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Posted by Russ Roth [24.21.77.67] on Saturday, September 22, 2012 at 12:17:56 :
In Reply to: Re: OT - ran when parked posted by Kaegi [24.16.253.154] on Friday, September 21, 2012 at 13:00:03 :
Yes, that's how they are supposed to work and do now but early rigs were prior to the introduction of spring brake air chambers.
Inside is a big coil spring that is held off by air until the release valve is pushed and automatically applies the brakes via spring pressure when and if you lose air.
I don't know about tractors but the older trailers used to use air from a separate tank to apply brakes when you lost air. I had that happen once when an air line broke and it did lock them up pretty solid without a load.
RR