Sm465 sounds like a rock tumbler in 4th gear

[dmac2590]

I replaced my 4 speed Transmission with a "good" Transmission early this year. It has penn GL-4 fluid in it. When I shift into 4th it sounds like a rock tumbler from 35 mph up to about 50 mph. I kicked the transfer case (np205) into 4 hi went down the road and zero noise from anywhere in the transmission or transfer case. Truck has new clutch, flywheel, throw out bearing, pivot ball and clutch fork. Anyone seen this or heard this before? Any input is greatly appreciated. Thank you all.

 

[nvrenuf]

Is it lifted? If so, recently?

I’d remove a driveshaft and drive it, reinstall and remove the opposite shaft then drive it. If it’s the trans the noise will continue.

 

[dmac2590]

I'll give that a try and see. No lift on the truck and it has new u joints as well.