In short, I went to install a rebuilt vacuum booster in my '89 jetta, and the rod that connects to the brake pedal is about an inch and a half too short, which means that if it's clipped onto the brake pedal, the pedal does not reach the button that deactivates my brake lights. As far as I can tell, the rebuilt booster I bought is the only one made for mk2 jettas without ABS, so.... it should fit.
I went back to the shop where I got my rebuilt booster, and picked up my old booster; installed it, and.... same problem; it's exactly the same size as the new booster. EXCEPT, that I didn't have any problems with my brake lights staying on before, which means .... either the rod-length is somehow correct and something else has changed (though I can't imagine what that would be, since I haven't changed anything), or, maybe there was a piece of foam from the dash/pedal-cover-piece that was stuck between the pedal and the brake-light button before....I can't think of any other ways this could happen.
I got this car through an insurance auction. Is there a chance the bracket that holds the brake and clutch pedals came from another model or something? Has anyone out there ever compared boosters from different VWs, and if so, is there a booster that would be compatible for my car, but that would have a longer brake-pedal connecting rod?