Changing the timing belt on any car, especially a high-end German model like the Audi TT, is a time-consuming task. It can be done by the experienced home mechanic with the proper tools and good factory manual, potentially saving a lot of money.
Jack up the vehicle and place safely on the jackstands. Remove the right front wheel, sound pads and wheel arch liner. Open the bonnet and remove the engine cover, coolant reservoir cover and charge pipe.
Remove the cap from the coolant reservoir and drain the coolant with the hose attached to coolant drain valve. Remove the coolant reservoir and disconnect the wires. Remove the power steering fluid reservoir with a 5-mm Allen wrench. Plug up holes to prevent dripping and wipe up spilt fluid.
Loosen the fan belt tensioner with a 15-mm wrench and remove the belt. Then remove the tensioner, held on with three 13-mm bolts. Remove the crank pulley with an Allen wrench. Remove the upper timing belt cover by releasing the front and back clips.
Support the engine with an engine hoist and remove the right side engine mount bolts with a 16-mm and an 18-mm wrench. Do not reuse the bolts. Loosen the engine mount bracket to pivot the bracket and remove the middle timing belt cover with the 10-mm hex tool.
Align TDC (Top Dead Center) timing marks on the camshaft sprocket and the valve cover using a socket on the cam sprocket. Clamp the belt and sprocket together to prevent moving. Confirm the marks by removing the rubber cap on transmission and checking to see if the TDC marks line up on the flywheel and transmission. Mark the timing belt at the crank sprocket. Remove the timing belt from the water pump and crank the sprocket by wiggling it back and forth and out. Transfer TDC, directional and 68th tooth mark (counted on old belt) marks to new timing belt.
Install the new tensioning damper with the 10-mm socket and roller with the 8-mm Allen wrench. Clamp on the new timing belt and align TDC marks. Install the timing belt on the crank sprocket.
Using a breaker bar and a 19-mm socket on the crank sprocket, tighten the bolt into the crank sprocket ensuring that the timing belt does not jump a tooth from the TDC marks. Install the belt on other components such as the water pump, cam sprocket, crank and tensioner roller. As you turn the crank, make sure there is not resistance from the pistons interfering with the valves, which indicates that the timing is not correct.
Rotate the cam sprocket to align with the TDC notch on the valve cover and check the flywheel to see if the TDC notch is visible. If it is not, the timing belt must be reinstalled. Rotate the crank twice to double-check the settings. Remove the securing pin from the tensioning dampener with pliers and reinstall the middle timing belt cover. Reinstall the lower timing belt cover.
Reinstall the engine mount bracket and mount using new stretch bolts. Put the upper timing belt cover on and reinstall the crank pulley. Reinstall all other parts in the reverse of removal, place car on level ground and top off coolant.
Replacing a timing belt is a time-consuming job. If done improperly it can destroy the motor. If you have doubts about your ability, have a professional perform the job.