can somone give me a dummis guide to haldex units

Me old mans ones has just been repaired but his been told it aint a fix. So wtf is it and whats to do when it goes wrong? Cheers.

I suspect they are to complex for there own good. The Haldax failed on my wife's VW Tiquan at 55K miles so this problem isn't confined to LR.

goonarmy said:

Me old mans ones has just been repaired but his been told it aint a fix. So wtf is it and whats to do when it goes wrong? Cheers.

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The basis of the Haldex coupling is a swash plate pump with the swash plate on one half of the coupling & the pistons on the other half, if the two halves of the coupling are spinning at the same speed the swash plate & pistons are also spinning at the same speed & the pump does not produce any pressure, when the front half of the coupling is spinning faster than the rear the swash plate depresses the pistons as it rotates relative to the rear. The pressure produced is used to apply pressure to a wet clutch which partially locks up & drives the rear half. This pressure can be regulated electronically to produce part of the terrain response trickery.
Some manufacturers & I think Land Rover is one have different ratios in the front & rear diffs (a la Freelander 1) so that the pump is always producing some pressure & is ready to do its magic at the drop of an electron

do they have issues with clutches ?

jamesmartin said:

do they have issues with clutches ?

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Dont know what the failure mode is but wet clutches are usually pretty reliable, think its more likely the pressure regulator which must have some sort of electrical connection

matacaibo said:

Dont know what the failure mode is but wet clutches are usually pretty reliable, think its more likely the pressure regulator which must have some sort of electrical connection

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they are but usually in locked /unlocked mode ,ive never had anything to do with haldex units so is interesting

jamesmartin said:

they are but usually in locked /unlocked mode ,ive never had anything to do with haldex units so is interesting

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They have been around for years & are fitted to many 4 wheel drive vehicles, Volvo X70 & the 4 wheel drive version of the Audi TT, dont think they have a bad reputation actually considering, not like the Freelander 1s VCU lol

I have posted the info on here several times. It is effectively an electrically controlled VCU which can be off, automatically controlled by the control module or locked .

So for me dad to say its broke-were ticking, was it running dry? And wil it need replacing? Sounds expensive. He were quoted best part of 2k.

goonarmy said:

So for me dad to say its broke-were ticking, was it running dry? And wil it need replacing? Sounds expensive. He were quoted best part of 2k.

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I know that the clutch pack failed on our VW Tiguan. It would have cost something like £1800 to fix but luckily it was under warranty

All Mode selectable all wheel drive system - normally front wheel drive vehicle, in AUTO mode rear axle engages when front wheels start to slip, power is variably distributed from 100:0 to 50:50 front to rear. In AUTO mode the system works as an automatic all wheel drive system.

In 2WD mode, the clutch is unlocked permanently. However, even when in 2WD mode, rear wheels can sometimes be engaged by electronic control unit, for example under heavy acceleration.

In LOCK mode the tranfer clutch is permanently locked - power distribution 50:50. If vehicle speed increases, the vehicle automatically goes to AUTO mode, then, when speed decreases, it switches back to LOCK. When transfer clutch oil is overheated, the vehicle goes into 2WD mode.

Figure: Nissan X-Trail All Mode 4wd system description

goonarmy said:

So for me dad to say its broke-were ticking, was it running dry? And wil it need replacing? Sounds expensive. He were quoted best part of 2k.

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It was ticking !!

The Mad Hat Man said:

I have posted the info on here several times. It is effectively an electrically controlled VCU which can be off, automatically controlled by the control module or locked .

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id say its more a wet clutch with variable clamping force

jamesmartin said:

id say its more a wet clutch with variable clamping force

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Whatever. yu know best

The Mad Hat Man said:

Whatever. yu know best

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mardy pants ,in its basic function it appears so using shaft differential to supply oil pressure,and your latter electomagnet clutch ,how ever fantastic the electronics are or do ,i like to know how it works mechanically

The X trail has a different coupling, the pressure on the clutch is controlled by an electromagnet pushing a control clutch which in turn applies pressure to the main clutch.
The FL2 has a 3rd generation Haldex coupling which actually has a pre charge pump as well as a swash plate pump which in the FL2 has 6 pistons

matacaibo said:

The X trail has a different coupling, the pressure on the clutch is controlled by an electromagnet pushing a control clutch which in turn applies pressure to the main clutch.
The FL2 has a 3rd generation Haldex coupling which actually has a pre charge pump as well as a swash plate pump which in the FL2 has 6 pistons

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cheers matacaibo your straight forward info earlier meant i learned something new

This is the Haldex coupling in its simplest form

matacaibo said:

The X trail has a different coupling, the pressure on the clutch is controlled by an electromagnet pushing a control clutch which in turn applies pressure to the main clutch.
The FL2 has a 3rd generation Haldex coupling which actually has a pre charge pump as well as a swash plate pump which in the FL2 has 6 pistons

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yup
X-trail is 2nd generation. Freelander 2 is 3rd gen. Haldex are now shipping 5th gen units. All are subtly different, but similar in principle.

Gaylanders aint selectable are they? His xtrail was but that hardly ever got used. So were does the faults come from? Dirty oil? Low oil?