Have you just replaced the two front tyres on your Freelander 1, and now have all sorts of noises happening beneath you?
Have you just had a puncture and replaced that one tyre to save some money, and are now faced with a staggering bill to repair your whole drive train?
Are you thinking of changing the tyres on your Freelander? – read this article to make sure the only bill you end up with is the one for the tyres!
The Freelander 1 is in constant four wheel drive. The system operates with an IRD (transfer box) connected to the gearbox at the front. This is what effectively drives all four wheels. The IRD is connected to the front wheels by the front drive shafts; and to the rear wheels via a front prop shaft, which connects to the viscous coupling unit (VCU) halfway along the Freelander, through a rear prop shaft which goes into the rear differential and then to the two rear drive shafts.
How does the Freelander Four Wheel Drive Work?
The viscous coupling unit (VCU) – if you take a look underneath your Freelander this is the bulbous piece half way along the prop shaft – is filled with a viscous fluid and two sets of vanes, one linked to the front prop shaft and one to the rear prop shaft. In normal driving conditions the viscous fluid remains, well, fluid! This is because the vanes for the front and rear are spinning at about the same speed. Hence it is primarily the front wheels that do most of the work, and the rear wheels just follow behind.
When in difficult conditions, such as snow or mud, if one or more of the front wheels start to slip they spin faster, and hence the vanes in the VCU also spin faster. This increased agitation within the viscous fluid causes it to stiffen and hence engages the rear wheels to the drive system. So now the rear wheels will push the Freelander out of the snow or mud. Once you are out of the situation and all four wheels are moving at the same speed, the viscous fluid liquifies again and you are back to what is effectively front wheel drive.
How does the Freelander viscous coupling unit (VCU) fail?
Effectively there are two ways a VCU can fail, one is very rare, and that is when the viscous fluid no longer stiffens and you are effectively running in front wheel drive all the time. The worst outcome of this is that in the mud and snow you become stuck – no other damage will be done to the drive train.
The second, most common VCU failure is due to the VCU seizing – effectively the viscous fluid is stiff all the time. This will start to happen naturally at around 70,000 miles, hence the importance of changing your viscous coupling unit regularly; however other things can cause the same effect – such as a mismatch of tyres.
What is the importance of matched tyres on a Freelander?
Having unmatched tyre sizes on a Freelander 1 creates the same effect as a seized VCU, and can cause catastrophic damage to your drive train in just a few miles. A seized viscous coupling unit will put a strain all the way along the drive train, from the IRD / Transfer Box at the front (and even as far as the gearbox) through the VCU bearings, to the rear differential at the rear. If you continue to drive the Freelander with a seized VCU then you could cause irreparable damage to all these parts.
The crucial thing is to make sure you match tyre manufacturer, type and size on all four wheels of your Freelander (please note that even if you match the tyre type and size then there can be enough of a difference between the sizes from two different manufacturers to cause the VCU to seize – the tolerance level is only 5mm). If you really cannot afford to replace all four tyres at once then you may be able to get away with replacing just two from the same axle (i.e. the two rear tyres or the two front tyres – never replace just one tyre, and never replace one from the front and one from the rear), but make sure you get the same manufacturer, type and size as the ones that are remaining on the Freelander, and put the newest ones on the rear – but we really would recommend changing all four at the same time.
How can you tell if your viscous coupling unit (VCU) has seized?
Well, there are a couple of tell tale signs that your viscous coupling unit is seizing. One sign is when you are turning on full lock, either forwards or reverse, your Freelander will feel tighter than usual, a little like the brakes are on. A seized VCU also tends to cause unusual tyre wear, often around the edges of the tyre or on alternating blocks. The other thing to check, particularly if your tyres may be the problem, is the temperature of the VCU after you have driven it for a few miles. The VCU should remain cool to touch – but be careful, if you have mismatched tyres it can become very hot – so don’t blame me if you burn yourself when trying to touch it, you have been warned! If your VCU is getting too hot to touch this is putting tremendous strain on the drive train – DO NOT DRIVE YOUR FREELANDER ANY FURTHER! You need to sort your tyres out as quickly as possible – or remove the prop shaft until you can – or you might find your bank account emptying very quickly as you have to replace the IRD / Transfer box, the rear differential and even possibly the gearbox!
How do you check if your tyres are all of the same size?
It’s not the size that is printed on the edge of the tyre that is important to the Freelander drive train, it’s the actual physical size – don’t get these two confused! Tyres of the same size and type, from the same manufacturer, fitted at the same time should cause you no problems. Tyres of the same size and type from two different manufacturers could cause you a problem – be warned!
What is important is the rolling radius of the tyres (in other words the circumference). However, the easiest thing to measure is the diameter of the tyre, that is from one end of the tyre to the other, straight across the middle. To measure this make sure your Freelander has all four wheels on the ground (preferably flat ground) and that all tyres are correctly inflated, then balance a plank of wood on top of the tyre, so it is parallel with the ground, and measure the distance from the ground to the bottom edge of the plank. Remember, the tolerance in the difference in tyre sizes for the Freelander 1 drive train is only 5 mm, so measure carefully. And as a precaution check the temperature of your VCU after you have driven a few miles.