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What is torque?

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At the outset I have to cover myself by saying: I accept no responsibility for any damage or injury related to your following any information on these pages. You're on your own.

This test shows how the QuadraDrive system works well enough on the rear wheels in a workshop environment but how the front diff just doesn't cut it.

Out in the real world, although the rear diff works far better than the front, even the rear diff will let you down in situations where you need a good amount of torque to get you through.

I've found that if I get cross-axled on a hill then I'm stuck. I'll have one rear wheel and one front wheel spinning freely while the other two wheels remain motionless. The two wheels with traction have more than enough grip to get me unstuck but the QuadraDrive system, having fallen on its butt, cannot deliver the torque the way the advertising promises.

Notes

• These tests require the use of three trolley jacks.
• Position jacks under the axle tubes as close to the wheels as possible.
• Use suitable rubber or wooden blocks on the jacks.

• Wheels should be lifted only until they are about one or two centimetres off the ground.
• All tests should be performed with the transfer case set to 4-Lo and the gearbox set to first gear. This will maintain uniformity between the tests.
• All tests begin with the engine running at idle and the brake pedal applied firmly.
• Once the brake pedal has been released, light pressure may be applied to the accelerator to smoothly increase engine revs if required.

WARNING! Someone should keep a close eye on the proceedings under the vehicle to ensure that the axles do not slip off the jacks as this could lead to serious damage

Test 1

Lift both front wheels and the left rear wheel.

As you release the brake pedal, notice how the rotational speed of the left rear wheel is “arrested” by the VariLok system as it transfers torque to the right rear wheel.

Notice how torque is transferred to the right rear wheel smoothly and progressively, with no shuddering, and how the right rear wheel tries to push the vehicle forward.

Slowly increase engine revs if necessary. The vehicle will either begin to move forward or the right rear wheel will begin to spin on the ground.

Carefully pay attention to the sounds made. No unusual clunking or clicking. Just the sound of the vehicle trying to drag trolley jacks over the floor and/or the sound of the right rear wheel slipping on the ground.

Once again, note the smoothness, quietness, ease and fluidity of the VariLok operation.

Test 2

Move the trolley jack at the rear from the left side to the right side so that you can repeat the previous test on the other rear wheel to confirm that the left and right sides behave in the same way.

Test 1 & 2 conclusions

Tests 1 and 2 very clearly demonstrate the following sequence:

1. Initially, the raised rear wheel begins to spin freely.
2. Almost immediately, the Gerotor pump uses the speed differential between the two rear wheels to build pressure and close the clutch pack in the rear diff.
3. The diff begins to lock and the spinning raised rear wheel slows down markedly.
4. Torque is transferred to the grounded rear wheel which begins to rotate.
5. The process happens at low revs and is smooth, quiet and progressive.

Test 3

Lift both rear wheels and the left front wheel.

As you release the brake, notice how the left front wheel spins freely and does not slow down as happened at the rear. The Gerotor pump and clutch pack are not causing the diff to begin to lock up as they should.

Increase engine revs somewhat and notice how the left front wheel is now spinning very fast while the right front wheel remains stationary.

Bear in mind that this axle is designed to achieve maximum lock when the rotational speed differential between left and right wheels is at around 80RPM or, in terms easier to visualise, just over one wheel rotation per second.

Think about how slow one rotation per second really is and compare that to how fast and freely the left front wheel is spinning while the right front wheel remains stationary.

Listen carefully to the noises being made. Lots of very unhealthy sounds.

Test 4

Move the trolley jack at the front from the left side to the right side so that you can repeat the previous test on the other front wheel to confirm that the left and right sides behave in the same way.

Test 3 & 4 conclusions

Tests 3 and 4 very clearly demonstrate the following sequence:

1. The raised front wheel begins to spin freely.
2. The raised front wheel continues to spin freely even when engine revs are increased.
3. The diff doesn’t lock up.
4. Torque is not transferred to the grounded front wheel.
5. There is also an unhealthy noise from the front diff.

Further testing

If you're brave enough, you can do the test again on the rear wheels and place some sort of chock, perhaps a building brick or something, in front of the grounded rear wheel to provide it with something to climb over in order to demand more torque of the system. You should find that the rear diff can't cope with much more torque than the front. I don't have anything handy to do this with in my own workshop but I know that offroad, in the real world, it's pretty easy to get the rear diff to slip when it shouldn't.