Contax IIa with 85 mm f/4 lens
Contax IIa disassembled to show its rangefinder, and shutter
From my book: "Restoring the SLR".
Both Nikon, and Contax had to have two mechanical links between the body, and the lens. The outer coupling was the bayonet mount. The inner coupling engaged with the rangefinder mechanism to rotate with the finger operated focusing dial next to the release button.
Contax IIa Shutter (left) is the only focal plane shutter in a camera that the first, and second curtain take up rollers are combined into a single but complex roller (bottom). The slit forming gears on top adjust the slit width as shown. This illustration also shows the shutter winding operation where both the first, and second curtains are wound by the charge gear on the right.
Winding
Gear
Curtain tension Adjustment gear
2nd Curtain
Not an easy Repair !
Drawing by Ali Afshari, From the book: "Restoring the SLR".