life expectancy of gearbox once fifth gear whine starts

Depends what the whine is I guess.

I have had it happen twice (not in a 4wd) , but both times , it happened quite quickly. The Sigma , within weeks , the Celica , a couple of months. Both were bearing related.

Oh yeah , Celica told me it was getting worse . . . sigma just bleep itself. Was able to limp home in a low gear

these landrover people will be able to tell you

http://www.aulro.com//modules.php?name=Forums

Had an '84 Range Rover that got a 5th gear whine and vibration through the gearstick when away on a trip. Drove it home from Bris to Perth via Melb and it was still running fine. Got it fixed in Perth and the 5th gear cog had a bit of wear on several teeth.

If it were me, I'd lessen the chances of the gearbox failing in the middle if nowhere and get it re-built/conditioned now.

Its Murhpy's law, when it goes you will be somewhere, miles away from a mechanic without mobile or UHF coverage.

Wizard
Prado TD.

Take it up north. Some of the natives will take the wine out for you. Rus.

The whine you speak of might respond well (or not worsen at least) with different oil. I know people who have done this very thing - drain and refill with a good gearbox oil (on the heavier side) and add a pack of STP the get it nice and sticky. The only snag could be difficult gear selection when cold, but that may not happen.
With respect, seeing the vehicle is not worth heaps now, the above experimentation carries little risk in my view.

I have a similar problem, about 2 years ago I reconditoned the motor after cracking the crank so while it was in bits got a quote to kit out the gearbox ($600) even though there was nothing wrong with it, I thought why not. Now two years later and no hope of waranty it has developed a whine in fifth and it is getting worse. Now I'm kicking myself for ever touching it in the first place(if it aint broke,dont fix it), and I have explain to the boss that it needs doing again. Ouch

Athol

Pathfinder

My Forerunner whines when in 5th, did before I rebuilt the box and did after….and still sings 60k down the track. I think all luxs do. In the falcon xf’s, lazers and telstar they us to run atf to ease the notchie gear changes. But I think it is advisable in your case to stay with a gear oil, say ep80w90 as 4x4 have a lot of torque related stresses in low gear. So maybe you might have scoured the surface of the gear teeth and it may just whine away…. then again……. only one way to find out.

If you look in your vehicle handbook it will tell you that ATF dexron 111 is the lubricant to use. These boxes have an oil pump to circulate the lubricant, and the heavy stuff just doesnt get pumped to where it should. There were many early defender/disco boxes destroyed by enthusiastic mechanics (even L/R service) simply refilling the gearbox with 80/90 oil (which the transfer case DOES use) at the first major service.
The problem is possibly the 5th. gear support bearing (roller) which could be pitted.This could also occurr even with correct lubrication. It will probably get noisier but by then you will no doubt have fixed it!
good luck kesh

pathfinder,

Does your radio work fine?

I've found the 5th gear whine in my Jackaroo seems to go away when I turn the radio up. Remarkable huh?

Seriously, some boxes are known to whine and run forever (eg jackaroo). Others give trouble much earlier. It's best to check with similar vehicles or those who work on alot of them.

Andrew