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Old 05-24-2018, 12:36 PM   #1
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Air Pressure Gauge Not Working - Help!

Hi Everybody. I'm a newbie and am mechanically and electrically illiterate, so please pardon my ignorance. My wife and I purchased a 2008 International RE300 recently and been demoing the inside. This bus has air brakes and the door is also equipped to be opened using air pressure.

Anyways, I had to disconnect the wires (no air line) going to the door in order to remove some of the interior panels. After doing so, I was able to park the bus. A few days later I went to move the bus and it will start, but the air pressure is not building up. I can tell the compressor is working but I cannot move the bus as the parking brake won't release since the gauge is showing low air pressure.

I believe one of the wires I disconnected may have had something to do with this. The only other things I disconnected were the security cameras internally and the radio, so I'm lead to believe it must have been something on the door. Someone told me it may have been a ground wire for the air gauge.

Anybody run into something similar or know what I should do to fix this issue?
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Old 05-24-2018, 01:05 PM   #2
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Originally Posted by AMDenels View Post
Hi Everybody. I'm a newbie and am mechanically and electrically illiterate, so please pardon my ignorance. My wife and I purchased a 2008 International RE300 recently and been demoing the inside. This bus has air brakes and the door is also equipped to be opened using air pressure.

Anyways, I had to disconnect the wires (no air line) going to the door in order to remove some of the interior panels. After doing so, I was able to park the bus. A few days later I went to move the bus and it will start, but the air pressure is not building up. I can tell the compressor is working but I cannot move the bus as the parking brake won't release since the gauge is showing low air pressure.

I believe one of the wires I disconnected may have had something to do with this. The only other things I disconnected were the security cameras internally and the radio, so I'm lead to believe it must have been something on the door. Someone told me it may have been a ground wire for the air gauge.

Anybody run into something similar or know what I should do to fix this issue?
Got a pic of the mechanism that opens the door?
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Old 05-24-2018, 04:10 PM   #3
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You have a SERIOUS air leak if the gauge is not working. By law, the air gauge has got to be a LIVE gauge, i.e., it MUST have air pressure. It is NOT electrical. When you disconnected the door and then reconnected it, you must have introduced a leak in the line. Retrace your steps.
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Old 05-24-2018, 04:57 PM   #4
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Parking brake won't release unless you have air pressure. If it's not releasing and both air gauges read zero, more likely then not, you have no air pressure. Open one of the pitcocks on the air tanks to confirm if you have pressure or not.

The wires up by the door are for lights. Some busses will also have an air solenoid that won't let you release the parking brake unless the door is shut.

If, you're without air pressure, remove the line from the compressor and see if it's pushing any air. If it's not, see if the unloader valve on the compressor is stuck. If that's free, then you've likely broken the compressor input shaft.
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Old 05-24-2018, 05:35 PM   #5
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The air-door operates from the auxiliary air-tank. That tank is isolated from the primary and secondary tanks, and a leak there should have no effect on the gauge or the brakes.

Something else is going on.
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Old 05-24-2018, 06:05 PM   #6
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Depends on the bus or body manufacturer. Most of the busses I've worked on don't have an auxiliary tank because they don't have the air demands that would necessitate having one (air ride axles, kneeling features, tag and pusher axles, etc.)

In those busses, air for the accessories comes from either the secondary tank or wet tank. Accessories such as air ride seats, stop sign arms, and air powered doors don't consume much air, so there's no need for an aux tank for that little bit.

Regardless, if his primary and secondary tanks both have 0 psi, his wet tank will have 0 psi. And, if he does have an aux tank, I'd bet money that that would have 0 psi in this situation aswell.

He needs to verify the gauges and figure out if he has air pressure. After that, we can figure out what's going on with the park brake and air door.
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Old 05-24-2018, 06:18 PM   #7
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I know its probably not electrical, but is the 08's electrical system multiplexed?
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Old 05-24-2018, 06:26 PM   #8
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Originally Posted by Booyah45828 View Post
Depends on the bus or body manufacturer. Most of the busses I've worked on don't have an auxiliary tank because they don't have the air demands that would necessitate having one (air ride axles, kneeling features, tag and pusher axles, etc.)

In those busses, air for the accessories comes from either the secondary tank or wet tank. Accessories such as air ride seats, stop sign arms, and air powered doors don't consume much air, so there's no need for an aux tank for that little bit.

Regardless, if his primary and secondary tanks both have 0 psi, his wet tank will have 0 psi. And, if he does have an aux tank, I'd bet money that that would have 0 psi in this situation aswell.

He needs to verify the gauges and figure out if he has air pressure. After that, we can figure out what's going on with the park brake and air door.
Yep. All that could be true as well.

I was trying to think what I had, that Thomas thought an aux tank necessary. I have an air-door, air Stop Sign and air throttle.
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Old 05-26-2018, 02:29 PM   #9
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I've tried adding some pictures here but every time I do it tells me my post is too long. I tried resizing the pictures as smaller files and it still didn't work...

Anyways, I fixed it! It was just the ground wire. Once I was able to reconnect it everything worked perfectly like before. I don't totally understand what happened but I'm glad things are working. Thanks for all the help and hopefully I can figure out the pictures thing so I can show what happened.
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Old 05-26-2018, 02:41 PM   #10
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Originally Posted by AMDenels View Post
I've tried adding some pictures here but every time I do it tells me my post is too long. I tried resizing the pictures as smaller files and it still didn't work...

Anyways, I fixed it! It was just the ground wire. Once I was able to reconnect it everything worked perfectly like before. I don't totally understand what happened but I'm glad things are working. Thanks for all the help and hopefully I can figure out the pictures thing so I can show what happened.
This forum requires you have 5 post minimum before you can post pics.
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Old 05-26-2018, 02:58 PM   #11
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A few days later I went to move the bus and it will start, but the air pressure is not building up. I can tell the compressor is working but I cannot move the bus as the parking brake won't release since the gauge is showing low air pressure.
I was under the impression that the parking brake release was strictly air/mechanical.

If it was a ground problem that kept the parking brake from releasing that implies that it is electrical.

Can anybody explain this?

I thought I had a pretty good handle on how my air brakes function. This has me doubting my understanding.
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Old 05-26-2018, 03:55 PM   #12
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the parking brake is mechanical and you must have a protection valve on ALL accessories on an air-brake equipped bus.. so at a minimum you should be building 60-75 PSI of air pressure... this is enough to m,ove the bus in an emergency if you had to..

these compressors pump 12-15 CFM at 0 PSI so if the compressor is running and pumping you should be able to follow the large copper line out of it down underneath and forward to the first tank... things should be hissing rather prominently underneath or someplace in the bus..

if there is No Hissing anywhere then....

the unloaders can stick as mentioned and you'll have this symptom.. usually hitting the top of the compressor with a MALLET (dont use a hammer!) will pop the unloader spring into action if thats the case.. its also possible the governor (oblong and mounted to the side of the compressor) has stuck.. pop that with a MALLET too ..

unusual to break the input shaft of the compressor without there being either timing gear issues or belt issues (some compressors are belt driven.. i think yours is gear drive)...
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Old 05-26-2018, 04:01 PM   #13
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Anyways, I fixed it! It was just the ground wire. Once I was able to reconnect it everything worked perfectly like before. I don't totally understand what happened but I'm glad things are working. Thanks for all the help
Sounds like OP fixed by reconnecting a loose ground wire. That has caused me some confusion. I didn't think that there were any electronics involved in applying /releasing the parking brake.
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Old 05-26-2018, 04:03 PM   #14
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oops i missed that.. yeah ive never heard of electronics for the park brake.. maybe its allowed on RE busses? ive always seen hard air lines going to the air gauges and the parking brake release.
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Old 05-26-2018, 04:10 PM   #15
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oops i missed that.. yeah ive never heard of electronics for the park brake.. maybe its allowed on RE busses? ive always seen hard air lines going to the air gauges and the parking brake release.
-Christopher
Me too. OP stated that the bus would start and run but the parking brake would not release. He reconnected the ground wire and the problem was resolved.

I am scratching my head..,
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Old 05-26-2018, 04:20 PM   #16
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Just a shot in the dark here..is there an idiot light on the dash to show when the parking brake is on/off? Could be that simple but I have no idea of the circuit he is talking about that he grounded out to make it work? I would think a light would be part of the design, no?

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Old 05-26-2018, 05:18 PM   #17
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My assumption from op posts is that there was maybe just a security feature tied into the door preventing parking brake release after he disconnected it, and he fixed it by reconnecting the door. I think any way.
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Old 05-26-2018, 09:20 PM   #18
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Originally Posted by AMDenels View Post
I've tried adding some pictures here but every time I do it tells me my post is too long. I tried resizing the pictures as smaller files and it still didn't work...

Anyways, I fixed it! It was just the ground wire. Once I was able to reconnect it everything worked perfectly like before. I don't totally understand what happened but I'm glad things are working. Thanks for all the help and hopefully I can figure out the pictures thing so I can show what happened.
Maybe it has to do with the possible multiplexed electrical system.
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Old 05-26-2018, 09:21 PM   #19
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Originally Posted by PNW_Steve View Post
I was under the impression that the parking brake release was strictly air/mechanical.

If it was a ground problem that kept the parking brake from releasing that implies that it is electrical.

Can anybody explain this?

I thought I had a pretty good handle on how my air brakes function. This has me doubting my understanding.
As I posted- Maybe its multiplexed. If so they're hell to work on the electronics.
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Old 05-28-2018, 07:47 PM   #20
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I believe what happened (and I could be totally wrong as I'm a newbie to all this) is that the air compressor was working perfectly and there were no leaks. This was confirmed by the fact that I did nothing but reconnect a ground wire and everything worked properly again. I was also under the bus all day today removing some other wires and didn't hear or find any leak. I think that ground wire must have had something to do with the gauge itself. I couldn't release the parking break because the gauge was reading as too low. Once I reconnected the ground wire the gauge shot up showing the pressure was high.

If I connected the wire and had the bus running and moving but then disconnected it, the gauge would only show me losing pressure as I used the breaks. Once I reconnected the wire the gauge shot up rather quickly, leading me to believe the pressure was always there but the ground being disconnected simply kept the gauge from working.

Not sure if this is correct...all I know is it's working now. Thanks again for all the help. I think I should be able to post pics soon as this might be my 5th post!
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