| Author | Message | ||
| george bruton (Tazman632000)
Registered Member Username: Tazman632000 Post Number: 12 Registered: 2-2007 Posted From: 65.184.183.4 Rating: N/A |
can any one tell me how long the pressure should stay up after the bus is shut down? mine goes from 120psi to 0 in about 15 mins thanks? | ||
| RJ Long (Rjlong)
Registered Member Username: Rjlong Post Number: 1214 Registered: 12-2000 Posted From: 71.195.112.181 Rating: N/A |
George - Time to get out the soapy water spray bottle - you've got a leak somewhere. It's very difficult to get all the leaks fixed, but you need to make sure that the most important component of the air system is leak-free - the brakes! Some buses will stay up for days, others will leak down just like yours. I've even seen brand new buses that will lose their air pressure within hours of being shut off. BTW, the DOT standard is no more than 2 psi/minute air loss statically, and no more than 3 psi/minute with the service brakes applied. Anything greater than that needs servicing. Be sure that you DO NOT crawl under your coach without blocking it up securely - don't want a squished busnut! FWIW & HTH. . .  | ||
| george bruton (Tazman632000)
Registered Member Username: Tazman632000 Post Number: 13 Registered: 2-2007 Posted From: 65.184.183.4 Rating: N/A |
also when i step on the brakes a few times with coach idling the pressure drops rapidly what should i look for brake diapham? thanks foe the reply | ||
| Jim Wilke (Pd41044039)
Registered Member Username: Pd41044039 Post Number: 137 Registered: 2-2001 Posted From: 69.77.151.82 Rating: N/A |
George, with a leak big enough to make the pressure drop as rapidly as you describe, the bus is going to have trouble keeping the pressure up when idling without using the brakes. But even a healthy air brake vehicle loses pressure fast when using the brakes numerous times while idling. I have had my buzzer go off numerous times while trying to turn around in small areas with a lot of "backing & filling". | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 479 Registered: 10-2003 Posted From: 71.58.117.21 Rating: N/A |
If you can buy a mechanic's stethosope, they are great for locating leaks.Shut the engine off while checking, and start at the air compressor. Also make sure that none of the tank drains are leaking.A leak in the air suspension system shouldn't leak down below about 60 to 80 lbs., as there is a pressure protection valve that prevents this, so you don't lose your brakes.So concentrate on the brakes first. But if the protection valve was bad, it could let all the air leak down, but I wouldn't worry about that till you check the brake system. Do you have a shop manual for it yet? If not, get one. Also the shutter system can have leaks, if you have them. | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 480 Registered: 10-2003 Posted From: 71.58.117.21 Rating: N/A |
Oh, I forgot.... air pressure can stay above 60 lbs. for days. Overnight is good on an average system. | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 481 Registered: 10-2003 Posted From: 71.58.117.21 Rating: N/A |
Every time you step on the brakes, the pressure is going to drop approx 10 to 20 lbs to fill the brake chambers. Does they keep on dropping if you keep the brake pedal depressed? Have someone hold the pedal down while you go outside and listen for a leak. BTW what kind of school bus do you have? You didn't indicate. | ||
| george bruton (Tazman632000)
Registered Member Username: Tazman632000 Post Number: 15 Registered: 2-2007 Posted From: 65.184.183.4 Rating: N/A |
its a 1961 model 4106 it got a new compressor,im thinkng about replacing all the brake diaphrams.what it the air hose made out of that runs from the back to the front? im worried about corrosion as i see some on the copper pipes under the bus | ||
| george bruton (Tazman632000)
Registered Member Username: Tazman632000 Post Number: 16 Registered: 2-2007 Posted From: 65.184.183.4 Rating: N/A |
the bus has a manual leveling system and it stays up around a week or so. im guessing there seperate systems for the brakes. ive got the manual so ill read about it | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 482 Registered: 10-2003 Posted From: 71.58.117.21 Rating: N/A |
Bad brake diaphrams only cause a leak when they are applied, except for part of the dd3's. If you could hook up a shop air compressor to the coach, and keep it far enough away, you could then have time to trace the leaks, without having to restart the coach. If it has separate manual air leveling system, maybe there could be a leak there if it was tapped off the main system. Does the coach drop at any of the corners or ends when the pressure drops off? | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 484 Registered: 10-2003 Posted From: 71.58.117.21 Rating: N/A |
Sorry, didn't notice the part about staying up on the bags for a week when I posted. | ||
| Jim and the XtremeFamily (Skyslayer)
Registered Member Username: Skyslayer Post Number: 29 Registered: 11-2004 Posted From: 70.112.105.118 Rating: N/A |
On mine I found a large leak in the shut off solionid/plunger and rebuilt it and until recently it would stay up for days now I get about 30 hours or so. It looks like I have another small leak to find it is a pretty easy job. (Message edited by skyslayer on March 25, 2007) | ||
| Len Silva (Lsilva)
Registered Member Username: Lsilva Post Number: 101 Registered: 12-2000 Posted From: 71.30.241.107 Rating: N/A |
One method of finding very small leaks is to charge the system with refrigerant and use an electronic leak detector. You should start with no air in the system so the gas gets into every part. I did this years ago when Freon-22 was plentiful and cheap. Not sure about it these days. Len | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 113 Registered: 8-2006 Posted From: 207.231.81.22 Rating: N/A |
Well, I hate to rain on Len's parade, and R-22 is only up to $3/lb, but. It is a $10,000.00 fine from the EPA for deliberate venting of Freon, not only that, but it is shared with the reporting party, so watch your neighbors. Soapy water is a whole lot easier. George | ||
| Len Silva (Lsilva)
Registered Member Username: Lsilva Post Number: 103 Registered: 12-2000 Posted From: 71.30.241.107 Rating: N/A |
George, you're right. Like I said, it was a long time ago. We used to use freon for leak testing microwave wave guide on towers. It was considered state of the art in the sixties. Now we'd go to jail! Len | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 489 Registered: 10-2003 Posted From: 71.58.117.21 Rating: N/A |
Ohhh, so you are the guy that put the big hole in the ozone layer.... | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 116 Registered: 8-2006 Posted From: 207.231.80.150 Rating: N/A |
Hey, appreciate the humor, Did microwave work in college in 1970-71, but didn't know anything about Freon then. What is really galling is the thought of all of the Freon horns at games, and on small boats, etc. People would blow off two or three cans at a game. R-11 was used by the 55 gal drum as a cleaning solvent, because it didn't leave a residue. Now we have to mix Freon with nitrogen before we can charge and check for leaks! Phooey... | ||
| Gus Causbie (Gusc)
Registered Member Username: Gusc Post Number: 325 Registered: 11-2005 Posted From: 63.97.117.11 Rating: N/A |
The funny thing is that AC Techs today use Nitrogen to test for home AC leaks, don't know why it wouldn't work on a bus. | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 491 Registered: 10-2003 Posted From: 71.58.117.21 Rating: N/A |
It would, but why the expense? use a home air compressor if you have it; if you have an electricity problem, you could rent a gas engine equipped one, hook up a hundred feet of harbor freight air hose, check over the whole system and take compressor back; shouldn't cost much for an afternoon. Refrigeration distributors sell a leak detector liquid that includes a swab that works quite well for locating leaks...just paint any connections. doesn't leave a soapy residue, and bubbles quite nicely at any leaks...appears to be similar to glycerin. Make a note of all the leak areas, and stary fixing them after you are done. Biggest ones or easiest ones first. If you can use either the coach service manual or Bendix air brake manual, there is diagnostic info that is essential for one that is new to coaches and air brakes. | ||
| Gus Causbie (Gusc)
Registered Member Username: Gusc Post Number: 332 Registered: 11-2005 Posted From: 63.97.117.32 Rating: N/A |
John, I got a good laugh out of that one. Somehow I got sidetracked and thought they were talking about charging the AC system and I knew it was the air system, just a senior moment I guess!! |