Blue Frost wrote: ↑September 16th, 2020, 12:49 pm
I knew that about trains, but not big rigs, I have seen the air compressors for them though.
This one guy was going to hire me for help on the big rigs once, but I turned it down.
He knew I worked on cars all the time, and thought I would fall for that job
no way.
Ya, in fact big trucks used to have the exact same system as trains (Westinghouse air brake system), but too many problems were happening (ranaways, parked trailers rolling away), so they eventually mandated a 'failsafe' to be incorporated on all axles except the steer, which is just a strong spring that will mechanically apply the brakes should system air pressure drop below a certain threshold. Whenever you hear a blast of air when a truck parks, that's the driver setting the brake by dumping the air out of the system, thus allowing the springs to hold the brake shoes tight against the drums. They are usually twin-cylinder compressors, and run directly off the engine, meaning they are always pumping. When they reach a certain PSI (around 130 psi or so), the system will 'unload,' and you can hear when it does that by the 'whoosh' or 'blast' of air!
And working on big rigs sucks! Everything is larger, heavier, and generally more of a nuisance to work on! The wide steer tire and wheel combo on my Kenworth weighs upwards of 300 lbs/piece!