Thread: Diff locks and traction control

Straight from the horses mouth.

Why do Land Rover transmission units fail? - ask the expert - YouTube

Originally Posted by tact

Absolutely!

An ATB is best described as an open diff that, by design, isn't very good at allowing differentiation to happen. The more weight on the driveline with an ATB in it (the more torque being applied) then the worse (by design) the ATB is at allowing differentiation.

My barge doesn't have traction control.

Thus with an ATB (and no traction control):
- if rolling along on a neutral throttle, very little "weight" on the driveline, very little torque applied.... then very little resistance to differentiation.

- if one or the other wheel is in the air there can be no "weight" on the driveline, no torque being applied (though a road wheel may be spinning off!) ... then also very little resistance to differentiation.

- if driving the wheels hard (forward or reverse) then the ATB resistance to differentiation will be magnified.... whether or not there is any call for differentiation action. i.e. can be "almost locked" in a straight line drive, or turning, if being driven hard.

- (as above on the overrun - wheels driving the engine when on a trailing throttle)

The behaviour noted in the above two points makes the ATB a "pre-emptive" traction aid so long as you keep the loud pedal engaged a bit (or keep the engine braking up).

But the moment you lift a wheel all bets are off. Some deft left foot braking, or some other aid like traction control, will have to kick in to keep you moving.

have is from the traction control[/QUOTE]

I agree the ATB is more of an LSD than a LOCKER. However it does lock and not slip like an LSD. So given the example of a lifted wheel the TC applies the load to the spinning wheel to enable the ATB to function, granted if the TC is not working you'll have issues unless you apply the brake yourself.

When there is a difference in wheel traction the ATB does in effect LOCK. So yes until you require a locker it is an open diff, and it does this automatically. This is arguably an advantage of a traditional locker.
I very rarely lift a rear wheel, but when I do the car does not stop. To clarify while throttle is required to drive the ATB at maximum potential, it does not mean you have to drive it like you stole it, only a small amount of throttle is required.

To say an ATB is not a locker is incorrect, it is a locking diff but only when you don't have traction, which is exactly when you need a locking diff.

From my experience 4WDing, unless you want to have a locker to have full control over traction aids, the extra expense of air lines or wires is a waste of time and money. I consider myself a pretty experienced 4WDer and have been around a bit and there is no track my ATB has not got me up the top.

To say an atb is a locker is incorrect! It is not, it is however a torque biasing diff. It does not lock!
And yes i have one up front and one in my transfer case.

Originally Posted by Jazzman

When there is a difference in wheel traction the ATB does in effect LOCK. So yes until you require a locker it is an open diff, and it does this automatically.

Gotta disagree here on two fundamental points.
1. I disagree with "...the ATB does in effect LOCK."

Quite the contrary - An ATB never "locks" fully. At best you can get maybe a 70/30 torque split. The only way to get full drive to one half shaft is to lock up the other halfshaft, stop it from rotating at all. (which would work on any diff - its not because the ATB "locked").

2. I disagree with "... until you require a locker it is an open diff"

The ATB will resist differentiation (but not lock) in proportion to the amount of load on the driveline
- regardless whether travelling in a straight line or turning,
- regardless whether on tarmac or ice.
- it is the amount of load, or "weight", or torque applied, onto the driveline that determines how hard, or how easy, it will be for the half shafts to rotate at different rates.
- and this resistance to differentiation, proportional to load on driveline, exists before its even needed/used. Before any differentiation action is even initiated. (by turning, or wheel slippage)

examples:
- If you are hard on the throttle on tarmac, even travelling in a straight line, the "weight" (applied torque) on the driveline overall is already causing the ATB to bind up (not lock fully) and make it hard for either half shaft to rotate slower or faster than the other.
- if you are on a light throttle, or coasting, such that there is little or no weight on the driveline then ATB effect is less but still present.

You mentioned climbing any hill you tackle easily with ATB's. I pretty much echo that. Whilst ever all wheels are on the trail, the hill climb puts a lot of weight on the driveline as you drive up. Thus lots of "resistance to differentiation" is already in play before any wheel even thinks about slipping. Almost like a locker, but its not "locked".

Once again, because of my rudimentary knowledge, I must default to the experts.

Ashcroft Transmissions

A very interesting post from an English Defender site.

DEFENDER2.NET - View topic - ATB (torsen) front and rear install

ATB is not a locker. Not ever. The way it's built literally prevents it from happening. End of.
They are an exceptionally nifty bit of kit, particularly in traction control equiped vehicles. They're on my list.
But they don't lock, and that's a fact jack

For questions regarding gearboxes/transfer cases, I find the Ashcroft Transmission web site is a wealth of information. They also have excellent you tube videos. For example, how the gearbox works. Here is the web site, with the frequently asked questions bit highlighted. [ most people probably know this, but for those who don't, I find the information really interesting. ]


Ashcroft Transmissions



here is the you tube video about the gearbox.


R380 gearbox how it works - ask the experts with Ashcroft Transmissions - YouTube