VW Quantum Syncro Differential Locks


A conventional differential provides the same torque to both wheels of an axle. But the wheel having the least friction on the road determines the amount or force being transferred.

When one wheel loses traction, the differential no longer distributes power to the other wheel of that drive axle. The result is that the car gets stuck when one wheel spins in the mud, ice or snow.

On the Syncro, the differential lock overrides the principle of the differential and physically connects the wheels of the axle together.

Pulling the lock engagement knob to the first detent locks the center differential. With the center differential locked, power is transmitted equally to the front and rear differentials.

The center differential lock should be engaged if the car is being driven slowly and is in danger of becoming stuck on snowy, icy, or muddy road surfaces.

23When the differential lock knob is pulled to the second detent, the rear differential is locked in addition to the center differential. In this position, no differential action can take place in either the rear axle or between the front and rear axle differentials, although differential action still occurs between the two front wheels.

With both differentials locked, at least three wheels, both rear and one front must spin before traction is lost completely.

Because the differentials are unable to compensate for cornering when locked, low speed vehicle maneuverability is reduced. Both differential locks should be engaged if the car has become stuck on the road shoulder, in ice, snow, or mud. The locks should not be engaged in city traffic, or on dry curving roads.


The heart of the Syncro’s unique all wheel drive is the center differential.

Engine power is transmitted from the transmission input shaft, through the selected gear set to the hollow shaft and from there to the center differential.

The center differential transfers the driving forces equally, to the pinion shaft and the rear driveshaft (arrows).

The center differential pinion gears provide for speed differences between the front and rear axle drives, just like a conventional differential.

To engage the center differential lock, the shift rod moves the shift fork to the left.

The shift fork pushes the lock sleeve into engagement with the differential housing splines and the center lock is engaged.

Now, the pinion shaft and the driveshaft to the rear wheels are locked together and turn at the same speed.

During engagement, if the locking mechanism becomes “tooth to tooth”, the lock will engage when a difference in speed takes place through the pinion gears.

When the center differential is locked, the center differential lock switch is activated, and the center differential light on the indicator panel is illuminated.

25The rear axle differential provides for speed differences between the two rear wheels. Like the center differential, it can also be locked.

When the rear axle differential lock is engaged, the shift fork pushes the lock sleeve into engagement with the splines on the differential housing, effectively eliminating the differential action between the rear wheels.

When the shift fork moves, the rear axle differential lock switch is operated via a pin. This illuminates the second warning light on the indicator panel.

As with the center differential, the rear differential lock may not engage instantly if “tooth to tooth” contact occurs.