Thread: Traction Control on 11MY Defenders

Originally Posted by isuzurover

Says who??? You may only be advised to ENGAGE the CDL at speeds <60 km/h, but there is no physical/engineering reason why the T-case cannot work at the same speeds open or locked.

When I drove the canning recently I engaged the CDL when we first hit sand, and disengaged it ~ 2 weeks later.

Right - OK - didn't know that, Ben.

In fact, having a look - although the badge in the car indicates what you suggest, Ben - the manual says you can engage /disengage at any speed - as long as the vehicle is moving in a straight line with no wheel slip - so I stand corrected, thanks.

A bit more from James on Defender2 Forum on this:

"its a bit more than a software patch, new system is made by Bosch old one is Siemens (IIRC).

All post 5 Jul 10 build are 11MY vehicles. there were a few (12 i believe) prior to that but they were all used internally by LR and LRE. i can't remember the chassis VIN change, could look it up though but yours won't have it.

Ref the rpm and keeping your toe in; TC reacts to a difference in wheel rotation speed. The greater that speed variation the quicker and the harder TC will interact. This explains why when you become say cross axled say 1st gear low at tickover the car will lurch fwd roll back and repeat and wont drive through. TC is working then BUT it is working slowly with limited braking forces on the spinning wheel. If you increase engine revs you will spin that 'hung' wheel quicker TC will therefore react more aggressively with a greater brake force on the spinning hung wheel thus diverting the torque through an open diff to the wheel that was turning slower (or stationary) and hopefully giving you drive. If you increase engine revs as you approach an obstacle that you know will need TC and you do it in the right place you can overcome the delay to your fwd movement without increasing the overall vehicles speed. Easier said than done, but if you drive the same section alot you can do it.

TC wont get you out of everything. you need speed variation between the wheels and you need at least one wheel to have traction.

You could sit on a wet grassy field at increased RPM all day with all 4 wheels (CDL locked) spinning at the same speed, TC not working (as they are all spinning the same speed) and just be digging holes!

Ref axle lockers, i have ARB's in mine and they always got my vote over KAM, although if you are thinking of going this route there is a very reputable transmission manufacturer about to bring out a rival for the ARB - still air operated. From the testing i have seen it works well. With a locker fitted you wouldnt need to disable TC as both wheels on the axle are turning at the same speed so TC just wouldn't come into play.

With respect to fitting lockers, rear is the normal way to go followed by front. If you are putting a locker in the front and wish to be able to steer then fit uprated (Ashcroft) CVs, a front locker in and a boot full of power on anything other than straight ahead will soon see std CVs off."

If you are interested in the full thread go to Defender2 - View topic - Traction control or diff. locks?

Cheers
KarlB

I dont know about you guys but I dont drive all of the big tracks in the centre of Aus with the CDL locked. I also dont lock the CDL when the roads are wet. You guys might, but I'd bet most users don't.

Originally Posted by rick130

Sorry, I don't buy that.I drive dirt/gravel/crap roads/farm tracks all the time (my Defender is my work vehicle) and only ever engage the CDL when going off road/tricky stuff where a wheel could potentially lift or unload. IMO there's much less understeer with the centre diff left open on fast dirt roads, and if your Defender has TC all the better (mine doesn't)

You should engage CDL as soon as you leave a sealed surface - tar, concrete, etc. It makes the landy more stable, less strain on individual drivetrain components and all that good stuff.

Also, without the CDL locked, if you go airborne you run the risk of flipping over when the last wheel touches the ground and suddenly goes from having 100% of the torque to 25%. Happened to a mate of mine, since then he also drives with CDL locked as soon as he leaves tar.

Land Rover Experience also instructs you to lock CDL as soon as you leave tar.

Originally Posted by Naks

You should engage CDL as soon as you leave a sealed surface - tar, concrete, etc.

Why?

Originally Posted by BigJon

Why?

My answer is going to relate to gravel roads because that is the most common loose surface SaFas drive on:

On very loose gravel where the wheels are searching for grip, power will be transferred back and forward between left and right wheels (unless axle diffs are locked) . This transfer left and right does not add to stability - in fact it can precipitate a slide. Add to this power transfer back and forward from front axle to back axle as grip is found and lost - this transfer causes rapid transition between over and understeer - not a good thing when driving on marbles.

The second factor is related to regaining control once the back end starts to slide. The first reaction if the back slides left (left is the most probable on a gravel road because of the roads camber) is left arm down (ie steer left) and right foot down (ie more power ) to pull straight .If the CDL is open, applying foot down is less likely to get power to the road - more likely that front wheels will spin and back wheels will not get any power - not good.

As far as wind up on a gravel road is concerned - very little with centre diff locked - not big differences between front and back wheel speeds. Easily relieved - without any wheel spin and resultant induced traction loss.

Another point to consider: a landy with CDL locked causes less damage to a gravel road than with open CDL vehicle since you have less wheelspin & sliding around.

The rule of thumb in SA is as soon as you leave tar, drop tyre pressures (halve current pressure) and engage CDL.

I have to say I don't really agree. I haven't driven over there, but I can't imagine the roads being too much different to central Australian roads which I have driven extensively on.

I am quite happy for you to lock your centre diff whenever and wherever you like. I will keep using the techniques that have worked for me.

Originally Posted by Naks

My answer is going to relate to gravel roads because that is the most common loose surface SaFas drive on:

On very loose gravel where the wheels are searching for grip, power will be transferred back and forward between left and right wheels (unless axle diffs are locked) . This transfer left and right does not add to stability - in fact it can precipitate a slide. Add to this power transfer back and forward from front axle to back axle as grip is found and lost - this transfer causes rapid transition between over and understeer - not a good thing when driving on marbles.

The second factor is related to regaining control once the back end starts to slide. The first reaction if the back slides left (left is the most probable on a gravel road because of the roads camber) is left arm down (ie steer left) and right foot down (ie more power ) to pull straight .If the CDL is open, applying foot down is less likely to get power to the road - more likely that front wheels will spin and back wheels will not get any power - not good.

As far as wind up on a gravel road is concerned - very little with centre diff locked - not big differences between front and back wheel speeds. Easily relieved - without any wheel spin and resultant induced traction loss.

Another point to consider: a landy with CDL locked causes less damage to a gravel road than with open CDL vehicle since you have less wheelspin & sliding around.

The rule of thumb in SA is as soon as you leave tar, drop tyre pressures (halve current pressure) and engage CDL.

Sorry, but I disagree with almost everything there. (except dropping tyre pressures)

Firstly, the only time you get torque transferring back and forth across an axle that will cause some sort of instability is if you have an LSD or torque biasing centre, an open diff is the most benign diff in operation for the vast majority of drivers.

Older style LSD's could be a pain on dirt, anyone that's driven an older Holden or Ford with some decent HP under their right foot will know what i'm talking about, put your right foot down and start to wheelspin and you will start to fishtail driving in a straight line unless you ease out of the throttle.
This happens as torque is biased from one wheel to the other and back again as the wheels search for traction.

Interestingly the much more tightly pre-loaded Nissan Patrol diffs don't appear to do this at all or at least to a much lesser degree, it acts more like a Detroit in this respect.

Secondly, dirt/gravel surfaces vary incredibly, from hardpacked shale through gravel, sand and that horrible small marbley pea like stuff in WA that Ben mentioned above.

I have yet to experience a surface on a normal, gazetted, occasionally graded made gravel/dirt road that I need the CDL engaged, although I reserve the right to change my mind if i ever get to drive on those tiny little marbles that seem to predominate in WA.

Rapid transition between over and understeer caused by not having the CDL locked ?

You're stretching it there.

I can throw a 130 heavily into a dirt corner, have the front start to plough and then it gently transitions into roll oversteer, a condition brought about by a combination of rear geometry and roll characteristics (spring rates and CofG), not because the CDL isn't engaged.
Engage the CDL and the understeer is greater, it just doesn't point into the corner as well and I can't get the tail where I want it as easily.
If I ran a locked rear end this may change.

I have driven 'normally' ie, brake, turn in and power out and I've payed with a left foot brake technique, bury the right foot under brakes to make sure the engine is under full boost as the brake is released and release the brakes and either style doesn't seem to cause any of the dire impacts you've listed above. (This was done on a private road under controlled conditions by an ex-race driver, please, don't do this at home, on a public road or in your car, ever )

I have tried running around with the CDL locked after reading about how many here prefer it, I've shuttled back and forth between locked and unlocked and i just can't see any benefit on the roads I drive.

IMO it reduces or impairs the characteristics that I like in a car, the ability to turn in and point with some sort of precision with an easy transition between under and oversteer, and the ability to control a slide easily, which considering the thing tares out over 26-2700kg most of the time is pretty impressive (or pretty irresponsible depending on your POV )

I have to specifically address this

The second factor is related to regaining control once the back end starts to slide. The first reaction if the back slides left (left is the most probable on a gravel road because of the roads camber) is left arm down (ie steer left) and right foot down (ie more power ) to pull straight .If the CDL is open, applying foot down is less likely to get power to the road - more likely that front wheels will spin and back wheels will not get any power - not good.

Absolutely wrong.
If you lose the rear (deliberately or otherwise) and wind in opposite lock (good) and try and power out and the power feeds to the front axle instead of the rear because the centre diff is open GREAT ! the drive to the front axle will tend to pull the vehicle straight, anyone that's ever driven a FWD car quickly on dirt will recognise this.
I suspect though that if the rear is sliding and is obviously traction limited that more power will feed to the rear axle anyway which is fine too, either way it is a more controlled slide than a 2WD vehicle (or part time 4wd in 2wd)


If someone feels more secure on dirt with the CDL engaged that's great, it will make the car more benign in characteristics by increasing understeer, a secure signal to the average driver to back off when they've stepped that little step too far, however there are those of us that know and appreciate that it's fine and safe to run unlocked too.