Product Overview
Quaife ATB Limited Slip Differential QDF13J – Ford Focus ST225 & Volvo M66
The Quaife ATB Limited Slip Differential QDF13J is a premium helical gear differential upgrade developed for the Ford Focus Mk2 ST225 and compatible Volvo vehicles fitted with the M66 six-speed manual gearbox.
Designed as a direct replacement for the standard open differential, the Quaife ATB improves the way torque is distributed between the driven wheels, helping reduce unwanted wheelspin and deliver more consistent traction during acceleration.
For owners of tuned Ford Focus ST225 models, this makes QDF13J an especially attractive drivetrain upgrade when increased engine torque starts to overwhelm the standard open differential.
Manufactured in Great Britain, the Quaife QDF13J combines precision-engineered components, progressive torque transfer and a low-maintenance design suitable for road and motorsport use.
Why Choose the Quaife ATB Limited Slip Differential?
1. Improved Traction and Reduced Wheelspin
A standard open differential allows each driven wheel to rotate at a different speed, but the available driving torque is limited by the wheel with less grip.
During hard acceleration or cornering, this can cause the inside front wheel to spin before the outside wheel reaches its available traction limit.
The Quaife QDF13J helical limited-slip differential uses an automatic torque-biasing mechanism to redirect more driving torque towards the wheel offering greater resistance.
This can improve traction and help make better use of the performance available from a standard or modified Focus ST225.
2. Progressive Helical Gear Technology
Unlike a traditional plate-type limited-slip differential, the Quaife ATB relies on precisely machined gears rather than friction plates and aggressive locking preload.
This produces smooth, progressive torque transfer without the abrupt locking behaviour sometimes associated with competition plate differentials.
The ATB differential allows the wheels to rotate at different speeds during normal cornering while responding automatically when driving traction becomes uneven.
This is particularly useful for everyday road cars and fast-road performance builds.
3. Helps Reduce Unwanted Torque Steer
High-powered front-wheel-drive vehicles such as the Ford Focus ST225 can experience steering disturbances during hard acceleration.
Quaife’s ATB system helps manage the distribution of driving torque across the front axle, which can reduce some unwanted wheelspin and torque-steer behaviour compared with a worn or standard open-differential setup.
Actual results depend on tyre condition, wheel alignment, suspension geometry, power delivery and the road surface.
A limited-slip differential cannot eliminate every cause of torque steer.
4. Designed for the Ford Focus ST225 M66 Gearbox
The QDF13J is specifically listed by Quaife for the Ford Focus Mk2 ST225 with the M66 six-speed manual transmission.
It replaces the standard differential inside the gearbox, retaining the original transmission layout.
This is a gearbox-internal upgrade, not a complete gearbox or external drivetrain component.
The existing gearbox must be dismantled and the replacement differential installed by a suitably experienced specialist.
5. Compatible with Selected Volvo M66 Models
The Quaife QDF13J is also identified in the manufacturer’s application catalogue for selected Volvo models fitted with compatible M66 six-speed manual gearboxes.
Applications include certain Volvo S60 T5, C30, S40, V50, C70 and V70 T5 variants.
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