The Mercedes Vito W639 with twin barn rear doors suffers from a weakness of the hold back spring that guides the check bar into the body mounted lock spring when the door is opened.
What happens is that when you open the door the quadrant arm (check strap) that locks into the fixed check, misses the receptacle and allows the door to open without restriction. Worse still is that when you go to close the door the quadrant arm bashes onto the bodywork or door seal preventing the door closing past this point. This requires the owner to push the check arm and assist it into the door frame guide pocket before the door will close. This is a real pain and becomes a chore. I looked at purchasing new strap assemblies for both rear doors but at over £30 a side decided to investigate what was going on !
The tension spring fitted to the door mounted check strap / bar that holds the arm under pressure in the guide pocket so that it locates into the body receptacle when opened, weakens. This seems to be common and I would wager is the reason for many unnecessary replacement straps being fitted. The repair is very simple and is achieved in a very short time with the assistance of a Dremel hand grinder and a mounted point grinding tip.
Open the door wide open to gain acces to the strap assembly, locate the tension spring as seen in the photograph below, hold the strap levered to one side to disengage the springs locating tip from the metal casting stop. With care remove two or three millimetres of material from the metal cast ‘spring-stop’ with the Dremmel. The material’s location and amount to remove with the grinder is shown in the second photograph. Remove a small amount at a time and try and keep the stop face as flat and perpendicular as possible.
Once this is done, the lever is now allowed to rotate about its axis a little further so that it now perfectly engages with the check strap locator on the main body as it exits the guide pocket. The only time you need now to touch the strap is if you need to open the doors wider than 90 degrees, just as it should be. A great little fix that will take no longer than 20 mins and save you over £60 !!