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Temporary Low Air Pressure
I thought I was going to have to post this in the Emergency section or pick up the bat phone and call Jeff.
We have made a pretty quick cross country re-positioning trip this week with no bus mechanical glitches until today. We stopped last night in our favorite rest stop along I-10 around the 320 mile marker in Arizona just as you enter Texas Canyon. It was a beautiful cool night in the desert.
We left this morning and I noticed within a mile that my primary air guage was down at 100 while the secondary guage was solidly 120+ as usual.
If both were down I would think the compressor was ready to cycle but only the primary was down. I touched my brakes anyway and primary dropped to 95 and stayed there. After a few miles of watching it I told my wife to find a place to stop. It worked its way to 100 while I made my way to the Love’s at exit 302. As I was coming up on the exit the primary guage moved up to 120 to match the other just like it had good sense. Nothing had changed and I had not touched the brakes again.
I was able to park away from the trucks so I could listen and could discern no obvious leaks. I had my wife pump the brakes several times while it was running and pressure always rebounded fine. I had her release the parking brake and all was the same.
For background, the compressor and air dryer were changed in the last 18 months and the air bags, norgrens and brake chambers were replaced by Jeff in June.
We drove another 120 miles or so and guages were both normal. When I exited for the RV Park where we are staying for two nights everything seemed to function normally. I plan to move to El Mirage on the northwest side of Phoenix on Saturday and I will be there a week before moving to Bloomington, California. If I have a glaring problem I would like to get it taken care of while I am here.
Any Ideas or suggestions?
Davy
By the way there is a nice Liberty XL with Arizona plates parked here. I have not had a chance to talk to them yet.
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11 Replies
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Davy,
I’ve had that happen before also and it never returned again. Gremlins….
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Some times a valve can stick keep eye on it , was it cold in morning what temp? Some times the SR1 valve can stick just keep eye on it. Or some dirt in gauge line
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Thanks Tom and Peter. It might have been upper 50’s over night but was up in the 70’s by the time we were rolling. What/where is SR1 valve? Where do these guages get their readings from? The Primary and Secondary tanks?
The primary always reads about 5 lbs lower but I think it might just be the guages. I have thought about switching them to find out.
Davy
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They will get the readings from the steering bay look around under there u will see them some are 1/8 lines some are 1/4 inch air lines , I would not change out the gauges , if I was thinking it was not right I would put gauge on primary tank and check there, most of the gauges have push in fittings and can leak , I have put comp fittings on all three gauges so no leaks. The SR1 valve is in steering bay don’t worry about it I highly doubt it’s bad , it’s about the size of your palm of your hand , if I was at home I could take pic of new one for u but I am not there Davey, the SR1 valve acts on pressure off the primary and secondary tanks its in case of emergency loss of pressure in primary so secondary can make emergency stop off of secondary tank to back brakes , simple example
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One thing everyone needs to understand completely is that if the brake system gauge(s) drop without apparent reason while driving there could be any number of reasons, some might even correct themselves.
But there is one thing that can create the problem, and that it will NEVER be detected while parked. If the emergency brake diaphragm develops a tear or leak the brake gauges will cycle while driving. That is because air pressure against the diaphragm holds the springs back, allowing the wheels to turn. When you stop, and apply the parking brake there is no air going to the brakes and the gauges will not show any cycling up and down if that is the problem. Other problems are going to cause the gauges to cycle up and down.
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I drove a couple of hours today with no problem. I am thankful that there is no evident problem but I was hoping that if it was going to manifest itself it would do it today while I am in a major city rather that on my way across I-10 next saturday or across the Grapevine the saturday after that.
Davy
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Davy it’s not that far from Prevost in Mia Loma from I 10 about 3 blocks so if you have problem u can go there
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One frustration is an intermittent problem, or like Davy has, a temporary problem. If the air loss continues when the bus is parked with the emergency brake applied it is highly likely a relay valve failed to close. Whatever the problem was, it got fixed probably by normal use of the brakes or emergency brake.
Kind of like a Schrader valve on a tire that doesn’t seal so when you give it another small shot of air, it seals properly.
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“Davy it’s not that far from Prevost in Mia Loma from I 10 about 3 blocks so if you have problem u can go there”
Thank you for pointing that out. I knew there was a Prevost facility in the LA area but I did not realize where. I figured it was closer to LA proper. 3384 De Forest Cir, Mira Loma, CA is 11 miles from the church where I will be parked and preaching beginning next Sunday.Davy
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No more glitches with air until today.
Cranked up this morning for a two hour run and everything came up to pressure. By the time I had turned around and pulled into place to hook up the car, the upper gage (secondary) was low enough to trigger the alarm. Once stopped and the parking brake was set the gage came up to 90 and the lower gage went right on up to 120 and normal.
With my wife watching the gages I listened for any obvious bad leaks all around and then stuck my head under the front on both sides to see as much as I could. When the dryer exhausted she said the primary was above 120 and the secondary (upper) was about 90.
I had her press the brake and hold with no change. I had her fan the brake until the compressor kicked on and it ran until the pressures were the same as before, the primary was above 120 and the secondary (upper) was about 90.
I was laying with my head under the front contemplating chocking the wheels, turning the engine off, releasing the brakes and listening for leaks and otherwise trying to figure out what to do when I heard an air sound up front. It was a quick “Pshew” Immediately the pressure started coming up and within 40 seconds it was normal. My wife heard the sound too and said it looked like somebody opened the valve to the gage it came up so quick. She thought I did something below.
Everything functioned normally for the rest of the day.
FYI: The temperature was in the 50’s when it happened and was not below freezing over night.
Any ideas?
Davy
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Davy,
Just for grins see if you lose pressure when you release the parking break. Obviously do this with the wheels chocked or the bus won’t roll.
If you lose pressure while you are rolling, but it builds when you pull up the parking brake it sounds like a ruptured diaphragm on one of the parking brake chambers.
This is a total guess but lacking other info that’s all it can be.
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