VCU Torque test results

austen said:

Its the same unit in operation, but v6 has no damper or the mounting face for it. Also the hanger bearings have a 25mm spacer on them to hang it lower. But to be honest you can just run a normal one in its place

Click to expand...

Thanks. So the actual viscous liquid and number/size of plates inside is the same on both versions of VCU. Interesting. I've seen graphs on ere of temp v torque etc. What I'm wondering is what would be the difference in time for a VCU one wheel up tested at different ambiant air temps, for example 0 and 25 degrees. At lower temps (this time of year) I would expect the VCU to resist the props turning more than at 25 degrees (summer time), if I'm reading the graph correctly. Hnce at 0 degrees the one wheel up test would take longer by x seconds compared to the same test at 25 degrees ambiant.

Hippo said:

Thanks. So the actual viscous liquid and number/size of plates inside is the same on both versions of VCU. Interesting. I've seen graphs on ere of temp v torque etc. What I'm wondering is what would be the difference in time for a VCU one wheel up tested at different ambiant air temps, for example 0 and 25 degrees. At lower temps (this time of year) I would expect the VCU to resist the props turning more than at 25 degrees (summer time), if I'm reading the graph correctly. Hnce at 0 degrees the one wheel up test would take longer by x seconds compared to the same test at 25 degrees ambiant.

Click to expand...

Yes same plates and fluid. Temperature will make a small difference, but would need to be fairly extreme. For example in the really cold spell we had the barrel was harder to pour. But the difference in temp of say 5 - 20 degs is minimal

That hysteresis curve is quite interesting.
The shear strength at 20C is similar to that @ 130C.
Does that mean that when cold, the VCU is locked up, until it gets warm?
Austen - have you tried heating the fluid to, say, 40C to see if it is runnier?

No not heated it up like that I'm afraid. And I know this isnt scientific, but if the vcu is to warm comfortably hold you hand on, the vcu will momentarily lock, I know this as I had a freebie lock its rear wheels on me while slowing down coming to see t of traffic lights. At this stage the rear diff was also overheating and melted the breather, pressuring the diff and blowing the drive shafts out a few miles further down the road. So at what ever heat that is, 70 degs???, the fluid is turning to jelly

That sounds wrong! According to that hysteresis graph it thickens at about 132C ( or at 20C )

The graph is for a vw, not the freelander, we tried different grades of fluid when working out how to refurb them, different fluids thicken at different temperatures. Remember the free lander vcu is designed to slip all the time, not sure if that's the case with the vw. I can guarantee you at 20degs the fluid is very much still a treacle like fluid, the same as when its 5degs

Oh BTW my temps are just estimates, no thermometer readings and temp of the fluid inside the vcu is going to be hotter than the outside of the vcu, defo just estimates

austen said:

The graph is for a vw, not the freelander, we tried different grades of fluid when working out how to refurb them, different fluids thicken at different temperatures.

Click to expand...

that is very true.

I spose it would be useful to do the same test to a Freebie VCU .

Did you know the correct fluid for the Freebie, or was it trial & error?
That means you could alter the operating characteristics then? Interesting .

Scary to think you lot are talking about temp when I've just taken my VCU off so I can naturally warm it up to room temp so I can retest what I did in the cold on Saturday.

The ambient temp makes a difference to my test results. The Turnip Test shows my VCU warms up by N +-2 degrees above ambient start temp, when travelling to work on the same route at the same speed. At very cold temps it's difficult to measure a significant change - I guess this is due to the cooling air flow. I agree the VCU case temp isn't a clear indication of what's going on inside, but it's the best indication of temp inside we have from a functional test in anger, as opposed to a static test like the One Wheel Up Test. I'm currently watching my results change over time which is why I need to retest at room temp to confirm my results for historic comparison. I've also been watching old video's of my props turning over a distance to see the rotational difference after a straight line drive, compared to recent video's. My test results show I'm currently recording my VCU's demise as it's characteristics change with the cliff of despair edging closer.

I always thought the shearing effect happened as per below:

Rave Disk said:

The cylinder is a sealed unit filled with a silicon jelly. The viscosity of the silicon jelly increases when subjected to shear. When there is a speed differential between the front and rear propeller shafts, adjacent slotted discs in the VCU rotate in relation to each other. The shearing action of the rotating slotted discs increases the viscosity and resistance to rotation of the silicon jelly.

The rear wheels are 0.8% under driven, so in most conditions the vehicle is effectively front wheel drive, with the rear wheels turning the rear propeller shaft slightly faster than the IRD drives the front propeller shaft. Since the speed differential is low, the increase in viscosity of the silicon jelly is marginal and there is little resistance to relative rotation of the slotted discs.

When there is a significant speed differential between the front and rear propeller shafts , e.g. the front wheels lose traction or traversing rough terrain, the viscosity and resistance to rotation of the silicon jelly increases to a level that slows or stops relative rotation of the slotted discs. With the front and rear propeller shafts locked together, drive is thus transferred from the IRD to the rear wheels.

Click to expand...

Originally posted by MHM:

So I did raise: .

Its was trial and error as my contacts within LR could not find a specification for the actual fluid as the unit was supplied by gkn. I guess lr told gkn what they wanted the vcu to do, gkn designed it and supplied it. Speaking to gkn direct gave us no indication to what the fluid grade was or the amount, I guess its in their interests to keep it too themselves.

There are 3 ways of altering the performance, fluid grade, amount of fluid and number of plates. This also means we had to try lots of different combinations to produce the correct result.

Oh and yes we could supply vcu's in lots of various tunes if required

Did the test today took 80 seconds to go from 90-deg to 45-deg and a further 60 seconds to go from 45-deg to bottom thereofre total time 125 (seconds to do it ) what do you make of it is it okay for a while yet or f****d and needs changing. The beast has done 137500 not sure when vcu was last changed ther is a little stiffness starting on full lock.

celt69 said:

Did the test today took 80 seconds to go from 90-deg to 45-deg and a further 60 seconds to go from 45-deg to bottom thereofre total time 125 (seconds to do it ) what do you make of it is it okay for a while yet or f****d and needs changing. The beast has done 137500 not sure when vcu was last changed ther is a little stiffness starting on full lock.

Click to expand...

We only need the 45 degrees to horizontal time. Also need to know what weight you used and distance between the weight and pivot point - which is the length of bar normally.

Hippo said:

We only need the 45 degrees to horizontal time. Also need to know what weight you used and distance between the weight and pivot point - which is the length of bar normally.

Click to expand...

Evening Hippo.
It took 80-seconds on a 1-meter bar with 10kg weight,

Hope it helps

Celt69

celt69 said:

Evening Hippo.
It took 80-seconds on a 1-meter bar with 10kg weight,

Hope it helps

Celt69

Click to expand...

That's quite a high value. I would be concerned if it were mine, when comparing the average values we receive. It's probably one of the highest if not the highest so far. A 1m bar and 10kg weight = 98Nm torque applied when the bar is horizontal which is roughly the same as the typical 1.2m bar and 8.3kg weight (for comparison).

Are you sure the rear wheels are turning freely? Chock the front wheels and lift both rears and check they turn freely with the handbrake off. Are you in the UK? It's been a bit cold recently but temps have risen in the last few days so try again on a warmer day. Did you use the 32mm drive shaft nut or a wheel nut to apply the force? Drive shaft nut is better if you can use it.

Just to confirm, are you starting at the black dot and timing the travel through the red arc? (45 degrees to the horizontal)


WheelTorqueGraph AcIP2Aa

I've just had mine replaced with a new one, before it was replaced I was loosing power around the 30mpr mark then it would pick up again. They replaced the bearing too which were totally shot! My car has done 78,000 miles and the driving difference is noticeable.

Just put brand new VCU and 2x bearings Took 3 1/2hrs to do not bad pretty straight forward followed tips on her and you tube for how to do it. now it takes 22 seconds to complete the wheel test. with 3ft bar and 20LB weight, previously it tools much longer bring on the winter.

just done a test, using 5kg ie 5ltrs of water on a bar 1.2 mtrs long I did a few times and the times were around the 35 to 40 sec mark to travel 45 deg. While looking underneath beimg a nosy son so notice that the rear diff mounts need doing oh hum its a land rover.The car done 115000 miles not sure of its history or if the vcu age.

just tried the test started with a 600mm bar on the 32mm hub nut with my full weight on it (11 stone) and it didn't move) think mine is goosed so will have to remove and go 2 wheel drive for a while, do i just remove the front prop or the whole lot? found a great how to on removal so thats easy but can you do any damage driving with the entire prop removed?