[allmightythor]

I posted this thread in the clasic mustang section but got no reply, maybe because it was the wrong place! anyway here is the problem, my stang was vibrating at different speeds and everytime I change gears from park to drive or reverse and vice-versa I have a loud thunk! noise coming from under the car.Also when I'm driving and the car is coasting in whatever speed I'm in and the car starts to slow down and I want to pick up speed again I step on the gas and the firs thing I hear is a loud thunk again! every time I go over a bump it feel like my hole rear end is lose and my rear axel is spitting grease or oil out of the breather valve. I have replaced the U-joints but was unable to put grease in them because someone told to put grease after I had installed them, well I can't find a grease gun that wuold fit inbetween the crack of the drive shaft arms securing the U-joint to reach the fittings, replacing U-joints help the problem a little but not much. Also I have air shocks in the rear and I know for a fact that they are bad because they don't hold any air anymore, maybe thats why it feels lose on bumps because only the leaf springs are holding the rear end. Well to cut it short this all started when I relaced the rear leaf springs and raise the back a little, before the leaf springs the car would bottom up you couldn't put no more than two people and it would bottom up scratching the tires. With the new leaf springs solve that problem but now I have this one, please help!!!

[GTRaptor]

Could be that you have a loose bolt or nut in the leaf mounts, have you checked them?
Might also be the shocks, if they are shot they could be making the noise.
Last, the differential, has enough lube in it?

To rule out the differential raise the rear end, then turn one of the wheels by hand (clock and counterclockwise) and then the other, see if theres any noise comming from the differential.

Also tighten all the rear suspension mount points, and if possible remove the shocks, and move them by hand.