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I had a noticeable whine on my 96 D1 coming from the transfer case - I drained the transfer case and found no metal bits so I flushed it out a bit with brake cleaner and changed over to a synthetic gear oil and no change - I had about 80k on it at the time. - I sourced a used transfer case with about the same mileage and swapped it out without doing anything to it as it was pretty dry - that did it - was now quiet as a mouse. Not sure what was going on with it but was a lot easier just doing the swap than going after changing bits on the original.
Not OP but that sounds a bit like the T-case to me. It's been a while since I had my old '04 with a similar sound but I believe it was exactly like that. It was happening at all speeds. T-case had water in it from a previous owner and was done. $800 later, I had a new low-mileage T-case and no more whining.
My current sound is a similar whistle/whine but only starts to happen around 70MPH.
Not OP but that sounds a bit like the T-case to me. It's been a while since I had my old '04 with a similar sound but I believe it was exactly like that. It was happening at all speeds. T-case had water in it from a previous owner and was done. $800 later, I had a new low-mileage T-case and no more whining.
My current sound is a similar whistle/whine but only starts to happen around 70MPH.
Same same. Starts at 70. So you're having that whine even with the new T-case?
Just wrapped up changing out the output shaft bearings on the transfer case, both front and rear, and found the process super straightforward. I used this as an overall starting point for the method, though I did it with the transfer case still on the truck. Keep in mind too, this video is on a Defender's transfer case, which uses a little wheel that interfaces with that spiral cut sleeve to feed the speedometer. The disco doesn't have that since it's electronic.
Couple notes on tools and some photos that might help the next person...
SLIDE HAMMER
I used this slide hammer from OTC: https://amzn.to/3K4DbH3
I then got these two adapters to attach the slide hammer to the output shaft threads. Worked like a charm: https://amzn.to/3K9Zb3u and https://amzn.to/3bXNWP2
There was plenty of room to use the slide hammer under the truck. It basically just rides in the space previously occupied by the driveshafts.
The threads on the output shafts are M20 2.50.
CIRCLIP
There's a big circlip that holds the bearing in place that needs to be removed in order to slide the output shaft out. I'm super partial to Knipex things, and if you're looking for incredible circlip pliers, this pair here is the correct one that will accomplish this task perfectly: https://amzn.to/3pq8zGn
SEAL PULLER
If you don't have one yet, I highly recommend one for this. Makes removing them a breeze. You'll use it for other things like axle seals, front main seal, differential seals, etc. Again, OTC to the rescue: https://amzn.to/3dsyNp0
BEARINGS
The replacement bearings I got were these from Rover's North: https://www.roversnorth.com/parts/pl...ia_rear_output
They weren't even in the Disco section. They were in the Series 2A part of the store since they're used in that too.
Older post I know but have used your parts list to order things to start this project. Great post and just wanted to thank you for taking the time...
EDIT: The part below can be found on ebay as it's not available on Amazon(per your link) anymore.
