75 series landcruiser Ute slipping out of 4wd

Harrison
DO you mean, while stopped and select 4WD it immediately slips out of 4WD before you move anywhere? That is how it reads! If so I would look at the gearbox mounting and centralization of the stick in the floor pan hole. If near the edge or the rubber boot is stiff or awkwardly compressed when selecting it may be simply pushing back because or either engine/gearbox mounts or the boot and stick position. I has to relieve a slight amount of floorpan on my HJ61 as it became/was made close to one side of the stick hole. Loosening GBox mount and repositioning fixed the problem. Maybe that!
Can be a Transfer case wear problem too.

Having owned one of these a few things come to mind.

First if it pops out of gear but you can hold the gear stick in gear there is a thing called the 'dedent spring'. A small spring pushing a ball bearing into place that helps keep the gear in place. Just google 'landcruiser dedent spring' you will find your answer.

I also found the hi/low gear stick mounting bracket gets bent out of shape. I had to make up a third bracket that goes off at a right angle, back to a housing bolt forward, that holds the gear stick mounting bracket from bending. This was needed because it became harder and harder to change into low gear. The mounting bracket had bent backwards and would not let me follow through far enough to engage low range.

Next if it pops out of gear but you can't hold it in place - bad, very bad. This is a bit past my knowledge but I think it has something to do with worn shims in the gear box. If you change your gearbox oil and metal filings come out. Bad.........

under the floor there is a bracket that can move which is bolted to the transfer case. this movement wont allow the lever to engage low range properly, check it out, loosen it and move gear stick into low then retighten, should fix it up.

Thanks for your replies, sounding like it would be the issue with the dedent spring. I am able to hold the car in 4wd Low and drive perfectly fine and same goes with 4 high however the car won’t hold itself there