Modern semi-tractors have lots of creature comforts, compared to their ancestors. Among them are seats with adjustable height, tilt, back support, seat firmness, and number of partridges in a pear tree. Fully half these adjustments are pneumatic--the truck's already compressing air for the brakes, the suspension, and a few other things, so why not?
So I got out of the truck to connect the air and electrical lines to the trailer, went back to the cab, and started to climb back in--and suddenly I found myself being swatted by something thin and snakelike that whipped around in the floorboard and hissed, loudly. After a few seconds of dodging and a few more seconds of chasing it around, I got hold of it. It was a tiny hose, the one that supplied air to my seat adjusters. Now it was supplying air to the whole world, and adjusting its own position.
This is a more serious problem than you might think. I was merely annoyed myself--until I heard an alarm go off on the dash. It seems the seat adjusters are powered by the same air supply that operates the trailer brakes. And the people who designed truck air brakes borrowed an idea from the elevator designers: a secondary brake system that's powered by heavy springs, and built so it's always trying to apply the brakes. The air system provides power to keep the brakes from locking up--that way if the air system fails, the brakes come into play by themselves.
In other words, as long as this little hose was loose, I couldn't move the truck.
It only took me about five minutes to figure out where it went, and another two or three to get it there. But I had time to think about just how oddly the systems on these machines work together. I've run into things like this before.
The driver's seat can lock up the trailer brakes. So can the passenger's. The self-leveling suspension can interfere with the driveshaft. On another model truck, the sleeper's fan switch can override the cab's air-conditioner controls. And so on.
You really do have to keep track of everything...
p.s.
I've mentioned this before, but I don't know how far into the past my readers may have looked. So I'll mention it again--my Internet access is kind of spotty. So I will often save up a bunch of these entries and upload them all at once, when I have a connection.
In other words, if you notice a post that you should have read the last time you came in, you haven't lost your mind. It's just me, trying to keep my posts in order. The dates you see are when I first wrote an item, not when it got on the site.
We thank you for your patience...
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