VCU Query

Hi Everyone,

I have just done the VCU test on the back wheel....took around a second to drop from the top to the floor.
I thought this would be the case as I could turn the wheel by hand with very little resistance.
I checked the prop underneath and as I turn the wheel the prop rotates, as does the vcu.
I didn't seem to make any difference whether it was in 1st gear or neutral, or whether I turned the wheel forwards or backwards (I did it on the passenger side).

I also jacked up the front and turned the wheel by hand (not in gear) and I could see the prop going to the VCU rotating.
I have some history showing that the VCU was replaced around 70k miles ago.
Has this one failed too and if so, is 70k miles about right? A lot of the things that I have read suggest that a failing VCU usually binds up and causes drag, especially on tight turns, but I don't get any of this.
Not sure if it's just the VCU or whether there's something else at fault.

Thanks.

If both front and rear props rotate when the respective end wheels are turned, then the VCU has failed open. This is a very unusual failure mode, as they normally go stiff with age. But it does sound like the VCU has failed open.

You definitely had only one wheel off the ground?

Are there any signs of tampering with the VCU - has someone drained out the fluid?

Definitely only one wheel - and that one was only just off as my jack doesn't lift very high!
I will get under the car and have a closer look at the VCU.

Nodge - thanks, that is what I suspected that it failed open but I thought this was very uncommon...

It was replaced back in 2010 about 70k miles ago but I suppose there's no way of knowing that it worked back then!

Just had a look underneath, looks ok I think with no signs of oil etc - here are a couple of pics.
Checked by hand and both props move independently (could only move them a small amount, just to take up the slack). If I held one side tight the other would move. Could also move each the opposite way at the same time.
Don't know if that's of any help or if that's the case on all of them.

Juzza6720 said:

Just had a look underneath, looks ok I think with no signs of oil etc - here are a couple of pics.
Checked by hand and both props move independently (could only move them a small amount, just to take up the slack). If I held one side tight the other would move. Could also move each the opposite way at the same time.
Don't know if that's of any help or if that's the case on all of them.
View attachment 153738 View attachment 153739

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if you can hold one prop and the other can be turned vcu or some spline has failed

Is it my imagination or is that VCU more rounded at the front than the stock one?

guineafowl21 said:

Is it my imagination or is that VCU more rounded at the front than the stock one?

Click to expand...

I would say most certainly good spot I wonder what that VCU is off? original GKN one in photo's below

When I read the first post, I thought that the VCU had been replaced with a reconditioned one with the incorrect grade of silicone fluid.

The pictures don't show a reconditioned VCU - or at least not one with a tapping showing how the fluid had been removed and replaced.

I agree with guineafowl that the VCU doesn't look right? They usually look like this:

Ignore the vibration damper that's fallen off in this image!

Basically as Artic has said! LOL

Or does the V6 one look like that?

guineafowl21 said:

Or does the V6 one look like that?

Click to expand...

The V6 VCU looks the same as a 4 cylinder VCU, only minus the damper and the mount to hold the damper on.

rob_bell said:

When I read the first post, I thought that the VCU had been replaced with a reconditioned one with the incorrect grade of silicone fluid.

Click to expand...

Or a dodgy VCU that has nothing in it at all?

Nodge68 said:

Or a dodgy VCU that has nothing in it at all?

Click to expand...

Makes you wonder doesn't it?

If the propshaft is not spinning on the splines to the vcu then I'd say it was an 'Emporers clothes' 2 wheel drive VCU conversion. Can't think of any way a stock vcu would go zero resistance even with very low fluid. Check splines each end areengaged with prop before removing and replacing.

Thanks for replies. I went underneath again to take a couple more pics of it to show how rounded it is on the front but then I spotted this....
I think I have found my problem!!

Wow, there really is some strange stuff thrown up on here

I wonder what the history is?

I don't suppose its a coupling off another car, the chances of it fitting is presumably very remote. Its dimensions look original - the only difference is the rounded leading edge.

Perhaps it’s reconditioned: the end cap cut off to clean, welded and then dressed (hence rounded edge) with a full hole - which in this case the screw has fallen out!

Yup, that’ll be the problem alright. Good news: it can be re-filled

rob_bell said:

Perhaps it’s reconditioned: the end cap cut off to clean, welded and then dressed (hence rounded edge) with a full hole - which in this case the screw has fallen out!

Yup, that’ll be the problem alright. Good news: it can be re-filled

Click to expand...

But would you refill it, or replace it with a guaranteed replacement?

How much is the silicone? For the price, I’d give it a go, and if I wasn’t happy with the result, I’d get a replacement