Tuning Variloc Differentials

Different types of race cars can demand wide variations in differential locking action. By careful attention to details during assembly, the Variloc can be tuned for almost every conceivable situation.

The 3 main tuning areas are:

1. Ramp angles
2. Preload
3. Clutchplate swapping

 

Ramp Angles

Differential locking action creates drag between the tires that in turn produces push. In general, the greater the locking action, the more push that is created. However, not enough locking can create looseness in many cars.

Most sedan cars require a certain amount of differential lockup-induced push just to counter-balance a built-in loose condition that normal chassis tuning cannot cure. In other words, not enough lockup will cause a looseness that you cannot tune out, but too much lockup will create unnecessary push.

There are three independent conditions of lockup that can be tuned individually:

1. Power-on (corner exit)
2. Power-off (corner entry )
3. Neutral Throttle (feathering the throttle in the middle of a corner)

Corner entry and exit are controlled by the ramp angles, and neutral throttle by preloading the clutch pack.

 

Tuning Example

If the car was originally equipped with a 60x60 ramp and behaves as follows:

To change the ramp angles, new ramps are needed – just exchange one for the other. If preload is needed add shims behind the preload springs, or change to stiffer springs.

Locking rate of both sides of the ramp can be lowered by reducing preload, or by rearranging the clutches to reduce the number of active surfaces.

For oval track cars, a good starting point for stagger is to reduce it to one-half of that needed for a spool or Locker. If the car pushes all the time, less locking is needed (ramp angles reduced), but can be temporarily overcome by adding stagger. If the car feels a bit loose all the time, first try reducing the stagger further. Don’t be afraid to go to reverse stagger – many customers have run that way and swear by it!