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Posted by Franz on Monday, August 25, 2008 at 03:20:50 :
In Reply to: Re: Electric Brake Booster? Picture #2 posted by John in NH on Sunday, August 24, 2008 at 20:52:42 :
What we have here is an intergenerational failure to communicate. You young bucks have no idea what the finest available was back in the 50s.
The dashboard rheostat is simply a variable resistance that is set by the driver to control the current flowing to the brakes to preset the braking force according to the load being stopped. A trailer might leave the yard in the morning with 5 poles (10,000 pounds) and need a lot of braking behind a Power Wagon. Coming back in the afternoon the empty trailer generally helped the driver kiss the windshield of he forgot to reset the rheostat. Some drivers needed a daily reminder. It also wasn't uncommon to have a TEST YOUR BRAKES sign in the poleyard, and nasty tempered Supers generally loved watching the test area.
The unit that is connected to the master cylinder is another rheostat that is operated by a hydraulic (wheel) cylinder. As hydraulic pressure to the vehicle brakes increases, the rheostat sends more current to the brakes for additional stopping power.
Companys with a lot of $$$ to spend on vehicles often duplicated the trailer brake control with a large Cole Hearse lever operated controller mounted dead center of the dashboard, just in case the hydraulic didn't work. The manuals were a lot better than the hydraulics because you could feather the manual to employ the trailer brakes on ice, or if the trailer started to jackknife.
I still preferr the manuals to the fancy crap Tekonsha sells today.
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