Having lost drive to the rear wheels I am going to change the IRD unit.
A warning from Ken at Bell engineering has made me aware that it might not be the pinion that has failed, but the splines to the gearbox - possibly necessitating a gearbox replacement.

So it sees sensible to buy a new IRD unit for £500ish, and also buy a 2nd hand gearbox from eBay for around £700 - just in case mine has gone. If all is well, sell gearbox back on eBay, and take a hit on sellers fees (£100?), saves stripping the car twice.

So the question is are the gearboxes for the newer cars the same as the old ones?
I know that the newer ones select neutral automatically at the lights (fuel saving?), does this imply that the controllers are not compatible? The last thing I need is to fit a new gearbox, and then not be able to get to work on Monday.

Reason for fitting newer gearbox - they should have done less miles Tangiers Orange - gone, missing her
Replaced by Ewok what a mistake - now a happy Disco Sport owner

Looks like no-one has tried to put a newer gearbox in an older car.

The bad news is that the splines that mate with the gearbox were completely stripped, pinion etc. were fine.
What I did find out is that the mating splines in the gearbox are on a separate sleeve that is available from LR
The part number is LR002619 - roughly £100

It would appear that the side of the sleeve that is inside the gearbox is lubricated, the side that mates with the transfer box runs dry. Dry splined couplings DO fret and die.
It turns out that the RH drive shaft (which has to be removed to change the transfer box) was also suffering from dry splines at the diff end, so a new one has been ordered. These are over £400 from LR, but can be had for £165 + postage if you search hard enough.

So in a couple of weeks I will be doing the job all over again, this time I WILL remover the anti roll bar link from the suspension, before trying to remove the lower ball joint

Remember if you order a transfer box - from Bell Engineering, who are a pleasure to deal with, also order the correct sleeve for your box, as doing the job twice is far more expensive than doing it once, once you have paid for the transmission oil and gearbox oil that will have drained out while you struggle under the car for a couple of days. Tangiers Orange - gone, missing her
Replaced by Ewok what a mistake - now a happy Disco Sport owner

Very informative Andy131

Hopefully your hard work will keep you mobile for the next 10 years or so The splines operating dry is pause for thought though!
Out of curiosity, what mileage has your vehicle done.? Back in the fold after 8 yrs. V8 Disco 300 series-Gone.07 Freelander 2 HSE Auto Rimini Red.
Gone.
2013 HSE Lux Havana ( Brown! )

161k miles
Lots of motorway - it's 40 miles each way to work and 30 of those are motorway. I am told my driving style is not mechanically sympathetic ie 25k is average for rear pads and I am happy to beat 28mpg, despite the bias to motorway mileage.
I do tow a 1100kg caravan mainly on bank holiday weekends, but that shouldn't give her much wear.

I do like off-road, and will go wading at every opportunity. The cavity between the auto box and transfer box has a nice open drain hole (1/2" dia) which will let water/mud/salt into "lubricate" the part of the coupling that has failed.

The new coupling and drive shaft are here, so just waiting for a dry weekend to fit them - pictures comparing new and worn parts will follow. Tangiers Orange - gone, missing her
Replaced by Ewok what a mistake - now a happy Disco Sport owner

Ok time for not so pretty pictures.

Worn sleeve

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That's some serious home /street mechanics!

Thanks for the info on mileage etc. I'm definitely having a nosey underneath the next time it's up on the ramps! !

 Back in the fold after 8 yrs. V8 Disco 300 series-Gone.07 Freelander 2 HSE Auto Rimini Red.
Gone.
2013 HSE Lux Havana ( Brown! )

Made in Japan then. FL2 MY10 TD4 GS traded in at 2 years
FL2 MY13 TD4 GS Current

According to Wiki
Aisin AWTF gearbox is built in Anjo Japan Tangiers Orange - gone, missing her
Replaced by Ewok what a mistake - now a happy Disco Sport owner

You mention the newer auto's selecting neutral if stationary for a bit, but I didn't think the FL2 did this. The D4 does but it's something I specifically asked the dealer about and they said the FL2 doesn't select neural when in drive and stationary for a bit.

Interesting repair you've done. Hippo's videos - Honorary Tratterer

"Neutral Control Functioning" is standard from MY13 onwards and is part of the "GRC" and EPB" functioning.
Not sure these features will work on an earlier model as the field/s don't exist within earlier models CCF's regardless of changing ATM.

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Mine drops into neutral on the overrun, as I can see the revs drop, when stationary it stays in D

So does mine.

J

Mine always stays in D when stationary. It's an SD4, so I just assumed they might be different. Ex AA Series III LWB Safari - Gone
300TDi Disco (bought new - terrible car) sent back after 18 months
Freelander 1 Estate - leased, given back at end of lease
200TDi Disco (bought from a mate with 100,000 on the clock) - Gone
Disco 2 TD5 - sold and exported to France
FR2 TD4 GS - Gone
FR2 SD4 HSE - Now changed for a DS
New model ex-demo Evoque S 180 in white
Unable to order a new DS, so gave up. Now have a Volvo S90 Recharge.

My SD4 HSE never dropped into neutral as far as I could tell when stationary. BMW X3 30d M Sport - Current (problem free)
2014 SD4 Auto HSE Lux - Gone (too many problems)
2012 TD4 Manual XS - Gone (too many problems)

It doesn't actually go into neutral, its called 'advanced neutral control logic'. It reduces drag when the car is stationary, idling and the lever is still in 'drive' and loading is greatly reduced.