| Author | Message | ||
| Mark Radius (24.247.10.59)
Rating: |
Well, we've got her home! Our MC-9 conversion adventure has only just begun. On our way back from Virginia, we noticed that we had no problem building air pressure from 0 to 75 lbs. and then no problem maintaining air pressure from 90 to 120 lbs. But getting the pressure from 80 to 90 lbs. required an act of Congress and some major engine rev's. There are some small air leaks, but nothing major. Once the air does get to 90+, normal idle will build and maintain things fine. Any suggestions on where to begin looking for problems? Thanks in advance..... MR | ||
| Henry,eh (24.70.95.206)
Rating: N/A |
You don't say whether this happens every time the compressor runs or whether it happens upon start up. If it is on start up, you might have some leaks in your airbag(s) or leveling valves. You see, when you have low pressure, the compressor starts to fill the tanks. Once it reaches a certain pressure, usually around 70-90 lbs, the air is allowed to exit the tank to then pressurize the other systems. The biggest one is your airbags. The tanks' one-way valves won't allow the pressure to drop in the tank so the gauge may sit on the same spot while the bags air up. Yes, that can take a long time! Once they equalize to the tanks, then everything will increase together past that to the max of 120 lbs. (approximately) Once it has done that, of course it cuts out and only starts up when the pressure drops 15-20 lbs. Unless you have a major leak, any compressor will have no problem keeping up with the loss of air in your system. After the bus has reached 120 lbs and the compressor cuts out, how long does it take before it kicks in again? If it is only a few minutes, you probably have a leak in your bags or the valves connected to them. That is where you are losing your air; the bags are emptying and then need lots of air to fill them up again. Henry | ||
| Mark Radius (24.247.10.59)
Rating: N/A |
Yes, Henry, it is only on start up. Once I have gotten over the initial "hurtle" the compressor has no problem keeping up. I do have a leak on the driver's side, because that settles down after about 15 minutes without the engine running. Sounds like that may be part of my problem. The thing that puzzles me is that I have to work the engine so hard for so long to get from 80 to 90 lbs. Even after the bus suspension has leveled out, getting up to 90 psi requires very high rpm's, but once it is to 90, it will finish the job at low idle. MR | ||
| Henry, eh (24.70.95.206)
Rating: N/A |
I remember on of our mechanics telling me about a similar problem. The valve was sticking and was emptying the air as fast as it was being pumped in. He told me to rev up the bus saying the increased air flow from the compressor quite often would force the valve closed. It did on that occasion. I would narrow your search to the valves. 15 minutes to settle down is very fast. One of these times that valve is going to stick open permanently and you know Murphy's Law, it will be in the worst possible time and place. Henry | ||
| Mark Radius (24.247.10.59)
Rating: N/A |
Ah ha! I have located a part of the problem! A blown pancake inside the parking brake side of one of my drive axle brake cans. I will start checking other valves as well, Henry. Thanks! | ||
| Chowbus (192.132.225.130)
Rating: N/A |
This is real obvious, but be careful under there! Chowbus. | ||
| Steven Gibbs (12.148.43.6)
Rating: N/A |
Mark, Just out of curiosity, where did you get your bus in Virginia? I looked at several there last year and purchased one from National Coach. You can email me at stevenog@aol.com I have the same problem bringing the air up after a shutdown. The wet and dry tanks fill up to about 80 psi then the valve opens to the accessory tank which takes awhile to fill. Problem is less now that I have fixed several air leaks. The brake problem should not have been a factor since the brakes are not supplied from the accessory side. I have found that rather than just sitting and running the engine high in idle, I get started after I have enough pressure to release parking brake. | ||
| RJ Long (66.74.169.186)
Rating: N/A |
Steve - I'm a little concerned that you start moving the bus after you have enough pressure to release the parking brake, for a couple of reasons: ~ Since the accessory tank also fills the suspension (on all air-ride coaches), it is "last-in-line" to come up to pressure. Consequently, you could be moving the bus while the bellows are not fully inflated, thereby drastically shortening their life-span. ~ This also tells me that you're not taking the time to do an air brake check, part of a daily pre-trip inspection that you should be doing for safety's sake. Check the "Articles of Interest" section of this site for one you can use. What price safety?? RJ PD4106-2784 Fresno CA | ||
| Bill 05 (152.163.201.197) Rating: N/A |
Mark clean out your air lines, our eagle has the same problem, or had anyway. We found that the previous owners had a lousy maint, program. there was a sludge build up all thru the air system. draining the tanks, alone wont get it clean, once you get them cleaned , drain them every time you stop anywhere, OR get a good air drier on the line. Good Luck BILL | ||
| Steven Gibbs (12.148.43.6)
Rating: N/A |
RJ, You are absolutly right based on the limited information I gave in the post. It was not stated clearly and could easily mislead someone into an unsafe practice. My current air problem is related to two leaking rear leveling valves that I have replacements for but have not yet installed. As a result, my accessory tank leaks completely after any shutdown and the wet and dry tanks feed that leak until they are down to about 75 psi. However, the ckeck valves in the leveling bag lines hold the suspension up for several days. So at initial start up I bring the whole system up until pop off, do the brake check and get under way. However, after a short shutdown for fuel or rest stop the air quickly starts up until about 80 psi when the accessory tank starts to fill. At that time I get going so that the high revs used for acceleration go to building the remaining air. Usually takes about two minutes. Sorry for the confusion and bad advice. Steve | ||
| Mark Radius (206.152.224.165)
Rating: N/A |
Bill, sorry about the delayed response, we are camping in the Upper Peninsula of Michigan where internet connections are not plentiful! I know of what you speak regarding the "dirty" air lines. My tanks were a mess and full of lots of ugly liquid. How do you suggest cleaning out the lines? Is blowing them out good enough? Or do I need to do something further? I have an air dryer in-line, but I think/know it needs a complete overhaul. MR |
