centre difflock switch 24v

[Towpack]

The owner's manual advises to use H ratio, CD unlocked for "Normal driving on all types of road from dry, hard surfaced to wet, icy or snow covered roads. This gives greater economy, quietest ride, least wear and better vehicle control"

For H ratio with locked CD it says, "Use this for greater traction when you experience loss of power, such as wheel slipping in the CD onlocked mode".

OK, so you could say the second bit contradicts the first bit to a degree but, IMO, there is no reason to use a locked CD on the road, that's what the VC is there for and in doing so you are pushing your luck and risking potential damage either short or long term.

 

[Chris]

Disagree I'm afraid, but that's the beauty of a free county isn't it? The VC only does so much. I have driven on snow covered roads with it unlocked and locked and the stability with it locked is vastly improved. Like I mean vastly. I drove from here to Ipswich one Christmas in my 120 with it locked virtually all of the way. My impression of the VC is that it does supply power to the front wheels yes, but in a sort of 'token' way. If you are on snow and you accelerate slightly the back end fishtails about all over. CD in and you can feel the front pulling and the back pushing - if that makes sense. From memory the VC supplies between 50% and 0% torque to the front with a corresponding 50% to 100% to the rear. The only time it gets 50% at the front is when it had total grip. OK could be wrong, but that's my understanding. So when you are on something less grippy, the front does slide a bit and this robs it of torque? The back wheels, being driven directly get min 50% no matter what - yes? Could it be that the VC is more about supplying 'slip' between the front and rear to avoid wind up than it is about actually supplying major usable DRIVE to the front wheels? Discuss.

I do not make a habit of driving around under normal conditions with it locked. But if it's only to be used when you are in an off road situation - why did Toyota provide us with a high range centre lock in the first place? I use my high, low, lockers etc on pretty much a weekly basis and have done on 5 cruisers now. No ill effects that I have seen.

The choice is everyone's to make, but I feel that anyone coming along for the first time reading some of these will get the impression that using the CD will result in immediate damage to their 4x4 mechanism.

Just my thoughts

Chris

 

[ajnabi]

How about one of these?

http://www.ebay.co.uk/sch/i.html?_n...r=true&_nkwusc=toyota+tracktion+switch&_rdc=1

Just to report back that the RAV4 Traction Switch did indeed fit and work as intended.
However the CDL graphic on the switch does not illuminate when the button is pressed compared to the original which does.

So the known switches to work other than the original are:
Hazard Warning Light
RAV4 Traction Switch

Moving on... I had the same issue with CDL locked in High Range on tarmac.
Turning a corner slowly resulted in some strange noises coming from the CV's joints, I believe (could be something else upfront).
Details of LC below.

hmmmm.... would dearly like to know if this is normal, which by the sounds of other peoples comments it is.
I do know that there is play in my current CV's (recently repacked)...
but I would have imagined the front diff (as does the rear diff) would have compensated for the difference in rotation (even on tarmac).

*shrug*....confused.

 

[Jon Wildsmith]

when you turn, the front and back wheels take different routes so the speeds will be different. Axle diffs can only compensate for differences between the wheels on that axle.

 

[Towpack]

Could it be that the VC is more about supplying 'slip' between the front and rear to avoid wind up than it is about actually supplying major usable DRIVE to the front wheels? Discuss.


Chris

IMO both. Useable drive to F & R which would be lost with a 'standard' open diff, and no windup, as with a locked CDL...on some cars!? My 80 certainly handles and drives much better in snow than my Disco did and the only difference, transmission wise, is the VC.

You could also ask why Toyota fitted a VC? I've already posted my opinion on that one.

As to the question that I guess everyone wants answered of why similar vehicles wind up and some don't, I have absolutely no idea! What we need is some Toyota transmission guru who actually knows for sure, to read this and post up. Anybody out there!!

Ajnabi,

IMO the symptoms you get with a locked CDL are normal but, as you have read, others will say and have experienced otherwise.

The axle diffs cannot compensate for the difference in rotational speed between the front and rear. If they could there would be no need for a centre diff.

Phil

 

[Andrew Prince]

From memory the VC supplies between 50% and 0% torque to the front with a corresponding 50% to 100% to the rear. The only time it gets 50% at the front is when it had total grip. OK could be wrong, but that's my understanding. So when you are on something less grippy, the front does slide a bit and this robs it of torque? The back wheels, being driven directly get min 50% no matter what - yes? Could it be that the VC is more about supplying 'slip' between the front and rear to avoid wind up than it is about actually supplying major usable DRIVE to the front wheels? Discuss.

Under normal conditions (all 4 wheels with equal grip/friction driving in a straight line) the drive split between front and rear will be 50:50 through an open CD. Presumably the VC allows a slight speed differential so that the front axle can turn faster than the rear when turning sharply for example. The VC locks up when there is a significant enough speed differential between the front and rear outputs. When the VC is locked, the split between front and rear is forced back to 50:50, assuming the VC can lock completely.
Sure the VC may allow a bit of limited slip while the rheopectic ( ) fluid heats up and eventually locks solid - how long this takes, I'm not sure but in my experience it's very quick, maybe a second. Of course, the beauty of the design is that as soon as the speed differential between front and rear is equalised, the VC is no longer driven and therefore stops heating up and stops its locking action. Of course the VC when locked will no longer generate the speed differential required to keep it locked, so will unlock and relock as conditions dictate (wheels spinning or not)The driver may conclude that the VC "switches" on and off quickly but it's more down to the front and rear props spinning at equal speeds again.

So Chris I have to disagree with your theory that the VC supplies between "50% and 0% torque" to the front. If the VC is engaging then it will supply a 50:50 split when it locks (assuming no slip in the VC), and it will lock quickly if a speed differential continues. It works on speed rather than torque - the two may be related but the VC does not not react to differing torque, it reacts to differing speed.

Interesting piece of kit and definitely a nifty bit of engineering from Mr T!

 

[ajnabi]

Jon/Phil (Towpack), thanks, it makes sense now.

Just have to be careful when to engage and up to what speed.

IQ

 

[Dave Docwra]

I would always engage mine when stopped, obviously no need to engage if you are entering and exiting roundabouts and very sharp bends at high speeds as the road surface is grippy enough and cd is not required.

Any difference in speeds between front and rear axles will be overcome by tyre slip on the loose / wet surface you are travelling on, I am sure MrT built the system strong enough to fit a switch to later models for when these circumstanceas change, as I said in an earlier post when my switch was engaged my LC was a much beter vehicle to keep pointing in the right direction, it reduced the oversteer immensly, so on really poor surfaces I would suggest to engage and enjoy.

 

[adrianr]

Fully Agree about using CDL on loose surfaces. makes the handling very predictable and less twitchy.

"Any difference in speeds between front and rear axles will be overcome by tyre slip on the loose / wet surface you are travelling on, "
And yep gotta agree 100%.

Caveat:
I took a sharp left on a track yesterday and normally i would disengage the cdl to make the corner, this time i didnt and my reward for driver error and not concentrating enough .... the tyre slip on the loose wet surface did its thing, understeer and front went wide and i slid ever so slowly into a drainage ditch at the front and marshy area at the side.

 

[Chris]

Phil - are you saying that a Disco doesn't have a VC in the middle? I have never owned one (nor really want to). I didn't know that. I have to say that in standard form, maybe with half decent tyres, the Disco is pretty good off road. I see a lot at P&P days where they gamely charge through stuff. If they don't have the advantage of that mechanism, then actually they have gone up slightly in my estimation.

Andrew - the torque split isn't a theory of mine. I read it somewhere, that was all. I gain a lot from reading these posts - I'm not just picking a fight you know. I actually benefit greatly from what you lads write. But sometimes I do struggle to match the theory with the reality that I experience. If that makes sense. So I don't quite get how the discussion about drive and torque can be separate. I'm working on it but I am not completely convinced that the VC can totally lock. If it did then why have a CDL at all? Having driven mine, as you all have, extensively off road. I know that when it gets tricky, you don't get full drive and the CD L is a must. So what is happening there? Front wheels have no grip so are whizzing around - massive front to rear speed difference, so why is the VC not locked up as you say giving equal drive. Is it because the rear wheels have more grip therefore are sending ALL the drive forward - is that possible? I thought the rear wheel were permanently driven with the fronts 'slaved' off the rear via the VC.

Hey, maybe mine is bust in some way and this is why my reality doesn't match your theory. But it is very good off road so it cant be very broken! I do have a spare VC.

Ready for next lesson.

Chris

 

[Jon Wildsmith]

The centre diff splits the torque equally between front and rear, no slaving involved The VC bridges the two outputs of the centre diff it just happens to live in the rear output housing, so if the front slips the VC will ensure some drive is sent to the rear, it works both ways round not only if the rear slips. I was never able to make my VC lock on my 80 when I experimented with a prop removed, there was always very limited drive and I've experimented with that on 3 80's now.

 

[Brett]

Phil - are you saying that a Disco doesn't have a VC in the middle? I have never owned one (nor really want to). I didn't know that. I have to say that in standard form, maybe with half decent tyres, the Disco is pretty good off road. I see a lot at P&P days where they gamely charge through stuff. If they don't have the advantage of that mechanism, then actually they have gone up slightly in my estimation.

Chris, none of the LT230 gear driven transfer boxes have a viscous coupling. The Range Rover was produced with a Borg Warner fully Viscous coupling type transfer box for some model years (can't remember which) but it was never very well regarded in offroad circles, fine for on road driving but off road you never acheive 100% lock so most offroad enthusiasts swapped them out for the LT230.

As you mentioned about the Land Rover performance offroad, on paper lots of the japanese trucks should perform better than Landys, but the Land Rovers still seem to outperform the majority, considering no Viscous coupling or axle difflocks. Shame they break so easily & rot so bad

 

[Towpack]

Chris,

My Disco was a 300Tdi which had 3 standard diffs and a CDL, no VC or cross axle locks. Not sure what the later models are equipped with. What you had in snow & ice was, effectively, as little as 1 wheel drive with the CD unlocked. This is not how my 80 behaves in the same situation. I once inadvertantly ran the Disco up onto a large block of stone in graves Park (don't ask ) which lifted the front OS wheel in the air and it was immobilised with the wheel spinning. Locking the CD got me out of trouble by driving the rear wheels.

Dave & adrianr,

I agree 100% with the loose gravel offroad scenario which will allow wheel slippage and avoid windup but, IMO a wet tarmac road surface still has far too much grip available to offer enough slippage to prevent windup with a locked CD. At least, this is what I've experienced with my 80 and the Disco.

John,

Your experience with a prop removed is similar to what I had when I removed the front prop trying to diagnose a transmission whine. Reduced but useable drive thanks to the VC. No idea of the %age torque spit but it would drive. With the CD locked the acceleration/drive felt normal. I'm sure relying solely on the VC in this scenario would overheat and ruin it.

 

[Chris]

All - interesting stuff.

Jon, duly logged and noted. I wonder if the 90 is different in this respect and maybe that's where I have this in the back of my mind.

I can't answer the CDL locked on 'drier' surfaces argument, but what I can say is that clearly Mr T did design a very well mated 4x4 mechanism that is able to cope extremely well with what we think it shouldn't. Yes, I get that the front and rear wheel sets describe different arcs when turning but on a long even bend such as a motorway, the difference between front and rear 'ruts' must be minuscule. At a T junction or anything approaching that, you will leave 4 completely separate tracks behind you.

I do get that for every revolution that goes into the T box, it must be split evenly across all 4 wheels, whether that it 25% equally in a straight line or something crazy that adds up to 100%. Anything outside that is wind up, or skidding. Agreed. I just think that, as I said, it's so well built that this spilt is well managed, so the rears may well be doing 55% - 45% and the fronts doing 60% - 40% but somehow it manages that front to rear split so the the actual rotations of the props are not that far apart. Perhaps it's very clever steering geometry on the front wheels. Or perhaps every LC that I have owned had a fnurked CD

Good fun. Keep it up.

Chris