HELP... rear suspension question

[GregWeld]

A buddy called today. He has a stock 56 Chevy frame - modified with triangulated 4 bar - Air bags.. This car is BEAUTIFUL... everything on it is PERFECT.

Everything except - he's asking me about a "wiggle" in the rear. When he steps on it a bit - or brakes - he says it sashays around "back there" -- is his description. So he's thinking it's the airbags -- and I'm saying "I don't think so" - they just go up and down = not back and forth...

There is no panhard bar - and for a street rod - and triangulated 4 bar - I wouldn't think a panhard would be required...

Anyone have any ideas what I should help him look for? Measurements I could take?

I was going to put it up on the lift == and put a laser pointer / level that I have on it - mark the point on the floor - raise and lower the rear and check for how much it moves side to side.... Look at all his bushings... and measure the degree of the arms etc. But from there - I'm not sure what else I'd do.