View Full Version : Yanmar 3GM30 intermittent rough vibration in fwd

05-26-2009, 03:59 AM
"My 3GM30 will run smooth for hours then randomly start a loud clanking vibration in fwd gear only. Sometimes it will smooth out after going back into neutral then fwd again. Smooth in neutral and reverse. Sometimes accompanied by delay in fwd gear engagement after shift lever is moved into fwd position. Diver says shaft and prop are ok. Couldn't get it to act up for mechanic who didn't think it was the transmission, but it sounds similar to a previous post about an intermediate shaft thrust washer problem. Any troubleshooting ideas?"

05-26-2009, 10:06 PM
"if it's the thust washer thing, the engine will act like it's about to jump off the mounts. only way I can think to troubleshoot is teardown, and good inspection. I've only seen this problem once, and it stumped 2 engineers from Yanmar. good luck, S."

05-27-2009, 12:41 AM
Thank you. Contacted another previous post owner who found bad shift cone caused similar symptoms. Either way sounds like I need to get inside tranny.