Well, honestly, the cable itself is self adjusting, as it has a spring loaded tensioner, with a locking pawl, to engage as soon as you start to pull up the handle.
As for things that happen with these, first, check to make sure that the leather boot does not slip inside the self adjuster, not allowing the pawl to engage the teeth. Specifically, look at the inside of the handle, to see if the leather boot has dropped down.
If this is ok, you will have to remove the rear wheel to get to the little shoe adjustment, located underneath the rear brake disc.
Let us know if you would like to proceed.
There are two problems with the park brake system one is to thick of grease used on the park brake lever adjustment paw which keeps it from being able to catch if pulled quickly, this can be either fixed by cleaning off the thick grease and then using engine oil or have the lever replaced. The other is the need for adjustment of the rear park brake shoes which are located inside the rear rotors and this would require removal of the rear rotors. If you have to adjust the rear shoes I would recomend you drill a 1/2" hole in the side of the rotor inbetween two of the wheel stud holes but up in the rough part of the rotor this will give you acess to the adjuster with the rotor is installed like what was done on the 84 to 87 C4s and also the C3. You would still have to remove the rotors now but will not have to in the future, you will also get a much better adjustment. What you do is after reinstalling the rotors turn the rotor untill you are able to see the star adjuster now turn the adjuster untill the rotor is unable to turn then back off 5 clicks and it will be just right when you are done you will have a good park brake something you may never have had.