Issues after GU 2.8 gearbox replacement

Hey fellas. Just finished doing a quick swap out of a gearbox. My 5th gear completely let go in a catastrophic way. Bought this one only a few days back, the box let go on the way home. Got it cause the missus has bailed and the 75 series ute wont cart 5 kids.

So I've swapped out the box for a 2nd hand one, i know it was working alright before hand.... I left the original clutch on there as it wasn't slipping at all.
Now, after the first test drive, it's slipping. Anything to check before i rip the box back out or take a match to it? 😬
Also another thing i noticed, sometimes it won't allow you to select 5th? But other times it will. Box sounds fine. Any help would be appreciated.

Have you bled the clutch?

I didn't think id have to since the clutch line wasn't opened. Plus, i thought that air in the line would cause issues with clutch not engaging fully? I dunno, am i wrong??

Check that the slave cylinder is retracting fully and the clutch pedal free play is correct. (Page CL 5 of the downloaded manual).

I think your bang on the money there mate.... might have to rig up a return sprint until the shops open up again. 😬

I've ordered a clutch slave and master... Just in case. Is there any way to strengthen the original 2.8 gearbox? Will a 3.0 or 4.2 box fit in its place?

The 2.8 is the same box as the 3.0. The 4.2 box is a truck box and entirely different - wont fit the 2.8. I had the 2.8 and it was a tough little gearbox - certainly strong enough for that engine and its limitations I believe. Why are you asking?

Someone posted a while back that there were adapters to fit the Nissan auto transmission RE4R03A to the back of an rb30. Don't know if it will carry over to the FS5R50A manual gear box. Try Marks Adapters.

I was thinking to do same thing after the bearings let go during a trip I towed my camper trailer. It was pointed out that the larger transmission would sap too much power from the smaller engine.

The secondhand box I fitted, now has noise from a bearing in the gear cluster. 4th is still quiet.

I was told that 360 Gearboxes and Diffs in Bayswater, Melbourne do mods to strengthen them.