Last summer we installed a Sherman step-up transmission in our TE-20. It runs great, no noise until I wanted to start up our saw bench… (PTO driven, not by belt) When I started up the saw bench there was a ‘knocking’ sound that definitely came out the Sherman transmission. Is this known by you guys? What could be wrong?
Do you remember if you checked the preload on the input shaft as instructed in the original installation instructions? Shims are installed or removed as needed to obtain the proper preload on the transmission input shaft bearings. Failure to do this will cause there to be excess end play in the shaft and the bearings to rattle around in their races. I believe there is a copy of the original installation instructions on the web site. If not, the web site authors should be able to provide them as they are pretty much the authority on these transmissions today. There are also bearings in the Sherman unit itself that may need to be checked and replaced as needed. Instructions for rebuilding the Sherman transmission can be found on the web site. Parts to rebuild the transmission are also available on the web site as well as from Red Rock Manufacturing. Other possibilities include the proper alignment of the universal joints on the PTO shaft on your saw. I the universal joints are not in proper alignment, they will make a snapping noise as they turn when the PTO shaft is at an angle. Still another possibility is that the saw blade is acting like a flywheel and trying to over-speed the transmission. The usual solution for over-speeding is to install an over-running clutch. All things considered, I think there is a strong possibility you will find the problem is in the preload on the input shaft bearings.