I kick my air pressure down by repeatedly hitting the brake pedal. You know how it's done.
The valves don't pop until the pressure drops to near zero, red first, then yellow. They do pop out, but not until the gauges are right at zero.
Is that a violation?
If so, is it an out of service violation?
dash valve - out of service?
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Protection valves Pop-off Test §393.43►
• Continue to fan off the air pressure starting with at least 60 p.s.i. in air system and noting air pressure at which valve “pops out.”
Between approximately 20-40 PSI on a tractor-trailer combination vehicle, the tractor protection valve and parking brake valve should close (pop out). On other combination vehicle types and single vehicle types, the parking brake valve should close (pop out).
NO-GO: If valve pops over 50 psi or does not work between 15 – 40 PSI.
Relay this information to your breakdown department and get routed to a repair shop, pronto.
Last edited: Oct 22, 2019
I was doing my test with the red line hooked up to a surge tank, in order to run my air wrench. When I hooked the trailer supply and the service line up to the trailer and ran the test again, the trailer supply popped out at 20 psi-good.
I have another problem with an air leak behind the dash. Actually I have several and I am in a bind to get back on the road.
I would like to cut off all the air going to the dash. There must be a main feed line that I can pinch with a pair of needle nose vise grips.
Any advice where that line might be?
I can track down the individual leaks when I have more time.
In the case of most air leaks, those plastic hoses on the firewall are the usual suspects.
Another potential suspect is your dash brake valve and its hoses. I've been in two tractor where the plastic air hoses weren't properly attached to the valve nipples. This caused excessive and long-lasting hissing from the dash brake valves. Very annoying.
Then there's the brake valve itself which may be faulty and require replacing. Remember that this may be warranty work and needs to be taken to a dealership.
I had yet another brake valve hiss excessively, but I fixed the problem simply by replacing the gladhand seals.
I didn't know it was going to fix the problem, an idea just popped into my mind, and I acted on it.
The gladhand seals I replaced weren't in bad shape by any means, just a little worn. It pays to keep new gladhand seals at the ready. I bought a bag of about 100 at a Peterbilt dealership for eighteen bucks.
Hope this helps.
Thanks for the reply, Earth. I'm about to go out there now and see what I can find. I bought a box of incense at the Dollar General last night. I'll open things up and see where the smoke swirls.
It sounds like it's coming from the right, near the glove box. The switch for the passenger side window was leaking and I clamped it off, thinking I'd found the problem. When I cranked it up and built pressure, I realized I'd only found one of the problems.
I could be wrong, but I think the problem is in the duct plumbing. None of that is necessary. It's nice to have, but I can run without it. I already discovered that with the blower on I get hot air coming out of the defrosters, and that is the only essential matter regarding vents as far as I'm concerned.
I just don't want to be out on the road and get pulled over and have a particularly enthusiastic diesel cop giving me hell about an air hiss. The pressure does drop. When I'm rolling or idling the pressure holds, but as soon as I shut it off, the secondary pressure begins to drop with the primary not far behind.
I'll get out there and see what I can find and post it.
I pulled off the top panel of the dash. There is an aluminum manifold with many yellow air hoses. One of them is the feed for the heat control vent control unit on the bottom center of the dash. It is a tiny yellow air line. The fitting is a swivel fitting. The swivel leaked and so did the plastic push-in fitting.
Problem solved. There is no audible hiss coming from the dash. The pressure gauges hold good. Plenty good enough to be within regulations. The secondary bleeds down slowly, but very slowly. I ain't worried. When I get the time I'll walk around the truck with a spray bottle. Maybe one of the air bags has a slow leak. The air bags are old, very old. Maybe they're passing air in tiny amounts because they're so old. It's time to replace them anyway.
Thanks for all the responses!
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