Im not sure what is going on here. But if I'm just rolling along in gear and I let my foot off the gas completely the steering wheel will twitch, the front end makes a pop and the car kinda jerks and then slows like I was pressing the break.

When I let off the gas to shift up this doesn't happen though, I'm assuming because I have the clutch pressed in. I'm hoping someone more mechanically inclined can tell me what this is because I have no clue.

I'm not positive but I think this has been worse since I had to drive a few hundred miles on a spare that was slightly bigger then my other front tire, so I was thinking maybe differential? Or axel? Is there a way to rule those out for sure?
Thanks in advance!

 

If it happened after the spare tire, yeah you probably damaged your transmission. There's a reason they say only 50 miles on the spare, it's not because the tire will explode.

 

This. Another reason why you never put a half spare on a drive tire or a not equally sized tire full spare.

 

Proper way is to put spare on the back and transfer the real tire to the front.

 

So the only way to know for sure would be a tranny swap? Is there other things I should check first?

 

You could try to feel how the diff is, by spinning the wheels by hand. But the forces involved when driving are so much higher that you may not notice it with no load on it.

Check your control arm bushings also. They can cause similar issues.

 

If this is on a SS/TC the spare won't fit under the brembos.

 

Thank you for the extremely relevant post.

 

Yay someone that doesn't hate me for crappy posts on here!