Thread: When to lock CDL

Originally Posted by rick130

i call BS.

I lived in roo central, drove dirt roads every day for 20 years and the amount of BS I read here sometimes we need a bloody D12 CAT to get through.....

If you want to lock the bloody thing fine, but saying you need to lock it, inferring it's unsafe without is utter crap

I have lived in "Roo Central" for the last 15yrs, That's why the Missus and myself drive 4WD's and not the little townie buzz boxes nearly everyone else drives.
Using the 4WD's for touring is just an added benefit for us because a 4WD is essential to be able to use the roads around here especially in winter.
I don't use the CDL or engage 4WD on the Tojo around here in summer because the roads are all hard packed gravel/clay and I travel them pretty much every day But in winter or when I am traveling on an unknown dirt road I have always used 4WD and since owning the Discovery I have engaged the CDL.
Why do I do this?
I do this because that is why I bought the 4WD for in the first place and that's to have good control on loose or slippery surfaces, If I didn't engage 4WD/CDL I may as well be driving one of those townie buzz boxes.
Anyway if Ashcrofts recommends engaging CDL on loose surfaces I tend to respect his opinion over ANY member of an internet forum

Originally Posted by djam1

I think there is a great diversity of experience here
Many city drivers that probably find dirt roads a novelty others have lived for years in the bush where driving on dirt is a daily event.
A couple of thousand ks of dirt roads while you are on holidays or a weekend in the mountains is vastly different than living in Yuendumu for 20 odd years and different practices arise.
The Defender instructions are "The differential lock should only be engaged when traction is likely to be lost"
and "a single axle roller rig may be used up to 5 kmh The Differential Lock must be disengaged" covers it
Like wise the swerving for wild life most who live in the country dont do it, its better to hit roos, emus than roll a Defender over.

I agree with this. I do like having CDLs locked for the stability they offer in braking and the occasion sideways drift over corrugations or pot holes. This is something no stability control or ATB setup will react to fast enough whereas a CDL is always there. But yes, if I lived on a road and knew it well, I probably wouldn't bother.

I find it interesting the comments from Ashcroft on the wear encountered inside the diff with one wheel spinning - you would think it wouldn't be a problem in a well lubricated unit... in my experience as a mech, I have not seen a failure that wasn't user driven.

Every Centre Diff failure I have seen has been in an LT95 I understand that the reason for failure is centrifugal force spinning the oil away from the critical components.
Might it be also that the engine oil recommendation for LT95s were a contributing factor?
I agree never seen a failed one that wasnt either driver apathy or ignorance

Another point is that there was a season of D2s that didnt have a CDL the manufacturer must of had reasonable confidence that the Centre Diff could survive. The TC was pretty rudimentry and took quite a bit of slip to get it to work.
Maybe these shouldnt be driven on dirt

Originally Posted by Arch

I find it interesting the comments from Ashcroft on the wear encountered inside the diff with one wheel spinning - you would think it wouldn't be a problem in a well lubricated unit... in my experience as a mech, I have not seen a failure that wasn't user driven.

Originally Posted by djam1

Every Centre Diff failure I have seen has been in an LT95 I understand that the reason for failure is centrifugal force spinning the oil away from the critical components.
Might it be also that the engine oil recommendation for LT95s were a contributing factor?
I agree never seen a failed one that wasnt either driver apathy or ignorance

Another point is that there was a season of D2s that didnt have a CDL the manufacturer must of had reasonable confidence that the Centre Diff could survive. The TC was pretty rudimentry and took quite a bit of slip to get it to work.
Maybe these shouldnt be driven on dirt

Well that is interesting about the LT95... yes it could have been the wrong spec, simply not enough oil or a manufacturing/design issue. We can only speculate as other diffs do perfectly well in an environment where the oil is spun away from the centre.

Yes, it was an interesting move on the D2s. I find this tend towards electronic traction controls is simple marketing. Some of it is very good to get you though the occasional problem... but not nearly as good as a diff lock. Interesting example of the G300 where the professional model despite all the fabulous trickery available to Mercedes, the professional has old school diff locks.

...after reading some excellent comments here and hearing Dave Ashcrofts advice, I’ll now be locking my CDL on all dirt road surfaces, even seemingly hard packed ones, from now on.
...definitely until I’ve saved enough for ATB’s and perhaps even with ATB installed in some circumstances, as they strengthen diff centres.

Originally Posted by 1nando

[...]A defender is only ever spinning one wheel when the centre diff is unlocked.

I think I get what you meant to say above (...that it only takes one wheel free spinning to unload the whole driveline, when centre diff is unlocked. Assuming also no TC etc).

Not quite true to say that a defender is only ever spinning one wheel, even it if is the most common scenario. It takes talent, skill, and devilishly good looks - but I have certainly had both fronts, both rears, or diagonals wheelspinning before cringing and remembering late to engage the CDL.

Originally Posted by 1nando

Now lets think about this;
[...]True 4wd requires the centre diff be locked.

Okaaaaaaaaay..... am calling this out too.
In a vehicle with open diffs (front, centre, rear) and no TC:
- Locking the centre diff just moves from the above situation (any ONE wheel freespinning unloads the whole drive train), to...
- a situation where the whole driveline is unloaded when ONE front and ONE rear are freespinning. (e.g. crossaxled)

"True 4wd" surely must require both front and rear diffs to be locked too. Locking just the centre diff is just a halfway step in that direction. Yes?

If locking the centre diff is such a good thing to do then locking all 3 diffs must be so much the better! Yes?

No.

I doubt anyone here will advocate locking all 3 diffs the moment you leave the tarmac - we all are so clever we know that we'd have a terrible time steering with all 3 diffs locked. Well.... not all the time, but sometimes.

Guess what... just locking the centre diff also has an undesireable side effect. It is just less tragic, less noticable, than driving around with all 3 diffs locked. It goes like this:
- we don't lock our centre diffs on the tarmac because we will get transmission wind up. We all know what causes that.
- if you jack up a wheel when there is significant transmission wind up present... just before that wheel leaves the tarmac it will slip/skid a bit and release the tension.
- on looser surfaces, even hard packed clay, that same little bit of wheel slippage on the track surface is going on and on and on - constantly as you drive down the trail.
- when there is no centre differential in play (not there, or locked) you are in effect going to have one wheel (any one of the 4, randomly) experiencing a little breaking of traction constantly.
- Is this "true 3 wheel drive"? Albeit somewhat "quantum" in nature since you can never really know which of the 4 wheels will be slipping at any specific instant.

- and under some situations this forced breaking of traction causes significant understeer. Not all the time, but certainly sometimes and its never a highly desireable handling trait.

This is also written up in the third epistle of Ashcroft to the unwashed about the benefits of the holy centre ATB:
"...when racing fast on a low traction surface, the vehicle will not handle well when locked but is likely to wheel spin when unlocked." (i.e. so buy an ATB from Ashcroft being the prescribed solution, so you can have the best of both worlds. Or possibly - leave the thing unlocked, don't be racing so hard on the throttle, avoid wheelspin that way and don't buy an ATB?)

One does not have to be "racing" and the surface does not have to be "low traction"... I have experienced sphincter clenching moments tootling along just a little too fast on a dirt road when a sneaky off-camber bit mid bend caught me by surprise - understeer causing me significant angst. Making me think that had I NOT locked the CDL - I'd have likely driven the bend much more comfortably with just a little "Tokyo drift" avoiding any one wheel wheelspinning wildly by lifting the throttle pedal just a little for balance.

I actually think the best handling situation is being able to drive all wheels differentially as needed on most surfaces - just avoiding wheelspin like the plague. For that open diffs will suffice if you have a good feel for the loud pedal to avoid wild wheelspin. If lacking that skill then:
- the poorest solution is to take all diffs out of the equation (3 locked)
- less poor but still not the best, take just the centre diff out of the equation (lock it, live with having a random wheel breaking traction at every moment)
- best driver aid being to fit ATBs all round to allow differentiation and control (within its limits) wheelspin.

If the only tool in the toolkit is a hammer (or a centre diff lock), then the best you might be able to do is to be wise about when to use it. When to lock the CDL. And when not to.

Very nice work Quantum Neil.

Roger. As said, Lock CDL off tarmac. Get ATBs asap.

Originally Posted by tact

I think I get what you meant to say above (...that it only takes one wheel free spinning to unload the whole driveline, when centre diff is unlocked. Assuming also no TC etc).

Not quite true to say that a defender is only ever spinning one wheel, even it if is the most common scenario. It takes talent, skill, and devilishly good looks - but I have certainly had both fronts, both rears, or diagonals wheelspinning before cringing and remembering late to engage the CDL.




Okaaaaaaaaay..... am calling this out too.
In a vehicle with open diffs (front, centre, rear) and no TC:
- Locking the centre diff just moves from the above situation (any ONE wheel freespinning unloads the whole drive train), to...
- a situation where the whole driveline is unloaded when ONE front and ONE rear are freespinning. (e.g. crossaxled)

"True 4wd" surely must require both front and rear diffs to be locked too. Locking just the centre diff is just a halfway step in that direction. Yes?

If locking the centre diff is such a good thing to do then locking all 3 diffs must be so much the better! Yes?

No.

I doubt anyone here will advocate locking all 3 diffs the moment you leave the tarmac - we all are so clever we know that we'd have a terrible time steering with all 3 diffs locked. Well.... not all the time, but sometimes.

Guess what... just locking the centre diff also has an undesireable side effect. It is just less tragic, less noticable, than driving around with all 3 diffs locked. It goes like this:
- we don't lock our centre diffs on the tarmac because we will get transmission wind up. We all know what causes that.
- if you jack up a wheel when there is significant transmission wind up present... just before that wheel leaves the tarmac it will slip/skid a bit and release the tension.
- on looser surfaces, even hard packed clay, that same little bit of wheel slippage on the track surface is going on and on and on - constantly as you drive down the trail.
- when there is no centre differential in play (not there, or locked) you are in effect going to have one wheel (any one of the 4, randomly) experiencing a little breaking of traction constantly.
- Is this "true 3 wheel drive"? Albeit somewhat "quantum" in nature since you can never really know which of the 4 wheels will be slipping at any specific instant.

- and under some situations this forced breaking of traction causes significant understeer. Not all the time, but certainly sometimes and its never a highly desireable handling trait.

This is also written up in the third epistle of Ashcroft to the unwashed about the benefits of the holy centre ATB:
"...when racing fast on a low traction surface, the vehicle will not handle well when locked but is likely to wheel spin when unlocked." (i.e. so buy an ATB from Ashcroft being the prescribed solution, so you can have the best of both worlds. Or possibly - leave the thing unlocked, don't be racing so hard on the throttle, avoid wheelspin that way and don't buy an ATB?)

One does not have to be "racing" and the surface does not have to be "low traction"... I have experienced sphincter clenching moments tootling along just a little too fast on a dirt road when a sneaky off-camber bit mid bend caught me by surprise - understeer causing me significant angst. Making me think that had I NOT locked the CDL - I'd have likely driven the bend much more comfortably with just a little "Tokyo drift" avoiding any one wheel wheelspinning wildly by lifting the throttle pedal just a little for balance.

I actually think the best handling situation is being able to drive all wheels differentially as needed on most surfaces - just avoiding wheelspin like the plague. For that open diffs will suffice if you have a good feel for the loud pedal to avoid wild wheelspin. If lacking that skill then:
- the poorest solution is to take all diffs out of the equation (3 locked)
- less poor but still not the best, take just the centre diff out of the equation (lock it, live with having a random wheel breaking traction at every moment)
- best driver aid being to fit ATBs all round to allow differentiation and control (within its limits) wheelspin.

If the only tool in the toolkit is a hammer (or a centre diff lock), then the best you might be able to do is to be wise about when to use it. When to lock the CDL. And when not to.

With centre diff unlocked power only ever goes to either the front or rear axle not both at the same time. So your comment about having all wheels spinning with a open centre diff means that the TC is working to lock the spinning wheel cause your prop shaft is spinning around stupidly and all of a sudden power goes to the next axle where there is the least resistance causing that wheel to spin, prop spins stupidly again all before the TC does its job again.....this will go on until you blow the centre diff. This is a fact and needs to be understood! Dave Ashcroft explains this in a youtube video!

A defender is not a AWD subaru! So dont say it is cause thats what your implying it to be, BS! It does not automatically send power to both front and rear axles at the same time unless the centre diff is locked. This is why people install atbs!

The amount of BS on this site drives me insane. Tact i respect the majority of your input most times but you've missed the mark on this one mate. I stopped reading after your comment on all 4 wheels spinning with the centre diff unlocked.

As for locking all 3 diffs for better control. Of course you wouldnt do that. Only time i did was in very slow, extremely complicated terrain requiring zero steering input where loss of traction was expected.

Rally cars have a very sophisticated AWD system becuase it helps keep the car stable and controllable on fast dirt, snow, gravel etc.....but according to most on this site they should all be driving a unlocked (centre diff) defender. Its not BS to state that a defender has much better vehicle control off tarmac with the CENTRE DIFF LOCKED and staying at speeds around 80kmph or less.