Help- First post and question. Have a 2002 3500 5.9 diesel with 5speed. It randomly pops out of 5th gear while hauling trailer on the interstate, mostly when I decelerate. It has a fairly new (3 years old) rebuilt trans installed. rarely does it when I am unloaded. When It pops out, I can pull down into neutral, over to left and then back to 5th and all is well. Total combined wt is only about 14,000 to 15,000 so I am not overloaded. Any Ideas?
Thanks

 

Welcome to DTR. A search of "5th gear nut" should give you all the info you need. In a nutshell, the nut that holds 5th gear in place will come loose under high torque conditions. On a 3 year old rebuild, this should have been addressed but you can never tell.

 

Could be a couple things, trans rebuilt incorrectly, though after 3 years I doubt this. Something is either not allowing it to fully engage 5th ( Shift fork pads worn or fork bent ), or your Synchros are not holding it in, either Synchro or engagement dogs on gear. Fortunately, 5th is the easiest to work on, you don't have to pull the trans, just drop the tailhousing and it is all right there.

 

It's not the nut problem . When it goes it goes. You have a sychro problem or a worn bearing on the tail shaft. When they wear they flex sometimes under the right conditions and let the gear pop out .

 

I agree, sounds like the trans has a problem.