Muni PCC cars had two different models of trucks. The 1100 cars were built originally to operate in St Louis. They had Clark B-2 trucks designed to operate on girder rail in city streets. The 1006-1040 cars had Clark B-3 trucks that were designed to give a better ride on open track than B-2 trucks. Since Muni had extensive open track operation in tunnels, it bought the B-3 trucks. The Magic Carpet cars, 1001-1005, had a mixture of Clark and Brilliner trucks. I personally thought the Brilliner trucks gave a better ride than the Clark trucks on Muni. All cars had resilient wheels to cut down on noise and vibration.

So that explains the different ride quality on Muni PCC cars.