Hi, yes you do need to remove the back wheels, turn the petrol tap off if fitted then stand machine on its nose up against a wall or other solid object, under neath you will see two metal plates either side in from the wheels held on by two bolts each, take these off then remove the drive belt with the aid of a large screw driver being careful not to damage anything!
then you should be able to pull the assembly out far enough to detatch the cable from the gearbox, once done you should then be able to pull the cable out from the gearbox end, fitting is the reverse of removal, start by threading the new cable from underneath the machine up through the hole in the deck etc etc, hope this helps ? Rob.....
rob
September 2008