The Lt85 gearbox in my County was rebuilt about 10 years ago, just before I bought it, and I have never been able to remove the drain plug for oil changes. Have been using another drain point which is inconveniently located directly above the chassis cross member, but really think I should get the other plug out so I can also clean out the filter.
I have tried belting the spanner with a sledge hammer, using a 1metre long extension on the spanner as a lever, even jacking under the spanner which just lifts up the car. Swearing with all these combinations doesn’t work either. Feels like the casing will give way before the plug!
Anyone got any other techniques to loosen stubborn parts like this? Have been warned not to use heat, but not exactly sure if this would cause a problem.
And yes, I am turning it the right way.

Thanks,
Adam.

Give the plug a good sharp rap with a Mash hammer (not too hard though)
Then try

I would try putting a ring spanner on it, applying pressure and then give it a good smack it with a hammer.

__________________
Cheers......Brian
1986 110 4BD1 Turbo Isuzu County Dualcab
1985 110 V8 County (soon to be Isuzued)
Ex RAAF No.5 trailer ARN 232-501
Haulmark 1 ton trailer

Got it!!
Just managed to loosen the plug off - what a relief.
I belted the plug a number of times (thanks djam1), then used a jack to apply lots of pressure to the spanner and belted the spanner with a large sledge hammer (thanks Bearman), and to my surprise after maybe 20 of the hardest hits i could give it, it came loose.
Never before have I been so keen to go and change the gearbox oil.
Thanks guys,
Adam.

Geez mate - thats some serious tightness
Be interesting to know if its got any locking compound on the threads when you get it out.
Maybe someone picked up the super bearing retainer instead of the thread sealant when it was last fitted.

You must be rapt that its out - and that the gearbox is still in one piece..

Steve

Couldn't see any obvious signs of any locking compound on the thread.
All done now, but that damn plug had the last laugh. As I tried to separate the copper washer from the plug (which was also stuck pretty hard) the plug flew from my hand at speed and dented the front of the truck - little b@#tard!

G'day Adam, That must be a relief to get it out. But seriously no plug should be that tight unless its been locktited or glued with some sort of compound. I would check the thread on the gearbox case for damage. Even the thread on the plug. After cleaning them both and if there is no obvious damage you should be able to screw it in by hand without using a spanner. If there is any tightness or restriction you might have to clean the threads before you tighten it up. Use a fibre washer when you put it back in.

__________________
Cheers......Brian
1986 110 4BD1 Turbo Isuzu County Dualcab
1985 110 V8 County (soon to be Isuzued)
Ex RAAF No.5 trailer ARN 232-501
Haulmark 1 ton trailer

Thanks for your input Brian. Got your message after I finished the job. Thread was possibly a little tighter than normal when screwing it in, however, I was sure not to do the nut up too tight. Next oil change i'll do as you suggested and have a better look at the thread in the casing and give a fibre washer a go.
Adam.

Was there a plastic mesh tube filter inside the plug?did you clean it?
jim.

Yes, there's a mesh filter in there Got it out and gave it a good clean (the reason why I was so desperate to get that plug off). Had some metal filings trapped within the mesh, and I know there was also some in the drained oil that came out if it - haven't had a good look to see how much yet. Been changing the oil about every 20,000kms using the plug on the bottom of the box, but I'm thinking that after about 150,000kms I should still be expecting to get a fair few that were being held back by that filter.
Gearbox does seem a little quieter now. Maybe the pump's working better now with a clean filter??