Might be a very silly question but ....

lenny1234 said:

So what the VCU has to do is be stiff enough to transfer some power to the rear wheels when the front are spinning, but not so stiff that the transmission winds up when turning a tight corner.

I am going to make the radical suggestion that the stiffness levels of those two conditions are MILES apart, and provided the VCU is somewhere in that range its 'working well enough'.

Click to expand...

lenny1234 said:

That is, unless its totally and utterly siezed solid, there is probably enough slip to avoid damaging the transmission.

Click to expand...

lenny1234 said:

So its unlikely that anything bar a totally locked solid VCU will damage anything.

Click to expand...

GrumpyGel said:

Absolutely - BUT working VCUs are engineered so they are transmitting bearing damaging torque at slippage much closer to turning corners than front wheels spinning - so when they start to go it gets to damaging levels.



I would suggest nobody uses this as a basis for running a reliable Freelander. It's a recipe for an expensive repair bill.



I would suggest nobody uses this as a basis for running a reliable Freelander. It's a recipe for an expensive repair bill.

Click to expand...

jamesmartin said:

?

Click to expand...

lenny1234 said:

I'm gonna throw in my 2 pennoth here.



What the VCU does is to lock front and rear wheel rates together. But allow for a bit of slip so you dont smash the transmission when doing tight corners.



Its a remarkably simple and effective way to get permanent 4WD on a vehicle without having complicated gubbins in the car to engage it etc.



So what the VCU has to do is be stiff enough to transfer some power to the rear wheels when the front are spinning, but not so stiff that the transmission winds up when turning a tight corner.



I am going to make the radical suggestion that the stiffness levels of those two conditions are MILES apart, and provided the VCU is somewhere in that range its 'working well enough'.



That is, unless its totally and utterly siezed solid, there is probably enough slip to avoid damaging the transmission, and unless its totally spinning freely by hand, there is enough stiffness to provide the get-out-of-mud-free card.



Judging by talking to people who fix hippos, its very rare to get the VCU gone, but its a great money spinner for garages.



I am suggesting that people not wrry about their VCUs - by all means do the torque test, but remember, the only thing a really stiff VCU will do is take a long time to unwind any front-rear wheel speed differential, and as long as it has some give and you dont spend your time going round and round in small circles, you wont be damaging transmission, In fact those of us who had locked solid 4WD in the old days on landies will know the sound of a rabbit hopping landy that unwound its transmission when a wheel skipped over a bump.



So its unlikely that anything bar a totally locked solid VCU will damage anything. Except the two items that go anyway - the centre rubber mounted VCU bearings.



I'd suggest that peole change those with good quality units and run their hippos 1000 miles or so if they get what they think are 'vcu issues' ...chances are that will solve any issues.

Click to expand...

lenny1234 said:

I'm gonna throw in my 2 pennoth here.

What the VCU does is to lock front and rear wheel rates together. But allow for a bit of slip so you dont smash the transmission when doing tight corners.

Its a remarkably simple and effective way to get permanent 4WD on a vehicle without having complicated gubbins in the car to engage it etc.

So what the VCU has to do is be stiff enough to transfer some power to the rear wheels when the front are spinning, but not so stiff that the transmission winds up when turning a tight corner.

I am going to make the radical suggestion that the stiffness levels of those two conditions are MILES apart, and provided the VCU is somewhere in that range its 'working well enough'.

That is, unless its totally and utterly siezed solid, there is probably enough slip to avoid damaging the transmission, and unless its totally spinning freely by hand, there is enough stiffness to provide the get-out-of-mud-free card.

Judging by talking to people who fix hippos, its very rare to get the VCU gone, but its a great money spinner for garages.

I am suggesting that people not wrry about their VCUs - by all means do the torque test, but remember, the only thing a really stiff VCU will do is take a long time to unwind any front-rear wheel speed differential, and as long as it has some give and you dont spend your time going round and round in small circles, you wont be damaging transmission, In fact those of us who had locked solid 4WD in the old days on landies will know the sound of a rabbit hopping landy that unwound its transmission when a wheel skipped over a bump.

So its unlikely that anything bar a totally locked solid VCU will damage anything. Except the two items that go anyway - the centre rubber mounted VCU bearings.

I'd suggest that peole change those with good quality units and run their hippos 1000 miles or so if they get what they think are 'vcu issues' ...chances are that will solve any issues.

Click to expand...

Nodge68 said:

Sorry fella but most of this ^^^^ is incorrect.
First off, a failed VCU isn't a money spinner for garages, if that were the case IRDs and Diffs wouldn't disintegrate, however they do. There are two possible causes for this. 1 incorrect mixes of tyres. 2 a stiffened VCU.

You say that a stiffened VCU won't damage the transmission unless it's seized solid. VCUs don't tend to seize solid but they do get stiff enough to cause damage, even when driving on a straight road. The reason for this is simple. The gearing ratio between front and back is different. The rear being driven 0.8 % slower than the front. This gives the Freelander a "Front Wheel Drive" feel. When a slippery surface is encountered, causing the front wheels to spin, the VCU's special fluid reacts to this increase in slip and thickens up. This thickening then transfers some drive to the rear. The higher the slip ratio between front and rear, the thicker the fluid becomes, increasing drive to the rear. As the VCU's input and output shaft equalise in rotational speed, the fluid thins again. This thickening and thinning happens very quickly keeping the input and output within a very tight speed ratio window.
As the VCU fluid ages, the fluid does tend to thicken. This thickening makes the VCU load up the transmission continually, even on a straight road. It's this continued load that causes the IRD gears and bearings to fail.
What causes this IRD failure? It's quite simple really. The excessive load causes a breakdown of oil film on the gears. This oil film reduction allows the metal to grind, taking off the handed surface. These hardened flakes then destroy the bearings. Eventually the oil becomes a soup of hardened steel abrasive particles, with catastrophic failure not far off.
So a correctly working VCU is vital, as are correct tyres being fitted. Ignore these and the transmission life is seriously shortened.

Click to expand...

GrumpyGel said:

Absolutely - BUT working VCUs are engineered so they are transmitting bearing damaging torque at slippage much closer to turning corners than front wheels spinning - so when they start to go it gets to damaging levels.



I would suggest nobody uses this as a basis for running a reliable Freelander. It's a recipe for an expensive repair bill.



I would suggest nobody uses this as a basis for running a reliable Freelander. It's a recipe for an expensive repair bill.

Click to expand...

lenny1234 said:

I think that replacing a VCU that is just a bit stiff is a recipe for an expensive repair bill.

Do you recondifion VCUs? Or just sell them?

Click to expand...

lenny1234 said:

I think that replacing a VCU that is just a bit stiff is a recipe for an expensive repair bill.

Do you recondifion VCUs? Or just sell them?

Click to expand...

lenny1234 said:

I think that replacing a VCU that is just a bit stiff is a recipe for an expensive repair bill.

Do you recondifion VCUs? Or just sell them?

Click to expand...

lenny1234 said:

I think that replacing a VCU that is just a bit stiff is a recipe for an expensive repair bill.

Do you recondifion VCUs? Or just sell them?

Click to expand...