Peter 2 replied:

John
I've had four troopies over the years, the early (pre 1990) mainly only had transfercase probs with the idler shafts, you knew when they were on the way out as the whine became intrusive.
Post 1990 they used a heavier t/case which was ok. What they did though to stop the oil siphoning problem (transfer case oil siphoned into the gearbox) of the earlier trucks was to fit a double lip seal between the two (was aretrofit on earlier ones) and an O ring on the actual shaft.
As the transfer gears are oiled by the lower gears lifting the oil up and depositing it on the others (higher up) , basically the system is splash feed. That works fine for the gears but that O ring and the new seal stopped oil seeping along the mainshaft from the gearbox and lubricating the main input gear on its splines at the top of the geartrain.
Once the oil used in assembly dried out the condensation would allow corrosion to start and this then caused the gear to work on the splines which eventually wore away resulting in the gear free spinning on the shaft and NO drive to the transfercase or wheels.
Repair involved removing gearbox and transfer, new mainshaft in the gearbox, new transfer input gear and bearings and seals in both. Parts alone cost big bucks from Toyota, never mind the labour.
Cheaper parts are available from Don Kyatt (like about a 3rd the price) and there was someone remachining the shaft and gear to enable them to be reused somehow but most owners want it back on the road asap so it wasn't an option for me.
My troopy needed the rebuild at about 110k (private use, travelling only, no city use and sometimes towing a 500kg camper). The 4mm square splines had worn to a 1mm triangle and I was about one low range clutch dump off no drive.
The way to check it is to remove the PTO cover and the black tin hat cover at the back of the transfer.
Hold the end of the mainshaft with one hand while attempting to rotate the input gear (the one closest to the front of the transfercase on the shaft. If there is any movement at all you have probs. Some people will tell you to just tighten the nut on the end up and while that may gain some time it will not stop the problem.

Member - Phil G (SA) replied:

John,

That problem happened with the 1999-2001 vehicles with the 1Hz motor and the R151F gearbox. Toyota recognised the problem, and strengthened the shaft. A call into a Toyota service dept should be able to identify whether a particular vehicle has been affected. If it is, then I'd suggest getting the shaft replaced, then the worry is gone.

The factory TD troopies and traytops were not affected as they have a different (H150F) gearbox.

Cheers
Phil

STEVE069 replied:

Hi John, I work up in the mines in WA as a light vehicle mechanic, We replace gearboxes all the time, mainly for very bad 2nd gear syncro problems, we have had one that stripped the splines on the mainshaft . On the model you are talking about the gearbox is a light alloy unit(non turbo) inbetween the box and transfer their is a short joining shaft,this is the one that stripped , the box shaft and transfer shaft had no damage at all so we only replaced the joining shaft. Please note these vehicles have done 40-60km but under extream conditions. I am quite sure the new shaft we got (from toyota) was a modified one. Hope this helps John.

Steve