Weird Grinding Noise after hitting bump

[Mudslutz]

Good Evening,
Have a question regarding an M923A1
When driving down the road everything is fine until going over a bump in the road then a grinding or popping sound happens. It continues until the vehicle comes to a complete stop then doesn't do it until another bump in the road. The noise seems to be come from the Jack shaft area. We greased it and drove again and it didn't occur as much. Took the jack shaft off cleaned and reinstalled and greased again and still occurring when driving over a bump. Seems to happen at approx 20-25MPH. Has anyone ever encountered this? We have gone over everything and cannot narrow it down.. Thank you in advance!!

 

[gimpyrobb]

Have you tried moving the T-case lever or parking brake lever? I can't think of anything that would cause this issue. I'm guessing the bolts holding the short shaft were tight when you took it out and are still tight now that you put it back? Did you just pump grease into it or did you check for a bad cap while it was out?

 

[Mudslutz]

T-case lever and parking brake levers work and function as they should. After cleaning the jack shaft u-joints they all were smooth and did not seem to be bound up. I will attach pic in a few mins of possible area of concern regarding one cap

 

[Mudslutz]

Here are the possible areas of concern but unsure

 

[gimpyrobb]

Ehhh, if you moved it around and didn't feel anything "crunchy", I'd say its serviceable. I haven't done much in that "mid section" of 939 trucks to guess further.

 

[M543A2]

Just a guess of something else to check; are the drive shaft slip joint splines free and well lubricated?