On my LV halogens, I had to use the dimmer upstream from the
120V/24Vtransformer to drop the power to the transformer, rather than
downstream dropping power to the lights themselves.

I had line voltage tracks with a dimmer and the dimmer worked fine. I
replaced the track with a newer track, hampton bay, and put in 3 low
voltage halogen light fixtures in it. Now the light turns on and off
but the dimmer doesn't work. Has anyone ever seen this? I thought you
could use a dimmer with low voltage halogens. The light still turns on
and off but it doesn't dim.