The new belts are too tight. Chances are that over the time the previous belts were on, the tension was adjusted to keep them tight as they wore/stretched.
For the transmission belt, check that the FULL movement of the clutch pedal is transmitted to the idler pulleys that tension the belt. Any lost movement here will cause the belt to remain tight enough to prevent gear selection.
For the deck belt, ensure that the blade brake mechanism is working properly. With a loose (old) belt, the blades would eventually wind down when the rive was removed. With a new 'grippy' belt, the brake mechanism has to overcome the residual drag of the belt. The pads wear out over time, and 30+ years is more than enough.
phil_saunders(a)bigfoot.com
Phil Saunders, September 2009
