ozjeff62 wrote:

...............Every tyre on a car rotates at a different speed and covers a different distance when cornering - the diffs easily compensate for that. .............It's when diffs get locked that there is a problem. But ours are always open........

Am I missing something?

As far as I understand it the Haldex is preloaded to transmit a certain amount of torque to the back wheels whenever you move off from standstill, and remain doing this until about 19mph is reached.

From the repair manual

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.

I also believe that the control of the amount of torque transmitted above this speed depends on a lot more than just wheel speeds, and this is what make the FL2 so good in poor traction conditions.

The control module, attached to the casing of the active on-demand coupling, forms a single unit with the control
valve/axial solenoid.

By analyzing information from other vehicle modules and sensors the control module regulates the
axial solenoid to control the hydraulic fluid pressure supplied to the clutch plates. Some of the modules and sensors the
control module communicates with are listed below:

Hardwired:
- Control valve / axial solenoid
- Electric hydraulic pump
- Oil pressure and temperature sensor

High speed CAN (controller area network):
- Engine control module
- Anti-lock brake system / traction control module
- Traction response switch
- Yaw rate sensor
- Steering wheel rotation sensor

The axial solenoid constantly adjusts the control valve output using a Pulse Width Modulation (PWM) signal. The fluid
pressure delivered to the clutch plates determines the amount of torque that is delivered to the rear axle FL2 XS SD4 Auto 2010 2012-2017 (21k - 91k miles) (MY2011)
FL2 Metropolis SD4 Auto 2014 2017- (16k - 77k+ miles) (MY2015)
Metro in its 11th Year of (Extended) LR Warranty / Full LR Service History
(Expensive, but Trouble/Worry free - hopefully?)

Ian,

That is excellent information.

I really like how my Gen 3 Haldex works.

But now that I read your post the Gen 4 seems like a better choice and you you are really making me want one.

In fact I was impressed by how well the system works even before I understood anything about it.

This feature of my LR2 exceeded my expectations and it continues to do so even after 13 years of ownership. And it is significant enough of a feature that it has left me with the impression that the team at Land Rover really understood their customer and what features to optimize to meet their customer's needs. In our modern world of generic soulless cars, attention to detail and acknowledging the voice of the customer is very uncommon. Well done Team Land Rover.

Looking at you signature Ian it looks like you own a Gen 3 and Gen 4.

Can you tell the difference on a rainy or snowy day?

Edit: I looked at the Bell Engineering page and it looks like both of your Land Rovers are 4th generation

Ian you can ignore my question (but if anyone reading this can compare the generations please do so)


Thanks again for sharing

Paul