axel wrap

youll hear it binding up and chattering way before it binds up enough to worry about it breaking

or more like you'll feel a vibration

well right now when i accelerate there is a huge knock in the rear. but my exhaust system is really lose so when i kick the pipe, it sounds like the knock. i'm repairing the exhaust right now and if the knock doesn't stop i'll start to worry. and as for the vibration, would i feel it at low or high speeds? cuz there is one when i'm giving gas at like 60 but i think its just my tires not being balanced very well.../

and if i do break a u joint, are they hard to replace?

yeah they are pretty easy to replace. i think its more likely to bind up at low speed acceleration but obviously more noticeable the faster the driveshaft spins as with any vibration from rotation parts. its kinda hard to say what it is for sure if your wheels arent balanced. i would recomend at least getting then balanced before 1000 mile trip.

yeah cause if you dont balance them before the 1000 mile trip... then more than likely you will have 1 maybe 2 bad tires after you trip or a flat (worst case) during your trip.