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His Highness of Vonore
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This will go down as a mystery. Assuming it was a failed diaphragm and the leak was enough to allow pressure to be insufficient to release the spring brake (that is what happened correct?) then the gauges should have shown low or cycling like crazy.
Peter…..What say you?
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Geo’s incident, Phil’s break chamber story, & Jon’s maintenance schedule just added break chambers to my zeroing out process. On the brighter side, we have enough PC members at Jeff’s to have mini no rally!
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Having had them fail in trucks, I am surprised too that the gauges did not cycle like crazy. Last time it happened to me in a truck, I noticed it right away, and was able to get off the road before a problem started.
I have not yet had that issue with the bus, and I hope I never will.
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Both gauges should cycle up and down if there is a leak in a brake can . I replace my brake chambers every five years , because of the miles I drive
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Jon and Peter, I know you guys are trying to figure out what happened. We had been moving that morning for about 5 hrs never shutting the bus off with 2 previous rest area stops and at least 2 previous toll booth stops. I constantly do a mirrors and gauge scan using the needle position method. I think it happened just that quick shortly before the toll booth stop where the smoke was noticed given the minimal mount of damage that occured. The brake was not dragging for very long. If the primary and secondary air gauges did react, it happened just before the last toll booth as I would have been concentrating on positioning myself for the booth. I never saw them do anything out of the norm even as I moved the short distance from the booth to where we stopped. Of course then I immediately shut down and addressed the fire. Geo. PS Jeff and Ben asked the same thing.
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FWIW a brake chamber leak, either on the service side or the emergency brake side should show up on the gauges. I don’t understand why that was not the case here, but for those who may not understand what is going on here is the Reader’s Digest condensed version.
Emergency brakes are released by a large rubber diaphragm (on older style combo brakes) pushing against and compressing the spring that holds the emergency brake in the “on” position. If the diaphragm starts to leak both pressure gauges will show this by cycling up and down. If there is any question while driving, pull into a safe spot and apply the emergency brake. The pressure should remain constant because when the emergency brake is applied all air to the chamber is shut off, so there is no leak.
On a pre-trip inspection this will show up as a pressure drop on the gauges as soon as the emergency brake is released. If the leak cannot be overcome by the bus engine driven compressor the brakes will automatically apply.
Service brake leaks also show up in the gauges. When the brakes are applied (all air brake systems regardless of vintage) a steady pressure drop will be noted. As soon as the brake is released pressure will build and the pressure on the gauges will be fairly constant. A service brake leak will only show on one of the two brake system gauges.
A pre-trip inspection will show this as a pressure drop on one gauge.
The leaks discussed above can occur in the brake chambers, air lines to the brake chambers, or at fittings from the relay valve. A leaky or failed relay valve can also exhibit similar characteristics on the gauges, but relay valves generally are reliable. I fully agree with the 5 year brake chamber replacement plan. A lot of good brake chambers will get thrown away, but the cost of one on road service call is going to exceed the cost of replacements.
If a problem with the brake system exists, block the air line, and in the case of emergency brake cage the brake, and keep driving to the service facility. Do not get a tow.
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