With the electrical system, it has to do with the duty cycle of the accelerator resistors. PCCs were designed to accelerate for a city block or two, then stop. What prolonged running does is to increase the chances of overloading the resistors in dynamic, because when a PCC "coasts", it actually goes into dynamic braking, generating just enough current to spot the brush arm (GE) or rollers (WE) on in the accelerator in a position which corresponds to the car's speed. If while coasting, the car slows down, the accelerator backs off; if it accelerates (going down hill for example) it advances. Riding a small amount of dynamic to limit car speed is the worst thing because in dynamic there is current regulation but not voltage regulation (same is true for DC-drive diesel locomotives, BTW). This means there is no limiting of the power output, which can get high enough to melt things, particularly with prolonged, fast running. Even the T's picture window cars, which had MCM control rather than TRC accelerators, had problems on the line to Riverside until they were "dumbed down" a bit.

It's been quite a while, but ISTR that eventually the small end of the equalizer bars of a B-2s will break off. B-3s are slightly better, but it's been too long. These trucks simply weren't designed for all the vibrations and jostling movement that come from running on open track. The Muni 1003 has Brill 97ER-1 trucks, as does the Brill liner at Baltimore (I think it's Baltimore). These are the only active 97ER-1s in existence. RVJ used to have a spare, which was painted yellow and used with the C-1 to spray weeds, but the current crop of guiding lights might have scrapped it because I couldn't find it the last time I was there.