Gearbox Nut for idiots


Hello chaps

I brought myself a 1996 Daihatsu Fourtrak TDX SE 2.8 three days ago, it drove very well on the test drive, and on the way back from the 4x4 centre. I have noticed now that I cannot come down into 2nd from 3rd. Thanks to your briliant community you seemed to have nailed the problem for me. Now I have a couple of questions:

1. My Dad is a farmer with a basic knowledge of mechanics will he be able to fix this? Will the gearbox need to be taken completely to pieces? Is there a step-by-step guide out there anywhere?

2. If not, how much money would you expect to shell out for it to be fixed professionally?

3. If this is ridicously expensive do you know if there is a statutory 3 month warranty that I have got from buying through trade?

Once again, thanks for having such an active and helpful community, I'll be a regular from now on i'd imagine anyway. See you around.


Good news ... you won't need to dismantle the gearbox

Bad news

You can check the nut at the back end of the mainshaft by removing the transfer box while leaving the gearbox in place. Unfortunately, getting the thing back on again might be a bit of a struggle because the internal spline on the gearbox and the external spline on the transfer box need to be lined up pretty accurately before they will slide together (I had enough fun doing this when I had the gearbox stood nose down on the bellhousing and was trying to lower the transfer box onto the gearbox .... I had to keep rotating the spline a fraction and trying again).

If you find the nut loose, then it needs to be tightened up to something like 200 ft lb ( I can dig out the correct figure if you like). Unfortunately, doing this under the vehicle won't be easy, especially as you have to lock up the gearbox to resist the torque you apply. I haven't done this, but I would suggest engaging 4th gear (this is direct drive through the box) and then locking the flywheel through the hole left when you remove the starter motor. The torque required is much bigger than can be resisted by jamming a screwdriver in the flywheel teeth, so the locking arrangements must be pretty substantial. The other thing that springs to mind is that the clutch must be pretty good too, as it must not slip with the torque, which, if memory serves, is greater than max torque generated by the engine.

Do a search for 'gearbox nut' and you should find lots of info. I've written some words on this already, especially about putting a bead of weld on the nut to stop it coming undone. This has worked for 20000 miles now, so, although it may be brutal, it seems bombproof !

Thanks for those tips, it see

Thanks for those tips, it seems that I will be taking it back to the dealer and getting him to sort it out for me. I am definately out of my depth.

Thanks again mate. See u around.


Useful tip ....

Diving through my big sockets yesterday, I came across a modified socket I had used on the gearbox nut. This reminded me to write up the mod on here for others to benefit from.

If you look at an ordinary socket, the first 1 or 2 millimetres of the socket don't have full engagement with the nut. The entry is scalloped to make slapping a socket on a nut easier if nut and socket aren't perfectly aligned. The fact that all the length of the nut isn't touching the socket and taking up the torque doesn't matter on a full-length nut.

Unfortunately the gearbox nut isn't anything like a full nut, it's maybe only 4 mm thick. When the socket has maybe 2mm of scalloping, this only leaves 2 mm of nut taking the torque ..... and there's a hell of a lot to take in this application ! All it needs is one slip, and whoops .... rounded corners.

The fix is to grind off the face of the socket until the scalloping is removed. OK, the socket is a bit more difficult to fit on the nut, but, by golly, it's a much better fit, all the more useful for 200 ft lbs.