Thread: Understanding diff lock in the P38

Your Rangie has front and rear diffs between the axles.

It also has a viscous coupling between the front and rear propshafts.

The diffs between the axles allow the wheels on either side to turn at different speeds.
The viscous coupling allows the front and rear propshafts to turn at different speeds.
This is essential for on road driving (going around corners all wheels travel a different distance and therefore rotate at different speeds).

For normal offroading that setup is fine.

If you wanted to venture into harder terrain where you were likely to get stuck through lifting wheels, then crossaxle difflocks will be your friend.

These work by forcing the left and right wheels on the locked end to rotate at the same speed.

For example a rear difflock will join the rear axles together making the rear wheels turn at the same speed, regardless of lifted wheels, lost traction, etc.

I would think that for your intended use, the standard setup will be OK.

Thanks BigJohn,

Since i couldn't see any evidence of a diff lock, I assumed that the P38 must have one that engaged automatically when it sensed that it needed both left and right to turn at the same speed through a lifted wheel etc.

Planning a big trip out west Vic later in the year so better get an upgrade i guess....

D

What sort of big trip are you planning?

The P38 is very capable straight out of the box provided everything is in good condition and working correctly.

I am pretty sure most if not all P38s had traction control of some sort, be it rear wheels only or all four wheels.

Still unsure of all the details. I was invited over beers (many beers) so a little hazy. I know it's from Albury to Gippsland area though.

Maybe getting diff lockers for the P38 is a bit of an overkill then...

See how it performs standard before you worry about expensive modifications like difflocks.

A decent set of offroad rubber gives a much better increase in offroad performance for less $$.

Agree with BigJon - spending $1500 on a set of 5 good tyres is a better investment than a diff lock. The P38A is an immensely capable vehicle in standard form.

I'm a big fan of Cooper ST's. Had a set of these on my previous P38A and never had a problem keeping up with any Jap or Yank 4WD's off-road.

Pre-99 models had traction control on the rear wheels at less then 80Kph, or thereabouts. 99-on had 4 wheel traction control up to 100Kph.

If you do decide on a diff-lock, consider the front rather than the rear. I have a rear air-locker on mine and it didn't quite cut the mustard on the weekend when I needed it. I'm pretty sure it would have be ok if I had a front locker instead. Then again I made a couple of mistakes on my approach up the slope so I shoudn't be blaming the vehicle see the video [ame="http://www.youtube.com/watch?v=cJjfudj511U"]YouTube - Failed attempt at bowl climb[/ame]

On a related subject that may also be useful to LavisLane, does anyone know how the TC works in low range? In the video above, I seem to be getting some excessive spinning of opposite wheels.

Cheers, Paul.

Lower your tyre pressures as well 20-25 PSI. This will increase traction immensely - more tyre surface in contact with gravel. I recently attempted a fairly steep incline (my p38 1996 TC in rear only). With full tyre pressure no chance but get a bit of air out of the tyres and up she goes.

Traction control isn't like a diff lock - the diff lock as the name suggests will lock the diff so that both wheels drive at the same rate/speed - that is why axles break when one tyre is wedged and doesn't want to turn but also why they perform better than a standard 4wd in many hard offroad conditions (steep muddy wet slopes).

Traction control is like ABS but in reverse. When the sensors sense a wheel is spinning they retard power to that wheel (either by applying the brake to that spinning wheel or through some sort of engine management which reduces the power and thus the spin).

Paul the clip didn't seem to work but i think i have seen it before. The TC won't help the wheel that isn't turning turn (diff lock in front would) but should reduce the wheel spin of the wheel that is spinning. You will notice the TC light flicker on and off as it applies some breaking force to try and slow that wheel down - it probably won't stop the wheel though. The feeling through the steering is much like hitting the breaks hard in a ABS car in the wet. You can feel the break be applied every few milliseconds.

Hope my crude explanation helps!

Thanks Remy, that all makes sense.

There were 3 things that I did wrong on that video...

1. tyre pressures were too high (28psi - should have been around 20)
2. not enough momentum - I let the car stop
3. bad line - I slipped in to the rut about half way up.

On the second attempt, I chose a slightly better line and kept the momentum up. Up and over no problem without the locker.

Couldn't be bothered to let the tyre pressures down... after all, I was out driving with a Pajero and Triton who had already let their tyres down to 20psi