I've had a Garmin Nuvi 255 on the bike and it worked fine, except for having to look at the screen because of not being able to hear the spoken directions. I did the 255 because it was nice, small, did the job, and I had it just laying in the house when I updated the car to a new one.
I kept thinking there had to be a way to be able to get around this without having to go to Harley and spend 5oo bucks, or buy a Zumo "special motorcycle gps". Did some research, and I found an article on another bike site where someone added bluetooth to a Garmin 500, and it worked.
I bought a bluetooth transmitter, and female 3.5 earphone jacks and set off to find a CB or electronics shop here in Vegas to install it.
I found one CB shop still in existance, and they said no way, it was working with micro electronics, and the electronics shops said well, we can open the Garmin, but we can never reseal it.
So, I kind of let the idea stall. I was on line again and found 2 places that would do what I wanted, and I contacted Chris Short at www.Palmdr.com and he said sure, we can do it. I sent the Garmin to him, and 60 dollars and 2 weeks later due to shipping, I had it back.
With the transmitter off, I plugged in the bluetooth transmitter into the earphone jack on the Garmin. I then unpaired my Galaxy S5 from my Sena SMH5 headset, and did a factory reset on the headset.
I turned on the bluetooth transmitter, and then the headset and paired them. I then repaired my Galaxy S5 using the multi-pairing procedure for the SMH5.
I turned everything on, and it works like a champ. The Garmin comes through loud and clear, and I can use my phone. What I did loose was the ability to play music from my phone through the SMH5. But I am very happy. The Garmin is hardwired by the way.

http://f800riders.org/forum/showthre...i-500-Nuvi-550

http://www.m-p-c.com/GPS_Bluetooth_Audio.htm

http://www.palmdr.com/