Originally Posted by lbranin
The air ride was not original equipment on this bus I have been told it was added later. And I will have the caster checked as a mechanic told me if the caster is off that will make it not steer correctly. Even though I had it aligned when the new tires were put on.
Have someone competent check the rear axle setup. If whoever did your alignment is honest, they would have checked/corrected any caster issue. Caster will cause the front end to be unstable and the steering wheel not to return straight after a turn, but it won't cause the rear end to fishtail. That has to be in the rear suspension.
I'd set the bag heights/pressures back to normal, and then check all of the bushings in the rear suspension for looseness. Something back there is amiss.