1920's Grandfather clock strikes 15 minutes late.

My grandfather clock has 2 weights - it is keeping time ok, but after I fiddled around with it when one of the arms was loose, it strikes the hour and half-hour, but 15 minutes late. I can hear the gear click prior to the strikes.
e.g., 3:00 strikes at 3:15. at 3:30 strikes at 3:45.
Would appreciate your input.
Thank you.
Joan