james Sams, make sure that you have the right drive belt. there are different length that could cause this. Otherwise, just follow the manual to replace the motion drive belt:"
TO REPLACE MOTION DRIVE BELT
Park the tractor on level surface. Engage parking brake. For assistance, there is a belt installation guide decal on bottom side of left footrest.
BELT REMOVAL -
1. Remove mower (See "TO REMOVE MOWER" in this section of manual).
NOTE: Observe entire motion drive belt and position of all belt guides and keepers.
2. Remove belt from stationary idler (A) and clutching idler (B).
3. Remove belt from centerspan idler (C).
6. Pull belt slack toward rear of tractor. Carefully remove belt upwards from transmission input pulley and over cooling fan blades (D).
4. Remove belt downward from engine pulley (E).
5. Slide belt toward rear of tractor, off the steering plate (F) and remove from tractor.
BELT INSTALLATION -
1. Install new belt from tractor rear to front, over the steering plate (F) and above clutch brake pedal shaft (G).
2. Pull belt toward front of tractor and roll belt onto engine pulley (E).
3. Pull belt toward rear of tractor. Carefully work belt down around transmission cooling fan and onto the input pulley (D). Be sure belt is inside the belt keeper.
4. Install belt on centerspan idler (C).
5. Install belt through stationary idler (A) and clutching idler (B).
6. Make sure belt is in all pulley grooves and inside all belt guides and keepers.
7. Install mower (See "TO INSTALL MOWER" in this section of manual).
You can get the manual from here.Hope this helps, good luck.