Back in the winter we had some snow. The LR2 acted as if the rear wheels weren’t engaging. Last week I did a brake job. While it was jacked up, all four wheels, I tested it and only the front were spinning. The rear were not spinning any, not 10%, -0-. Is this normal? How do I determine if I have a problem?

 

Start by finding out if the computer has any relevant error codes. If you don't have a reader you can go to just about any major auto parts store and they will read them for you. WRITE THEM DOWN.

 

That is probably normal. The rears are not normally driven, only when the computer traction system determines a need (saves gas).

The prop shaft rotates all the way back to the front of the rear diff. There it connects to the Active On Demand Coupler (aka the Haldex). The haldex unit is a clutch system which instantly connects the prop shaft to the rear diff input to drive the rears when needed.

I'm not sure if you can test it accurately when jacked up without any load... it may well need some engine load above idle so it knows it's not just coasting down a hill. There should be DTC codes if somethings wrong... I'd be surprised if there weren't warning messages on the dash too.

As an aside if you only drive on non-icy pavement, the haldex might never engage. I try to engage it a couple times a year just to exercise it's mechanism... gun the motor hard from a standing start on snow, ice, sand, or gravel. Same with the ABS, I do hard stops on snow/ice occasionally.

 

Of course, the parking brake was disengaged?

 

<rimshot!> I've always considered Captain Obvious to be a severely underappreciated superhero. <chuckle>

 

I remember posting, but losing my WiFi and couldn’t tell if it went through or not.

The emergency brake was not engaged.

I have been trying to learn and understand the Haldex system.

I will run a code check and get back to you.

Thanks,

A. B.

 

This thread interests me. My understanding of Haldex is different than yours.

Yes, its true that the rear drive component of the vehicle is enabled by electronics and managed by the traction switches.

As for Haldex: https://en.wikipedia.org/wiki/Haldex_Traction
And this does activate the rear drive shaft to the differential; which in turns through the clutch system of Haldex enables one rear wheel.
Should there be wheel “slip” the Haldex clutch system allows the other rear wheel to engage??
(seems to be a pretty fancy, electronic, delicate system in comparison to a good old fashioned mechanical LSD but what do I know)

Either way, this does beg the question ‘WHY’ does Quaife offer a mechanical LSD for our vehicles and ‘HOW’ does this work in cooperation with Haldex?

Please correct my understandings!

 

My understanding is that the haldex (active on demand coupling) just provides torque to the rear diff, then the diff allocates it between the rear wheels as needed. The traction system also includes transmission, engine, and ABS so the rear wheels can also be managed by differential braking via the ABS.

From the shop manual....

DIFFERENTIAL
The differential unit is a low-offset-hypoid spiral-bevel design, based on a 167mm crown wheel geared to deliver a ratio of
2.58:1. The design of the differential gears and the 4 mountings that control the torque reaction of the unit within the rear
subframe, provide a differential unit of excellent efficiency and refinement.
The torque delivered to the differential is controlled by the active on-demand coupling, mounted into the void at the front
of the differential's cast-aluminum casing, which also provides the oil reservoir for the coupling.

Active On-Demand Coupling Control
The active on-demand coupling control module has 2 operating strategies; pre-emptive and reactive.
The pre-emptive strategy anticipates and predicts the locking torque value required to minimize slip and maximize
stability. Each Terrain Response program has a different threshold and input criteria for the pre-emptive strategy. For
example, a higher locking torque would be applied on slippery surfaces.
The reactive strategy varies the amount of locking torque in response to the actual slip level and the dynamic behavior of
the vehicle. Each Terrain Response program has a different threshold and input for the reactive strategy. The reactive
strategy improves vehicle traction and composure by eliminating any wheel spin which has occurred after the pre-emptive
strategy was applied. The locking response applied is applicable to the terrain program selected. For example, very
sensitive on slippery surfaces to provide maximum traction and minimize surface damage.
The locking torque calculations use various signals from other sub-systems, for example, engine torque, accelerator pedal
position, selected gear, steering angle, vehicle speed, lateral acceleration, yaw behavior.
The DSC function of the ABS system can override the active on-demand coupling control and reduce any applied locking
torque during DSC action.

The active on-demand coupling provides the benefits of a permanent 4x4 system with the efficiency and economical
benefits of a part-time system. Located between the differential and driveshaft, the coupling is a self-contained unit
combining mechanical, hydraulic and electronic functions to distribute drive between the front and rear axles with
transparent automatic control.
The active on-demand coupling provides the following functions:
Electronic management of torque transfer.
Rapid engagement in response to traction demands.
Rapid disengagement to ensure its operation cannot corrupt wheel speed signals and compromise stability control
system operation; this is especially important on very low friction surfaces.
Pre-engagement from rest to minimize the risk of wheel-spin.
No opposing forces when maneuvring or parking the vehicle.
Not sensitive to brake testing on a chassis dynamometer.

Generation 4 Active On-Demand Coupling - Vehicles from 2009MY
The generation 4 coupling does not have the differential speed driven pump used on the previous generation 3
coupling, but is fitted with a bigger capacity electrically operated axial pump and a high pressure accumulator.
The proportional throttle valve and pressure sensor on the generation 3 coupling is replaced with a proportional
pressure reducing valve.
The torque limiter pressure reducing valve on the generation 3 coupling is replaced by an electronic control valve
and controlling software.
The generation 4 active on-demand coupling gives the following improvements over the previous generation 3 coupling:
Reduced base torque at high differential speeds
Torque activation is now independent of differential speed
Accurate torque limiter control
Energy stored in high pressure accumulator giving a low maximum current consumption of the electric pump and
faster response.

 

:-(. I wish I had a late model shop manual.

 

I downloaded in a pdf from somewhere years ago, i'll email it to you if you like.