DIFFicult to confirm??? - Land Rovers Only

Landy-Andy · 10-04-2004, 11:38 PM

Hi Guys,
I have a 1991 RR classic which has the "auto" diff lock. This has no switch & no light. So, what is the easiest way of checking that it is all functional?

Thanks,
Landy-Andy

worms · 10-05-2004, 02:20 AM

Don't know about the "auto" switch but can you not just jack up a corner and see if you can drive it off the jack? Carefully let out the clutch and see if it starts to move on the jack. I can't see why it should be any different than checking whether the manual switch works - I used to have to do this regularly when I had a an early Range Rover with the vacuum diff switch.

scoobymick · 10-05-2004, 01:25 PM

From a safety point of view i would rather jack it up and try rotating the wheel by hand,this should prove the viscous coupling is ok.
Mick

worms · 10-05-2004, 01:53 PM

I bow to the safety advice! Perhaps the most fun way is to take it somewhere suitably muddy - if you need towed out by a 2WD then its not working!

Landy-Andy · 10-05-2004, 09:13 PM

Thanks guys for the feedback.
Am I right in saying the Viscous coupling works on Centrafugal force so engages when the spinning reach's a certain speed?
So am I right in thinking that the center diff is only working when the wheels are turning? So how does the one wheel jacked up test confirm this?
Or am I way off the mark?
Now I know why I stuck with my simple 67 11a for so long

Cheers,
Landy-Andy

troverman · 10-06-2004, 09:42 AM

Jack one whole side of the Range Rover up so both wheels on the same side are off the ground. Put chocks under the two other wheels on the ground so the car can't move. Put it in gear and gently accelerate. Since the RR has open front and rear diffs, one wheel should spin first, then the other wheel will spin as well (the wheels off the ground) The other wheels won't move at all. This is safe to do. The way we checked our 92 was drive one side of the car into a 6-foot snowbank and gunned it with a helper checking to see which wheels were turning. Not sure how the VCU works-I think it locks when there are different speeds between axles. The car is phenomenal in snow.

scoobymick · 10-06-2004, 02:18 PM

The viscous coupling passes drive from the rear output shaft to the
front output shaft. When the silicon fluid in the viscous
coupling becomes warm its resistance to shear
increases passing more drive to the front drive shaft
increasing traction.
Mick.

Landy-Andy · 10-07-2004, 10:28 PM

Thank again for the feedback,
I dont have any 6ft snow banks here in sunny BC, but I will jack up one side & try that method.
I will let you know how it go's

Cheers,
Landy-Andy

1955diesel · 10-08-2004, 03:12 AM

If you just jack up one side of the car, both the wheels that are off the ground will spin and you will learn nothing.

As one of the previous posts says, the fluid in the diff has to get hot in order to start locking it up. This is achieved when one axle is turning and the other is not (or there is a big difference in their speed).

You could perhaps get this effect by jacking one side of the car then lightly applying the parking brake. If you then run the engine slowly in gear, first only the front wheel will turn. Then, as the diff begins to lock, it will overpower the brake and turn the rear wheel as well. I've never tried this, but it should work. However, the viscous diff is so simple that I do not think it will be prone to failure. OOps! forgot it was a Land Rover for a minute.

Character is the black stuff that drips from Land Rovers!

10-04-2004, 11:38 PM	#1 (permalink)
Landy-Andy Senior Member Join Date: Sep 2004 Location: Beautiful British Columbia, Canada Posts: 124 Gallery: 0	DIFFicult to confirm??? Hi Guys, I have a 1991 RR classic which has the "auto" diff lock. This has no switch & no light. So, what is the easiest way of checking that it is all functional? Thanks, Landy-Andy

10-05-2004, 09:13 PM	#5 (permalink)
Landy-Andy Senior Member Join Date: Sep 2004 Location: Beautiful British Columbia, Canada Posts: 124 Gallery: 0	Viscous coupling... Thanks guys for the feedback. Am I right in saying the Viscous coupling works on Centrafugal force so engages when the spinning reach's a certain speed? So am I right in thinking that the center diff is only working when the wheels are turning? So how does the one wheel jacked up test confirm this? Or am I way off the mark? Now I know why I stuck with my simple 67 11a for so long Cheers, Landy-Andy

10-06-2004, 09:42 AM	#6 (permalink)
troverman Senior Member Join Date: Aug 2004 Location: New Hampshire, USA Posts: 293 Gallery: 0	Jack one whole side of the Range Rover up so both wheels on the same side are off the ground. Put chocks under the two other wheels on the ground so the car can't move. Put it in gear and gently accelerate. Since the RR has open front and rear diffs, one wheel should spin first, then the other wheel will spin as well (the wheels off the ground) The other wheels won't move at all. This is safe to do. The way we checked our 92 was drive one side of the car into a 6-foot snowbank and gunned it with a helper checking to see which wheels were turning. Not sure how the VCU works-I think it locks when there are different speeds between axles. The car is phenomenal in snow. __________________ Current: 2005 Land Rover LR3 V8 SE w/ factory winch 1992 Land Rover Range Rover County Also current: 1995 Mercedes-Benz E320 Wagon 2002 Volkswagen Eurovan GLS 1996 Ford Explorer LTD 2WD 1982 Volvo 240 GL Diesel Previous Rovers: 2000 Land Rover Discovery II SD 1995 Range Rover 4.0SE

10-07-2004, 10:28 PM	#8 (permalink)
Landy-Andy Senior Member Join Date: Sep 2004 Location: Beautiful British Columbia, Canada Posts: 124 Gallery: 0	Difficult to confirm center diff.. Thank again for the feedback, I dont have any 6ft snow banks here in sunny BC, but I will jack up one side & try that method. I will let you know how it go's Cheers, Landy-Andy

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10-05-2004, 02:20 AM	#2 (permalink)
worms Member Join Date: Sep 2004 Location: Scotland Posts: 41 Gallery: 0	Don't know about the "auto" switch but can you not just jack up a corner and see if you can drive it off the jack? Carefully let out the clutch and see if it starts to move on the jack. I can't see why it should be any different than checking whether the manual switch works - I used to have to do this regularly when I had a an early Range Rover with the vacuum diff switch.

10-05-2004, 01:25 PM	#3 (permalink)
scoobymick Senior Member Join Date: Aug 2004 Location: UK Posts: 121 Gallery: 0	From a safety point of view i would rather jack it up and try rotating the wheel by hand,this should prove the viscous coupling is ok. Mick

10-05-2004, 01:53 PM	#4 (permalink)
worms Member Join Date: Sep 2004 Location: Scotland Posts: 41 Gallery: 0	I bow to the safety advice! Perhaps the most fun way is to take it somewhere suitably muddy - if you need towed out by a 2WD then its not working!

10-06-2004, 02:18 PM	#7 (permalink)
scoobymick Senior Member Join Date: Aug 2004 Location: UK Posts: 121 Gallery: 0	The viscous coupling passes drive from the rear output shaft to the front output shaft. When the silicon fluid in the viscous coupling becomes warm its resistance to shear increases passing more drive to the front drive shaft increasing traction. Mick.

10-08-2004, 03:12 AM	#9 (permalink)
1955diesel Member Join Date: Sep 2004 Location: Solihull England Posts: 75 Gallery: 0	If you just jack up one side of the car, both the wheels that are off the ground will spin and you will learn nothing. As one of the previous posts says, the fluid in the diff has to get hot in order to start locking it up. This is achieved when one axle is turning and the other is not (or there is a big difference in their speed). You could perhaps get this effect by jacking one side of the car then lightly applying the parking brake. If you then run the engine slowly in gear, first only the front wheel will turn. Then, as the diff begins to lock, it will overpower the brake and turn the rear wheel as well. I've never tried this, but it should work. However, the viscous diff is so simple that I do not think it will be prone to failure. OOps! forgot it was a Land Rover for a minute. Character is the black stuff that drips from Land Rovers!

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