NV3550 Grinding Noise at high speeds without load


Original poster
Jan 12, 2021
NW Indiana
Hello all, I recently tore apart my NV3550 and replaced all of the synchros. I checked all of the bearings and determined that they were all good, so I did not replace them. I am confident that the transmission was assembled correctly, and everything felt smooth and solid after going back together. The clutch and flywheel only had 20k miles on them, so I did not replace them again. I did, however replace the throw-out bearing with a timken. The transmission shifts great and the jeep drives great, but after a 10+ minute drive at highway speed, after getting off of the gas (at highway speed), whether the jeep is in gear, out of gear, clutch in, or clutch out, there is a horrible grinding or "loose" component sound coming from the transmission area until I slow down to about 10 mph. My first thought is to drop the trans and check out the throwout bearing then move from there, but with it happening whether the clutch is in or out makes me not sure about that being the issue. Has anyone experienced anything like this? Any input would be appreciated.