---|---|---|---|
| 1RA1–8RA1 | 2400 | 1 3/8"Z6 | 138–171 | 21 |
| RAS1 | 2400 | 1 3/8"Z6 (F+M) | 142 | 21 |
| 5RA2–8RA2 | 3500 | 1 3/8"Z6 | 172–189 | 21 |
| RAS2 | 3500 | 1 3/8"Z6 (F+M) | 161 | 21 |
Key Features
Prevents implement inertia from back-driving the PTO shaft, eliminating dangerous whipping and driveline shock.
Transmits power from tractor to implement only. The implement freewheels when it spins faster than the PTO.
Precision-ground prongs engage positively with the hub for reliable directional locking under full load.
Up to 3500 Nm in the RA2 series handles the heaviest PTO-driven implements.
No adjustment needed. Simply grease periodically and the mechanism self-maintains.
RA (housing with yoke) for universal joint connection; RAS (housing with splined shaft) for direct spline-to-spline coupling.
How an Overrunning Clutch Works
Inside the housing, a set of spring-loaded prongs or rollers engage with ramps machined into the hub. When the tractor PTO drives the input side, the prongs lock against the ramps and transmit full torque to the implement. When the operator disengages the PTO or the implement outpaces the input (e.g. on a downhill slope), the prongs disengage from the ramps and the implement freewheels without transmitting energy back through the shaft. This prevents the hazardous scenario where a heavy, spinning implement tries to drive the PTO shaft backward.
Where Overrunning Clutches Are Essential
Heavy flail drums store enormous rotational energy. The overrunning clutch prevents this energy from feeding back when the PTO is switched off.
Multiple tine rotors carry significant inertia. Freewheeling prevents damaging torque reversals in the driveline during PTO shutdown.
Fast-spinning cutting discs require safe deceleration. The clutch isolates the PTO shaft from the implement coast-down.
Chopper drums with heavy flywheels pose serious kickback risk. The overrunning clutch is mandatory safety equipment.
Installation & Care
- Disengage PTO and switch off the tractor.
- Mount the overrunning clutch on the implement input shaft (1 3/8" Z6 spline).
- For RA series: attach the yoke to the PTO shaft universal joint. For RAS series: slide the splined shaft into the mating profile.
- Secure with the push pin kit and circlip.
- Grease via the grease nipple. Check rotation direction – the arrow on the housing must point in the tractor-to-implement direction.
⚠ Critical: Verify the rotation direction before first use. An incorrectly installed overrunning clutch will freewheel under drive and lock under coast-down – the opposite of safe operation.
Quality & Warranty
ISO 9001:2015 certified, CE marked. 12-month warranty. Australia-wide shipping. Contact sales@australia-drive.com.
FAQ
Do I need an overrunning clutch if my implement has low inertia?
For light implements the kickback risk is lower, but an overrunning clutch is still recommended as best practice for operator safety.
What is the difference between RA and RAS?
RA models have a housing with yoke for connection to a universal joint. RAS models have a housing with a splined shaft for direct spline coupling to the implement.
How often should I grease the overrunning clutch?
Grease every 50 operating hours or at the start of each season, whichever comes first.
Customer Reviews
“Essential safety item for our flail mower. Smooth engagement, solid build quality. Would not run without one.”
“Fitted the RA2 to our heavy mulcher. Complete peace of mind when disengaging the PTO – no more kickback.”
“Good product, arrived quickly. Only four stars because the installation direction arrow was a bit hard to see.”
“Running a 7RA1 on our rotary harrow for two seasons. Zero issues. Great value for the protection it provides.”
“Excellent freewheel clutch. GBC team advised us on the correct size over the phone. Highly recommend.”
Related Products
Browse GBC’s complete PTO driveline catalogue at australia-drive.com – PTO shafts, yokes, shields, adapters, torque limiters and universal joints.
Keep Your Driveline Safe from Kickback
Order your overrunning clutch from GBC today. Expert advice and fast shipping Australia-wide.
Email: sales@australia-drive.com
The Overrunning Clutch (also called a freewheel clutch or one-way clutch) is a uni-directional torque transmission device for PTO shaft systems. It allows the implement to continue spinning freely after the tractor PTO is disengaged, preventing dangerous kickback forces from travelling back up the driveline. This protects both the operator and the PTO shaft components from shock loads caused by implement inertia. With a maximum torque capacity of 2400 Nm (RA1 series) to 3500 Nm (RA2 series) and standard 1 3/8″ Z6 spline, the overrunning clutch is essential for high-inertia implements such as flail mowers, cutter bars and rotary harrows. GBC supplies both housing-with-yoke (RA) and housing-with-splined-shaft (RAS) configurations for full compatibility.
