[77newell]

On my 77 coach I have changed all the airbags and I surprised that the upper and lower plates were typically out of line a bit and my coach never did the jiggly thing yours is. What you are experiencing is probably caused by looseness in some parts related to steering. I would suggest starting by looking at your tire wear. If the wear is consistent from side to side then the cause of your symptoms is most likely in the parts that effect both wheels. Next check out tie rod ends for "play". There should be none from the end of the arm on the steering gear all the way out to the wheels. If these are all tight, then it is either the steering gear itself (I experienced just a bit of this prior to having it overhauled) or the king pins on the axle ends are worn (this unusually produces odd tire wear).

You stated that the tire were balanced, depending on how that was done it balance may still be an issue. I had a new tire installed on the front with the balance beads and it darn near shook the front off when triggered by a small steering correction at moderate speed. It turned out the aluminum wheel was hugely out of balance and it really needed massive lead weights to correct it.

Everything I know just ain't so