I had a similar situation with my 430W (which has identical pinout and wiring to the IFD440) and my HDX. Turned out to be a broken wire from the GPS side of the unit, wasn't giving the GS to the ARINC 429. Once I found and fixed that, it works fine.
The glideslope to the ARINC 429 comes from two different sides of the navigator with separate wiring - there is a GPS side and a radio NAV side - if you are getting one but not the other, that's a hint for where to look.