VCU Torque test results

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This is all interesting. The Freelander replaces a Nissan X-Trail and they have a completely different 4WD system. There's a multi-plate clutch in the nose of the rear diff which is electrically actuated, so you can have a switch on the dash for 2WD, "Auto" and "Lock". I thought that was a better system than the viscous one that LR use, and true enough, it was one of the few parts of the X-Trail that never gave us a minute's bother in the whole time we had the car
Sounds like the Haldex used in F2 and many other SUVs. Not so sure it is without problems though, there's plenty of F2s that have had their diffs chewed up by Haldexes that few (inc professionals) know how to maintain - just like the VCU!

The Haldex setup looks to have cornered the market nowadays. I think the 'best' system was probably that employed on the RR and Subarus which have a center diff, so you do get a real distribution of torque, but with a VCU in there to limit slip so you have immediate locking when needed. The Subaru one was probably a better design because the VCU is engaged electronically, so you can pull a fuse and it is disabled - eg if you're running mismatched tyres, have a slow puncture or the VCU has gone tight etc.
 
The Freelander replaces a Nissan X-Trail and they have a completely different 4WD system. There's a multi-plate clutch in the nose of the rear diff which is electrically actuated, so you can have a switch on the dash for 2WD, "Auto" and "Lock". I thought that was a better system than the viscous one that LR use, and true enough, it was one of the few parts of the X-Trail that never gave us a minute's bother in the whole time we had the car, but from the little bit of driving on mud and wet grass that I've done, the Freelander does seem to have better traction!

The Freelander VCU allows the wheels to still turn independently of each other, while still driving the vehicle along. This is better than clutched systems, as the VCU slips slightly, instead of forcing the tyres to break traction, which is unavoidable on clutch based AWD system. The moment a tyre is forced to break traction, it's not providing the grip needed for stability control.
 
The VCU is also brilliantly and gloriously simple! What no one figured on was the expected life-span of a Land Rover, or the mileages that Land Rovers are expected to cover. Otherwise, this item would have appeared in service schedules and would have posed a bit less of a problem IMO.
 
Ah! The wheel with the rope round it is a brilliant idea! Yes, that would give you a pretty constant torque. (Although how on earth did you get a metre diameter wheel into the wheelarch)?! Did you have something like a tractor wheel bolted to the outside of the road wheel to get it clear of the bodywork or something? Just out of interest, when you use the rope, is your graph a straight line? Does the VCU (or should I say, does a healthy VCU!) have a linear characteristic, or is there a step in it above a certain speed? When you say you've had enough torque on there to "activate" it, I'd always imagined that these things had a fairly linear response so that the faster the speed the greater the torque and that torque would be proportional to the speed, but does there come a speed where it suddenly just "locks"?

This is all interesting. The Freelander replaces a Nissan X-Trail and they have a completely different 4WD system. There's a multi-plate clutch in the nose of the rear diff which is electrically actuated, so you can have a switch on the dash for 2WD, "Auto" and "Lock". I thought that was a better system than the viscous one that LR use, and true enough, it was one of the few parts of the X-Trail that never gave us a minute's bother in the whole time we had the car, but from the little bit of driving on mud and wet grass that I've done, the Freelander does seem to have better traction!

Thanks you so much for doing this. It's a really valuable resource.

P.S. I think you can neglect acceleration completely. Certainly at the speeds I've been looking at, it's been negligible. If anything, if you wanted to "finesse" it more, might the weight of the bar itself be the next thing to try and account for?
All the factors we don’t need to worry about were put to one side a long time ago. Numerous old fred’s with it all on. Some deleted due to it getting out of hand.

I like the simplicity of the vcu but also like the haldex.

We cut two big circles from sheets of wood, about 1.1m diameter. We sandwiched them together with more wood in the middle which was 1m diameter. So very much the same shape as an alloy wheel but thinner, with the rope going round the 1m diameter part in the middle. It was built like this to stop the rope coming oft.

The spare wheel on my hippo was tied to the side of the rear wheel to use as a spacer to keep the wooden wheel away from his bodywork. The wooden wheel was tied to this. Took a few attempts to get this done and secure. A hole was dug under it to allow for the wooden wheel to fit as it was bigger than my road tires. My hippo was supported to stop the body tilting when the rear wheel wasn't on the ground.

Had to leave the hand brake oft so two Freelander’s were used as anchors. One in front and the other behind. The one behind was carefully positioned so it could guide the test rope with a pulley to control the angle of the rope coming oft the wooden wheel as the forces involved were trying to move my hippo and twist the wooden wheel a bit.

The end result was a rope with a 30 foot drop holding a weight which applied a constant force to the wooden wheel to turn it, and my vcu. It worked ok and the path of the rope followed pulleys. You need a second rope attached to help pull the weight up so someone else can wrap the test rope round the wooden wheel at the same time.

The magic question about what does a vcu do when full power is applied... From what I have seen it doesn't actually fully lock up and pass all the force applied to it, through itself. It passes a percentage of it. The same happens if you apply too much power on grass and spin all 4 wheels. The rear wheels don’t spin as fast as the front wheels. We checked this by measuring all the wheels spinning in a separate test at a later date. If you think about the sheering effect which makes the alternate plates lock up, which then causes them to release as they're not slipping anymore… the plates lock up, then release a bit, then lock up, then release a bit, repeatedly very quickly. Hence they find an equilibrium point, which is why not all the power into the vcu is passed through and out of it.
 
Sounds like the Haldex used in F2 and many other SUVs. Not so sure it is without problems though, there's plenty of F2s that have had their diffs chewed up by Haldexes that few (inc professionals) know how to maintain - just like the VCU!

The Haldex setup looks to have cornered the market nowadays. I think the 'best' system was probably that employed on the RR and Subarus which have a center diff, so you do get a real distribution of torque, but with a VCU in there to limit slip so you have immediate locking when needed. The Subaru one was probably a better design because the VCU is engaged electronically, so you can pull a fuse and it is disabled - eg if you're running mismatched tyres, have a slow puncture or the VCU has gone tight etc.

No, the Nissan setup (as far as I can tell) is Nissan's own. It's much smaller and simpler than a Haldex. The Haldex is actually a hydraulic pump that pushes on a piston to ram the plates in the multi-plate clutch together to transmit drive. The Nissan system uses a little solenoid (or it might be a tiny little 12v actuator) to push the plates together. Now obviously, it can't supply anything like enough force to do this on its own, but I think the gear ratios for the front and rear axles are slightly different and there are tapered surfaces that mean the gear train tries to push its geared surfaces out of mesh because of the difference in speed between the front and rear wheels, that that's what rams the plates in the clutch together. (I've just read that back to myself and it's a rubbish description, but hopefully, you'll get the idea)! The little actuator just provides a "control signal" and then the cars own drivetrain and the difference in speed between the front and rear wheels winds up the drivetrain and transmits the drive. The rear diff on the X-Trail wasn't much bigger than the one on th Freelander, even with all this gubbins in the nose.

Some people who drive with it permanently in "auto" reported rear diff and multi-plate clutch failures but ours never gave a minute's bother. We ran in 2WD most of the time and only used "Auto" when we expected slippy conditions. Like Freelander, they were acutely sensitive to tyre differences at each end (in the handbook, Nissan even tell you to rotate the tyres front to rear every 3000 miles)!
 
The Freelander VCU allows the wheels to still turn independently of each other, while still driving the vehicle along. This is better than clutched systems, as the VCU slips slightly, instead of forcing the tyres to break traction, which is unavoidable on clutch based AWD system. The moment a tyre is forced to break traction, it's not providing the grip needed for stability control.

Although the Nissan multi-plate clutch does allow different amounts of slip depending on the current being supplied to the actuator. (That said, it might not be possible to control the amount of slip as finely as with a viscous setup and yeah, maybe that's why I'm getting the impression the Landy puts its power down better)?
 
All the factors we don’t need to worry about were put to one side a long time ago. Numerous old fred’s with it all on. Some deleted due to it getting out of hand.

I like the simplicity of the vcu but also like the haldex.

We cut two big circles from sheets of wood, about 1.1m diameter. We sandwiched them together with more wood in the middle which was 1m diameter. So very much the same shape as an alloy wheel but thinner, with the rope going round the 1m diameter part in the middle. It was built like this to stop the rope coming oft.

The spare wheel on my hippo was tied to the side of the rear wheel to use as a spacer to keep the wooden wheel away from his bodywork. The wooden wheel was tied to this. Took a few attempts to get this done and secure. A hole was dug under it to allow for the wooden wheel to fit as it was bigger than my road tires. My hippo was supported to stop the body tilting when the rear wheel wasn't on the ground.

Had to leave the hand brake oft so two Freelander’s were used as anchors. One in front and the other behind. The one behind was carefully positioned so it could guide the test rope with a pulley to control the angle of the rope coming oft the wooden wheel as the forces involved were trying to move my hippo and twist the wooden wheel a bit.

The end result was a rope with a 30 foot drop holding a weight which applied a constant force to the wooden wheel to turn it, and my vcu. It worked ok and the path of the rope followed pulleys. You need a second rope attached to help pull the weight up so someone else can wrap the test rope round the wooden wheel at the same time.

The magic question about what does a vcu do when full power is applied... From what I have seen it doesn't actually fully lock up and pass all the force applied to it, through itself. It passes a percentage of it. The same happens if you apply too much power on grass and spin all 4 wheels. The rear wheels don’t spin as fast as the front wheels. We checked this by measuring all the wheels spinning in a separate test at a later date. If you think about the sheering effect which makes the alternate plates lock up, which then causes them to release as they're not slipping anymore… the plates lock up, then release a bit, then lock up, then release a bit, repeatedly very quickly. Hence they find an equilibrium point, which is why not all the power into the vcu is passed through and out of it.

Thanks, I can picture that now. In your earlier post, you said "hundreds of Nm". I'm curious to know what you did actually end up putting on? Also what happens when you double the torque in the "pulley" test, rather than the "bar" test. Do you halve the time, or is it not as simple as that?
 
Thanks, I can picture that now. In your earlier post, you said "hundreds of Nm". I'm curious to know what you did actually end up putting on? Also what happens when you double the torque in the "pulley" test, rather than the "bar" test. Do you halve the time, or is it not as simple as that?
Not sure on the final weight and times. It was a long day and we kept increasing it. I joked about doing it earlier in the day when doing the OWUT and some auto gear box oil changes. Then we bought the bits needed and had a go. It rained all day. There must have been easily over 300Nm of force applied. We started low and kept increasing it. As with the normal test, the more force you apply the faster it will turn. There seems to be a point where it wont turn any faster. That's the bit when it's "activated" as much as it can, like in real life where it carries the force through it when powering 4 spinning wheels. That's when you see it start to slow down on the time taken because it's fighting the most. Well that's the thinking behind what we did and found out. Yer have to be careful of doing this sort of thing. The vcu generates heat quickly when turning it fast like this. Especially if you repeat the test several times. Get it too hot and its destroyed. Hence the Turnip Test to check for temperature.
 
Not sure on the final weight and times. It was a long day and we kept increasing it. I joked about doing it earlier in the day when doing the OWUT and some auto gear box oil changes. Then we bought the bits needed and had a go. It rained all day. There must have been easily over 300Nm of force applied. We started low and kept increasing it. As with the normal test, the more force you apply the faster it will turn. There seems to be a point where it wont turn any faster. That's the bit when it's "activated" as much as it can, like in real life where it carries the force through it when powering 4 spinning wheels. That's when you see it start to slow down on the time taken because it's fighting the most. Well that's the thinking behind what we did and found out. Yer have to be careful of doing this sort of thing. The vcu generates heat quickly when turning it fast like this. Especially if you repeat the test several times. Get it too hot and its destroyed. Hence the Turnip Test to check for temperature.
OK, ta - although I guess 4 spinning wheels isn't worst case for the VCU? Presumably 2 front spinning wheels is the worst case?
 
OK, ta - although I guess 4 spinning wheels isn't worst case for the VCU? Presumably 2 front spinning wheels is the worst case?
The fronts can't spin that much before the rears gain more power from the vcu activating. It happens quite quickly. The vcu and transmission is designed to take the stress. When i think of what i have done oft road, its pretty solid. Lots of moaning about ird's etc but when yer think of the forces involved... It's not a bad setup and certainly works.
 
Recently I have noticed a slightly increased resistance on full lock reverse. Not much but I fealt it warranted checking. I also heard one of the rear wheels grab a little when pulling away quicky from a gravel driveway. As a result, I read through the entire thread - that was a mission! Anyway, results below.

Recon VCU from Bell, fitted November 2017

Current vehicle mileage 141000, VCU mileage ~22,000

Test 1 - after driving 8 miles or so, 8kg at 1.2m gave me an average time of 19s
Test 2 - very cold frosty morning having rested over night, 8kg at 1.2 gave me an average of 23s
Test 3 - very cold frosty morning after test 2, ~5kg at 1.2m gave me an average of 41s

I guess the above means it's okay, but one to be monitored?
 
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I guess the above means it's okay, but one to be monitored?
Yes, it needs monitoring. Out of interest, are the front tyres a lot more worn than the rear? I've found that transmission drag increases, when the front tyres wear below about 50% of the tread remaining on the rear. This is why I swap my tyres front to back every 3K miles.
 
Yes, it needs monitoring. Out of interest, are the front tyres a lot more worn than the rear? I've found that transmission drag increases, when the front tyres wear below about 50% of the tread remaining on the rear. This is why I swap my tyres front to back every 3K miles.
Funnily enough, I changed my tyres in November, but on the set I replaced, the fronts were on the limit and the rears had a few mm left. I might try your trick Nodge. I guess if you do it at short enough intervals the difference is negligible enough to not cause wind up?

P.S. Over what time for 45 to 90 with 8kg at 1.2m should I be looking to replace? 30s?
 
Funnily enough, I changed my tyres in November, but on the set I replaced, the fronts were on the limit and the rears had a few mm left.
I can feel when my fronts are worn more than the rear. Or should I say, the FL1 feels different when fitted with 4 tyres of equal wear, compared to when the fronts are worn more than the rear.
I might try your trick Nodge. I guess if you do it at short enough intervals the difference is negligible enough to not cause wind up?
I found that the difference in wear over 3K miles is under 1mm, which doesn't seem to affect my old VCU.
 
Funnily enough, I changed my tyres in November, but on the set I replaced, the fronts were on the limit and the rears had a few mm left. I might try your trick Nodge. I guess if you do it at short enough intervals the difference is negligible enough to not cause wind up?

P.S. Over what time for 45 to 90 with 8kg at 1.2m should I be looking to replace? 30s?

I can't answer your second question, but mine's also reconditioned and has done slightly fewer miles than yours (say 15,000). Mine also feels slightly "draggy" on full lock and I'm getting about a 50 second time with 5kg. Received wisdom on here seems to be that any more than a minute at 5kg and 1.2m and the VCU needs changing.
 
Just checked my G4 as it is getting a bit road noisey. 55 seconds. So rebuilding a VCU for it promptly.
It does have Grabber AT tyres which I know are not the quietest.
 
Interestingly....
Checked my TD4 in Jan 19 at 156k miles.
1.2m 5Kg gave 18 seconds.

Detected a tightness when reversing on gravel the other day so retested it.
172k miles, VCU fitted at 90kmiles.
1.2m 5Kg didn't move at all!!

So life for this VCU was 82k miles. Always had equal tyres and pressures.
I meant to check it more frequently as stated but didn't!!!

New VCU to be included in rear end rebuild me thinks.
 
Gosh that's interesting! Thanks for sharing. I checked mine the other day (a warmer day than the last time I checked it) and the result was much the same - maybe a bit better at 48 seconds (again with 5kg at 1.2m). In view of what you've said, I'll keep an eye on it regularly.
 
Interestingly....
Checked my TD4 in Jan 19 at 156k miles.
1.2m 5Kg gave 18 seconds.

Detected a tightness when reversing on gravel the other day so retested it.
172k miles, VCU fitted at 90kmiles.
1.2m 5Kg didn't move at all!!

So life for this VCU was 82k miles. Always had equal tyres and pressures.
I meant to check it more frequently as stated but didn't!!!

New VCU to be included in rear end rebuild me thinks.
Geepers, that went downhill quick!

Can't have been much change in 66k miles and trashed within the next 16k.

Given that it didn't move, I wonder if there's a mechanical failure inside somewhere? (plate bent)

Presume you're sure the brake wasn't binding.
 
Thanks GG. All ideas considered. It did seem quick but I have had a fast decline before, not this fast!!

Will double check your ideas before condemning the VCU.

Started a rebuild on a spare anyway, always useful!!
 
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