Popping out of reverse
 

Hi Folks,
Put the carrier in reverse, and back up, all is fine. Start to turn and the extra revs seem to be too much for the girl. The shifter will pop out of reverse and come to neutral.

This has been doing this since the original rebuild when I had a specialist shop overhaul the tranny and driveline. Have just lived with it.

Time to get it sorted out though.

I have seen some shifters where they have removed some metal from the slot so that the shift lever goes just a little farther forward. Tried this and seemed to help a bit, but there is not a lot of room left (aside from not being the proper way to fix it,)

Any ideas?

Cheers
Jim Burrill

Just for starters.
 

The problem should not be with the tranny itself, unless the Reverse Idler gear, Cluster gear, or Mainshaft gear have worn to such an extent that the gear teeth are tapered. These gearboxes have straight cut gears and do not create thrust forces like helical gears would. You say that the popping out of gear is happening after a professional rebuild, so I would presume the shop has not re-installed severly worn gears. The detent ball and spring in the shift tower of the gearbox might be worn, but once in gear there should be no thrust force on the selector fork to push it back out of gear.
I think your problem might be in the linkage from the shift lever back to the gearbox. Check for slackness when operating the shift lever or wear in the bush near the starter motor or the ball that connects with bowed rod on the gearbox. Do you have similar problems with 2nd and 4th? Will it stay in Reverse if you keep your hand on the shift lever when you make a turn? (A habit you should never get into normally).
It's unlikely, but check the engine mounts and the mounts under the rear of the gearbox. The engine and gearbox could be twisting under torque and making the shift lever rod from the front pull out of the selected gear.
At the base of the shift lever there is a socket that the shift lever sits in. This has a cup arrangement like a tie rod end and might need to be tightened up to take out any slack.