austen
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You cannot drain fluid from a Naggered vcu as it turns into a jelly, the only way to recon a vcu properly is to cut it open.
VCU Repair
- Thread starter celt69
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Grayo
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Hi Austen,
Thanks for the input and I'm sure you know what your talking about. But it would be interesting to find out what Jonaf, is talking about.
I'm interested as he said he can change how much rotational speed difference is needed to lock the VCU, that's very interesting to me.
jonaf
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My VCU slip adjustments are just experiments. But the results work OK for my needs. It would be interesting to know in which way others' attempts to loosen up stiff VCUs have failed.
When I get time I will make further experiments. The unit I took out yesterday was just a little bit stiffer than a new one but I will try to adjust it by diluting the fluid with thin silicone oil, which is easier to find.
I like my VCUs to be on the loose side and I think they transfer enough torque even if they slip a little.
Grayo
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austen
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We have come across units that have had various fluids pumped in, including paraffin, engine oil, diff oil. All of these just loosen them to the point nothing is transferred, especially as they get hotter and the added fluid gets thinner due to the heat
the VCU should use something similar to the VW Syncro cars. Their VCU is maintainable! This is the Fluid used. 25 kg = 800 Euros
http://www.reiff-tpshop.de/shop/de/...ilikonpasten-und-le/1568-wacker-ak100000.html
http://www.reiff-tpshop.de/shop/de/...ilikonpasten-und-le/1568-wacker-ak100000.html
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An interesting comment, but what do you make your hypotheses on?
Are the mechanicals inside the VW, the same?
Is the Torque transfer requirements the same?
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Austen - having just read this article on the VW VCU, the following comments were made.....
"The plates inside the Viscous Couplings have microscopic burrs on them that are critical to the proper torque transfer of these units. This means that the plates wear out and cannot be reused!
Since replacement plates are not available, this means Viscous Couplings should not be rebuilt until a source of replacement plates can be identified.
Any viscous coupling under pressure is likely a bad viscous coupling! If you open the unit, and a lot of VC juice comes out, the VC is likely bad.
Viscous Couplings have a useful life of 60,000 to 90,000 miles. After that, they are worn out and should be replaced. This makes it sound like they should be replaced as often as your clutch!"
I know that the Freelander VCU also has the "burrs" on the plates - what is your take on this?
"The plates inside the Viscous Couplings have microscopic burrs on them that are critical to the proper torque transfer of these units. This means that the plates wear out and cannot be reused!
Since replacement plates are not available, this means Viscous Couplings should not be rebuilt until a source of replacement plates can be identified.
Any viscous coupling under pressure is likely a bad viscous coupling! If you open the unit, and a lot of VC juice comes out, the VC is likely bad.
Viscous Couplings have a useful life of 60,000 to 90,000 miles. After that, they are worn out and should be replaced. This makes it sound like they should be replaced as often as your clutch!"
I know that the Freelander VCU also has the "burrs" on the plates - what is your take on this?
austen
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Yes they have burrs on, this is what helps create the shearing effect through the silicon. None of the burrs touch each other and its purely the fluid that flows against it. We looked at the state of these plates when first looking into reconditioning the units and comparing a new vcu plates against and knackered vcu, and could not detect any wear/difference. Plus when rebuilt with new fluid they both performed in exactly the same manner. The plates are very hard, like a spring steel so it would take a hell of a lot to wear them out. I don't know the full ins and outs of the vow system, maybe the plates aren't as hard, or there are other factors which could cause the wear.
Brack
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Think VCU's should be left well alone to the experts, anything DIY to an important part like this that can fail and cause a dangerous situation should not be attempted IMHO 
Think VCU's should be left well alone to the experts, anything DIY to an important part like this that can fail and cause a dangerous situation should not be attempted IMHO
What about brakes, are they "important" and should therefore not be touched by "the DIYer"?
Brack
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Brakes are designed to be fully servicable whereas the vcu is a sealed unit therefore not designed to be servicable - so tamper with it at your own risk - best left to the experts who would be fully responsible if their reconditioned vcu failed and caused an accident.
BOOMER
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I actually wonder whether there isn't a way to junk the VCU altogether and engineer a way to fit a simple electromagnetically activated dog clutch in its place.
It's commonly used in the agricultural sector as a robust way of engaging/disengaging drive so why not on a Freelander?
Has anyone tried this yet?
It's commonly used in the agricultural sector as a robust way of engaging/disengaging drive so why not on a Freelander?
Has anyone tried this yet?
jamesmartin
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you would need a center diff ,the answer is just fit a new one
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BOOMER
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Why not, dog clutches have worked well on tractors, dump trucks, series motors and the slittys for years.
Off road use only, drive is split 50/50 off road, disengage on road/hard surfaces so no transmission windup.
True that less hassle and probably cheaper to just replace VCU.
Just adding a variation to the debate
jamesmartin
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it is a good one, but freelander isnt 50/50 split rear wheels are driven slightly slower to give 4wd car with fwd feel ,incedently the 4wd mfs had front wheels driven faster in 4wd so that front wheels didnt hinder rear
jonaf
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Of course the only way to recondition a VCU is to disassemble it, clean it and fill it with the proper amount of correct fluid
However it is possible to drain some of the old silicone and replace it with thinner fluid. If the unit is left with the plugs removed, the fluid will seep out. This takes a very, very long time (weeks) but can be sped up by attaching a compressed air line to one of the holes.
A stiff VCU does not have any value anyway so I do not think there is any risk making experiments with it.
I do not expect Bell Engineering to share their business secrets but I assume the professional way of making a VCU less stiff involves thinner liquid?
BOOMER
Bloke from Dorset
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That is very true, tractors do have a 2/3% lead on the front wheels, easily done on a Freelander by putting the more worn tyres on the rear if a dog clutch was fitted - which is the exact opposite of best practice when standard VCU fitted.
