On my G16XT the 'clutch' is a belt tension arm operated by the clutch pedal. I believe all the XL series tractors are this way. When released a spring hold the arm against the belt to hold it tight to make it drive the transmission. This arm has a bad bounce, enough that the clutch pedal with bounce up and down an inch or more. The pulleys are tight to their respective shafts, run true with no out of roundness. Bearing in the idler pulley is good as it turn free and quite and smooth. The belt is a new OEM. I thought it might be the spring, that it lost tension over the years. Put a new spring on that was stronger but just a little longer. Nothing changed. If the clutch pedal is held down slightly most of the bounce goes away. It reminds me of an old vehicle that has worn out shocks and one wheel hits bump in the road and that wheel keeps bouncing for the next 1/2 block.
The two drive pulleys run steady and true, it is just the idler that is doing the bouncing. Any suggestions as to which way to go to stop this action?