If the shifter bracket on the transmission is installed on the wrong side of the casting then engaging 2nd and 4th is usually the problem. As for first, third and reverse the only adjustment would be if the shift rod connection is not fully seated. The usual causes for 3rd or 4th gear pop out are bad teeth on the gear or the slider and a bad main ball bearing on the main shaft or that bearing is moving in the gear carrier housing. I have seen where a miss aligned clutch disk or other bad event can push the main shaft hard enough to force the reverse idler mount out and make for a loose main bearing. 

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of paul guard
Sent: Wednesday, March 2, 2016 10:43 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Manual tranny 3rd gear jumpout

It sounds as though the shifter has been adjusted so that it doesn't quite allow full engagement in 3rd gear.  It won't take long for 3rd pop-out to become a permanent problem, if driven in this condition ..

John wrote:
 After adjusting the shifter from" no shift" to operational on my van, it now jumps out of third gear ocassionally. Any ideas as to why?