VCUs - The sweet spot

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Also like the graph on the wheel up test.
But a word of caution, always be wary of extrapolating data.
At Work there had been fatigue testing done on titanium and we extrapolated the data, designed a new Fan Blade ( the blades you see at the front of the engine.) The blades failed dramatically when tested. The investigation found that actual test did not follow the extrapolated data, Costly redesign followed.
in this case you are looing at a fairly complex interaction.
If i asked one of black belts at work to do us a design of experiments to get true root cause data there would be so many variables we would be swapped with tests to carry out.
Having said that I think there has been some very very good work with some very good data produced
 
Lowbank said:
Hopefully I can also add some info to the thread that might help some people. I have a couple things that maybe of interest or at least add light onto some things that have been said.
In the manufacturing industry there is some thing called the bathtub curve and the "mean time between failure".

you can google them for detailed explanation.View attachment 95214
This is used in reliability engineering and puts Data to what people see. You will get early VCU failures and you will get ones that last 120,000 or more. So when some have said 70,000 miles is the service life that could argued as the "mean time between failure".
I have know idea if LR used these principles but they are statistically proven. Some manufacturers design it for a mtbf.
So personally when I saw a couple of specialists mention that figure, it probably gut feel and not based on data, but I thought why gamble. its going to fail and it will take more expensive items with it.
hopefully that puts some data around the debate of times of failures and perhaps some enlightenment.
Click to expand...

VCU's don't suddenly fail. They all have the same metal plates, the same fluid and the design is so simple sudden failure is not possible. they will only fail at lower mileage if they are abused by incorrect tyres or uneven tyre pressures. Even then the 'failure' will take place over a prolonged period of time as the fluid inside deteriorates.
This makes buying a 2nd hand Freelander a bit of a lottery as a well looked after one will be in near perfect condition at 70k while yours was probably already shot by then.
 
wammers said:
All this talk proves nothing other than the fact that a VCU as used on the Freelander is a consumable item. ;);)
Click to expand...
Not according to Landrover! :rolleyes:

But at least it can be tested to confirm if it needs replaced immediately or if it is good for another 20k miles. Unlike a timing belt it will not suddenly fail taking out your drive train.
 
Alibro said:
Not according to Landrover! :rolleyes:

But at least it can be tested to confirm if it needs replaced immediately or if it is good for another 20k miles. Unlike a timing belt it will not suddenly fail taking out your drive train.
Click to expand...

The way it is used on a Freelander it cannot be anything other than a consumable unit, it has far to much work to do. Cam belts are service items.
 
Alibro,
I understand they probably dont fail in a short space of time.
I would however disagree with words, the same plate, the same liquid. Manufacturers also change the design without telling anyone.
I could give loads of examples I have been involved in where variation within spec led to failures of parts.
 
For me to really helpful, I need to fully understand how the VCU works and then I can look at failure modes. For that I need to strip one but mine has to go back to Bell. I understand the theory, its the detail parts I need to view. if anyone has any pictures or a duff one I could strip that would be good.
There are no photos or diagrams on the net that ate detailed enough or not that I can find.
 
Lowbank said:
For me to really helpful, I need to fully understand how the VCU works and then I can look at failure modes. For that I need to strip one but mine has to go back to Bell. I understand the theory, its the detail parts I need to view. if anyone has any pictures or a duff one I could strip that would be good.
There are no photos or diagrams on the net that ate detailed enough or not that I can find.
Click to expand...

Lots of photos of the internals on here somewhere. Possible on this section.
 
@Lowbank, have a look at this thread for some images of broken down VCUs...

https://www.landyzone.co.uk/land-rover/diy-vcu-service.252957/

On your Freelander, I would consider replacing the bearings on the IRD's rear pinion. After driving such a long distance with such a badly performing VCU - I'd be worried about the damage it had done. While the pinion is off, you can check the condition of the crown/pinion gears.

I'd also check your tyres are all the same make/model/spec - on a straight downhill road with matching tyres, I wouldn't expect that much braking effect even with a 'siezed' VCU. edit: and pumped to the same pressure.
 
Lowbank said:
Alibro,
I understand they probably dont fail in a short space of time.
I would however disagree with words, the same plate, the same liquid. Manufacturers also change the design without telling anyone.
I could give loads of examples I have been involved in where variation within spec led to failures of parts.
Click to expand...
Fair point about the fluid but would be surprised if the plates changed much, my 04 and 02 Freelanders had identical plates but can't comment on older or newer cars.
As for photo's page 19 of the thread Grumpy linked to and first page of this thread https://www.landyzone.co.uk/land-rover/looks-like-ive-done-it-again-doh.293904/ will give you a good idea of how it works. As I said they are extremely simple devices in their design even if the properties of the fluid are complex.
 
Thanks for the links, will have a look over the next couple of days.
I checked the tyres before I test drove the car, they are all same make, same size and roughly same wear rate.
I have been searching and reading up on the GKN site to understand there take on the units.
 
I believe VAG have a similar system for some of their 4WD cars but they had the sense to make them a service item and theirs can be opened without resorting to a grinder. I've never looked at theirs so don't know what other differences there are.
 
Quick update, tonight fitted the VCU from the kind chap at Bell, car is transformed. massive difference just driving but in reverse on full lock the difference is very noticable.
Glad I read the advise,
before when reversing car felt tight but once on full lock, deffinstely like the brakes were full on.
after when reversing car will freewheel but on ful lock there is some resistance but not so the car stops.
result.....
Grumpygel, thanks for the advise, chrcked pressures and all within a few psi. You are also corrct about checking the bearing but dont have enough time at the moment.
need to go pick up a TD4 engine with ancillaries I just got for £120, just to mess with and ultimately rebuild, then look for 3 door with a blown motor for the misses
 
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