4 wheel drive - is it?

The Mad Hat Man said:

coz if yu switched on the dog-clutch with the propshaft turning - it would be like trying the starter motor with the engine running - not very effective!
So yu wud have to stop to engage 2 or 4wheel drive - hence an interlock - I just thought handbrake would be an easy system to use.

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So anyone going to make this happen??

i'm workin on it.
Any help wud be appreciated.

lookin for an electrically (12v not mains) operated dog clutch capable of takin 200-300bhp.
oh yes - and poss a spare prop shaft to try it out on.
oh yes agin - poss a car that aint 8 feet in the air to try it on. Minge - yu game?

The Mad Hat Man said:

i'm workin on it.
Any help wud be appreciated.

lookin for an electrically (12v not mains) operated dog clutch capable of takin 200-300bhp.
oh yes - and poss a spare prop shaft to try it out on.
oh yes agin - poss a car that aint 8 feet in the air to try it on. Minge - yu game?

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What does Nissan X-Trail use?

ta Dearot
will have to check. Unless anyone here knows -= maybe Clutchdust?

it would have ta go before the vcu cos of the fluid mechanics of the magic vcu, ad a look and depend on the dimensions of the dog/solenoid bit tight but fee sable. . .

wot a super alien yo is.
Why do yu suggest before the vcu?
I woz thinkin about a modified propshaft - coz yu just take the prop off normally - dont ya? - is that the front or rear prop Minge?

oh by the way - top o' the mornin' to ya, my fine space alien.

by the way - the poll has had a "shut it down vote" - by accy - yu reckon - or aint he allowed to vote as he shud be impartial - or is allowed proxy votes - coz of all the e-mails hes had?

Well no proper reason ,only here's my logic ,why have the vcu spinning if yer in two wheel drive, no point, and at a given rpm it does its thing, best save on any wear un tear,so stick it afore. . .

The Mad Hat Man said:

wot a super alien yo is.
Why do yu suggest before the vcu?
I woz thinkin about a modified propshaft - coz yu just take the prop off normally - dont ya? - is that the front or rear prop Minge?

oh by the way - top o' the mornin' to ya, my fine space alien.

by the way - the poll has had a "shut it down vote" - by accy - yu reckon - or aint he allowed to vote as he shud be impartial - or is allowed proxy votes - coz of all the e-mails hes had?

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Its open to all,Accy is entitled to his say. . .

ming said:

Well no proper reason ,only here's my logic ,why have the vcu spinning if yer in two wheel drive, no point, and at a given rpm it does its thing, best save on any wear un tear,so stick it afore. . .

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seems a good reason to me - can ya send my any piccies and/or dims? i aint got mine handy at the mo ...

a question to anyone technical.

If the engine puts out between say 150 and 300 BHP - does the dog-clutch have to be able to cope with all of that - or only half (cos 1/2 goes to front wheels)?
Any thoughts/calculations mite be useful.
I have found a suitable? Dog-clutch - but it is only rated at 85BHP!

Hi guys - I opened up a thread on an engineering site regarding the disconnection of the rear drive and this is the feedback I got. Please read. Basically they are saying that you dont reduce fuel consumption and dont gain any power. This seems to contradictory to what you guys are saying having removed the propshaft. Your (meaningful) comments would be apreciated.

With a dog clutch, you will still be turning almost all the 4WD drive train, it will just be disengaged from the engine, but it will still absorb about the same amount of power. Turning the axles and especially the differential will consume some power. Not having to try to drive both axles at slightly different speeds should save some power.

Freewheeling hubs as used on OEM part time 4WDs saves more as the second diff is not being turned.


When Audi introduced the Quattro they claimed that the reduced drag from the wheels more or less compensated for the increased drivetrain loss, so the fuel consumption was not hit by the AWD.

If the intention is to save fuel then the /maximum/ benefit would be of the same order as the difference between a 2wd and 4wd version of the same vehicle.

The six-speed model meanwhile is rated at 12.2 litres/100km for RWD and 12.8 litres/100km for AWD.

However, the AWD weighs 90 kg more, from 1995 for the 2wd, and I suspect that about half that fuel saving is due to the weight change.

My guess then is that you would save a maximum of 0.3 litres/100 km, and if we believe Audi it will be less than that. At today's fuel costs in the UK (taking a wild stab) that is 0.6p/mile for which you have to install this thing and risk blowing up your transmission. That's 60 pounds a year.

ming said:

If ya vcu or rear bit playin up ,can get yer outa trouble while ya order ya parts, go's like eh bat outa hell ,front wheels can spin very easy and mpg fantastic , if i could find somthing to switch this on and orft i would do it. . . .

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After drawing blanks on LR forums all over the world, I have decided to replace my siezed VCU with a switchable unit of my own concoction. The unit simply splines into each end of the tail (sorry Prop!!) shafts in place of the VCU/Harmonic damper assembly.
It consists of a yoke driven sleeve over a pair of splines fitted into a housing (plenty of bearing support!!)which bolts to the same mounting points as the VCU support bearings.
Car operates as front 2WD drive, completely freewheeling the rear until switch operated solenoids put vacuum onto a small diaphragm, causing the yoke to slide the sleeve over the splines which give drive to the rear!!
can't be any worse than a permanently totally siezed VCU because its only used on slippery grass, gravel etc -- not on hard capped highway. ie 4WD when you want it, and no more self destructing drive train.
Using only freely available components from US and Japanese 4WD.

If you are interested, am prepared to discuss further.
Cheers
Ian Hughes
Tassie

PS
Most of that info earlier in this thread about proportions of front and rear torque split with a VCU in place is IMHO crap. Depends on how stuffed the VCU fluid is, and which relative diff ratios front to back you are running.
Humble chemical engineering perspective!!!!

Hi Ian
if yu got something that works, let us into the secret - better still write it up as a how to and post it on the forum.

give us some more info - we are all ears (especially Minge -but then he is an alien)

The Mad Hat Man said:

I woz thinkin about a modified propshaft - coz yu just take the prop off normally - dont ya? - is that the front or rear prop Minge?

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yes ming which one? i think it doesnot make any diff right?!

The Mad Hat Man said:

Hi Ian
if yu got something that works, let us into the secret - better still write it up as a how to and post it on the forum.

give us some more info - we are all ears (especially Minge -but then he is an alien)

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Hi Mad hat man,
The components are over at the engineering shop ready for assembly.
I'll take a few pics and see if I can post them. In essence the unit I am getting made simply replaces the VCU/harmonic damper. I'm using the male splines off my old vcu unit so that it simply fits into the female splines on the the front and back prop shafts. This means a standard VCU unit could be easily refitted if need be. (For resale??)
Any of the many Japanese and US medium 4WD vehicles which are normally rear wheel 2WD with independent front suspension incorporate a facility which Toyota call Automatic Disconnect Differential. This is simply a sleeve/spline disconnect/connect coupling in one of the two front axle shafts which is actuated (in most cases understand) by a solenoid switched, vacuum driven diaphragm (like a mini brake servo), which slides a yoke, hence engaging/disengaging the spline sleeve over the splines.
On these vehicles (normally rear wheel 2WD) when the sleeve is disconnected, the open front diff sees the disconnected axle as slipping, so no drive goes to either front axle.-- normal two wheel drive. When the ADD unit is actuated, the front half axle connects and torque is then distributed to the front and rear axles and wheels, as the diffs deem appropriate.
My idea is to simply reassemble these bits in a housing (with generous bearing support)and instal it in the propshaft shaft replacing the VCU/harmonic damper unit.
A couple of downsides are:
1. Once engaged, the system provides absloutely no slip whatsoever. Therefore must only be used on slippery surfaces (no worse than a totally siezed VCU!!!!)
2. Because (on early models at least) the two prop shafts spin at relative 0.8%slip, care should be taken when engaging --slow vehicle speed and on forgiving surface.
The upside is that in front wheel 2WD mode the system absolutely freewheels the rear propshaft/diff/rear axle system. No more drive system howls and whines, no crap rear tyre wear, no scrubbing grinding etc going slowly backwards on full lock, -- better still no ludicrous overload and wear and premature failure of the drive train when one is simply driving innocently along the highway.
The biggest laugh of all is LR TSB (001 - I think) which reads something like this --- If the customer complains (about any of the above symptoms) --tell him/her its perfectly OK -- happens on all cars with VCU's !!!!!!!
Feel much better after that
Cheers Ian

ianh1 said:

2. Because (on early models at least) the two prop shafts spin at relative 0.8%slip, care should be taken when engaging --slow vehicle speed and on forgiving surface.

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why not just fit an interlock - such as on the handbrake, so that the handbrake has to be applied before the system can then be engaged. If the vehicle is stationary, then there is no problem, right?

what sort of costs are we talking about here?

The Mad Hat Man said:

Hi guys - I opened up a thread on an engineering site regarding the disconnection of the rear drive and this is the feedback I got. Please read. Basically they are saying that you dont reduce fuel consumption and dont gain any power. This seems to contradictory to what you guys are saying having removed the propshaft. Your (meaningful) comments would be apreciated.

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Cant speak for Audi, but I have removed my prop for the warmer months of the year for last few years. I havent broken it down into the fuel saving costs but would say I am getting about 20-25% more efficiency due to the free wheeling of the Rear diff and yes with the weight reduction due to no prop - this will help too, by fractions all be it.

No power increase form the power unit but all the power goes to the front wheels - amazing spin when you want it and usual under steer as normal driving of 2wd car. Mine has no HDU or EBS, simple and effective. I thought the ratio of power was 60% front and 40% rear in Freelanders and this was achieved by gearing in the IRD/RDU

IanH1 - A new prop costs £1500 complete - dear!! If you were replacing the VCU with a splined unit this would make sense. Would it be like diff lock in vechicles with diff lock/unlock selection?? How would it handle on gravel, sand and loose terrain.

This is getting interesting I am sure I would not be the only interested prospective buyer/modifier.

The VCU is described as active, whereas diff lock is described as passive and is already in play before wheel spin occurs.

The Mad Hat Man said:

why not just fit an interlock - such as on the handbrake, so that the handbrake has to be applied before the system can then be engaged. If the vehicle is stationary, then there is no problem, right?

what sort of costs are we talking about here?

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A handbrake interlok is a nice idea -- Until I actually fit and test the unit I intend keeping it simple. If the car is driving at say 10kph (no wheel slip), the rotational difference between front and rear prop shafts as seen at the coupling is only around 3rpm (much less on later models) so I'm not sure its going to be a great issue. (Sleeve/Spline movement is only around 1cm axially) It may be advantageous to actually be moving slowly at the point of engaging the coupling to assist with spline alignment.

Using components from a wreckers ("breakers" for all my UK friends) and a reasonably friendly engineering jobbing shop, ---well under A$1000 -or around say 300 -400 UKpounds


Cheers
Ian

Thanks Ian
I take it you have taken into account the comments from the Engineering forum about next to no benefits.... ??

here is the link to the site in case any of you wish to put anything there.
http://www.eng-tips.com/viewthread.cfm?qid=164453&page=1
be wary - they are very touchy - i was flamed from the beginning - you will see

The Mad Hat Man said:

Thanks Ian
I take it you have taken into account the comments from the Engineering forum about next to no benefits.... ??

here is the link to the site in case any of you wish to put anything there.
http://www.eng-tips.com/viewthread.cfm?qid=164453&page=1
be wary - they are very touchy - i was flamed from the beginning - you will see

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if you mean the post two or three earlier mentioning Audis and fuel economy etc then the answer is from my perspective tha that post is irrelevant. -- musings from someone without a Freelander???
The driving reason for replacement of the VCU on early model Freelanders is not fuel economy but savings on capital expenditure --big lumps of it. Persist with a vcu in a vehicle with the differential differential (thats not tautologous!) and you will be up for premature repair/replacement of the entire drivetrain starting with the rear tyres and working upwards and forwards --10's of thousands of unnecessary dollars up to and including the gearbox. To say nothing of the safety implications of vcu induced catastrophic crownwheel/pinion failure under motorway conditions etc,etc,etc.
burn away babies!!!!
Ian Hughes
Tassie