Traction Control on 11MY Defenders

[KarlB]

There has been some discussion over the last couple of days on the Pommy Defender Forum (Defender2 (http://www.defender2.net)) concerning traction control (TC). I thought AULRO Defender people would be interested. What was particularly interesting was posted by James from Taunton who obviously works for Land Rover. James was saying that in pre11MY Defs TC works across each axle, while in post 11MY Defs it works on all 4 wheels. His explanation follows:

"So i will attempt to explain using my job, this one and last one for 6 years, plus pre production work we completed on 11MY TC systems.

TC will work on all 4 wheels. what i am saying is that it only senses across axles on pre 11MY. so:

CDL unlocked;

front axle left is spinning, TC will brake the front left to divert power to the front Right. regardless of what the rear is doing. the rear axle wheels could be stationary and no TC working. all the power is taking the easy route through the mid diff to the front diff. TC is then splitting that power at the front diff. (power being used as a generic term)

or the rears could say have right hand wheel also spinning, in which case TC will brake rear right and divert power to rear left. TC is working and it is working on all four wheels but it is not sensing the speed differences between front and rear axle wheels.

to continue this same example, therefore, if the front TC interacted and ended up with both front wheels doing say 5mph, the rear could of interacted and ended up with the rears wheels both doing 10mph. there is nothing to (pre 11MY) to make them all do the same speed from a TC perspective. (TC aims to have the wheels turning at the same speed within tolerances, the system obviously allows for turning corners, hence the delay at slow speeds when you loose traction before TC cuts in, you need to exceed the expected turning speed of one wheel for it to be going around a corner at a set engine speed)

The reason the original system was across axle only was the CDL, this should be engaged prior to conditions where you feel you may loose traction. you then get power 50% power front and rear. the TC is still working across each axle, but these are now joined by the CDL will mean all 4 wheels will have TC interaction as required to turn them all at the same speed.

On your loose gravel tracks or wet tarmac you can still get TC working. see the first para example. Go into a corner, loose traction on a front wheel as you apply power and TC will cut in. There is no CDL locked then.

on 11MY defenders the TC senses speed across all 4 wheel stations, such as D2, T5 platform and LR2s. It is therefore more efficient as it does not need the CDL to be locked as it can mimic this, granted from a reactive point of view. Use of the CDL is a preventative measure."

Cheers
KarlB
:)

[stig0000]

sooo??? what there say is it has tc;)

and about the disco and NOT having the cld cos of tc, and what is the fisrt mod most ppl do, put CLD back in;);)

i personly cant see it been any better then it is,

[Slunnie]

sooo??? what there say is it has tc;)

and about the disco and NOT having the cld cos of tc, and what is the fisrt mod most ppl do, put CLD back in;);)

i personly cant see it been any better then it is,
It will be better when the CDL is unlocked such as on wet roads, fast or hilly dirt, when you're driving to the snow etc.

[miky]

All of this begs the question: Why would you not lock the centre diff when you leave a bitumen road?

The whole point (IMO) of having a CDL is to use it!


.

[rick130]

All of this begs the question: Why would you not lock the centre diff when you leave a bitumen road?

The whole point (IMO) of having a CDL is to use it!


.

Sorry, I don't buy that.

I see it posted all the time in this forum and yet I don't understand why. By that rationale you should engage the CDL on wet bitumen too ?

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)

[roverrescue]

Rick,
you have obviously been driving a superior wheel base 'fender for too long.
back in the old days when I had a disco, I would use the CDL on most gravel roads when driving with spirit... it helped control the vehicle through corners and choppy bits.

With the 130 I now like you dont bother much with CDL... the extra wheel base does amazing things at loose speeds on gravel, a 130" outcorners a 100" on fast dirt - you just dont need to back off and at the outer apex where the corries are at their nastiest the 100" would pitch forcing a backoff where as the 130" just lopes along power down !

Steve

[BigJon]

I am with Rick, I don't lock my centre diff unless I need it 4wdriving. On "high speed" dirt I prefer the way the car feels with it unlocked.

Perhaps this comes from lots of years driving V8 Holden utes with leaf rear ends. They tend to be pretty "taily" and that is what I am used to.

I find locking the centre diff makes the car feel like it won't turn in (understeer).

What I do need is another trutrac in the front axle to stop the inside front wheel from spinning (usually left turns on bitumen in town).

[waz]

break an axle and see how good TC is without CDL.

TC alone is not a smart replacement for CDL and TC.

my $0.02.
W

[isuzurover]

I usually lock the CDL when on gravel/sand tracks. (1) It makes a HUGE difference to handling on WA pea gravel. (2) It is kinder on the centre diff.

[Scallops]

I agree with Rick and BigJon - you're only supposed to drive at a max 60 km'h with the CDL in anyway. I only use mine if I'm going to lift a wheel or likely actively need TC.

[isuzurover]

you're only supposed to drive at a max 60 km'h with the CDL in anyway.

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.

[Scallops]

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.

[KarlB]

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? (http://www.defender2.net/forum/topic4032.html)

Cheers
KarlB

[Slunnie]

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.

[Naks]

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.

[BigJon]

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

Why?

[Naks]

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.

[BigJon]

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.

[rick130]

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 :angel:)

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 :D)

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.

[stig0000]

Well today we took stock of our first BA car(2011 model) defender 90. d4 and sport. and well.. the abs and tc seem to be identical and running the same softwere as the AA defender(2010 model) all so the general grabbers on the fenders have gone and been replaced with onother brand. Cant remember what they were called.. soz :p

[KarlB]

Well today we took stock of our first BA car(2011 model) defender 90. d4 and sport. and well.. the abs and tc seem to be identical and running the same softwere as the AA defender(2010 model) all so the general grabbers on the fenders have gone and been replaced with onother brand. Cant remember what they were called.. soz :p
Tyres are Continental Conti Cross Contact AT.

[robharvey]

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

That's because most of the guys here drive Japs that aren't permanent 4wd, so the only way they gain a semblance of traction is to engage 4H.

I've tried the CDL locked/unlocked experiment on both my Puma 110 and 80 Cruiser, and honestly didn't feel any difference in driving characteristics - I now just leave the CDL unlocked. For me, personally, and as you have mentioned, tyre pressure plays a much greater role in vehicle stability on gravel.

[Naks]

I've tried the CDL locked/unlocked experiment on both my Puma 110 and 80 Cruiser, and honestly didn't feel any difference in driving characteristics - I now just leave the CDL unlocked. For me, personally, and as you have mentioned, tyre pressure plays a much greater role in vehicle stability on gravel.


I had a 110 DC Td5 - that one you definitely feel a difference between CDL locked/unlocked. Less so on my subsequent D2 Td5, but you could still feel it. Even less so on my current Puma 90, but still some tail-happiness without CDL locked.

[rick130]

That's because most of the guys here drive Japs that aren't permanent 4wd, so the only way they gain a semblance of traction is to engage 4H.

[snip]


Same here, and most of the farm utes that abound here always have the hubs locked so they can't forget when on farm.
Having said that I don't know any cockie or farm worker that uses 4WD on road either, they don't think about it that deeply.
If traction's limited they bung it into 4wd, otherwise they even trundle around paddocks in 2wd, I know I always did.

I have to say the Patrol is fun in 2WD as you can get the tail sliding so much more easily than a Defender, but the limits on dirt/gravel are so much lower it's almost scary (unless in 4H)

[rick130]

I had a 110 DC Td5 - that one you definitely feel a difference between CDL locked/unlocked. Less so on my subsequent D2 Td5, but you could still feel it. Even less so on my current Puma 90, but still some tail-happiness without CDL locked.


That's really interesting as I would have thought the opposite would occur just based on wheelbase lengths.

Generally speaking the longer the wheelbase the greater the stability (the slower/more benign the response)

What differences in tyres and maybe vehicle rideheights between the 90 and 110 ? Did the 110 have TC ? (The DII's rear suspension geometry is vastly different so might be hard to directly compare)

[Naks]

That's really interesting as I would have thought the opposite would occur just based on wheelbase lengths.

Generally speaking the longer the wheelbase the greater the stability (the slower/more benign the response)

What differences in tyres and maybe vehicle rideheights between the 90 and 110 ? Did the 110 have TC ? (The DII's rear suspension geometry is vastly different so might be hard to directly compare)



The 110 DC had full OME setup with 2" lift, no ABC/TC. Being a double-cab, the rear was always lighter than the front, I think that's why it was tail-happy.

The D2 had OME coils instead of air suspension but no lift, ABS/TC.

The Puma is stock standard.

[Xul]

Same here, and most of the farm utes that abound here always have the hubs locked so they can't forget when on farm.
Having said that I don't know any cockie or farm worker that uses 4WD on road either, they don't think about it that deeply.
If traction's limited they bung it into 4wd, otherwise they even trundle around paddocks in 2wd, I know I always did.

I have to say the Patrol is fun in 2WD as you can get the tail sliding so much more easily than a Defender, but the limits on dirt/gravel are so much lower it's almost scary (unless in 4H)

Yep that's the same way I was taught to drive.

I don't know what all this talk of engaging the CDL on a dirt road is. I personally don't think it's necessary at all! I agree with others that it handles better without it engaged. I drive on dirt roads all the time and to be honest until I read this I never even would have considered turning it on.

Also in regards to the post about getting airborne, I don't know how you're driving to get yourself in that position but not sure if a CDL would make a massive difference there.

[Naks]

I don't know what all this talk of engaging the CDL on a dirt road is. I personally don't think it's necessary at all! I agree with others that it handles better without it engaged. I drive on dirt roads all the time and to be honest until I read this I never even would have considered turning it on.

So, there seems to be a difference in driving techniques bet Oz & SA.. interesting.



Also in regards to the post about getting airborne, I don't know how you're driving to get yourself in that position but not sure if a CDL would make a massive difference there.

Dirt road, 80+kmh, there's a dip in the road, when you crest the other side, you are suddenly airborne.

CDL would help because when you land the front wheels are rotating at the same speed as the rear ones. Without CDL the last wheel that touches the ground will be putting down 100% of the power.

[Xul]

Yeah that's fair enough with dips, might be another difference between SA and Aus because I've never struck that. When there are dips you can either see them from a mile off, or know the kind of country that would have dips.

I also don't bother with air pressures on dirt roads unless that's the only thing I'll be driving on for a whole day. Would be an absolute nightmare to drop pressures and reinflate all the time.

[BigJon]

CDL would help because when you land the front wheels are rotating at the same speed as the rear ones. Without CDL the last wheel that touches the ground will be putting down 100% of the power.

Personally, if I am driving fast on a dirt road and I happen to get airborne, I lift off the throttle while in the air so that I don't have the wheels spinning much faster than the "ground speed" when I land. In that instance it doesn't make any difference whether the centre diff is locked or not.

[flagg]

Dirt road, 80+kmh, there's a dip in the road, when you crest the other side, you are suddenly airborne.


wow you have faith in your roads. When I'm on dirt, I slow right down when I can't see what I'm going to be driving on ahead. I've seen too many deep washouts and other nasties. If I drove like that around here, I'd definitely be dead right now.

[disco2hse]

Interesting discussion this.

I see no one has mentioned the main reason for NOT driving with a CDL on, in any case. That of the risk of binding up of the transfer case. Other than that there is no particular reason for disengaging it, but of course every situation and vehicle is going to be different and have its own handling characteristics. I am not advocating having CDL engaged when not specifically required however.

I only engage CDL in the Stage 1 when I am going to need the added traction it affords. When running down hill or across sidlings I have it disengaged unless there is a specific need to have it engaged, for example yesterday a particular sidling I had slipped into (off the track) that was composed of rounded volcanic river rocks bound by loose clay and gravel. I tried twice to gently climb back onto the track without CDL but needed the additional traction to get the job done. The effect on downhill runs and sidlings is for the back to swing around down the slope as the wheels turn regardless of the amount of traction they have. Disengage CDL and each wheel will find its own speed and one is not exerting much power anyway, so there is going to be little wheel spin.

Most D2's have TC and ABS so unless there is a specific need there is no reason to have CDL engaged. As the pommie postings illustrate, TC emulates the effect of CDL in most cases and it is only in the more extreme situations or where the wheels are revolving too slowly for TC to respond that you might need CDL engaged (which is probably also the reason that the D2 behaves well on metal roads, mentioned earlier, and mine certainly does). I have seen TC engage even at very slow speeds with very minor shifts in wheel spin in my D2, so that effectively rules out 95%+ situations where you might want to use CDL.

[rick130]

Personally, if I am driving fast on a dirt road and I happen to get airborne, I lift off the throttle while in the air so that I don't have the wheels spinning much faster than the "ground speed" when I land. In that instance it doesn't make any difference whether the centre diff is locked or not.

Absolutely, either bitumen or dirt.

The other thing is to always hold the wheel straight and correct after landing, otherwise it could get very nasty with some lock on when hitting terra firma.

[Xtreme]

Scenario - Straight, flat, heavily corrigated gravel road, CDL engaged or disengaged?

Most of the discussions to date have been in relation to cornering etc so I would be interested in opinions on the above circumstances where rapid and repeated loss of traction occurs.

[Naks]

Scenario - Straight, flat, heavily corrigated gravel road, CDL engaged or disengaged?

CDL locked.



I see no one has mentioned the main reason for NOT driving with a CDL on, in any case. That of the risk of binding up of the transfer case.

That only occurs when driving with the CDL locked on a sealed surface. IME, on dirt/gravel, there is enough 'give' in traction to not bind the transfer case. If it does bind, quick reverse for 2-5m should do the trick.

[isuzurover]

I see no one has mentioned the main reason for NOT driving with a CDL on, in any case. That of the risk of binding up of the transfer case. Other than that there is no particular reason for disengaging it,

That is my criteria/reasoning. When I am on a surface where there is no chance of windup occurring, I usually engage the CDL.

The centre diff is the weakest, most fragile part of the LT230. IMHO keeping the CDL engaged when offroad on loose surfaces can only help prolong the life of the centre diff.

EDIT - however I don't engage the CDL on bitumen - wet or otherwise.

[disco2hse]

That only occurs when driving with the CDL locked on a sealed surface. IME, on dirt/gravel, there is enough 'give' in traction to not bind the transfer case. If it does bind, quick reverse for 2-5m should do the trick.

Umm, yeah. That's the point I was making. :rolleyes:

As for reversing, that is likely to cause further damage if the transfer case gearing is already locked up. Disengaging the CDL while the gearbox is in neutral or between hi and lo ratio is safest.

[stig0000]

ok,, so now i can say how it was after driving a defender WITH the new ABS sys, it was in a 90 so they are abit twitchy on wet roads as is,

the sys is very fast to react, much better then the sys on the d2 but not as good as the freelander 2, when going around a known very slippery roundabout,

for a cross up situation without cld, it did stop as soon as the front lifted and took a fear bit of skinny pedal b4 it had enough go to move ford, dident feel much better then the current sys, just alot smother when activating,

but as you'd expect cld ON and over the same rut, the car walked it and the tc keeped things moving like you'd expect, left at engine idle and the engine compensated well for the tc activating and reving up slightly

this was on very wet grass over a prity big gutter on the side of a rd, and prity slipry, the new tyres seemed ok but i think id still want the old grabbers back on;)

just my thorts after driving one,

[rick130]

Scenario - Straight, flat, heavily corrigated gravel road, CDL engaged or disengaged?

Most of the discussions to date have been in relation to cornering etc so I would be interested in opinions on the above circumstances where rapid and repeated loss of traction occurs.


CDL locked.

[snip]


I'd go along with that, the shock loading going back through the gears is pretty high as you hit each corrugation at speed so anything to minimise or avoid the impact on the centre diff gears is good.
As Ben said, it's the weakest part of the t/case.

[Xtreme]

I'd go along with that, the shock loading going back through the gears is pretty high as you hit each corrugation at speed so anything to minimise or avoid the impact on the centre diff gears is good.
As Ben said, it's the weakest part of the t/case.

Thanks for reply.
So if engaging CDL on corrugated road reduces 'the shock loading back through the gears ...... " would this not also be the case when travelling on any gravel road where traction is likely to be lost, however infrequently, and therefore be a reason FOR engaging CDL in such circumstances?

[disco2hse]

Thanks for reply.
So if engaging CDL on corrugated road reduces 'the shock loading back through the gears ...... " would this not also be the case when travelling on any gravel road where traction is likely to be lost, however infrequently, and therefore be a reason FOR engaging CDL in such circumstances?

He was referring to the specific case of corrugations being a potential cause of failure in the transfer case where the drive chain is weakest. The surface, I think, of the corrugated roads he is referring to are mostly gravel. But, a gravel road or may not have them, and the surface can vary significantly, as has already been said. You cannot extrapolate his conclusion to therefore include every gravel road.

Again. The only positive reason for not having the CDL engaged is the risk of binding up, although I think that speed was mentioned too. Binding up will only occur in those cases where traction cannot be lost. Therefore CDL can be engaged at any other time when traction is lost.

The choice is then when to use it. The are many models and each has their own idiosyncrasies. Add to that the surfaces over which the vehicle is driven, the wetness/dryness, the condition of the vehicle itself, and lots of other factors. When to use the CDL is up to the driver and their expertise.

Alan

[BigJon]

When to use the CDL is up to the driver and their expertise.

Alan

Ain't that the truth! :cool:

Praise be for manual vehicle controls, rather than having a computer deciding what is best for you!

[rick130]

Thanks for reply.
So if engaging CDL on corrugated road reduces 'the shock loading back through the gears ...... " would this not also be the case when travelling on any gravel road where traction is likely to be lost, however infrequently, and therefore be a reason FOR engaging CDL in such circumstances?

I don't know if anyone has ever lunched a centre diff just from pounding around in high range, but how you'd measure a cumulative effect of shock loading or overloading on gears and bearings I'm buggered if i know.

We've all heard stories of people exploding the centre diff in low range though, all that torque going through some small side gears just spits pieces everywhere, this is less likely to happen in high range as theere is far less torque multiplication.

What i was thinking out aloud about was I remember my old kart engine builder built rally cars in another life time (he was sponsored by GMH for a number of years) and they always told me that the shock loads from jumps and corrugations was pretty high back through the transmission and IIRC was worse if you back off at the wrong times, ie. the peak of the bumps as it loaded the gears on the coast side and that usually broke gearboxes.