Automatic PTO Torque Limiter – Cam-Type Heavy-Duty Protection with Auto Re-Engagement
The automatic torque limiter (cam-type safety clutch, auto-resetting overload coupling) represents the pinnacle of PTO overload protection. It employs precision-machined cams held in engagement by a powerful spring pack. Under normal loads, the cams lock and transmit the full rated torque. During an overload event, the axial force on the cams overcomes the spring pre-load, the cams separate, and the drive disconnects cleanly. When torque drops back to normal, the springs push the cams back into engagement and full power transfer resumes – all without any operator action or consumable parts. GBC’s automatic torque limiter range spans 1600 Nm to 4500 Nm across the SC151, SC176 and SCF151/SCF176 series.
Technical Specifications
| Series | Torque (Nm) | Spline | A (mm) | B (mm) | C (mm) |
|---|---|---|---|---|---|
| 4SC151 / 4SC151.D | 1600 | 1 3/8″Z6 / Z21 | 207.5 | 28 | Φ152 |
| 6SC151 / .C / .D / .E | 2100–2600 | 1 3/8″Z6/Z21, 1 3/4″Z6/Z20 | 213 | ||
| 7NSC151 / .C / .D / .E | 2600–2800 | 1 3/8″Z6/Z21, 1 3/4″Z6/Z20 | 213 | ||
| 8SC151 / .C / .D / .E | 2600–2800 | 1 3/8″Z6/Z21, 1 3/4″Z6/Z20 | 220 | ||
| 8SC176 / .C / .D / .E | 3000–3500 | 1 3/8″Z6/Z21, 1 3/4″Z6/Z20 | 224 | 28 | Φ176 |
| 9SC176 / .C / .D / .E | 4000–4500 | 1 3/8″Z6/Z21, 1 3/4″Z6/Z20 | 233 | ||
| SCF151 / SCF176 | 1600–4500 | 1 3/8″Z6/Z21, 1 3/4″Z6/Z20 | 171–175 |
Key Features
Cams re-engage under spring pressure as soon as overload clears – zero operator intervention.
Up to 4500 Nm – the strongest PTO torque limiter in the GBC catalogue.
No bolts to replace, no friction linings to wear. The cam mechanism is inherently self-maintaining.
Positive cam separation provides a sharp, defined cut-off – no gradual slip like a friction clutch.
1 3/8″ Z6, Z21, 1 3/4″ Z6 and Z20 – covering all common Australian PTO standards.
SC series with yoke connection; SCF series with flanged housing for direct bolt-on mounting.
Working Principle
Four precision-ground cams on the hub mesh with matching profiles on the outer housing. A spring pack applies axial force to keep the cams fully engaged. When an overload occurs, the torque creates a cam-separation force that exceeds the spring’s holding capacity. The cams push apart along their tapered faces, the hub spins free of the housing, and the drive is interrupted. The moment the external torque subsides, the springs force the cams back together and the clutch re-engages on the next alignment of cam profiles. A locking plate prevents the spring pack from loosening over time.
Applications
High-torque implements demand the strongest protection. The automatic limiter handles peak loads while re-engaging for continuous operation.
Large-frame cultivators in rocky soil benefit from the clean disconnect and instant re-engagement.
Extreme shock loads from hardwood roots require the highest torque capacity and fastest re-engagement.
Pumps, generators and industrial equipment driven by tractor PTO benefit from zero-downtime automatic protection.
Installation
- Disengage PTO and shut down the tractor.
- Mount on the implement shaft, matching the spline profile.
- Secure with snap ring and locking plate.
- Grease all points, engage PTO at low RPM and verify the cam engagement is smooth.
Quality & Warranty
ISO 9001:2015 certified. CE marked. 12-month warranty. Australia-wide shipping from GBC. Contact: sales@australia-drive.com.
FAQ
How quickly does the automatic limiter re-engage?
Within one revolution of the hub after the overload clears, the cams find alignment and lock in.
Is the trip torque adjustable?
The trip torque is set by the spring pack pre-load. Some models allow shimming to fine-tune. Contact GBC for details.
What is the difference between SC151 and SC176?
SC151 has a Φ152 housing diameter suited for torques up to 2800 Nm. SC176 has a Φ176 housing for the highest torques up to 4500 Nm.
Customer Reviews
“The 8SC176 on our large round baler is phenomenal. Trips cleanly when we hit a problem and re-engages instantly.”
“Premium product. No more stopping to replace shear bolts. Worth every dollar for the time we save.”
“Running the 9SC176 on our stump grinder – it handles incredible shock loads without missing a beat.”
“Solid build quality and fast delivery. Only four stars because we wish there was a visual indicator showing when it trips.”
“Best torque limiter we have ever used. The cam mechanism is incredibly reliable and maintenance-free.”
Related Products
Pair your automatic torque limiter with GBC’s full PTO driveline range: shafts, yokes, shields, adapters and more at australia-drive.com.
Upgrade to Fully Automatic Protection
Contact GBC for expert advice on the ideal automatic torque limiter for your heavy-duty application.
Email: sales@australia-drive.com
