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Discussion Starter · #1 ·
Hey there Great to get back on this site, I have found my viscous unit in the transfer case has
locked up solid. So turning on a hard surface it makes lots of binding noise's.
So I thought I'd just get a new one, turns out there not made any more.
I found that John Craddock in the UK did change over units.
But I got an email back saying none in stock & no eta on new stock.
What are people with this problem doing ?? Seems 2nd hand is the only way to go,
but you don't know how many miles or what sort of driving the unit has done, so it
might last a week or a couple of years.. Look forward to find out what others have done..

Thanks Jeff
 

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1995-2002 Range Rover P38A
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I have just done a search and you are correct. A number of suppliers are now saying they are no longer available.

You could try Ashcroft Transmissions to see if they still have one in stock.

I did however find a place that rebuilds them Bell Engineering.
 

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Seems a lot of quite common parts are getting hard to find lately.
 

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Not to beat a dead horse but is there genuinely no way of servicing this viscous units? Drain the fluid and all?
 

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They are a sealed unit, the only way to open them up is with a hacksaw.
 
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I have just had a quick look on YouTube and I found a video how to service the viscous unit viscous unit unfortunately it is in Russian.
It is fairly self explanatory. The guy changed the oil and freed off the clutch. Bell engineering must do the same.
Apparently it is a silicon oil @ 10,000 cp viscosity and takes 250mls. Don't throw your old one away just yet.
 

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The viscous unit is supposed to slip at slow speed and act like a central diff does. The principle is that the oil viscosity increases at high slipping speeds, like when a wheel is spinning, and it grips more. The oil thickens up.

When I have tested mine on the car using a bar on a wheel hub, there is high resistance even at low speed. It needed a lot of force to turn it.

Interesting comment down below in the video comments section that Ashcrofts disagreed with his method.
 

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Discussion Starter · #11 ·
Well my problem is still there, on full lock there is a racheting sound from the front.
I've replaced the front diff as the oil was pretty silver & now I've replaced the viscous unit as I did the test that has been talked about here & still have a racheting sound on full lock . Whats the next thing to look at ??
thinking hub bearings & cv joints.. Should'nt be the cv's as I've got the RCV cv's & axles..
Any thoughts would be great.. Thanks Jeff
 

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A ratcheting sound is likely to be CV joints. A locked up VCU will make the tyres squeal going around a roundabout. With the "test" I assume you did the basic one, front wheel off the ground, transfer and gear box in neutral, using a socket and breaker bar on a wheel nut you should be able to very slowly rotate the front wheel. It takes some force, but you know it isn't locked solid. A good guide is if you have the wheel nuts correctly torqued, then you should be able to get the front wheel to rotate at about the slipping point of the wheel nut (i.e. the wheel nut is about to/does slightly tighten as you get the wheel to turn).
 

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He says the front. If it was coming from under the seat or rear floor pan area, then guaranteed to be a drive chain, however would cornering make it jump?
 

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Cornering will require extra power, so a worn chain is more likely to slip. I agree if it's from a front corner it's more likely to be CVs. Easy test for the chain is a standing start with a healthy dose of loud pedal.
 

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In a straight line, would the chain make a single sound from it jumping a row or would it just be a continuous ratchet noise tearing it up away from the lights?
 

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If you give it plenty of go, it will sound like a machine gun as they say. Moving off gently it might not jump at all. To test it, find a gradient. Pull up, select sport mode, floor it. If it sounds like you have machine gun where your transfer box should be, then it is the chain.
 

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If worn but not completely trashed, you may get a single click as it jumps one tooth when pulling away. Treating the throttle gently and it won't jump at all, flooring it, particularly on a gradient and you'll get a machine gun. It all depends how much torque you are putting through it. Be aware that if the chain is worn and you ignore the noise and let it keep skipping a tooth or two, the shock put through the gearbox will invert one of the internal clutches so you'll end up needing a replacement gearbox as well as a transfer case.
 
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