hey guys, 1988 f150 300 6 cyl 5 speed 4x4... when im driving I shift gears and theres a clank sound,,, like theres slack in the drive line or tranny somewhere, no othere issues at all. but the noise is making me think there are problems to come . any ideas?

 

a good place to start would be to check the u-joints.

 

ive already replaced them, first thing I checked

 

Just going to throw something out that I have done in the past for slack. I'm not an expert but I have rebuilt my 8.8" diff and my fathers 9.75" differential before in the past.

Check the diff and transmission fluid.

If that's good jack the rear end up on the truck and put it on jack stands . Don't start the truck...Place it in Neutral. Get up under their and start moving the drive shaft back and fourth by hand to see how much slack your rear end diff has. If your diff clanks and has slack in it that might be it. If you can wiggle and see the drive shaft move at the differential yolk I would start their.

Optional way- Keep it on jack stands - have some one start it up and run it and you get down to the side of the vehicle and check it out. While they shift through the gears.