P38 viscous coupling

[samd35]

I have a P38 4.6 HSE that i suspect that the viscous coupling has gone on, i haven't done the front wheel test yet but have blown 1 diff 2 weeks ago and i think its gone again by the sound and feel of it driving im going to investigate tomorrow i was just wondering what the exact steps are to test it and also how to test one that's out as i have a spare gearbox and transfer box of unknown condition that i can remove one from if its good. I have no idea how easy they are to change either so any advise would be appreciated.

Thanks Sam

[dave88sw]

well the only way i know to test them is with 2 good diffs, full lock on the steering at slow speeds it will feel like the brakes are applied and the steering pulls. They're very easy to change though if you need to, drop the front prop off the box and remove the ring of bolts around the front output shaft housing and just swap the lot over. Hope that helps

[David Sparkes]

Refer to the RRC Workshop (not Overhaul) Manual, Transfer Case, Overhaul.

Viscous unit - rolling resistance Bench check

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

11. Apply a clockwise torque of 27 Nm to (front) 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 (front) 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.

27Nm = 20lbf/ft, 20Nm = 15lbf/ft.

[samd35]

tested the unit earlyer all seems ok but still drive train making noises and sounds like someting has let go again i ony replaced the back diff 2 weeks ago. any ideas on what could be causing this?

[David Sparkes]

Tested the unit earlier, all seems OK, but still drive train making noises and sounds like something has let go again. I only replaced the back diff 2 weeks ago. Any ideas on what could be causing this?

Propshaft UJs, or possibly the sliding joint. IMHO it's always best to test them by removing the shaft from the vehicle, or at least disconnecting each end in turn.

Oh, unless it's the Morse chain in the transfer box. This will (apparently) make a slapping noise at speed, as the chain hits the case, or a loud banging under high torque (generally pulling hard in low gear, as in starting from rest). This is due to the chain jumping teeth.

You can drive the vehicle with only one propshaft in place, to eliminate one of them as the noise source, but if the rear one is removed then beware of wheelspin on wet tarmac. The front wheel geometry isn't set up for front wheel drive.

HTH

[samd35]

The chain sounds feasable as the ujs are all good is there any specific tests for the chain or just take box to pieces and have a look?

Thanks

[David Sparkes]

I'm not aware of any other tests apart from listening for different noises as I've already mentioned.

You could ask Ashcroft Transmissions, I see nothing on their website, apart from a 'time to change' evaluation at around 100,000 miles, contained in the Viscous Coupling section.

The 'specialist' forum for 38A Range Rovers is http://www.rangerovers.net/forum/ - you may get more experiences expressed there, try a search first.

There was a thread with pictures showing a chain being changed, but I don't know if it can be found again. I don't know if they have a Technical Section.

I'll attach a couple of photos I saved from the post in March 2008 when I frequented that Forum (which I no longer do).

HTH