Hey guys, just the other day my car developed a loud terrible clunking and grinding sound (along with vibrations) while accelerating. Its coming from the rear of the car, I'm thinking its a bad rear end..

On thoughts on this??

Wow!! Wouldn't hurt to check the U- joints...
But it seems the ring // pinion may be missing some teeth.

( edit )
also check rear brakes, & lugs are tight enough.

Check the u joint first. This is the easiest thing to check. If you don't find anything then remove the cover and look for broken teeth. There are 6 gears in there that need to be checked. Also check the shaft in the center of the differential. It's not uncomon for this shaft to break.

Check the transmission mount too. When I broke the one on my old 83, I thought I broke the rear end - it also makes a loud clunk on acceleration, and it feels like the rear end.

if its a hard and one clunk when you gas it its the trans mount or tq arm mount, if its a clunking that gets faster the faster you go than you cracked or broke your pinion or ring gear ..... i been there and done that, its fun, you get to put better parts in and hopefully get a posi unit

Thats what happened to me, I thought that my U-joints were going bad but I put in a new mount and it wasn't the right one, so it was pushing the transmission up too high making some weird vibrations and sounds, plus it wasn't shifting right.

I would check the mount, and the u-joints and just both ends of the drive train to see if anything looks abnormal.

Could just be a mount going bad.

Definitely not the tranny mount, It's brand new, but I did go ahead and check it just in case. The clunking does get louder and more severe as I accelerate, but when coasting, its not as noticeable. I'm going to pull the cover off here shortly, and will report back with what it is.

If it is the ring and pinion, is it just a part store differential kit that I need or something I need to order from Summit or Jegs?

Okay slight problem, the bolts on the differential cover won't budge, 1/2in is too big, spins way too much, 12mm is too small and just fits the tip of the bolt head of a few, 13mm fits but is a little loose and the bolts won't budge so it just spins on the bolt head (only tried 1 so i didn't strip the bolt) any suggestions??

There is a lot to replacing the ring & pinion gears. It's a long way from a simple bolt in job. If you don't know how to set the pinion depth, bearing preload and backlash then you would be better off finding another complete rear end and swapping it out.

That may be the route I need to go then, I can handle motor work, but this may be a little out of my ability at this point.