[Tim]

I have the Garmin C330 and the C340 successor. Both work in the front windshield under normal conditions. Sometimes it can take up to 5 to 10 minutes before the unit will be ready to navigate.

However, when going into the city, it loses reception pretty fast in between buildings. I Notice that the windshield causes the GPS to lose communication with a few of the satellites, because the signal strength indicator lowers by 1-2 bars when placed there.

A solution might be able to purchase the external antenna lead that you can run toward the back windows. This would allow your GPS to function the way it should.