I did get odd readings like that with mine at first also (I forgot about this until you mentioned checking your connections) I had the wires crossed when I soldered the first one up. I think it was VCC to leg 3 and VOUT to leg 1 or some such, the reading jumped all over. I wound up killing that sensor. Until I replaced it I was pulling my hair out (dont have much left to begin with). When I purchased mine (the allegro units) I got a baggy full for a couple of dollars on Ebay (I think it was) so replacing one was not problem.
By the way, I do not know what ujoint assembly you are using but mine is off an old Yamaha street bike. It is much smaller than a car ujoint assembly so I could fit it into a tighter box, etc. 20.00 on ebay did the trick.
Here is one for 10.00, notice the flange on the bottom to make it easier to mount to a flat surface. I removed the shaft itself and made my own so I could run the wires up through it and mount my top flange for spring center return.
http://cgi.ebay.com/ebaymotors/1980-Suzu...sQ5fAccessories