clutch adjustment advice

[Geegc@aol.com]

I have to explain to my 19 year old son who has my 66 1600 at school how to 
adjust the clutch (he told me it is slipping in 4th gear).  I am not sure 
whether an adjustment below the tranny will help, but it is worth a shot.  
Anyone have a good explanation of how to do it for me to send to him, or a 
reference to a website where a picture may be found.  He is even less 
mechanically adept than am I.

Thanks in advance.

Gary C