VCU Torque test results

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MollyNomad said:
All true and correct.....If we were all scientists and into electrickery diagnostictrickery no one would trust anything that was published on here...

As there is no definitive answer to the specs its up to the enthusiast to come to some sort of consensus...LR and those that refurbish VCU's(and this goes for other components too) would never give away the secret of the 'elixir' that they covet.

Forums don't need science they need practical solutions.....A data base of VCU specs may have been of benefit but the starting point would be the forums and chat rooms as to 'when something' is dead or about to die...The layman/enthusiast requires that info first........
Click to expand...

There is actually official VCU test data available. However it is well beyond the equipment of average owner mechanic/ tinkerer to perform correctly.

I'm going from memory here but I reasonably sure that the figures are as follows.

The VCU should produce 390 to 440 Nm of torque if one end is held still, whilst the other is rotated at 75 Rpm. However this requires a lathe of over 5Hp and torque measuring device to carry out the test.


The OWUT doesn't "load" up the VCU, but does tests for general degradation of the fluid.
 
The Mad Hat Man said:
@Hippo suggested, and I agree, that peeps supply certain info so that we have a "standardised" set of figures and also for both old and new VCUs, as per the spreadsheet above. Peeps never bothered, or at least rarely bothered, to supply that info.
By all means use the above spreadsheet as a starting point and add any correlated info you find.
I, for one, have a headache from banging my head on a brick wall over the last 10-12 years!
Wonder what @Hippo thinks?
Click to expand...

I do agree that the 5Kg 1.2M is a bit short of the needed test figures worked out in the past by Hippo.
However over the last few years, far more data has been collected in various threads at this lighter weight, than was ever collected in the original VCU table.

I can say with absolute certainty that the VCU is serviceable if a time of under 1 minute is recorded with a 5Kg weight hung on the end of a 1.2M lever.
A new GKN VCU records under 20 seconds for the same test weight.
A good used VCU will record up to 45 seconds in the same test.

I personally believe using a lighter weight makes the test more sensitive and therefore is what I'd go by.
 
It's not difficult to do both 5Kg and 8kg at 1.2M - you can then compare with all the realistic guys who have done it conscientiously and reported their results.
(I got a Hippo Cookie (;-)) )
 
True!
As Hippo has done much of the research ground work on this, perhaps we can persuade him to call the standard for OWUT2: 8kg on a 1.2 metre bar or 5kg on a 1.9 metre bar. And then we can work out what the acceptable duration should be for the wheel to fall from 45 degrees above horizontal to the horizontal.

PS The test should be started with the bar above 45 degrees and the clock only started as the bar passes through 45 degrees to avoid confusion regarding the transmission tacking up slack :)​
 
Sorry Rob but why over complicate with other versions - I would worry about my paintwork trying to control a 1.9M bar sideways - but find it no bother to do both the 5Kfg and 8Kg with the 1.2M tube I knocked up for the purpose - and the two tests tell you slightly different things - see above.
There are 48 pages of this thread and yet as Hippo observed only a handfull of people have actually just simply done the test and reported the result. Most are far more interested in pitching their own pet theories - but from those handful of results we have a good idea of what is hot and what is not.
 
Alibro said:
I guess if the car is used off road a lot there will be much more strain on the rear diff than most........ Quilshaft from here ... I'm reading all the threads on VCUs and there is much focus on time tests ,which is a good way to test its true but I'd like to add my 2p worth and point out that actually a stiff VCU will load the transmission more ON road because the wheels are held more rigidly by the Tarmac in a " wound up " condition. The wind up is caused by the fact that it is not possible to ever get all the wheels exactly the same diameter and therefore revolutions per mile. It can be seen therefore that the stiffer the vcu the more stress will be present and this compounds with vehicle speed because the faster the vehicle is moving the greater wheel rpm discrepancy that must be dissipated by the the vcu and at 60 mph it only takes 60 seconds to cover a mile so ... The resultant difference must be able to be released AS it is occurring. I don't know any numbers but personally I'd like to be able to turn my VCU fairly easily. When I lose front wheel traction the vcu operates similarly to a torque converter in providing " a proportion " of the torque sufficient to move the vehicle to the next place the front wheels can grip again and that's all it does. The freelander is a front wheel drive car with some standby rear wheel push if needed
Click to expand...
 
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Hi all this is a long post but needed I'm reading all the threads on VCUs and there is much focus on time tests ,which is a good way to test its true but I'd like to add my 2p worth and point out that a stiff VCU ( they do seem to tighten up as they get old)-,will load the transmission more ON road because the wheels are held more rigidly by the Tarmac in a " wound up " condition. The wind up is caused by the fact that it is not possible to ever get all the wheels exactly the same diameter and therefore revolutions per mile. It can be seen therefore that the stiffer the vcu the more stress will be present and this compounds with vehicle speed because the faster the vehicle is moving the greater wheel rpm discrepancy that must be dissipated by the the vcu per minute and at 60 mph it only takes 60 seconds to cover a mile so ... The resultant difference must be able to be released AS it is occurring. I don't know any numbers but personally I'd like to be able to turn my VCU fairly easily. When I lose front wheel traction the vcu operates similarly to a torque converter in providing " a proportion " of the torque sufficient to move the vehicle to the next place the front wheels can grip again and that's all it does. The freelander is a front wheel drive car with some standby rear wheel push if needed
 
This is why I love my slack vcu...I no longer have to worry about my ird, rear diff, cracking subframe etc..but it still has enough umpf to stop the fronts lighting up in the wet and so far can still get me out of muddy fields....My hippo is 99% on the tarmac so the loose/slack vcu suits me fine..I put a 30cst fluid in mine
 
My curiosity has got the better of my fear of this thread. Oh dear :)

I do tests at work in my Uni (not on this type of thing tho - I break fibreglass - but the thought processes are the same in terms of standardisation etc) so this kind of thing just interests me.

I must admit I haven't read through all 48 pages, the first ones kind of put me off, and 48 pages is just too much for me. So this might have been asked before. If so, or for any other reason, real or imagined, then please do feel free to crucify me since crucifixion via forum is actually pretty painless.

The idea of doing a test on a new VCU to see how quickly it turns with a 'standard' torque (a given weight at a given lever arm and a given starting angle from upright) seems like a good idea to me to see how viscous the fluid is, at least relatively, in a given VCU, by the time it takes to drop to a given angle. Like a benchmark test to compare the time for a given older VCU to those times of some tests done on new VCUs. It could even be used, very roughly, to see if the VCU is 'goodish' (purposely vague definition of 'good' since I relate more to engineers than scientists).

But one of the few things that I remember from a long while ago when I studied Chem Eng was that viscosity is usually highly dependant on the fluid temperature - even a couple of degrees can make very large change in viscosity for some fluids.
So if I did the same test on the same car with the same test set up in Essex in February and then repeated the test exactly on the same car with the same test set up in Lisbon in August, wouldn't it be probable that I would get two different drop times?
So, shouldn't ambient temp be specified when the 'standard' says to tests 'cold'? At least stated to give a feel for the data since its difficult to control unless everyone had a thermostatically controlled heated garage :)

Kind of related to the above, but another separate question:
When the front wheels start to slip and the VCU is subject to (rotational) shear, does the fluid become thicker due to higher shear rates (shear thickening) or is it due to the shearing heating the fluid which gives an increase in fluid temp and then viscosity (which is the opposite of most fluids that get thinner with higher temps)? If it was the latter (temp controlled) then I think my test in Lisbon would be slower than my test in Essex. Am I right?
 
Bife said:
My curiosity has got the better of my fear of this thread. Oh dear :)

I do tests at work in my Uni (not on this type of thing tho - I break fibreglass - but the thought processes are the same in terms of standardisation etc) so this kind of thing just interests me.

I must admit I haven't read through all 48 pages, the first ones kind of put me off, and 48 pages is just too much for me. So this might have been asked before. If so, or for any other reason, real or imagined, then please do feel free to crucify me since crucifixion via forum is actually pretty painless.

The idea of doing a test on a new VCU to see how quickly it turns with a 'standard' torque (a given weight at a given lever arm and a given starting angle from upright) seems like a good idea to me to see how viscous the fluid is, at least relatively, in a given VCU, by the time it takes to drop to a given angle. Like a benchmark test to compare the time for a given older VCU to those times of some tests done on new VCUs. It could even be used, very roughly, to see if the VCU is 'goodish' (purposely vague definition of 'good' since I relate more to engineers than scientists).

But one of the few things that I remember from a long while ago when I studied Chem Eng was that viscosity is usually highly dependant on the fluid temperature - even a couple of degrees can make very large change in viscosity for some fluids.
So if I did the same test on the same car with the same test set up in Essex in February and then repeated the test exactly on the same car with the same test set up in Lisbon in August, wouldn't it be probable that I would get two different drop times?
So, shouldn't ambient temp be specified when the 'standard' says to tests 'cold'? At least stated to give a feel for the data since its difficult to control unless everyone had a thermostatically controlled heated garage :)

Kind of related to the above, but another separate question:
When the front wheels start to slip and the VCU is subject to (rotational) shear, does the fluid become thicker due to higher shear rates (shear thickening) or is it due to the shearing heating the fluid which gives an increase in fluid temp and then viscosity (which is the opposite of most fluids that get thinner with higher temps)? If it was the latter (temp controlled) then I think my test in Lisbon would be slower than my test in Essex. Am I right?
Click to expand...


nothing to do with viscosity, per se. It is a non-newtonian fluid. that is how it works. it changes viscosity at nominally 100C.
see https://www.landyzone.co.uk/land-rover/the-definitive-freelander-vcu-testing-thread.99163/
 
Thanks.
All very clear now that I can see that the fluid viscosity is completely independent of temp until 100 C when it has a step change to high viscosity
Except now I dont understand how the torque in the next graph drops as temp increases and why there isnt a large increase in torque at 100C
What am I not getting?
Edit: Is it that the torque drops a bit with increasing temp in the test graph since the previous plot of viscosity v temp is an idealised case and actually the viscosity does drop a bit with temp in reality until the step change?
Then the torque goes right up at roughly 130 C in the experimental graph when the step change in viscosity occurs?
 
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Pressure seems to have an effect too as it is much stiffer with no (or too small) an air gap.
My experience of this being an issue was when doing the one wheel up test after refurbing my VCU. It gave a high time so I let some fluid out and it was fine afterwards.
 
I guess if the car is used off road a lot there will be much more strain on the rear diff than most........ Quilshaft from here ... I'm reading all the threads on VCUs and there is much focus on time tests ,which is a good way to test its true but I'd like to add my 2p worth and point out that actually a stiff VCU will load the transmission more ON road because the wheels are held more rigidly by the Tarmac in a " wound up " condition. The wind up is caused by the fact that it is not possible to ever get all the wheels exactly the same diameter and therefore revolutions per mile. It can be seen therefore that the stiffer the vcu the more stress will be present and this compounds with vehicle speed because the faster the vehicle is moving the greater wheel rpm discrepancy that must be dissipated by the the vcu and at 60 mph it only takes 60 seconds to cover a mile so ... The resultant difference must be able to be released AS it is occurring. I don't know any numbers but personally I'd like to be able to turn my VCU fairly easily. When I lose front wheel traction the vcu operates similarly to a torque converter in providing " a proportion " of the torque sufficient to move the vehicle to the next place the front wheels can grip again and that's all it does. The freelander is a front wheel drive car with some standby rear wheel push if needed
I agree with you if talking about a car with a stiff VCU but with a good one the rear diff shouldn't be under much strain on the road. Off road however, especially when climbing hills the rear diff will be under a lot of strain.
 
HI all, just bought a 06 freelander - booked in for 4 new tires on her on sunday, and was thinking about ordering a refurb VCU as I dont know the history (TD4 done just over 100k) . All the running gear appears to be there, rear prop still in place, but wondered if there was any indication of damage to the IRD or prop that I would have noticed? Would I hear anything or notice anything? no banging, dragging or knocking from the back end, feels tight on a full lock reverse but that doesnt always mean the VCU does it? Just dont want to be spending 300 if the rest of the system is naff. I am going to try the one wheel up test on sunday to see if it is siezed or not, but I would imagine if it had I would have noticed something? Have to say she drives lovely and pulls like a dream.
 
Cheers, have to say I had a look under the car and there isnt a mark on the VCU, so I am wondering if it has been replaced somewhere in the past. I will do the wheel up test at the weekend and see how it goes. Was tempted to just order a refurbed VCU, bu if the missus found out I spent 300 when I didn't need to I might end up sleeping in the car haha
 
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