5th gear popping out

[tweake]

my 5th gear is popping out but only at cruise. no problem under load, but long off throttle coasting it come out of gear.
it did it once or twice but i've since done a minor overhaul and replaced the main bearings and the completely munted shifter seat.
now its popping out a lot more but still only when coasting.

shifter feels a bit loose when in 5th.
wondering if the fork or hub sleeve etc is worn ??

any ideas?

edit: r151f gearbox

[Jerry]

worn syncro in gear or detent ball at bottom of gearstick

[Mud Camper]

Mine did the same - but in 1st. It was the body lift and trans tunnel mods causing it. Trimming out a bit of the 2nd rubber boot around the lever and moving the lever boot flange forward a bit fixed it.

[tweake]

finally gotten around to pull the gearbox out. well partly out. hope to change the 5th gear syncro without taking box right out.

however i did notice the whole counter shaft slides back and forth about 1mm.
am i missing a clip/spacer somewhere?
seams to be nice and tight from nut to thrust washer.

[tweake]

had it apart today.
what i did find was the brand new syncro on the 5th gear was a different fit to the others. it fitted like it was heavily worn on the inside part (ie not the teeth). it looks to be manufactured incorrectly. had a couple of spare new ones so swapped it over.
fingers crossed its the culprit.

[tweake]

unfortunately the syncro was not the culprit.
while changing the syncro did make the gear shift a lot better it still kept popping out.
my thoughts are half the problem is the front C clip, but the manual shows no measurements or checking for it. however the part manual does show different sizes available.
it also could be worn gear.

spoke to local mechanic and he suggested another route, pack out the detent ball/spring a bit to put more pressure on the 5th gear rod which will hold the gear lever in place more.
so i added a small washer, a fat one was to much and couldn't get it into gear, but the thinner one seams to be working fine. so far it hasn't popped out of 5th again.

[tweake]

so far the addition of a washer to the 5th gear detent spring has fixed the problem......or at least hidden it.