DIY VCU service

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Alibro said:
Agreed, They are separated by a thin film of fluid with nothing mechanical holding them apart.
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Doesnt have to be mechanical - if 2 plates are close, then a gap, then 2 more plates, the fact that 2 plates are close, will mean they will act as pairs.

Alibro said:
Ehmmm, I thought that was what I said I had done. After taking the top off I carefully marked the first 10 or so I removed and found they all followed the same pattern.
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Hadnt read that bit - good to know :)
 
The Mad Hat Man said:
Multiple disks cannot operate as pairs, if the gap between plates is identical.
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The Mad Hat Man said:
Doesnt have to be mechanical - if 2 plates are close, then a gap, then 2 more plates, the fact that 2 plates are close, will mean they will act as pairs.
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GKN's doc on VCUs doesn't give hardly and info, but it does show plates touching in Hump mode...

http://www.gkn.com/driveline/about-us/Documents/datasheets/Viscous-engl.pdf

This effect is also backed up by this document...

http://www.easy2design.de/stuff/visco_sae.pdf

Alibro said:
They are separated by a thin film of fluid with nothing mechanical holding them apart.
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Alibro said:
There was no sign of wear on mine, not sure how they would wear with silicone between each disk
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I think there was a reason your old fluid came out a grey metalicy colour. If you look at section 2.4 in that doc, it describes the wear on (the alternating sides of) plates. It also states that Silicone fluid is not a good lubricant, so its not going to help close (touching) plates move against each other freely - this obviously helps transmit drive, but will not stop wear.

TBH, I think that document is about as good definition of how the VCU works as anyone is likely to put together.
 
>Silicone fluid is optimised with specific additives for lifetime performance
> The degressive locking characteristics (viscous mode) can be tuned by fluid viscosity, number and size of plates, and fluid filling percentage
> The “Hump” mode activation is tuned by the fluid filling percentage

so it has special additives, viscosity and amount of fill affects its characteristics and operating point. - not a quick "just replace the fluid then"?
 
htr said:
I referred to that particular publication earlier. It, and the Aussie site I found it on, discuss the fill amount and its calculation - see post 279 I think.
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Yeh, it sort of looks like a document that can be ignored - cos its "old fashioned" - scanned/typed doc from the 80's. But in actual fact its from when all the tech was developed for VCUs that were used in loads of cars including Freelander - so in actual fact it is absolutely relevant to Freelander.

All the "sales slang" used in the GKN doc is probably just flannel. They talk of additives etc - but nobody uses just "silicone oil" in their VCUs, its probably just 'good old' Polydimethylsiloxane that everyone uses in their VCUs and that document talks about.

TBH even if GKN do use a "secret mix of herbs and spices" their VCUs don't exactly appear to be the best performers - at least for life expectancy (even though their sales slang says they are optimised for 'lifetime performace'). So I recon if you're rebuilding, using the hardware of your old VCU and that document to tell you what fluid to use and what air gap to leave aint a bad way of going about it.
 
Question re' the VCU's construction:
#1 How thick is the side wall of the VCU - the cylindrical part.
#2 How thick is the piece that's lathed off, I'll call it the 'cap', at the section where it's separated from the main VCU body, that would be the outer edge. It looks quite thin.
#3 How thick is the steel of the 'cap' away from the lathed area.
#4 Finally inside the VCU are there any seals or bearings?
 
htr said:
Question re' the VCU's construction:
#1 How thick is the side wall of the VCU - the cylindrical part.
#2 How thick is the piece that's lathed off, I'll call it the 'cap', at the section where it's separated from the main VCU body, that would be the outer edge. It looks quite thin.
#3 How thick is the steel of the 'cap' away from the lathed area.
#4 Finally inside the VCU are there any seals or bearings?
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Probably 2 or 3mm but it also has the splines which hold half of the disks.

At the edge it is 2 or 3mm like the wall.

The thick part is around 10mm.

There are bearings but I didn't touch them.

All the above should be taken with a large pinch of salt but are not too far away.
 
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GrumpyGel said:
...TBH even if GKN do use a "secret mix of herbs and spices" their VCUs don't exactly appear to be the best performers - at least for life expectancy (even though their sales slang says they are optimised for 'lifetime performance')...
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How can the original vcu by GKN be judged as not being the best performer?

Yes they fail but they would have been tested by GKN and LR to find the correct setup they wanted. LR would have done a lot of testing on and oft road to get things right. We don't have a comparison vcu as the setup the reconners use won't compare as they're looser and it's doubtful they use the same type and amount of fluid in reconned vcu's.

Interesting discussion.
 
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GrumpyGel said:
TBH even if GKN do use a "secret mix of herbs and spices" their VCUs don't exactly appear to be the best performers - at least for life expectancy (even though their sales slang says they are optimised for 'lifetime performace'). So I recon if you're rebuilding, using the hardware of your old VCU and that document to tell you what fluid to use and what air gap to leave aint a bad way of going about it.
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I'm working through the idea of lathing of the 'top' [input end] and cleaning it out. Welding a ring collar, 'O' ring and circlip arrangement to seal it up again like the VW arrangement. I'd also add to holes 180º apart to either add a bit more fluid or remove some in order to adjust that air gap.

I've read and reread that article several times so have got what's what reasonably well sorted in my own head. The physical machining is the easy bit. Getting silicone fluid is also easy, as is the filling. I'd go for a 8% air gap myself and see how that goes.

What I want to find out now is what antioxidant is added to the silicone fluid?
I found this site which looks interesting Kingindustries see pages 11 & 12. Has anyone else heard of other manufacturers/suppliers. I saw on eBay some diff silicone fluid of 100,000cst which was available in 59g bottles. It originated from Lucas Oils USA. Not sure it it's intended for automotive use of RC cars!
 
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Alibro said:
As my VCU was pretty well solid I figured the drive train may have been weakened so that is why I wanted the 60,000 as I figured it would cause less strain. Am now thinking of getting some 30,000 and substituting 40 or 50% to see if it loosens things up a bit. I should be able to bleed it from one of the holes I've made and squirt the thinner stuff back in with a syringe.

I took the car out today for a 70 mile round trip including town, A road and motorway driving. It felt sooo much better than when Mondo mode as everything felt tighter. It was a wet day so I deliberately drove like a hooligan at junctions and round roundabouts and the car handled much better. No sign of the chronic understeer it had before.
The only issue was a slight vibration between 60 and 70 which I wasn't surprised about. Apart from the work I did and the dodgy welding I noticed the damper wasn't completely round. When I was testing the VCU for wobbliness after welding it together I spun it and found the VCU was fine but the damper had a wobble. Not sure how or why but it has three possible positions, I marked it before removing so I know it is in the right position but will try turning it to see if it helps.
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A quick update, I rotated the damper by one bolt position anticlockwise on Saturday and took it back onto the motorway and the vibration has gone. :)
I then did the one wheel up test and it still seems fine, although I was busy so I just pushed the wheel round without adding weights and measuring the time. I think I might inject some more fluid in though as I'm not convinced I had enough in it.
As for it being loose I would say it is not, Like I said I haven't measured it properly yet with 8kg weights but I could turn the wheel fairly easily with a wheel brace when it was up and I could see the rear wheels spinning on a steep grass hill so the only two measurements available to us seem to have been met.
 
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Alibro said:
As my VCU was pretty well solid I figured the drive train may have been weakened so that is why I wanted the 60,000 as I figured it would cause less strain. Am now thinking of getting some 30,000 and substituting 40 or 50% to see if it loosens things up a bit. I should be able to bleed it from one of the holes I've made and squirt the thinner stuff back in with a syringe.

I took the car out today for a 70 mile round trip including town, A road and motorway driving. It felt sooo much better than when Mondo mode as everything felt tighter. It was a wet day so I deliberately drove like a hooligan at junctions and round roundabouts and the car handled much better. No sign of the chronic understeer it had before.
The only issue was a slight vibration between 60 and 70 which I wasn't surprised about. Apart from the work I did and the dodgy welding I noticed the damper wasn't completely round. When I was testing the VCU for wobbliness after welding it together I spun it and found the VCU was fine but the damper had a wobble. Not sure how or why but it has three possible positions, I marked it before removing so I know it is in the right position but will try turning it to see if it helps.
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Hi
I have been following your post with much interest and I like what you have done.
I purchased a recon vcu from bell's which is good and I have a slight vibration from propshaft.I have had the prop turned to see if it was the cause but still have vibration.
After reading your post I wondered if my Damper was slightly out of true as this recon vcu was from another car and bell's just recon the actual vcu and do not touch the damper.
 
roshe25 said:
Hi
I have been following your post with much interest and I like what you have done.
I purchased a recon vcu from bell's which is good and I have a slight vibration from propshaft.I have had the prop turned to see if it was the cause but still have vibration.
After reading your post I wondered if my Damper was slightly out of true as this recon vcu was from another car and bell's just recon the actual vcu and do not touch the damper.
Click to expand...

The front and rear parts of the propshaft turn independently anyway so I don't know what 'turning' it would achieve, other than maybe repositioning it on the bolts.

That could be your issue right enough, It took me all of 5 mins to turn it, I drove two wheels on the drivers side onto wooden blocks and crawled under. Undid the bolts with a spanner and moved it round.
Certainly worth giving it a go, I was going to try each position to see if it worked and if none did I was going to cut it off. To remove it would mean pulling one of the bearings off the VCU and I didn't think I could do that without damaging it.
 
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Alibro said:
The front and rear parts of the propshaft turn independently anyway so I don't know what 'turning' it would achieve, other than maybe repositioning it on the bolts.

That could be your issue right enough, It took me all of 5 mins to turn it, I drove two wheels on the drivers side onto wooden blocks and crawled under. Undid the bolts with a spanner and moved it round.
Certainly worth giving it a go, I was going to try each position to see if it worked and if none did I was going to cut it off. To remove it would mean pulling one of the bearings off the VCU and I didn't think I could do that without damaging it.
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Hi
Thanks for reply,As I have back problems I will have to wait till my son has time to work on it.
I will be getting him to mark the position it is on then turn one hole clockwise at a time.

By the way how are you getting on driving with your vcu is everything working ok,I think what you have done with putting all your knowledge and pictures on this site is great
 
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roshe25 said:
Hi
Thanks for reply,As I have back problems I will have to wait till my son has time to work on it.
I will be getting him to mark the position it is on then turn one hole clockwise at a time.

By the way how are you getting on driving with your vcu is everything working ok,I think what you have done with putting all your knowledge and pictures on this site is great
Click to expand...

Thanks for the kind words, It's fun doing stuff others say can't be done, I'm stupid enough to give most things a go and worry about the consequences later. Sometimes it works out well.

Sorry to hear about your back, Mine ain't too special either so I feel for you.
The car is driving great now apart from the clutch is sometimes very jumpy and sometimes not???? I think the previous owner had a caravan and has probably burnt it out and had it replaced with some cheap crap. That will be my next project, I've spent the last couple of weeks fitting poly bushes and new brakes to my MGF to get it ready for MOT tomorrow so haven't had time to sort it yet.
 
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Stumbled on this today. Its No. 7 in a series of at least 10 videos rebuilding a "Freelander Differential". Naming aside, its a complete documented drain and refill of a VCU. I haven't a clue what language its in and presume there's no speaking (no speakers on PC) so don't know what thinning fluid he used - but he drills holes at both ends and uses an air line to push it out. Looks like he fills with 10,000 CST so it probably won't pull the skin off custard and would definitely have trouble shifting a Freelander by it back wheels up a hill - but a good tutorial.

 
GrumpyGel said:
Stumbled on this today. Its No. 7 in a series of at least 10 videos rebuilding a "Freelander Differential". Naming aside, its a complete documented drain and refill of a VCU. I haven't a clue what language its in and presume there's no speaking (no speakers on PC) so don't know what thinning fluid he used - but he drills holes at both ends and uses an air line to push it out. Looks like he fills with 10,000 CST so it probably won't pull the skin off custard and would definitely have trouble shifting a Freelander by it back wheels up a hill - but a good tutorial.

Click to expand...

Interesting video but I don't believe the results will be that good. One thing he is doing wrong is having the VCU vertical, This means all the plates are pressing down on each other and makes the VCU much harder to turn than if it was on it's side.
Also even if he spends days squirting in whatever cleaning fluid he was using to soften the 'glue' inside he will never clean in between the plates properly. This means at best he will have some horrible mix of the old fluid, the cleaning fluid and the new fluid. Probably why he is using 10,000 as it will mix with what is left of the old stuff which will still be like glue to make something close to what it is meant to be.
I'd say it's much betterer to cut the end off, clean the plates properly, weld it back together and squirt in new fluid.
 
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I thought a wee update was in order. What I did was far from scientific and I have no way of knowing how close I came to getting the quantity or type of fluid right but in the real world I'm not sure it matters that much. My reason for saying that is personal experience. Doing the one wheel up test with a 5kg weight at 1.2m I got times between 11 and 15 seconds. This would indicate my VCU would be rubbish when pushed and might leave me stuck in 2wd if things got slippy. I am happy to confirm that is not the case. Last week I used my hippo to drive through some very soft sand while pulling a pallet as I was trying to flatten out a new horse arena. It pulled with no problems at all even though the wheels were sinking in over 6 inches at first. I really thought I might struggle as the sand had been dug up a lot by horses and was really soft. I was very please and surprised how well the car pulled through it.
 
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nice posts Alibro, after feeling mine tightening up over the last few weeks even with a 30 second count I might just might get a reconed VCU, the guy from bar props said he will bench test it for me and compare it to a reconditioned one before I commit to buy. Incidentally would yours feel tight in reverse, on full lock on tickover after say 10 meters
 
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