help & advice re gearbox/popping out of third

[smartiepants]

got a bit of a head scratcher here, i'm not mechanically minded so have to pay to get my work done so please bear with

got issues with my 1980 Aircooled T25 Westy 4 speed box, it keeps popping out of third gear mainly when lifting off, I know what you are going to say "Gearbox" and thats what we thought, its been off the van and has been reconditioned put back on the van and its still doing it, the guys who rebuilt the gearbox are adamant that they have done a full recon and there is nothing wrong with it and they are one of the best according to this place so I have no reason to doubt them so i'm about a grand down but without solving the problem

mechanic has checked the gearbox mounts and they are fine,

is there anybody on here that would have the faintest idea on what could be causing this? i'm in desperate need of advice

thanks

Martin

[kevtherev]

Ask to see the build list of components.
Can't be much else.
£700 for an Aidan Talbot box

[Oldiebut goodie]

Not aircold though.

[itchyfeet]

who reconditioned it?
I'd make sure gear linkage is correctly set and then if you are out of ideas take it to the reconditioners for them to test drive and comment.

[Aidan]

could it be an issue with worn gearbox and or engine mounts allowing the engine and gearbox to move backwards when lifting off causing the linkage to pull it out of gear ? The synchroniser is designed to snap into neutral when you start to change gear to reduce any wear on the dog teeth as they disengage it doesn't take much persuasion to pop out

the Aircooled box requires a jig to set up the clearances on the selector forks and synchroniser slider and synchro rings which I don't have hence I don't do them, maybe it wasn't set up right even if the necessary parts were replaced

has the van been to the refurbisher to demonstrate the issue or the box been back under warranty and checked ?

[smartiepants]

I have a list of what they found and replaced it was all done through my mechanic that has been dealing with them as its all double dutch to me

they have noted no excess wear found, carried out full rebuild and test all engagement in drive and coast good
parts replaced as listed below

1 recon gear carrier
1 front mainshift bearing
2 diff bearing
2 drive flange seal
1 input shaft seal
1 clutch release bearing sleeve
1 shift rod seal
1 1st gear synchro
3 2-3-4 syncro
1 consumables

like I said one of the recommended transmission specialists up in the west midlands

i'll feed back anything on here back to my guy to see if that makes sense, he is not a VW specialist but is a mechanic with his own business that I know and trust and was someone who was prepared to look at it