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ZF Race Engineering's SACHS motorsport clutches have stood for top-tier quality in international racing for decades. The ambition: continuous improvement and the drive to keep pushing the limits. From the lightest clutch used in Formula 1 to proven twin-plate and multi-plate systems in WRC, DTM, NASCAR, Le Mans and the Dakar Rally - ZF Motorsport technology is a core component of many winning cars worldwide.
SACHS Racing Clutch
RCS 140 Anti-Stall Clutch (ASC)
Centrifugal 140 mm multi-plate racing clutch with rpm-dependent clamp load
The SACHS RCS 140 ASC from ZF Motorsport is a centrifugal multi-plate racing clutch with engine-speed-dependent clamp load. It was developed for race cars with a long first gear to simplify launch and reliably prevent stalling – while retaining a compact 140 mm package, low inertia and high durability.
At idle the clutch operates “normally open” and transmits no torque. As engine speed rises, the centrifugal force of the internal levers increases the clamp load on the friction pack – the clutch closes automatically and the car moves off. The driver modulates slip primarily via the throttle; with a steady pedal the engine speed and transmissible torque remain very stable. On low-grip surfaces this allows fine control right at the tyres’ traction limit.
The RCS 140 ASC is based on the proven RCS-140 platform with forged aluminum clutch cover (housing), sintered metallic friction pairing and multi-plate pack. Depending on configuration it uses 2, 3 or 4 sintered discs and covers ~500 Nm to 1,000 Nm maximum engine torque. It eases launches, pit-exit moves and manoeuvring without acting as traction control – the optimal launch point remains with the driver.
Benefits
Anti-stall function – no engine stalling
Consistent launches in varying grip conditions
Compact 140 mm system with low inertia
Centrifugal anti-stall function
At the heart of the SACHS Anti-Stall Clutch is a set of L-shaped pivoting levers mounted in the housing. Their centres of mass face the pressure plate; with rising rpm centrifugal force creates a moment about each pivot. A short cam on the lever tips acts on the pressure plate, compressing the friction pack against flywheel and intermediate plates – the clutch closes.
At low rpm stall springs and stall pins hold the pressure plate back and prevent unwanted drag. If rpm drops below the set threshold, the clutch opens automatically and decouples the driveline. This prevents stalling even with locked wheels, spins or abrupt deceleration.
Quick launches with less heat build-up
Conventional race clutches often require high safety rpm at launch to avoid stalling, which creates slip and heat in the pack. The RCS 140 ASC reduces this load because transmitted torque is directly linked to engine speed.
The driver meters launch torque via the throttle; with a steady pedal a stable operating point for rpm, torque and tyre slip is reached quickly. In combination with a launch button and adjustable rev limiter the system adapts to different grip levels. Lower heat build-up increases friction-pack durability, especially in long races with frequent pit stops.
Technology
Technical data RCS 140 ASC:
- Design: centrifugal racing clutch
- Friction pairing: sintered metallic / steel
- Number of discs: 2 / 3 / 4 (application-dependent)
- Variants:
– 2 discs, 7.8 mm sinter pad: max. engine torque 500 Nm
– 3 discs, 5.2 mm sinter pad: max. engine torque 750 Nm
– 4 discs, 2.6 mm sintered: max. engine torque 1,000 Nm - Release diameter [mm]: 38
- Flywheel: flat type
- Optional: hydraulic concentric slave cylinder for torque interruption during shifts
Clutch cover (housing)
The RCS-140 housing is forged high-strength aluminum. Geometry supports efficient heat rejection from the pack and stabilises the temperature window. A hard-wearing surface minimises fretting and fit wear at bearing/guide faces and extends service life. The integrated lever mechanism is designed for the high centrifugal loads in racing and remains dimensionally stable under endurance use.
Friction lining
The ASC uses 140 mm sintered metallic discs available in different lining thicknesses. Thicker pads increase mass and heat capacity, reduce local hot spots and keep friction stable over long duty cycles. Thinner pads reduce inertia for especially quick engine-speed changes.
Overview:
– 7.8 mm sinter pads (2 discs): maximum thermal reserve for moderate-torque, long-slip applications (e.g. off-road).
– 5.2 mm sinter pads (3 discs): balanced compromise of torque capacity, heat buffer and agility.
– 2.6 mm sintered (4 discs): highest torque density and very low inertia in a compact stack – ideal up to ~1,000 Nm.
Operating principle
Eight L-shaped levers pivot on pins in the housing. Their free ends act through a short cam on the machined face of the pressure plate. With rising rpm centrifugal force generates an outward force that becomes clamp load on the pack and transfers torque between engine and input shaft.
Stall springs and pins set the rpm at which engagement starts and limit the axial travel of the pressure plate. A stall-pin retainer prevents the free ends from bending outward under centrifugal force. Properly set, engine stalling at race starts, after spins or with locking wheels is virtually eliminated – without acting as tyre-slip traction control.
Scope of supply
RCS 140 ASC clutch unit with centrifugal anti-stall mechanism
RCS 140 friction pack (2-, 3- or 4-disc configuration, sintered metallic)
Adjustment kit for stall springs, air gap and rpm thresholds
Individual configuration with ZF Race Engineering
Setup & application data
The RCS 140 ASC is not a plug-and-play part. The optimal setup is vehicle-specific and defined together with the works engineering team. Engineering effort is included: each ASC is configured jointly with ZF Race Engineering to tune launch behaviour, torque capacity and thermal robustness to the application.
Information required for specification and tuning includes:
- Engine torque curve across the full rpm range
- Engine idle speed
- Typical operating-window vehicle speed
- First-gear ratio / overall length
- Vehicle mass incl. driver and operating states
Quality & top-level motorsport use
The SACHS Anti-Stall Clutch has been proven in numerous international motorsport projects – including GT cars, prototypes, off-road racers and special applications such as Alex Zanardi’s BMW M8 GTE at the 24 Hours of Daytona. It eases car control in demanding scenarios such as long pit stops and changing grip, and reduces the risk of engine stalling and resulting on-track hazards. Decades of ZF Race Engineering clutch development, extensive rig and track testing and modern materials/manufacturing underpin the ASC range.
Applications
CIRCUITS / TOURING
GT and touring series with long first gears and demanding launch procedures, e.g. IMSA, GT World Challenge, DTM, ELMS, NLS, TCR.
ENDURANCE / PROTOTYPES
24-hour races and endurance series with high clutch thermal load, e.g. 24h events, WEC, Asian Le Mans Series, LMP and GT prototype programs.
RALLYCROSS / OFF-ROAD
Rallycross and off-road series with highly variable grip and frequent launches, e.g. World RX, national rallycross/off-road championships, US off-road racing.
RALLY
Rally cars with high torque and mixed surfaces where preventing engine stall after spins or wheel lock-up is crucial, e.g. WRC, national series, GT2/GT4 rally programs.
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