The clutch needs ajusting and yes it is 1/2 inch as ks8780 said.  After you take the cover off of the clutch housing turn the engine over untill you see the lock on the pressure plate. It takes a 3/8 bolt to tighten the lock.  Rotate the half moon piece and slide the lock out of the ring and tighten the bolt just snug.  Depress the clutch; this will alow you to rotate the ajusting ring.  Without the book in front of me, I can't remember, but I think turning it clock-wise closes the gap on the brake.  When the brake is at 1/2 inch slide the lock into the ring and rotate the half-moon piece into place.  Do this w/ the clutch pedal depressed so that the lock ring will move and align perfectly w/ the lock.  Tighten the 3/8 bolt as tight as you can w/o breaking it.  This is the most important part of the whole procedure.  Double-check to make sure that the half-moon piece is flush w/ the lock and the bolt is tight.  Now you have to adjust the clutch linkage so you have 1" of free pedal.  My recommended shifting procedure:  Always use the clutch at idle.  These tractors will pull any load at 1000 rpm.  In doing this, the clutch will last forever.  When shifting the transmission, you must have the power shift in "low"; this releases the pressure on the gears and allows you to shift the main transmission.  It is very important to have the clutch and transmission brake adjusted properly.  At no time do you want to grind the gears when shifting.  This will knock the snap ring off of second gear and eventually wear out the shifting fork.  This can be fixed w/ the transmission in the tractor; however, it is not a lot of fun.  Hope this helps; good luck.