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Hi,

I recently put my 2005 Freelander V6 in for MOT, it was perfectly fine and I expected it to pass.

Unfortuantely it failed on the front tyres and also the back box of the exhaust was blowing a little bit and needed to be replaced.

The garage replaced the front tyres (with a different make to the back) and the back box of the exhaust (non genuine).

Since then there is a loss of power, a vibration when I drive and a strong smell of gas inside the car. Also the VC is piping hot after a few miles.

The garage have told me that the VC has gone and that it is a coincidence and not related to anything they have done. I don't know a great deal about cars so can someone please tell me if I am being lied to by the garage? I have read that if you are only replacing two of the four tyres in a 4x4 transmission then it should be the rear tyres that you replace...is this true?

I would be really grateful of any helpful comments as I am not sure what to do.

Many thanks
 

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I have always heard to replace all four tires at the same time as to not damage the VC. If the tires have different outer diameters the Viscous Coupling will always be working and it would probably overheat as you mentioned and cause a failure.

Inside this coupling there are discs attached to the center shaft and seals that hold a variable viscosity oil inside the shell of the “outer shaft”. During normal driving conditions when all the wheels are traveling at the same RPM this oil is thin and there is no coupling and the car is driving in a front wheel drive manner. This is because the inner and outer walls (front and rear driveshaft) are moving at the same speed and there is no relative motion in the oil. It is just dragging the rear wheel along. When the front wheels would start to slip that shaft would turn faster than the other; churning the oil and thickening it transferring power from the slipping wheels through the oil to the rear wheels. This action happens instantaneously. The oil thickens to the point where it acts like it is a solid coupling even if it’s only for some microseconds.

If your tires in the front are smaller it would have this effect constantly.

I would buy a matching set for the rear and in a hurry.
 
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