I've just been watching an old 'how to drive off road' video and they were describing transmission wind up when off road etc and just wondered if this was still an issue for modern day land rovers? including the FL2 or is it a thing of the pass thanks to terrain response?

Gary

The FL2 can suffer transmission wind-up in the special program modes, which is why it is recommended not to use special programs on the road (unless in snow or ice). I've not tried this, but I suspect that setting M&R, for example, and doing tight turns somewhere like a car park would demonstrate this quite nicely!

Don't think it's a problem as the diffs don't physically lock on the freely as I understand it.
I could be wrong though?

Front and rear diffs don't lock (the brakes are used to control slippage), however, the center 'diff' (Haldex) does effectively lock under certain conditions and that can lead to wind-up. The different programs use a variety of parameters to decide when to lock and when not to, with the 'normal' program attempting to avoid wind-up, whilst the special programs tend to assume that the ground surface will be low grip and therefore traction is more important and wind-up can be released through slippage of the wheels.

As an example, all programs usually move off from rest with the Haldex 'locked' in order to give 4WD and maximum traction on any surface. In normal mode, however, the system uses steering angle to determine whether wind-up is likely, and if it is (i.e. if you're moving off with the wheels turned) the Haldex is set to allow some slippage. In the special programs steering angle is largely disregarded as traction is assumed to be the priority.

Note, BTW, that front and rear diffs don't lock on a standard Defender either - just the centre diff. So an FL2 with locked Haldex is effectively in the same configuration as a Defender with diff lock engaged.

So wind up should never be an issue then as the haldex should not lock up the front/rear wheel drive if wind up is possible?

In 'normal' mode that's true, but in special programs modes it's not - priority will be given to traction so wind-up can occur. In practice it shouldn't be a problem as special programs should usually only be used where there's limited traction, so wind-up can dissipate easily through wheel slippage. If special programs are used on high-grip surfaces, however, wind-up can occur.

This is how LR put it:

Quote:

Vehicles fitted with Terrain Response also add further benefits by varying the level of pre-charge to deliver optimum traction over a range of different terrain surfaces. The level of pre-charge is varied depending on the particular terrain response mode, for example:

Terrain response in 'Special Programs Off' mode as common with vehicles without terrain response, the coupling is programmed to transmit 500 Nm 369 lb ft of torque on Generation 3 couplings and 1500 Nm (1106 lb ft) of torque on Generation 4 couplings to the rear axle when the vehicle moves from rest in a straight line. This strategy minimizes traction loss from a standing-start regardless of the terrain. When the vehicle accelerates the pressure in the coupling is decreased to improve fuel economy.

The ability to sense the steering angle allows the coupling to be programmed to provide no torque transfer through the coupling. This prevents the coupling locking when the vehicle is maneuvring at low speeds and acute steering angles.

In 'Grass / Gravel / Snow' mode the coupling is programmed to maintain its pre-charge state until much higher speeds are obtained. The same applies even if the vehicle is traveling at low speeds and acute steering angles, as traction takes precedence over coupling lock-up on low-friction surfaces.

Exactly so the haldex would not lock up in m+r on the road as it would not need to?

As soon the control unit felt that wind up/conditions etc did not need the haldex clutch to engage then it wouldn't and wind up could not occur?

anyone know which Haldex system the FL2 uses? Or does it depend on the age of the car?

Gen 3 pre-MY09, Gen 4 MY09 onwards.

The Haldex will still lock up in M&R on the road, working to the same parameters as it would off-road (as it doesn't know what surface it's on). At higher speeds the lock will release whether off road or on, but up to that point the coupling will remain locked and wind-up can occur. This is why LR warn that continued use of special programs on high-friction surfaces can affect the durability of the drive train.

ok, cheers for that!

pab wrote:

Gen 3 pre-MY09, Gen 4 MY09 onwards.

The Haldex will still lock up in M&R on the road, working to the same parameters as it would off-road (as it doesn't know what surface it's on). At higher speeds the lock will release whether off road or on, but up to that point the coupling will remain locked and wind-up can occur. This is why LR warn that continued use of special programs on high-friction surfaces can affect the durability of the drive train.

The Haldex actually locks up as soon as you start the car, irrespective of TR mode. (The exception being special programs off and steering wheel turned from the straight-ahead position, in which case the Haldex doesn't lock.) This gives maximum traction for moving off, whatever TR mode you're in and whatever surface you're on. So even in 'normal' mode on tarmac the car moves off with the Haldex locked unless there's significant steering offset.

Then, as the car's speed rises, the Haldex will gradually release to give predominantly front-wheel-drive. At any speed, and in any mode, the Haldex will re-engage if wheel slip is detected.

What varies in the different TR modes is primarily the speed at which release takes place (higher in the special programs modes) and whether any notice is taken of steering angle (not in the special programs modes).

Thus, the only reason wind-up tends not to be an issue with the special programs is that the terrain tends to be low-friction and thus the wind-up releases naturally via wheel slippage.

So to answer the ops question wind up is not an issue as the haldex would disengage in any mode before the trans was loaded up.

I understand what the haldex unit is doing, but dull question alert: what is transmission "wind up"? 2010 Freelander 2 HSE Auto Santorini Black / Ebony Leather

Transmission wind up, is caused by the front and rear wheels traveling at different speeds round corners. This is because the outer wheel is traveling round a larger circle than the inner wheel, so the outer wheel actually goes round more and travels a greater distance than the inner wheel.

The differentials, one in each axle, share out the power to the wheels, so that the outer wheels when turning a circle can rotate faster than the inner wheels. All cars have differentials otherwise the car would not be able to turn a corner very well. One wheel would always be dragged round rather than pushing the car round. On a four wheel drive car these differentials are still permanently attached to the engine at one point. The front pair of wheels are also traveling at a different speed to the rear wheels, when traveling round corners. This can mean that the drive shafts, which at one point are connected together, are traveling at different speeds, gears eventually mesh tightly and the drive axles twist. Sometimes a wheel will spin to release pressure, but on Tarmac with good grip this is unlikely

Knicked from Google as my explanation was turning in to an essay!