Need help - what are symptoms of bad differential?
 

I finished the base H22 Civic Coupe swap and everything start and runs fine, no codes, etc etc . . BUT:

When I drive it down the road the car vibrates like a wild banchee. Not a mild vibration more of a slam Slam SLAM SSLLAAMM shock that increases to the point that I literally can not take the car over 20 miles per hour. at 20 MPH, it feels like it's about to explode, literally. The frequency of the vibration increases with the speed of the vehicle. It does not happen whan the car is not moving, at idle.

Initially I suspected that an axle was too long. After trying BOTH axle/midshaft combinations that are supposed to work, and having it not go away, I'm quite stumped.

I put the car on jackstands, removed the tires, started it and put it into gear. I braced one side to prevent it from spinning, thus forcing the other side of the car to spin (open diff). THe vibration was still there with the axle not spinning. I did this on BOTH sides and the vibration never went away.

So I am convinced it is not the axles, as the vibration was still there when the axles were not spinning, but the car was running in 5th gear.

So, my question is, for those who know, what are the symptoms of a bad differential? Does the above sounds like it could be a differential?

It's possible the dif got destroyed when the donor car got totalled, I'm thinking.

I just don't want to waste anouther 10 hours of labor if there's no way that is it . . .

Thanks SOOO much in advance

Jeff