Well my 10 bolt has developed a clunk and has gotten worse and worse to the point i will not drive it. What are the chanced my 4.10s are shot too? I havent ripped it open but figured id ask first. Really dont want to have to install them in another 10 bolt and have more issues. I love the 4.10s but dont really have the money to pull to buy new gears and rebuild kit ontop of the used diff.

Should i just keep the 3.42s as is and just drive it?

 

Has the rear developed a whine that it didn't have before to go along with the clunking?. I think if the clunk is caused by excessive backlash developing between the ring and pinion you would also pick up a whine that you didn't have before. Pull the rear cover and get your hands on the ring and pinion to find out where the play is. How are your u-joints? At the end of your post you mention 3.42s, is this a reference to the gears you took out of the rear to install the 4.10s? If you're thinking of re-installing these did you measure the backlash and pinion shim thickness when you took them out? If you have these dimensions you probably could re-install them okay.
Use a solid pinion spacer next time you rebuild the rear end, they are harder to setup than a crush sleeve bet are worth the effort.

 

The whine was getting worse and i knew it was on its last leg something inside was not right. I was showing off and it was afterwards that the clunk developed and i stopped driving it since. I have a spare 3.42 rearend i was going to swap in but i feel its going to be not as fun to drive going from 4.10s. So the question im asking what are the odds the 4.10s are still useable?

 

won't know until cover is removed and gears inspected.

 

If your gears turn out to be good, make sure you take all the appropriate measurments on the gears before you take it apart. If you don't install them exactly how they were broken in, they will whine and become weak.