Hi, try taking the washer out from this detent on the selector box this may cure the jumping out. If it does fit a new detent.
Hope this helps
Ah Mossdog …
A man who knows his stuff …I have infact replaced the detent which has improved it a “little” …but sadly not cured the problem …i should have known a 6 quid part wouldnt sort it !!!
Any more ideas ■■
Hi actually i think there are two detent plungers one each side
once it is in gear there is nothing internally which would physically make it jump out of gear - the hard part is getting the synchro gears and baulk rings to let it go into gear
once ths has happened it actually holds itself into the gear as such
have you checked the gear linkage for touching the gear hole inthe cab floor - some times if the cab bounces it can knock the lever out of gear and its just an adjustment fault
or the cab mounts worn or air bags not self leveling
cheers
Steve
DoYouMeanMe?:
DAF and Iveco gearbox man.
Can’t remember the name, but stick these co-ordinates into google maps and that’s the place.It’s on the A34 between Cannock and Stafford, taken dozens to him. Paul somebody?
52.754659,-2.048156
Been there his number is 07785303604 or it was a few years ago, he will remember my old vw passat turning up with a 16 speed eaton where the back seat should have been 
rob.
take it to the bloke just past the bp service’s on the a14 at spitals those wooden buildings that standback of the road behind the services. what he does not know about zf’s you can write on a postage stamp and last year he was only 45 quid an hour. well recomended from me if only i can remember his damm name lol.
R Slicker…
This man has gone to the effort of finding my phone number and called my office to inform me of a chap who can help with my gearbox problem …
Top man thanlyou … 
robdorling:
Luckily i have an independant enginerer/mechanic as opposed to a Daf dealer “fit new bits only trained chimp” , i use the main dealer for non comlicated routine inspections etc but anything more comlicated goes to Simon …very often i find sharing a problem usually brings out someone with a similar problem thus giving us a starting point …thanks guys …
being a main dealer trained chimp who only fits new parts ,if it is only jumping out of low split and the gear lever is still in gear then ,synchros for split are shot ,being a new part only fotter i would fit new hi low split synchros as a kit if under warranty ,but you obviously want old parts fitted ,ref water ingress ,it was often entering throught the mushroom style breather ,i would fit the modified pipe ,but again that’s a new part ,water also entered through the reverse light switch on top of the box ,main culprit ,as ZF used an alloy washer below the switch ,it corrodes ,switch is then loose and water enters,again i would fit a new copper washer ,but that’s another new bit ,detent for split is front bottom of box at the bellhousing …i dare say your truck ends up at DAF whenever a warning is on the dash ,that you lad who does your comlicated or did you mean (complicated work )can’t handle …and that isn’t a slant on him ,as certain issues require the use of DAVIE …hope your box is ok with all it’s old 2nd hand parts you will generally find dealer won’t fit 2nd hand brake ,clutch parts and with most valves also being electrically controlled ,which you can’t get repair kits for ,then new parts are required .
robdorling:
Luckily i have an independant enginerer/mechanic as opposed to a Daf dealer “fit new bits only trained chimp” , i use the main dealer for non comlicated routine inspections etc but anything more comlicated goes to Simon …very often i find sharing a problem usually brings out someone with a similar problem thus giving us a starting point …thanks guys …
hey buddy…before moving to canada i was a fully skilled technician at a daf dealer for 10 years… we most certainly were not “fit new bits only trained chimps” as you so mistakenely put it. .get your facts straight first before you upset anyone else…
Did you know that the ZF box requires a ‘Special’ oil which has either some special ingredient, or something removed, can’t remember exactly which way round it was, however, only Castrol make this oil to the exact spec and we used to be one of half a dozen firms that ever bought it. Funnily enough, our synchros lasted forever…
Not looking to upset anyone - merely personal experience in the past which has cost me !!!
And we dont fit secondhand bits - just repair something repairable as opposed to replace it …
And apologies to a decent technician who falls outside my bracket …
Problem solved …a little linkeage adjustment !!! …
robdorling:
Problem solved …a little linkeage adjustment !!! …
Ahem! 
Rob or R Slicker could you tell what the number for the chap at Spittals’ phone number, I’ve got a little LF with a knackered 3rd gear syncro!
Thanks
Dave