2004 TD4 transmission problems.

Hi Guys. An update on my post of the 19th Dec last year.
Turns out that the whooshing noise was caused by a failed bearing in the IRD which was allowing something big and spinny to rub on the inside of the casing. The IRD has been away to a specialist in northern Spain and has been re-built.
I think I know the answer to the following question but if I could provide a bit of background info, it might help.
The question is, should I now replace the VCU?
It appears to be working, although I have not performed a definitive OWUT. When the transmission problems appeared I parked the car at the side of the road without driving it further. To confirm the VCU wasn't seized, I jacked up a rear wheel and was able to turn the wheel by hand with resistence but not excessive.
When I bought the car the rear tyres where worn beyond those on the front and although new ones were fitted, I don't know how long the previous owner had been driving the car like this but it did cause rear diff problems.
Also after having had a new clutch fitted, I drove to Madrid and back (600 km) only to notice a very strong smell of gearbox all. A look under the car showed it to be covered in gearbox oil as the fill plug to the IRD had not been tightened by the plonkers at the garage!! Needless to say I've not taken the car there again!!
Could these two things have caused the IRD bearing failure, not the VCU, which appears to be OK?
What time results should I be looking for from a OWUT using a 5kg weight and a 1 metre bar? Do I measure the time taken for the bar to fall from a 45 deg angle to 90 degs?
I don't want to replace the VCU needlessly as I seem to be spending bucket loads of money on the car although I am fully aware of more potential damage to the IRD.
Any advice greatly appreciated.

In many ways, it doesn't matter whether the VCU, tyres or loss of oil did the damage to your IRD, that's history and you'll probably never know. What's important is that they don't damage your rebuilt unit

If you can turn the wheel with resistance and you're not feeling binding when reversing on full lock, the VCU is probably OK, but you need a definitive answer - the OWUT will give that. 1.2m bar and 5kg weight over the 45 degree travel you mention (to horizontal) should take (IIRC) 30 seconds with a new VCU and no longer than a minute before replacement is 'advised'. Sounds like you're clued up on the tyres - all 4 should be identical make/spec, pumps to same pressure and the ones with more tread on the back.

It sounds like there are some outfits on the Iberian pen that recondition VCUs and your car may have had one of them. One member on here found that the his Portuguese recon was very 'loose' - ie the fluid was not viscous enough to give proper 4WD traction. So this would obviously relieve stress on the IRD, diff etc - but compromise 4WD ability.

Thanks for your prompt reply. When I get the car back this week I'll carry out the OWUT.
Cheers.

Cat amongst the pigeons!!
If I drive my car home tomorrow (30km) and the VCU is knackered, could that shaft the newly expensively refurbed IRD?

Jonny H said:

Cat amongst the pigeons!!
If I drive my car home tomorrow (30km) and the VCU is knackered, could that shaft the newly expensively refurbed IRD?

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If you can turn a rear wheel by hand, the VCU hasn't got that stiff.
So going on that assumption, the answer is no, it'll be fine. Make sure the tyres are all the same, least worn on the rear and all are pumped up to 30 Psi.
For the record, I can only just turn my rear wheel by hand, without a lever.

Cheers Nodge. Thanks for the advice. Spent enough on the IRD without having to fork out for a VCU.

Jonny H said:

Cheers Nodge. Thanks for the advice. Spent enough on the IRD without having to fork out for a VCU.

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Anyone know why the makers of 'the best 4x4 by far' build a transmission that is so fragile?

Jonny H said:

Anyone know why the makers of 'the best 4x4 by far' build a transmission that is so fragile?

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It's not that fragile. However it's easy to massively overload it by fitting the tyres in the wrong position. The VCU is designed to transfer drive when the rotation between the front and back exceeds a set threshold. However if the difference between the props exceeds the preset threshold, huge amounts of torque is generated. If for instance, the tyres are different diameters, the VCU starts transferring torque and the IRD takes a pounding.
The components themselves aren't fragile. But sustained over torque will shorten the life massively. I well maintained IRD will last as long as the vehicle. However one abused with incorrect tyre fitment, will fail in a few thousand miles.

Jonny H said:

Cheers Nodge. Thanks for the advice. Spent enough on the IRD without having to fork out for a VCU.

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If it does need replacment............
You can either recon this yourself. Buy a recon unit from Bell engineering and fit yourself about £200+P&P without bearings or with about £250+P&P (Both options are exchange). Or buy a new unit from ashcroft-transmissions.co.uk currently £250 +VAT +P&P less bearings (No exchange)