I found this, from the good oil, to be most informativeQuote:
Originally Posted by gavinwibrow
Posted by Pedro the Swift;
This from URBAN PANZER,,
Heres a "few" scenarios REF Diff locks and ETC, you will see that the Defender ETC works a little different to the D2. The FACTS below
With respect to the mechanical effect of adding traction diffs with or without CDL, it breaks down like this:
Without CDL:
No traction diffs: 1 wheel must turn
1 Traction diff: 1 wheel must turn
2 Traction diffs: 2 wheels must turn (both on same axle)
With CDL:
No traction diffs: 2 wheels must turn (one on each axle)
1 Traction diff: 3 wheels must turn
2 Traction diffs: 4 wheels must turn
This will tell you that fitting a single traction diff is a total waste of time if you can't lock the CDL. Fitting 2 traction diffs offers no more traction and is in practice inferior to just adding CDL (CDL ensure drive to both axles and is approx 1/5th the cost). This is why most people agree that the single most effect traction modification is to add CDL.
Given that you have a traction diff installed it is 200% more effective if CDL is engaged. With 2 traction diffs installed they are 100% more effective if CDL is engaged.
It is for this reason that I chose to install CDL first then fit an ARB locker to the rear. This guarantees 3 wheels must turn with ETC assisting on the front axle. This provide awesome traction and no bad handling traits whatsoever.
What happens if you add ETC into the equation?
ETC for all its mysteries simply applies the brakes to a wheel that the ABS sensors detect is spinning faster than the others. The more mechanical diff locks you have, the less ETC will have to do, as more of the wheels are mechanically forced to turn at the same speed.
There are 8 possible diff combinations for the DII:
Standard - Front Diff Open, Rear Diff Open, Centre diff Open:
Mechanical Result: all four wheels may spin at different speeds.
ETC solution: compare speed of each wheel to that of the average of all four and apply brake to up to three wheels at any one time if their speed is greater than the average.
(Note: This is how the standard DII ETC program works. It needs to compare each wheel's speed to that of the average of all four. As designed, the DII's ETC needs to be able to apply the brake to up to three wheels simultaneously. This gives it the ability to send power not only across each axle, but also from front to rear. This is why it is said to function diagonally.)
Front & Rear Diffs Open, Centre diff locked:
Mechanical Result: Wheels on each axle may spin at different speeds but average speed of wheels on front & rear axles is the same.
ETC solution:-compare speed of wheels across each axle, apply brake to up 2 wheels, one front and one rear at any one time if their speed is greater than opposite wheel on same axle.
(This is the standard ETC program for the Defender Extreme. Its program needs only ever to compare the speed of each wheel to its opposite number. It only ever needs to send power across each axle. This is why the Defender Extreme ETC is said to work across the axle.)
(Note D11's ETC will compare each wheel to average and will only ever find one wheel on each axle that is spinning faster than the average, therefore will operate correctly.)
Front diff Open, Rear Diff Locked, Centre diff locked:
Mechanical Result: Wheels on front axle may spin at different speeds. Average speed of wheels on front & rear axles is the same. Speed of both rear wheels is the same.
ETC solution: compare speed of wheels across front axle, apply brake to which ever front wheel is spinning fastest.
(Note: DII's ETC will compare each wheel to average and will only ever find one front wheel spinning faster than average, therefore will operate correctly)
Front diff Locked, Rear Diff Open, Centre diff locked:
Mechanical Result: Wheels on front axle must spin at same speed. Average speed of wheels on front & rear axles is the same. Rear Wheels may spin at different speeds.
ETC solution: compare speed of wheels across rear axle, apply brake to which ever rear wheel is spinning fastest.
(Note: DII's ETC will compare each wheel to average and will only ever find one rear wheel spinning faster than average, therefore will operate correctly)
Front diff Locked, Rear Diff Locked, Centre diff open:
Mechanical Result: Wheels on front axle must spin at same speed. Front & rear axle may spin at different speeds. Rear Wheels must spin at same speeds.
ETC solution: compare speed of front and rear axles, apply brake to both front Or both rear wheels to slow which ever axle is spinning the fastest.
(Note: DII's ETC will compare each wheel to average and will only ever find that both front or both rears are simultaneously spinning faster than average, therefore will operate correctly)
Front Locked, Rear Diff Locked, Centre diff Locked:
Mechanical Result: All wheels must spin at same speed.
ETC solution:-None required, no matter which way it compares it can't find any difference in wheel speeds so does nothing.
(Note: DII's ETC will compare each wheel to average and will never find any wheel spinning faster than the average, therefore will operate correctly)
** Front open, Rear Diff Locked, Centre diff open:
Mechanical Result: Wheels on front axle can spin at different speeds. Front & rear axle may spin at different speeds. Rear Wheels must spin at same speeds.
ETC solution: compare speed of each front wheels and rear axle, apply brake to up to three wheels, i.e. both rear and one front, or both front or one front.
(Note: DII's ETC will compare each wheel to average and will find that one or both fronts are spinning faster than the average, both rears are simultaneously spinning faster than average, or both rears & one front are spinning faster than average, therefore will operate correctly)
** Front locked, Rear Diff Open, Centre diff open:
Mechanical Result: Wheels on front must spin at same speeds. Front & rear axle may spin at different speeds. Rear wheels can spin at different speeds.
ETC solution: compare speed of front axle to each rear wheel, apply brake to upto three wheels, ie both front and one rear, or both rear, or one rear.
(Note: DII's ETC will compare each wheel to average and will find that one or both rears are spinning faster than the average, both fronts are simultaneously spinning faster than average, or both fronts & one rear are spinning faster than average, therefore will operate correctly)
** This is why ARB advise that there is little point installing a locker without CDL as it still require brakes to be applied to up to three wheels, as does the standard DII.
So basically :-----------
What this all means is that the DII ETC programing simply becomes more redundant as mechanical locks are installed. But no combination of lockers can ever cause it to incorrectely detect which offending wheel needs braking. It just that more simple programing could have done the same job.
The only shortfall with the simpler program of the Defender Extreme is when the Extreme doesn't have its CDL engaged it cannot force power fore and aft, so can only ever force power to the wheel with the second least amount of traction. The DII can always force it to the one with the most traction.
Once CDL is engaged, both systems will work in effectively the same way.
(Note: Throughout, "Traction diff" refers to either a front or rear aftermarket diff lock or limited slip diff, e.g. ARB Air Locker/Detroit Tru- Trac
