WHAT DOES MY FREELANDER’S VCU DO?

lro

QUESTION: I’ve been told that the viscous coupling on my 1999 Freelander 1.8 petrol is bound to fail at some point and that it’ll cost a fortune. Can you tell me what this part does? What are the warning signs when it starts to go wrong?

ANSWER: The Freelander has an intermediate reduction drive (IRD) attached to the gearbox. This supplies drive to the front and rear axles. This rear axle drive goes through a propshaft to the viscous coupling unit (VCU), then through a second in-line propshaft to the rear axle differential. The VCU is midway between the rear propshafts.

viscous WHAT DOES MY FREELANDERS VCU DO? Freelander 1’s famous (or should that be infamous?) viscous coupling unit

In road driving, the front wheels do most of the work and the rear wheels more or less trail behind, with the VCU providing four-wheel drive if needed. In the VCU are two sets of vanes, one linked to the rear propshaft, the other to the forward propshaft. The vanes are immersed in a viscous fluid that stiffens if it is agitated. In normal driving, front wheels rotate at a similar speed to the rears, so the alternate vanes of the VCU are also rotating at similar speeds. If the front wheels lose grip they spin faster, while the rears stay at the same speed. This causes the vanes connected to the front propshaft to spin faster than those connected to the rear shaft, so the fluid inside gets churned up and becomes stiff. That produces a solid drive through the VCU so the front propshaft begins to turn the rear propshaft at the faster speed, thus transmitting drive to the rear wheels. The rear wheels now push the car until the fronts find grip. When grip is regained, all the wheels are rotating at the same speed, so the VCU frees up and you’re back in front-wheel drive.

When using full steering lock at slow speed, you may need more accelerator to overcome the tightening of the VCU. This is normal, but avoiding full lock or keeping the speed as low as possible during such manoeuvres helps prolong the life of the VCU.

The VCU can fail in two ways. It’s rare for a VCU to fail free, (ie, incapable of putting drive to the rear wheels). If this happens, there will be no indication during normal driving, but if the front wheels lose grip you’ll become stuck because drive won’t be transmitted to the rear wheels. Apart from becoming stuck, this condition will not cause further damage to the vehicle.

The most common failure mode is seizure. This means you are in four-wheel drive all the time, and the VCU’s centre differential effect is lost. This shows up as unusual tyre wear, causing the edge blocks of the tyre tread to chamfer or for alternate blocks to wear down. It will also make the steering feel unresponsive or jerky, and the steering’s natural tendency to self-centre will be reduced.

If the VCU seizes, it puts strain on the rear differential and the front IRD, especially the IRD’s pinion and output bearing. It also puts extra load on the VCU support bearings. If you detect a seized VCU, you should have it checked and replaced quickly. Noise from the area of the VCU is likely to be worn support bearings.

Because the IRD exerts a slight gearing effect between front and rear drive, incorrect tyre sizes can alter this to produce the symptoms of a seized VCU, and to load the transmission in a similar way. The critical dimension is the rolling radius of the tyres, measured from the wheel centre to the ground, with the vehicle’s weight on correctly inflated tyres. Because actual sizes vary between tyre manufacturers, it’s worth ensuring the same make of tyre is fitted to front and rear. If differing makes are fitted, or just two tyres need to be renewed, ensure the tyres with the greatest rolling radius are fitted to the rear. This makes life easier for the VCU and the whole transmission. Ed Evans

The above content originally appeared in LRO magazine and is reproduced here with their kind permission.  Any advice or opinions are those of LRO magazine and its writers.

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Comments 13

13 Responses to WHAT DOES MY FREELANDER’S VCU DO?

  1. Rob says:

    Excellent article. Really helpful for people looking at buying a Freelander as well as those that already own one!

  2. Andy Cutler says:

    Great info on the workings of the freelander 4×4 sytem.

  3. eliot everton says:

    my freelander is making a juderring sound when i go arrond corners,can i fix this my self and save money,or is it going to be a big jo,what is it i need!!!!!!?

    • eva says:

      This had been happening to me, then my power steering colum failed, get this checked.
      Hopefully its not this as part alone cost £270

  4. eliot everton says:

    how much are the rubers, on the diff,thers two about 3 foot apart.could i fix this my self.

  5. eliot everton says:

    how do i fit ,,,monster wheals to freelander,i think the freelander get”s bad credit.!!!!! my freelander does very well compaird to a lot of 4%4 off road ,,,ill prove peaple rong,its still a landrover,but PADOCK MOTORS@MATLOCK!!!!dont do much for them,its a shame because it such a good bissness,its all good if you whant brake pads,”,but-”you can get THEM els wear for cheaper anyway,IT A SHAME, because its locall to!!>>>>.thers alot of peaple with freelanders,!!!!!!!!!!!!!!!!!! LANDROVER.>BE PROUD.

  6. Les Dalton says:

    Could someone lease answe this question.
    I have just bought a 2001 Land Rover Freelander with the 2 litre Turbo Diesel engine.
    The VCU siezed up with the previous owner, which led to him having a 5000 euro replacement fitted, it currently runs on 2wd only, which we find no problems with, my question is this, if we continue to tun it on 2wd, could it cause more mechanical problems to any part of the transmission train?
    Another problem I have found with it, is when you kick down to overtake (auto box) it appears to try to change between 2 gears and does not feel right, also under hard acceleration, it feels like the engine is hitting a governor!!! someone said this could be linked to a faulty FLOW METER?
    Any ideas anyone?
    Thank you in anticipation of some repllies,
    Les Dalton,
    Charmant,
    France.
    Thank you

    • Les Dalton says:

      Further to the above message, it was a 5000 euro replacement GEARBOX that was fitted.
      Regards,
      Les.

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  8. source says:

    Fantastic Stuff, do you have a facebook account?

  9. Steve says:

    when replacing the bearings on the VCU which way around do the 2 washers face.?

  10. TonyR says:

    Could someone help me please..l have a Freelader Seringetti 1,2003,1800cc Petrol. The Viscous Clutch the the center of the drive shafts has broken apart..Its the large round outer ring that looks like there are clutch plates inside.It has dropped onto the narrow shaft thats just before the rear bearing.Could anyone tell me what has happened to it,and what i need to do ? l can’t use the car because of the banging of this round metal outer clutch case hitting the underside of the body work

    Tony…

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