Junghans bracket clock speed adjustment

by Mark
(Canada)

Hello,

Just got a Junghans bracket clock with Westminster chimes but have no idea how to adjust the speed.

It has a pendulum that has no lenth adjustment, but does have a small coil spring inside the bob which I don't know what it's purpose is. Also does not have an adjustable suspension height that most clocks of this style have.

This is not a very old clock maybe mid to late 1900's. It's loosing about 1/2 hour per day.