Take a look at this FAQ article. It's not really how far out the rod is, it's how does it move in response to vacuum. http://www.myturbodiesel.com/1000q/a4/VNT-wastegate-adjust.htm If you have a new one and don't have a vacuum pump the best thing is to get a hand vacuum pump/gauge but you may be able to adjust it to the old length.
it is locked in place with a combination of security paint, (from the factory) and rust from age typically.
if you buy a new one, there is no security paint or rust to worry about, but you must be able to set the actuator response while it is mounted on the car.
I usually do this thru trial and error as I fiddle with the length. my fingers are too big to get in there and spin the knurled nut so I have to unbolt and rebolt it in with one of the two nuts each time I need to make a setting change.
it is very important to fully bolt it in each time. and do not lose the little clip thing that holds it on the turbo actuator shaft once you do get it acting right. (easy to do)
you want the actuator to start moving between 3-5mm Hg and be completely against the stop between 18-20mm Hg.
if it starts moving immediately, it needs to be lengthened.
if it stops moving after 20 it needs shortened.
I just went through this dance on an 03 Jetta, I did measure the actuator rod for referance. It was 88mm from base of the vacuum can to the center of the hole, I eventually ended up at 92mm to get this particular one to work.
that is at least a starting point if you have nothing to go on.
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