Thread: Diff locks and traction control

Originally Posted by DiscoMick

Interesting discussion.
All I would add is our D1 had a CDL, a rear auto locker, but no TC. It would spin a front wheel which had lost traction, but the rear would not spin because of the locker. If both rears were stuck it would not down and stall
Our Defender has a CDL, TC and anti-stall. The TC stops any wheel from spinning. The whole vehicle can beg down, but it won't stall because of the anti-stall.
I think the Defender's system is superior to what our D1 had. The TC is really effective and so far I haven't seen any advantage in adding a locker. Maybe if I was rock climbing it might be useful, but those days are over.
The only option I might consider is an ATB for the centre duff, to vary the front-rear torque split.

That's interesting to me. My D1 has a MaxiDrive rear locker, and (obviously), a CDL, and I have more confidence in it's off road capability than I do of my D2. The two cars have other differences, but not really enough to justify that statement. Perhaps there is something not quite right with my particular D2.

Originally Posted by AK83

So the traction control doesn't look at each wheel as an individual item, it only looks at each wheel on a per axle basis?

I ask this because I don't understand the traction control system on a D2.
My brother's D2 has diff locks front and rear, but no CDL.
I'm telling him the CDL is more important in many respects than front and rear difflocks, and trying to get him to do the CDL lever upgrade to give him more grip in all situations.

Happened a few months back along a couple of tracks that got him 'stuck'.
First was a very steep rocky climb, where first up the rears had grip and fronts (both) spun.
I got out of the vehicle to be sure that the wheels spinning were both on each axle, and sure enough fronts first spun up(ie. front locker working), then as he pushed a bit more with a bit of a run up, then the rears spun as they slid on the wet rock, both rears spun which confirmed that rear locker was engaged.
What didn't work so effectively was the traction control, which allowed each axle(ie both wheels per axle to spin too long).

I thought that the traction control(considering that no CDL is fitted) would minimise spinning wheels on a per wheel basis, rather than on a per axle basis.
On a D2 fitted with factory CDL, it'd make sense that wheel spin could be assessed on a per axle basis.

The other 'slip up' we encountered on this same trip(different track) was a large bog hole covered in water. Depth up to just below bonnet line, must have been slushy inside the water hole. One axle in, one axle out situation.
On entry into the hole, rears still on the solid high ground, car had forward motion. Once the rears dropped in, but at the same time front axle drove out, the front axle now with less weight on it, even tho it's on solid ground had no drive, and the mushy ground inside the water hole no enough grip to drive the rears out easily.
For my liking there was wayy too much front wheel(s) spin before they finally bit and pulled the car out.
Traction control didn't appear to help .. but of course can't tell.
For me standing outside watching it all, it seemed as tho 'Jeremy Clarkson style brute force and powwerrrr!!!' is what got the D2 out, rather than good traction and or traction control.

TC is looking at differences in average wheel speed between front and rear axles, and difference in speed between left and right.
If there is no speed difference across an axle the TC doesn't work. When the CDL is locked, both front and rear driveshafts are locked together, so there can be no difference in average speed between front and rear axle.

This is from RAVE...

At speeds up to 31.3 mph (50 km/h), ETC uses individual brake intervention to maintain even torque distribution between wheels on the same axle.

Vehicles up to 03 model year – At speeds between 0 and 62.5 mph (0 and 100 km/h), ETC also uses brake intervention in axle pairs to maintain even torque distribution between the front and rear axles. In effect, this modeof operation replaces the centre differential lock of the transfer box which, although still incorporated, is nonoperational under normal driving conditions.

Torque is balanced by applying braking torque to a slipping/spinning wheel. As mentioned earlier the wheel with least traction sets the limit to torque that can be transmitted by an open diff due to the 50:50 torque bias ratio. By applying braking torque to the wheel without traction increases the amount of torque that can be transmitted by the wheel with traction by the same amount.

The other factor is that tractive force - which is the amount of torque that can be transmitted to the ground - is determined by the surface, tyre characteristics, weight on each wheel, and torque. Dropping tyre pressure works by increasing the area and reducing the amount of tractive force per cm^2.

When you have situation where there is very little weight on the front wheels as in exiting the bog hole, the amount of tractive force that can be applied by the front wheels is significantly reduced, and the amount that can be applied by the rear wheels is increased.

TC can't increase the limit of traction on a wheel, it can only balance torque to the limit of traction.

Originally Posted by johntins

My understanding, and believe me, I could be wrong, is that the TC requires stored energy to operate the brakes for the TC to work, and that energy doesn't last long in prolonged low traction situations.

Braking force is provided by the ABS modulator pump.


The D2 brake system is basically a WABCO Series D system with "add-on" Hydraulic Anti-Lock Brake system...

This is from the WABCO HABS information - it corresponds to the RAVE information for cross axle ETC but provides a little more detail.

Purpose of electronic traction control (ETC)
In a speed range from zero to 50 km/h, electronic traction control ETC guarantees the maximum possible traction and constant vehicle stability with minimum steering intervention. If braking takes effect on a wheel which is spinning, the corresponding torque is transferred via the axle differential to the wheel with the higher coefficient of friction. The limits of traction control are represented by the maximum engine or braking torque and the available adhesion between the tyres and the carriage-way.

How the ETC system functions
The ETC system uses largely the same components as the ABS, i.e.wheel speed sensors, an ECU and a modulator with integrated ABS solenoid valves for each wheel. Using the ABS wheel speed signals, the algorithm in the ECU calculates the speed difference between the wheels on one axle. As a result, it can determine when a wheel is slipping excessively. The electronic control unit actuates the return pump and the ABS solenoid valves of the modulator in order to direct hydraulic power to the brake. The brake pressure is then adapted by the corresponding ABS solenoid valves of the modulator. The pressure at the spinning wheel is increased until the speed of both wheels is once again synchronised.

This means a torque is transmitted to the wheel which is not spinning. ETC is switched off as soon as the electronic control unit detects a fault in the vehicle wiring harness or in the system components.

Originally Posted by Pedro_The_Swift

I think the build dates for CDL is in TGO

Well, well, well, so they are: CDL in D2's

Originally Posted by land864

Is there an issue with fitting a rear diff lock and traction control

I have a TD5 D2a. It has a Centre Diff lock and a rear Ashcroft ATB Ashcroft Transmissions with the standard front diif.

This setup is the bees knees. Because mine is a D2a the traction control is less aggressive when the CDL is activated, this enables the ATB to kick in very well. Since fitting the ATB the traction control does not activate nearly as much, due to the amount a 4WDing I do it has also improved the life time of my brake pads a little. The ATB still works well when the traction control is at its most sensitive, I just prefer the way it drives when it is less sensitive.

I fitted the ATB as it meant I could have a locking rear diff without the need for airlines or electric solenoids etc. I can drive almost any terrain now, slippery clay up hill is still a small challenge. But wheel lifting is not an issue at all anymore, the combination of locking the centre diff and (when) the rear is locked gives me ample traction with plenty of steering control. It is very rare the traction control cannot sort the front out anyway.

You would have to be doing some real hard core 4WDing (rock steps for example) to need front and rear lockers, especially in a Disco they seem to just go everywhere. But it is 100% possible to have front, rear and centre diff locks with not issues. I wouldn't suggest front and rear lockers without a centre diff lock, you would be better off with centre and rear if you only had two.

Parting comment though, don't let anyone tell you traction control is a substitute for a locker! Sand dunes are the only off road terrain I've seen where a locker was counter productive (unless idling in gear).

If you would like to know more PM me.

Originally Posted by Jazzman

I fitted the ATB as it meant I could have a locking rear diff without the need for airlines or electric solenoids etc. I can drive almost any terrain now, slippery clay up hill is still a small challenge. But wheel lifting is not an issue at all anymore, the combination of locking the centre diff and (when) the rear is locked gives me ample traction with plenty of steering control. It is very rare the traction control cannot sort the front out anyway.

You would have to be doing some real hard core 4WDing (rock steps for example) to need front and rear lockers, especially in a Disco they seem to just go everywhere. But it is 100% possible to have front, rear and centre diff locks with not issues. I wouldn't suggest front and rear lockers without a centre diff lock, you would be better off with centre and rear if you only had two.

Ashcroft ATB is not a locker and will never lock. when one wheel on the axle with the ATB is in the air its just another open centre and the only help you have is from the traction control

I'd get front and rear aftermarket diffs and lockers of any reputable brand within my budget and fit stronger axles, not because of torque biasing or any of that other gobbledygook, but simply because Rover type banjo diffs are made of earwax and chalk.

TC with traction control is a great system, got me through a few spots... but it's more a reliability and upgrade thing for me.

Although with 200K on it I think I may be being melodramatic.

Originally Posted by komaterpillar

Ashcroft ATB is not a locker and will never lock. when one wheel on the axle with the ATB is in the air its just another open centre and the only help you have is from the traction control

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.