There is NO ONE SPECIFIC TRIGGER PULL WEIGHT FOR A GLOCK.
The best you can do is to determine a range by using a series of pull tests. You have to be consistent, too; and state exactly where on the trigger's face each measurement is taken.
When fitted with a standard connector and springs, new, out of the box, Glock pistols usually demonstrate a trigger pull weight between 5.5 and 6.5#'s when measured from the center of the trigger's face.
Without screwing around with ALL of the springs I very much doubt that you're going to get a true 3.5# trigger pull on an otherwise normal Glock pistol; and, even if you do, that's not a Glock you want to be carrying.
Last edited by Arc Angel; 10-23-2012 at 05:49..