Handbraked VCU Symptom

Read this somewhere but cant find it now.

When you turn into a carpark space or reverse out of one it feels like the handbrake has come on and slows the car.

Is this a normal symptom or a sign of VCU failure?

Badger_1 said:

Read this somewhere but cant find it now.

When you turn into a carpark space or reverse out of one it feels like the handbrake has come on and slows the car.

Is this a normal symptom or a sign of VCU failure?

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Anything which causes the rear propshaft to turn at a different speed from the front propshaft will cause the two sections of the VCU to turn at different speeds, and that will tend to make it start locking up.

Turning ANY corner, will cause this to a slight amount, but in normal driving the difference in rotation should be so slight that the VCU doesn't respond by locking up. But, on full lock, especially going on full lock backwards, and quickly, the VCU could easily start to cut in. You might notice this in heavy steering, and a bit of tyre noise and a feeling of drag.

Moral: take it easy doing full-lock manoeuvers in a Freelander.

CharlesY

mine has similar problems so i had vcu checked and it was ok been told it could be fault with ird.Just dont worry about it seems like alot of freelander owners have this problem and just live with it

It's normal for em to drag thert feet a bit in full lock forards or backads mine does same

This test seems to be invented to convince you to get the VCU changed I don't belive it, mine has been doing it for 40K miles and it's got no worse.

Boxer said:

This test seems to be invented to convince you to get the VCU changed I don't belive it, mine has been doing it for 40K miles and it's got no worse.

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Thats the kind of good news we like to hear.

Going do the tippex test tomorrow just to be sure. Believe I have to mark the 2 propshafts and not the VCU as some have done.

Boxer said:

This test seems to be invented to convince you to get the VCU changed I don't belive it, mine has been doing it for 40K miles and it's got no worse.

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Just so.

The VCU is a VISCOUS Coupling Unit, like a viscous coupling fan.

In the VCU, the design allows the two sections of it to rotate at different rates. There are a whole lot of discs attached to each shaft, and they are interleaved one for one, close together, with silicone goo between them. If one shaft rotates slightly slower or faster than the other, the goo gets pulled, and provided that happens very slowly it will let the discs move at different speeds, even though it drags a little bit. But if teh speed difference increases, the sllicone gunge inside starts (instantly, by the way) to refuse to move quickly, and so it causes a huge drag between the two sets of discs, almost but not quite acting like a single shaft. This effectively creates a strong drive to the other shaft AS LONG AS THE FRONT SHAFT IS TURNING FASTER THAN THE REAR ONE.

This is a bit of a problem because in effect it means there will be no 4 wheel drive unless at least one of the front wheels is actually slipping.

It may be a bit late by then to apply 4-WD.

CharlesY

i posted some pics. which may help on this thread
http://www.landyzone.co.uk/lz/f9/vcu-again-52387.html

CharlesY - great explanation, with the 0.8% difference between early IRD/rear diff ratios, the rear wheels have an extra revolution in 120 revolutions. Does this mean the VCU is spinning / slipping, 3degrees in every 360degree rotation?

dose it feel worse when reversing a trailer? ((mine dose)
especialy up a slope

VCU should only slip if one back wheel needs to rotate quicker than the other, like when going round corners or spinning a rear wheel

ianda12 said:

VCU should only slip if one back wheel needs to rotate quicker than the other, like when going round corners or spinning a rear wheel

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surely thats the diff that allows that, the vcu only deals with power to the rear as a pair

If one rear wheel needs to turn faster than the other the diff can only allow that if the prop shaft can turn at a different speed, as this is goverened by the front wheels the VCU has to move. Unless the front wheels are in the air.

ianda12 said:

VCU should only slip if one back wheel needs to rotate quicker than the other, like when going round corners or spinning a rear wheel

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Not so.

The back wheels are not normally driven, and so you will never get into a situation of spinning one or both back wheels unless first the FRONT wheels are spinning after losing grip, or in the event the VCU is seized solid of course.

Going round corners should never cause enough shaft speeds differences to make the VCU lock up. The VCU is designed to allow that much variation so that in normal driving the car is front wheel drive.

CharlesY