I tried prying on them a bit with a crowbar to if either one was causing my annoying thumping noise, and while they both of them did move a bit, neither of them really seemed like they were broken (the rear ones may have moved more than the front).

But I wonder, what is the acceptable amount of movement in the mounts before they start causing noises? Should they not move at all?

I can't imagine what could be causing the thumping since my U-joints seem to be in OK condition, and my exhaust isn't hanging loose or anything.

 

Could it be a ball joint? Don't our cars have ball-joints in the rear?

 

Ball joints are part of the steering, so I would think no.

 

Well, I've heard of some cars having rear ball-joints.... and withour cars having rear-steer....

I honestly don't know anything about the rear suspension... I spent the last year working on solid-axle Jeep's.

Just throwing it out there.

 

its ur front diff mount, i broke mine a while bak and it is very annoying, u can buy a new one from mazdatrix.com

 

More than likely yes, but it doesn't seem broken at all.

I was asking what sort and how much movement is normal.

 

Well it's a piece of rubber sanwiched between 2 metal plates. There shouldn't be that much movement. Worst case scenario, the "tab" that holds the front diff mount is also broken (happened to 1 of my FC's, I'm still looking for another rear subframe with the "tab" still intact).

 

What confuses me about the rear diff mounts is that on one side they have the ridges (which is apparently normal for the factory mounts), but those ridges aren't touching the "arm" of the differential at all (so what is holding in place besides the bolt and the rubber on the other side of the arm?). I wonder if maybe that's normal, of if they need to be replaced.

I realize it's normal for a rubber mount to move somewhat (otherwise they would have just made it metal-to-metal), but the question is how much can it move, with what foce, before it starts causing the infamous thumping.

It should also be obvious that if you pry on something rubber with a crowbar, it should move, at least a little.

On another note, my transmission mounts are really soft and probably need to be replaced as well. The crossmember seems okay though... Engine mounts on the otherhand seem very hard, for rubber mounts. I don't know if maybe they're competition mounts, although the engine still does have some movement when you give it throttle. An engine brace will probably help that...