Manual vcu conversion

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N.Murdoch

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Right, I'm new to this, had a look but I couldn't find any posts/threads for this so here goes.

I'm thinking about making a manual VCU conversion, as a bolt in unit to replace the original, so I could run front wheel drive with the back wheels/shaft assembly from the vcu back freewheeling when driving normally, and engage four wheel drive when needed.
What problems can everyone think if I use a dog type clutch i.e. ease of use/longevity of dogs when disengaging/engaging drive? Or should I go for some kind of multiplate friction clutch assembly?

Any help/input would be much appreciated,
Cheers
 
This again?

There isnt a dog box out there for reasonable money that will allow on the move shifting, so on a snowy road you will have to stop, engage 4wd, drive it.....uh oh a clear section, cant wind up the transmission and blow the IRD so disengage back to 2wd.......oh, more snow, need to stop to engage 4wd again and so on.....

There is no fuel saving to be had running 2wd on the road so that shouldnt be your motivation either.

Its a lot of trial and error (and believe me I know how much time actually gets sunk into this sort of project) potentially a lot of money and potential unreliability in order to make the car LESS competent that standard.

Buy a good VCU and forget about it. If you are really worried, change the VCU every 5 years, its only £200 for a recon. unit.
 
Thanks for the link hd3, really helpful.

I guess the motivation would be to reduce strain on the drive components and only engage 4wd when really necessary, realistically once the front wheels have slipped. So surely if you've lost traction already it's not that bad having to be stationary to engage four wheel drive, although I get what you mean dave.
I'm no expert when it comes to off-roading, and a lot of my interest in this project just comes from wanting to see if I could do it, but from an engineering perspective making a clutch forms scratch to act as a simple on/off doesn't seem too difficult, rather than trying to modify the vcu into something else.

Anyway, thanks for the replies, wasn't aware anyone had a made a serious attempt at this yet.
 
The whole point of the VCU is that there is no real drive to the rear anyway under normal use and its when the front wheels slip faster than the rears that it tightens up, driving the rears as needed. It does this pretty much instantly with no intervention needed from the driver.

The entire point of having an all wheel drive car is that you have the sure-footedness when you need it....a road partially covered in snow....putting a wheel on a muddy verge, a suddenly soft bit on a gravel track.... You dont want to loose momentum and have to fanny about engaging this system yourself and it is often dangerous to do so....ie on a snowy road, keeping momentum up is key and suddenly finding some bloke in a Freelander in front of you having to stop to engage his experimental four wheel drive could really spoil your afternoon.

If you really want to - fit your clutch or dog box or whatever, but leave the VCU in place as well, that way the car can still drive and perform as designed to when needed and can be disengaged for inexplicable reasons when you fancy 2wd.
 
How about modification of a honda CRV rear diff to replace the rover unit , as then you could just have a solid prop , and the honda unit is pretty much bomb proof , a fluid change usually sorts when it gets a bit juddery. ?
 
Listen to Dave. It's been an idea that has been tossed about for ages. The VCU is good at what it does. So much so that LR used them in the RR for a while. The systems now employed by LR are all electronic controlled clutched units. They work well but are hideously expensive to fix when they fail. As said, simply replace the VCU every few years and forget about it in between.
 
Have you tried driving your Freelander in 2wd? Many peeps here (including me) have removed the propshaft at some stage and found the car unpleasant to drive. Lots of wheelspin and understeer especially in the wet.
If you have the skills to do what your suggesting then fix the VCU yourself. Check out the DIY VCU thread.
 
The closest we ever got to a change of vcu was the hcu. There's a fred on it on ere but it's a lot of hassle. Recons are available and new ones have come down in price massively. The hcu involved nicking a suspension damper fing oft an Evoque. ;)
 
I can only agree with what's been said above. You won't make a better 4WD system than standard or a cheaper one. If you want to build something, that's fine, people have been chopping and changing Landies since they were first produced. However, the only motivation would be for your fun and personal challenge - not for transmission benefit.

As a matter of interest, when you are losing traction, often the last thing you want to do is to stop and engage diff lock (from permanent 4WD) or switch to 4WD as you lose momentum. Freelander's VCU is great for this - unlike Disco, Defender (permanent 4WD) and Jap/American trucks/UTEs (RWD switchable to 4WD).
 
GrumpyGel said:
I can only agree with what's been said above. You won't make a better 4WD system than standard or a cheaper one. If you want to build something, that's fine, people have been chopping and changing Landies since they were first produced. However, the only motivation would be for your fun and personal challenge - not for transmission benefit.

As a matter of interest, when you are losing traction, often the last thing you want to do is to stop and engage diff lock (from permanent 4WD) or switch to 4WD as you lose momentum. Freelander's VCU is great for this - unlike Disco, Defender (permanent 4WD) and Jap/American trucks/UTEs (RWD switchable to 4WD).
Click to expand...
The variable clutched system used in the D3/4, RRS and FFRR are far superior compared to open/ locked transfer box of the older LR models. As to weather the clutched system is much of an improvement over the cheap to fix VCU, I'm still not sure. The clutched system is good, but expensive to repair when it's messing around.
 
Nodge68 said:
The variable clutched system used in the D3/4, RRS and FFRR are far superior compared to open/ locked transfer box of the older LR models. As to weather the clutched system is much of an improvement over the cheap to fix VCU, I'm still not sure. The clutched system is good, but expensive to repair when it's messing around.
Click to expand...
I've wondered how the later 'big' Landies handle their center diff, thanks for the info.

The VCU has no inputs other than the prop shafts. It sounds like with these clutches JLR can put a big round knob in the console, maybe even 1 that mysteriously rises up when the ignition is turned on, and could put lots of fancy looking icons on it that maybe control these clutches - that's gotta be worth a good few K on the asking price :)
 
GrumpyGel said:
I can only agree with what's been said above. You won't make a better 4WD system than standard or a cheaper one. If you want to build something, that's fine, people have been chopping and changing Landies since they were first produced. However, the only motivation would be for your fun and personal challenge - not for transmission benefit.

As a matter of interest, when you are losing traction, often the last thing you want to do is to stop and engage diff lock (from permanent 4WD) or switch to 4WD as you lose momentum. Freelander's VCU is great for this - unlike Disco, Defender (permanent 4WD) and Jap/American trucks/UTEs (RWD switchable to 4WD).
Click to expand...
disco and defender and pre v/c rrc have a center diff lock thats can be engaged on the move, permanent 4wd does give better handling compared to selectable 4wd
 
jamesmartin said:
in reality,its designed so to do
Click to expand...
Admittedly the linkages can probably be made to work better, but every Disco that I've (tried) to switch between high/low or into/out of diff lock, the stubby little lever has been very difficult to shift. So in practice you have to stop and fight with the lever to get it to where you want it!
 
GrumpyGel said:
I've wondered how the later 'big' Landies handle their center diff, thanks for the info.

The VCU has no inputs other than the prop shafts. It sounds like with these clutches JLR can put a big round knob in the console, maybe even 1 that mysteriously rises up when the ignition is turned on, and could put lots of fancy looking icons on it that maybe control these clutches - that's gotta be worth a good few K on the asking price :)
Click to expand...

The Discovery 3/4 uses something called Terrain Response. It's a very clever system that automatically engages and disengages the clutches in the transfer box, as and when required. The user can preselect one of 5 different modes depending on the surface being traversed. These are selected on a rotating knob in the center console located behind the hand brake switch. The 5 modes are.
1: Normal mode for general driving.
2: Grass, Gravel and Snow.
3: Mud and Ruts
4: Sand.
5: Rock Crawl.
Each will preselect a centre diff setting giving optimum slippage for the particular surface the vehicle is on. The TR system works in conjunction with the ABS system, Air suspension system and Engine ECU, tailoring things like suspension hight and throttle pedal sensitivity for optimum performance. For instance, if G,G,S mode is selected, the throttle sensitivity is softer than normal. However if Sand mode is selected, the throttle response is sharper than normal, ensuring plenty of power.
In addition to the 5 position rotary TR knob. There are additional controls for selecting vehicle hight and low range box. There's also a HDC control button. The difference on the Discovery HDC is the target speed can be altered using the cruise control buttons.
The system works very well and will get the heavy weight Discovery pretty much anywhere as Top Gear showed back in 2004. It's for this reason I always fancied one. When I happened to come across a D3 that I could afford, I bought it.
Here's the TR controls.
Screenshot_2015-10-26-18-05-04.png
 
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