You didn't say A833.. so could the trans be something else? The reason I ask is because the AX15 has a 4.22 reverse ratio, compared to something like 2.33 in the Mopar.
But I doubt you have an AX-15, you wouldda said so.
This I think is where all the confusion begins.
After putting it in reverse the problem occurs when trying to let clutch out.
If I read it exactly like you wrote it, it says that you are beginning to back up; and
this; severe thud and wheel hop in reverse. confirms it.
You also mention that this severe thud was also there before the new springs went in. And you say the severe thud comes first.
So now I'm thinking maybe the axle is rotating in the saddles. Here's my thoughts;
If while backing up, the pinion rotates severely nose down, it will bind up the U-joint and make an awful chattering. Yeah if the driveshaft stays in the back of the trans by some miracle, I suppose the wheel action could get violent.
But in this scenario the thud would not come until you put it in first and begin to take off. Now the pinion would rotate back up and the snubber would hit the floorpan, causing the thud..
Of course all the guys who are pointing to a torn mount have a much better, more likely idea; but again the severe thud comes after declutching and the engine falls back down.
I just can't think of anything that would cause the severe thud to come first, except maybe a shackle flipping over; but if only one side flipped over, the car would be listing to that side, like a barge with a shifted load.
Or something in the trunk.........tipped over,lol. Don't laugh, years ago such a thud was found to be something in the space between the quarter and the trunk-extension, flipping around.
Or I suppose if one of the rear brakes is bound up and dragging, but not seized.. Then all the torque would be transferred to the other wheel which is wanting to turn at double-speed. That would be kindof hard to modulate with a manual trans. But I'm having a hard time imagining a "severe thud" on this.
I just don't know
