Turn the tumble-drier upside down and start on the back.
Remove all the screws, there are an awful lot so use an electric drill with screw-head affixed.
Remove the locking pin holding the spindle of the drum.
You will need a diagram from a web-site of your tumble-drier however I managed without one, mine is a Creda Reversair which has two pulleys attached by a spring, these will be anchored to the base of the tumble-drier.
Here's where things got hard.
I righted the tumble-drier removed the drum, put the belt around the drum and reinserted the drum, replacing the locking pin. Turn the drier upside down.
I removed the exit pipe (the actual piping inside the tumble-drier to gain access at this point.
The two pulleys came loose and I had to reinsert them using heavy paint pots to stop them slipping back in and then by touch alone, reconnected the spring. I cursed a lot at this stage and took a break of a night.
Once the spring was back on I pulled the belt over the farthest pully and the motor. There is now not enough slack in the belt to get it over the last pulley. I squeezed my second arm through the exit pipe alongside the first and I am not skinny. With one hand I pulled the pulley against the spring until I could get the belt over it with my other hand. This was quite tough.
At this stage I ran my fingers over everything ensuring the belt was on straight. It should have worked at this point but I noticed the drum was very tight and would not turn when the drier was turned on.
I now need to find out how to loosen the drum from the front or rear, I have a feeling I may have lost a washer taking it apart but I can't be sure, any suggestions would be gratefully received.
Glenn, October 2007