To capture the ILS, I use VOR LOC and to capture the Glide Slope, I use GS AUTO. Capturing and tracking ILS and Glide Slope works perfectly fine for me.
You might want to have a quick read on the Autopilot in the ‘707 Captain’ FLIGHT MANUAL Part II – Aircraft and Systems (cs707_manual2.pdf) on page 69-71 and make sure you are doing it correctly.

Mark