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Author Topic: Can't maintain air pressure.  (Read 2623 times)
bcaddel
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« on: August 27, 2011, 07:22:01 PM »

We left Las Vegas Friday evening in our mci-7 (8v71) for a couple of weeks of visiting friends and family in Texas. Just outside of Gallup New Mexico out air pressure dropped down to about 40 psi (we just barely got off the road before the parking brake popped on) but after a short rest the compressor started working again so we decided to see if it would make it to town (5 MILES). We did make it to the TA truckstop and the compressor seemed to work well until we actually pulled into the truckstop. After some discussion it was decided our air compressor governor had probably malfunctioned. We purchased a new one and installed it and all seemed well but about 50 miles down the road the same thing happened but luckily we were able to get into a Petro truck stop before the air pressure dropped and stayed around 80psi as we got parked.

I don't seem to have any air leaks that I can hear, and it will build and hold hold air pressure when I plug in a portable air compressor, but the engine mounted compressor seems to come and go as it wants. The compressor is very hot to the touch but I think that might be normal. Does anyone have any suggestions or clues on what could be causing the problem? I am thinking since we replaced the governor already and there doesn't seem to be any air leaks that I can hear, the compressor may have just cooled down during the hour that it took to replace the governor and it started working due to cooling down, not because of the new governor and once it got hot it stopped working again. Does it sound like the only option is a new air compressor and if so how hard are they to come by?
I just talked to a truck driver and he thinks it is probably an issue with the drier and something blocking the line back to the governor.
Any thoughts or suggestions would be greatly appreciated.

Bob Caddel
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Bob Caddel, Las Vegas Nevada
1971 MC7, 8V71, Allison MT654
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« Reply #1 on: August 27, 2011, 08:01:46 PM »

You may have sheared a key on the compressor or the drive gear is stripped disconnect the 1/4 line on the dryer and see if it pumps up if it does it will be a dryer problem.
Not to start a contest her but if you can use the aux compressor and get to Albuquerque and stop on the west side at Flying J so you are not in any traffic.
 I have a friend there with a service truck if he is home he will help you get going he is a bus owner and knows how you feel several bus owners there we can get you some help from ok

good luck
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eddiepotts
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« Reply #2 on: August 27, 2011, 08:04:52 PM »

You need to check for air leaks with the engine running. Make sure it is not the airline off the compressor or the line going to the governor leaking. Check your drier valve also while it is running. sometimes it is hard to hear while running. you may need to run your hands down the lines and under the drier.
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bcaddel
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« Reply #3 on: August 27, 2011, 08:43:35 PM »

Thanks Eddie, I am pretty sure it doesn't have any air leaks but I haven't gone under to take a hard, close look/listen yet but I need to do that first thing in the morning.

Clifford, I just started it up and the air compressor seems to be working just fine. I think what ever is wrong it clears it's self after a hour or two of sitting. We are on I-40 so there is plenty of room to pull of the road when/if it starts acting again. I am pretty sure we can make it to Albuquerque in the morning even if we have to pull over for a rest,  if your friend is available and we could hire him to check her out and or repair it that would certainly be a blessing.

If everything seems to check out again in the morning, we will head to the flying J. If the compressor starts acting up we will just pull over and wait to see if a little time will reset it. If not we have CoachNet. I will let you know when we make it to flying J.
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Bob Caddel, Las Vegas Nevada
1971 MC7, 8V71, Allison MT654
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« Reply #4 on: August 27, 2011, 08:58:44 PM »

Bob, he is home I am going to PM his phone number his cell and home to you he is a sharp guy.
The Albuquerque bunch are all good guys even Melbo lol 

good luck
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bcaddel
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« Reply #5 on: August 27, 2011, 09:03:48 PM »

Thanks, I will give him a call first thing in the morning. Things are looking up.
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Bob Caddel, Las Vegas Nevada
1971 MC7, 8V71, Allison MT654
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« Reply #6 on: August 27, 2011, 09:09:28 PM »

Let me know if you got the PM you are dealing with a not so good guy here with PM's lol


good luck
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bcaddel
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« Reply #7 on: August 27, 2011, 09:18:45 PM »

Thanks Clifford, I just got the PM with the numbers. I will call him as soon as we get to flying j. Does he know we are coming? Thanks for the help, the wife is very happy so obviously that makes us all happy if you know what I mean. Bob
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Bob Caddel, Las Vegas Nevada
1971 MC7, 8V71, Allison MT654
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« Reply #8 on: August 27, 2011, 09:24:57 PM »

I haven't talked to him he just got back from New York and was a sleep but not a problem just call him Sun


good luck
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Ed Hackenbruch
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« Reply #9 on: August 27, 2011, 09:28:18 PM »

Have you been draining your air tanks? Saw a bus last winter that had quit building air, and after changing the governor and then the compressor, it turned out that the problem was that the ping tank had gotten plugged up solid.
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1968 MCI 5A with 8V71 and Allison MT644 transmission.  Western USA
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« Reply #10 on: August 28, 2011, 11:35:17 AM »

Bob you are having the same exact symptoms that Vivian had leaving the rally in Arcadia 2 yrs ago. (and if I remember correctly you both have about the same model bus!)

Anyway Jack, Tom, and I went up to the gas station where she was broke down at and we thought it was a governor too. We played with the adjustment some and it didn't make no difference.

We still couldn't get it to build air. So we backed it over to the stations air hose and aired it up.

It was a straight shot out of town with only one stop/turn on the way to Jack's. And since I had the most experience driving thses things with issues I got volunteered to follow Jack to his ranch. 1/2 way there it started building way too much pressure (140-160). But we made it there and got it parked.

After parking it we tried to check it again, no such luck no air!

After it cooled off and we'd ate lunch we tried it again, and walla it was working again. So we adjusted the pressure back down to 130.

Sometime later we checked and would not build again.

I thought it would be the un-loader valves. And Jack had an old compressor laying around and we showed her what we were talking about.

I had to leave town and bring my group back to TN.

But I believe Jack & Tom did stick with it and find & fix the problem later in the week.

Maybe one of them will chime in and give you some help.
Grin  BK  Grin
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Busted Knuckle aka Bryce Gaston
KY Lakeside Travel's Busted Knuckle Garage
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« Reply #11 on: August 28, 2011, 12:38:20 PM »

Guy's
Bob and his wife just headed east out of here headed to TX. There were multiple probable causes for his problem. I found no air dryer so it is out of the equation.
I looked real hard at the discharge piping from the compressor to the wet tank (which was dry and oil free). There was oil staining at the discharge fitting and the half union was loose and leaking while it was pumping. Checked the compressor inlet to see if the air was bleeding back through the compressor, it wasn't at the time I checked but the hose was soft and collapsing. Replaced the inlet hose. The fitting to governor loose and leaking (may have been loose from the earlier replacement), line loose and leaking on 'skinner valve' shutdown solenoid, other multiple air leaks. Started out that the governor would cycle the compressor on to build air and air pressure would drop immediately after the governor unloaded the compressor. Pulled the skinner valve down to make sure that the plunger in it wasn't worn out and sticking open. It looked acceptable. Checked the 'wet tank' for air leaks. I didn't see any signs of tell tale oil or find any leaks. Checked the belt tensioning cylinder and it was good with no air leaks. Cycled the bus multiple times through air building and the compressor builds air well while I was observing it. It was building air from 90 psi to 120 psig at idle in less than 60 seconds wished mine did that good. The bus was holding and building air fine. As he drove off it dawned on me that the only thing I hadn't done was check for an air leak in the DD3 brake system. I realized this as he made the brake application to release the brakes to leave.
Instructed Bob to call if he has any more problems and it has been silent. He and his wive, along with Cozy, are welcome here anytime.
I suspect that Bob may let us know how he is doing.
Happy Trails
Larry
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Zuzax, New Mexico (Exit 178 I-40) 12mi East of Albuquerque

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« Reply #12 on: August 28, 2011, 12:42:49 PM »

You da man Jones thanks

good luck how was New York
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« Reply #13 on: August 28, 2011, 12:51:44 PM »

NY State was good and it is good that I got out of there before Irene hit.
These JayWho's  want me to work for them in a new semiconductor FAB start up. I'm starting to think that it is going to cut into messing with buses too much and they leave the freezer door open too long in the winter
Who is to say I've done other dumb stuff

Happy Trails
Larry
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Zuzax, New Mexico (Exit 178 I-40) 12mi East of Albuquerque

1956 PD4104 6-71T
1988 Eagle 15 CC Conversion
1983 Mack W Utility Bed Service Truck (road assistance in New Mexico)
bcaddel
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« Reply #14 on: August 28, 2011, 12:52:50 PM »

Guy's
Bob and his wife just headed east out of here headed to TX. There were multiple probable causes for his problem. I found no air dryer so it is out of the equation.
I looked real hard at the discharge piping from the compressor to the wet tank (which was dry and oil free). There was oil staining at the discharge fitting and the half union was loose and leaking while it was pumping. Checked the compressor inlet to see if the air was bleeding back through the compressor, it wasn't at the time I checked but the hose was soft and collapsing. Replaced the inlet hose. The fitting to governor loose and leaking (may have been loose from the earlier replacement), line loose and leaking on 'skinner valve' shutdown solenoid, other multiple air leaks. Started out that the governor would cycle the compressor on to build air and air pressure would drop immediately after the governor unloaded the compressor. Pulled the skinner valve down to make sure that the plunger in it wasn't worn out and sticking open. It looked acceptable. Checked the 'wet tank' for air leaks. I didn't see any signs of tell tale oil or find any leaks. Checked the belt tensioning cylinder and it was good with no air leaks. Cycled the bus multiple times through air building and the compressor builds air well while I was observing it. It was building air from 90 psi to 120 psig at idle in less than 60 seconds wished mine did that good. The bus was holding and building air fine. As he drove off it dawned on me that the only thing I hadn't done was check for an air leak in the DD3 brake system. I realized this as he made the brake application to release the brakes to leave.
Instructed Bob to call if he has any more problems and it has been silent. He and his wive, along with Cozy, are welcome here anytime.
I suspect that Bob may let us know how he is doing.
Happy Trails
Larry
Thanks for all the suggestions, we took Clifford's advice and called Larry Jones. Larry was kind enough to meet us and spend the morning troubleshooting the problem. Larry found a couple of issues that could be causing the problem. The most likely in my opinion was a very soft air supply hose to the air compressor. The fitting coming out of the air compressor was loose also. He tightened up several other small air leaks but we couldn't duplicate the problem so we don't know for sure if we (Larry) fixed the problem yet but it is working great so we decided to head on to Texas.

I didn't remember meeting Larry previously but once Pearl came out of the bus And Larry saw us together he ask if we had been to Paul Lowry's Texas Bus Rally last year. Sure enough we had met last year at the TBR. Small World and it is filled with some great folks. Thanks Larry for all your work this morning and sure nice seeing you again.

Been about 50 miles now and the air pressure is building just fine.

Bob & Pearl
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Bob Caddel, Las Vegas Nevada
1971 MC7, 8V71, Allison MT654
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