Caterham 420 Workshop Manual

An unofficial workshop manual

Measure static LSD preload

The static LSD preload is the torque needed to turn one wheel while the other is stationary. Measuring and monitoring the static LSD preload gives and indication of the health of the Caterham 420R Titan LSD.

Check the torque wrench being used before starting this procedure. If the torque wrench can read anti-clockwise torque the measurement can be taken from either side. If the torque wrench only reads clockwise torque take the reading from the RHS.

Chocking the front wheel to prevent the car from moving. Loosen (but don’t remove) the one of the rear wheel’s wheel nuts.

With a trolly jack under the centre of the DeDion tube (a small piece of carpet is the perfect way to protect the paint of the DeDion tube) lift the rear wheels just off the ground.

Remove one of the rear wheels. Ensure the handbrake is off, and the car is in neutral. Lower the jack slowly, so the other wheel touches the ground, as soon as it does lock the jack off again, so it is still taking the weight of the car.

If the torque wrench used can read “peak” torque applied this setting should be used. The socket size is 41mm (or 42mm for RHS 2019 models) as used to torque the rear hubs. The torque being measured is in the region of 20 lb ft to 40 lb ft, therefore a torque wrench accurate in this range is preferred. Therefore 1/2″ to 3/8″ adaptor may be required.

Using the torque wrench, turn the hub via the hub nut clockwise for the RHS (or anti-clockwise LHS) and measure the torque needed to turn the hub / turn the prop shaft. The reading on the torque wrench is the differential static preload.

If the torque wrench cannot read peak torque, just monitor the display as the hub is turned and note the highest number. Mechanical (non-digital) torque wrenches can also be used, gradually increase the setting until it no longer clicks – the first non click reading is the static preload.

The general rule of thumb – based on comment from a specialist from Road & Race Transmissions – is to expect 40 lb ft when the differential is new (often set a little higher). This will reduce as the clutches wear. At 20 lb ft it’s time to speak to a differential specialist about a rebuild.

Lift the car again with the jack, and refit the removed rear wheel, refitting the wheel nuts and tightening the before lowering the car off the jack. Finally, with the car on its wheels, torque the rear wheel to 80Nm. Check the wheel nut torque again after 100 miles. Reapply the handbrake and remove the chocks.

Tools Required

  • Trolly Jack (with carpet to protect paint)
  • Digital 3/8″ drive torque wrench
  • 1/2″ drive torque wrench
  • 19mm 1/2″ drive socket
  • 41mm 1/2″ drive socket (42mm socket for some model years)
  • 1/2″ drive extension
  • 1/2″ drive ratchet
  • 1/2″ to 3/8″ drive adaptor

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