rasheed said:
Trying really hard to learn something from this thread, but a lotta reading between the lines required! :rolleyes: The things is, I AM driving with the front prop removed at the moment and there is certainly propulsion from the rear. Also, there was a definite jerkyness when reversing slowly with full steering lock before I removed the prop which I only noticed now that its gone. From what I read..
TheViscous Coupling: How to Test & Replace it

.. this is a sign that the centre viscous coupling/diff was already in trouble. Where I'm a little confused is that if the rear wheels are driving and the front prop is missing and therfore the front bit of the VC is not turning, does that put the VC in full time lock? I know it has little resistance to deal with (from the front at least) but that can't be good?? :confused:

christ i hope the solution does not end up being to throw a complete new drivetrain at this car. its just not worth the money anymore.
Click to expand...

Ok transfer box operation. Drive is taken from back of gearbox through input shaft. On the input shaft is located reduction gear set for selection of high/low axle. Drive from this is taken via a chain over to the output side. The output side consists of a viscous coupling driving two outputs, one for the front axle one for the rear axle. The viscous coupling contains fluid and acts as a centre differential smoothing out any difference in rotational speed between the front and rear axle. Where this movement is small, as in normal driving conditions, the fluid allows the plates in the viscous coupling to slide past each other thus preventing axle wind up. If however the movement becomes quicker as in the front wheels having no grip whilst the back ones have or vis versa the viscous coupling locks up to put drive to the wheels with grip. If the viscous coupling is siezed then there is no compensation for differing axle rotational speeds and you will get windup. The viscous coupling and how it operates is why you can disconnect a prop shaft and still have drive, you CANNOT do that with a conventional centre differential as the unconnected output would just spin and no drive would be passed to the live prop unless the diff could be locked. If you are getting axle windup. You need a new viscous coupling fitted to your vehicle. About £250 or less if you look around. Checking for viscous coupling siezure is simple, jack up one front wheel leave the other one grounded. You should be able to turn the lifted wheel with difficulty, this means your coupling is ok. If you cannot turn the wheel the coupling is siezed. In your case you would of course have to replace the front prop to do this check.
 
Thanks Wammers. Starting to see the light and just based on the axle windup alone I think I agree about a new VC for now. Quick question, lets say I want to verify all 3 diffs, front, centre and rear. The test you described with one front wheel will isolate problems to the centre VC or would it just indicate both centre and front for further examination (similarly the rear)?

Happy New Year!
 
rasheed said:
Thanks Wammers. Starting to see the light and just based on the axle windup alone I think I agree about a new VC for now. Quick question, lets say I want to verify all 3 diffs, front, centre and rear. The test you described with one front wheel will isolate problems to the centre VC or would it just indicate both centre and front for further examination (similarly the rear)?

Happy New Year!
Click to expand...

Centre one you have already had the check explained. Front and rear diffs. I harldy think front and rear diffs will be siezed if that's what your asking. Jack axle front or rear so both wheels are off ground, turn one wheel, other wheel should turn in opposite direction. Your front axle will not do this unless you replace prop or get someone to hold the diff drive flange. This check proves the diffs are doing what they should do, which is to compensate for slight rotational differences left to right, also when cornering as the inner wheel travels less distance than the outer wheel.
 
the viscous couplein sieze up after about 100k therefore if it is siezed take off the front prop and that wil stop the wind up and still propel the p38 and it wil also save ur diff but also aim to get a reworked viscous couplin and fit it
 
Datatek said:
There is no centre diff
Click to expand...
Datatek said:
If there was a centre diff the VCU would have no effect because as with any diff if one side slips there is no drive to the other side which is why diff locks were invented. The VCU does away with the need for a diff as it allows a certain amount of slip and then progressively locks.
Click to expand...
wammers said:
Nonsense. The viscous coupling IS the centre diff.
Click to expand...
Datatek said:
The VCU is on the front output shaft and is a self contained unit so cannot lock the mythical diff, therefore if you remove the front prop, you would also lose drive to the rear. Anyhow, you have it your way and dream of your mythical diff:behindsofa:
Click to expand...
You are a pair of bullsh1tting feckwits.

There is a diff in the transfer box and a as well VCU. Part number STC3239.

How else does the drive get propotioned 50;50 front rear? A VCU only reacts to slip - like the old VW Synchro system, making it a part time 4WD system. RR P38 is permanent.

I've never read such a load of old sh1te in my life.
 
Widget said:
You are a pair of bullsh1tting feckwits.

There is a diff in the transfer box and a as well VCU. Part number STC3239.

How else does the drive get propotioned 50;50 front rear? A VCU only reacts to slip - like the old VW Synchro system, making it a part time 4WD system. RR P38 is permanent.

I've never read such a load of old sh1te in my life.
Click to expand...

So, if there is a centre diff, explain how you get drive with the front prop disconnected? as any pratt knows, no grip on one wheel = no drive on the other wheel unless you lock the diff.

Equally if there was a centre diff, as I had on my Pajero, a viscous coupling would be irrelevant.

The drive is not 50 ; 50 it is 70% rear wheel drive with a variable proportion the the front according to LR. Watch the rear wheels spin before the fronts drive on the video of doughnuts on another thread. doughnuts are very difficult on a 50 ; 50 split drive as you can't spin the rear wheels to cause breakaway.

I reckon if you order part number STC3239 you will get a chainwheel assembly with 2 output flanges.

Still if you want to believe in the mythical centre diff thats your problem.

LR probably intended a centre diff at the design stage but VCU's were fashionable at that time and much cheaper than a diff.

My last 4 X 4 also used a VCU instead of a centre diff, so it is not uncommon.
:multiply::mil36:
 
excuse me kids!
please excuse my ignorance on rangies, but shirly if yu have a central diff and then lock it (for example with diff lock) then you will get drive to the rear with the front prop removed.

The gaylander has a central diff (the IRD) which permanently drives the rear. The VCU allows that to slip, until such time that it thinks it needs to be locked.

Isnt that the way it works?
 
The Mad Hat Man said:
excuse me kids!
please excuse my ignorance on rangies, but shirly if yu have a central diff and then lock it (for example with diff lock) then you will get drive to the rear with the front prop removed.

The gaylander has a central diff (the IRD) which permanently drives the rear. The VCU allows that to slip, until such time that it thinks it needs to be locked.

Isnt that the way it works?
Click to expand...

Except that the VCU is a self contained unit on the front output with no means of locking anything except itself?

I'd love to have a transfer box apart to settle it once and for all, but preferably not mine:eek:
 
The Mad Hat Man said:
how does a Gaylander work then?









when it works, that is ;)
Click to expand...

You tell me, probably another marketing lie:eek:

I suppose you could have a limited slip centre diff but the LSD mechanism would be working overtime to compensate for the VCU slip and again a seized VCU would not cause wind up in the transmission:D
 
Datatek said:
So, if there is a centre diff, explain how you get drive with the front prop disconnected? as any pratt knows, no grip on one wheel = no drive on the other wheel unless you lock the diff.
Click to expand...
Cos the VCU locks/

Datatek said:
Equally if there was a centre diff, as I had on my Pajero, a viscous coupling would be irrelevant.
Click to expand...
Nope - the VCU and centre diff combination was also used on the RR Classic - the diff proportions the drive, the VCU locks the props under shear force. A VCU unit without a diff = part time 4wd. With a diff full time 4WD.

Datatek said:
The drive is not 50 ; 50 it is 70% rear wheel drive with a variable proportion the the front according to LR. Watch the rear wheels spin before the fronts drive on the video of doughnuts on another thread. doughnuts are very difficult on a 50 ; 50 split drive as you can't spin the rear wheels to cause breakaway.
Click to expand...
Complete sh1te. Your talking L322 Range Rover which has a Torsen torque biasing diff which does this. A plain diff can't do this - let alone a VCU.

Datatek said:
I reckon if you order part number STC3239 you will get a chainwheel assembly with 2 output flanges.
Click to expand...
Have a look at what the chain wheel drives - not just a plain cog but a diff.

Datatek said:
Still if you want to believe in the mythical centre diff thats your problem.
Click to expand...
Tw@

Datatek said:
LR probably intended a centre diff at the design stage but VCU's were fashionable at that time and much cheaper than a diff.
Click to expand...
B0llocks - you're talking gaylander.

Datatek said:
My last 4 X 4 also used a VCU instead of a centre diff, so it is not uncommon.
:multiply::mil36:
Click to expand...
Clearly a gay spas car rather than a full time 4WD system then. Both systems exist, with diff and without - neither proves that the other dunt exist.

Right - the P38 has a conventional diff and a VCU. Drive from the epicyclic high/low passes to the centre bevel differential through an inverted tooth chain instead of a helical gearset (LT230). Check the pic out. See the diff under the chain - see the VCU on the front output?
 

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Widget said:
Cos the VCU locks/


Nope - the VCU and centre diff combination was also used on the RR Classic - the diff proportions the drive, the VCU locks the props under shear force. A VCU unit without a diff = part time 4wd. With a diff full time 4WD.


Complete sh1te. Your talking L322 Range Rover which has a Torsen torque biasing diff which does this. A plain diff can't do this - let alone a VCU.


Have a look at what the chain wheel drives - not just a plain cog but a diff.


Tw@

B0llocks - you're talking gaylander.


Clearly a gay spas car rather than a full time 4WD system then. Both systems exist, with diff and without - neither proves that the other dunt exist.

Right - the P38 has a conventional diff and a VCU. Drive from the epicyclic high/low passes to the centre bevel differential through an inverted tooth chain instead of a helical gearset (LT230). Check the pic out. See the diff under the chain - see the VCU on the front output?
Click to expand...

So, you tell me how you get drive to the rear wheels with the front prop removed. In your picture there would be no drive to the rear wheels with the front prop removed as the front prop drive would just spin as is always the case with a "conventional diff". And again a seized VCU would not cause transmission wind up as the diff would take care of rotational differences front to rear.
 
Widget said:
Cos the VCU locks/


You clearly have no understanding of how a VCU works or a diff for that matter. VCU Locked or unlocked with the front prop removed with a diff there should be no drive. Look at your own picture and tell me how a locked VCU affects the diff and provides drive to the rear with the front prop removed?

A diff splits torque evenly across both outputs whilst allowing rotational differences. A VCU allows limited drive in normal circumstances but progressively locks as slip increases, even if there is a diff, the VCU does not transmit full torque to the front unless the rear wheels are slipping so your comments about full and part time 4 X 4 are are best incorrect.

With a VCU there is only full torque transmission when sufficient slip occurs to cause it to lock, so with or without a diff by your definition the P38 is part time 4 X 4.
Click to expand...
 
Stop overthinking it - the P38 has a centre diff.

If you take the front prop off a P38 or RRC with the Borg-Warner box drive goes to the rear. Just because you can't work out how it works, doesn't mean it can't.

I can't be bothered to explain the rest.
 
Widget said:
Stop overthinking it - the P38 has a centre diff.

If you take the front prop off a P38 or RRC with the Borg-Warner box drive goes to the rear. Just because you can't work out how it works, doesn't mean it can't.

I can't be bothered to explain the rest.
Click to expand...

Ahh, so it's like religion, you believe it cos someone says it's true even though logic tells you it can't be:D
 
well its right the thing does sieze up AND WILL drive only the rear axle if the front prop removed they go about 100k
 
Children, Shut up and Listen.....


Your all wrong and right at the same time, including Land Rover.

Widget you posted a picture of a LT230 transfer case to support your arguement, TUT TUT, the P38 is fitted with a BW 44-62, at least lets use the correct pictures/infomation.

Land Rover say its a diff, incorrect, its a planetary gearbox, but Land Rover directly couple it to the VCU and use it to control slippage and allow for the difference in rotational speed between front and rear props, hence some T**t in Land Rover doesn't know what a diff is and what hes talking about.

Now Children, go to seperate corners of the room, open google, now type in " 1188291644.pdf " open with the "quick link" button and read, learn, then shake hands and be friends.......Bloody Children....:behindsofa:


PS. Happy New Year....:clap2:....:D
 
Last edited:
zzr1200 said:
Children, Shut up and Listen.....


Your all wrong and right at the same time, including Land Rover.

Widget you posted a picture of a LT230 transfer case to support your arguement, TUT TUT, the P38 is fitted with a BW 44-62, at least lets use the correct pictures/infomation.

Land Rover say its a diff, incorrect, its a planetary gearbox, but Land Rover directly couple it to the VCU and use it to control slippage and allow for the difference in rotational speed between front and rear props, hence some T**t in Land Rover doesn't know what a diff is and what hes talking about.

Now Children, go to seperate corners of the room, open google, now type in " 1188291644.pdf " open with the "quick link" button and read, learn, then shake hands and be friends.......Bloody Children....:behindsofa:


PS. Happy New Year....:clap2:....:D
Click to expand...
Basically what i said a few days ago people must learn to listen or at least read Rave and understand it.
 
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