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BW Viscous Coupling


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I've a BW transfer box (unknown history) on the bench. Thought I would check it over before throwing it into the 110 while the gearbox is out for a new clutch arm.

The front drive flange takes 100-150lb.ft to turn it when the rear flange is locked. Is this normal or has the VC seen better days?

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I'm a little surprised Ashcrofts still have that test procedure on the site, as it seems to me a more exact alternative is in the manuals.

RRC, Workshop Manual (NOT Overhaul Manual), Section 41 Transfer Gearbox, Overhaul, Dismantle, Inspection & Overhaul.

Now this test shows the VC removed from the TC, with one of the VC shafts held in the vice, but I really don't see why it cannot be applied to a VC in the TC, with the output flange to the rear propshaft locked still.

If the box is in the car then I suggest applying the handbrake, but the front propshaft will have to be disconnected from the Transfer Case.

With the box on the bench, as in this case, then pehaps adjust the handbrake on hard?

Edited from the book

Viscous unit - rolling resistance Bench check

NOTE: Testing should be carried out in an ambient of 20 °C.

9. Secure the output shaft ...

11. Apply a clockwise torque of 27 Nm to the (front propshaft) output flange nut. If no resistance to turn is felt, unit requires replacing.

12. If resistance to turn is felt, apply a clockwise torque of 20Nm to the (front propshaft) output flange nut for 1 minute, this should result in a rotation of approximately 25° - 30°. If no rotation or a greater force is required, unit requires replacing.

27 Nm = 20 lbf-ft

20 Nm = 15 lbf-ft

Subject to peer review, I think this method could go in the Tech Archive, as "has the VC seen better days?" is a perennial question.


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Sounds about right to me, test I have always used on the car is to jack one front wheel up and try to turn, if the wheel nuts come undone it's goosed, or you cant move the wheel at all (can you daughter !) Daughters seized solid but still could be driven but took out the prop shaft and a cv and shaft. Now instructed to jack it up and check regularly.

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A Technical Forum Peer Review, he says with tongue in cheek.

A standard Range Rover Classic, fitted with a VC.

Gearbox and Transfer Case in the car, both propshafts connected.

Both rear wheels on the deck, with handbrake firmly applied, so the rear wheels cannot rotate.

One front wheel on the deck, chocked so it cannot rotate.

The other front wheel in the air.

What torque settings would you have to apply to the hub nut of the airborne wheel to simulate 15 and 20 lbf-ft at the VC front propshaft flange securing nut?

For bonus points, in which direction would the torque be applied to the hub nut it order to give the Clockwise application specified at the VC, and would this be the same for a 38A as for a Classic, given that the axle differentials are on different sides of the car?


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