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Author Topic: not holding air  (Read 3827 times)
eddiepotts
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« on: May 24, 2010, 07:25:15 AM »

On my 82 Prevost I lost air this weekend. I could only hold about 30#. I found what I think is the a brake canister and had air blowing out tho bottom. I took the nozzle off of it and seen a bolt in the middle. I turned it a couple of time and got pressure back. But to loose it 10hrs later. So now what is the fix. Is there an O-ring or something to replace or is there something else that causes air to come out there. I am glad it happend only because I found some loose bolts on the driveshaft with one missing. So what I hope is a little problem here it might have saved me some big problems. Any advise or drawings of what is there would be helpfull. Thanks
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bobofthenorth
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« Reply #1 on: May 24, 2010, 07:37:03 AM »

Any chance of some pictures Eddie?  Maybe somebody else can tell from your description what you are looking at but I can't.
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R.J.(Bob) Evans
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robertglines1
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« Reply #2 on: May 24, 2010, 09:22:37 AM »

if you go to the prevost web site they have tech diagram online for pneumatic system...last letter in your serial number plus last 4 digits....sounds like a pressire control valve not a brake canister   both are rebuildable...
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Bob@Judy  98 XLE prevost with 3 slides --Home done---last one! SW INdiana
wildbob24
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« Reply #3 on: May 24, 2010, 10:06:34 AM »

,
« Last Edit: May 25, 2010, 07:56:37 AM by wildbob24 » Logged

P8M4905A-1308, 8V71 w/V730
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eddiepotts
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« Reply #4 on: May 24, 2010, 10:28:06 AM »

This is next to right rear wheels inside the frame. It is tall with air lines going to what looks to me like air actuators for the brakes. The nozzle was just a tin cover that had 3 little Phillips head screws. it blows strait to the ground. The bolt that was exposed was holding a part that may be a piston or valve. Depending on where I turned it it would blow harder or less. My last fix was when I pushed up on it. I hate not knowing what it is but I will try to get some pics of it when I get home. I just did not want to turn it much in case there was a setting. It may even need to be tight and that's why it is blowing. I did make several rounds but it did not feel like it was getting tight.
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DaveG
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« Reply #5 on: May 24, 2010, 10:36:02 AM »

Sounds like an exhaust port cover to something.
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robertglines1
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« Reply #6 on: May 24, 2010, 11:16:16 AM »

air dryer...about 6 inch diameter and about 16 inches tall...should not leak out bottom except to exhaust moisture on occasion .usually when the compressor reaches 120 lbs..between tag and drive on passanger side..prob take apart and clean replacing filter...should have a pressure relief valve on side also...
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Bob@Judy  98 XLE prevost with 3 slides --Home done---last one! SW INdiana
eddiepotts
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« Reply #7 on: May 24, 2010, 11:32:15 AM »

Robert, that's it. is there a gasket kit I need to buy before taking it apart. or is it something that will just bolt back together. If anyone has a drawing of this I would greatly appreciate it. I have a run coming up in two weeks and I have to know I am good.
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robertglines1
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« Reply #8 on: May 24, 2010, 11:41:08 AM »

sent you pm with my phone number
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Bob@Judy  98 XLE prevost with 3 slides --Home done---last one! SW INdiana
bevans6
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« Reply #9 on: May 24, 2010, 01:30:08 PM »

When I come up against things like that, maybe original to the bus, old, generally worn out, I tend to try to see if I can replace with current new stuff rather than rebuilding the old.  New air dryers aren't all that expensive, may be a way to go in this case.

Brian
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stevet903
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« Reply #10 on: May 24, 2010, 03:34:25 PM »

I think you have an AD-2 air dryer.  Here's the manual for it:

http://www.bendixvrc.com/itemDisplay.asp?documentID=3604

Look on page 12 for a picture of the end cover - is this what you are talking about?  If so, you can get a reman cover for $93 at Napa, probably much less at Fleetpride or your local truck parts store...  You most likely have a 24V heater in it, so check that before you go.

Steve
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eddiepotts
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« Reply #11 on: May 24, 2010, 04:12:28 PM »

Steve, This is what I needed. The bolt I was turning holds the purge valve. It should be torqued to 50 inch pounds. Mine is loose. fist thing is try to tighten it and see what happens. I bet the valve is off it's seat and just blowing. I got pressure when I pushed up on it but never got it to stop completely.
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niles500
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« Reply #12 on: May 24, 2010, 11:46:37 PM »

I'm with steve - sounds like an AD-2 air dryer - purge valve replacemant/rebuilds can be found for less than $10 on E*** - HTH
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robertglines1
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« Reply #13 on: May 25, 2010, 04:03:39 AM »

You could have a Rockwell Wabco #RWABK-095..System Saver 1000..Prevost tech manual on line(prevost car website)under parts and service...use your last letter in serial # plus last 4 numbers(unit number) or just skip the enter part (year model etc)and hit search and it will give you a list of all wiring and pneumatic diagrams available...or try unit K-747 in unit box...Prevost parts Charlie....1 800 621 5519...on line manuals you can copy available there also....shop parts prices,lots of times they are less expensive including freight and no tax..
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Bob@Judy  98 XLE prevost with 3 slides --Home done---last one! SW INdiana
eddiepotts
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« Reply #14 on: May 25, 2010, 07:30:20 PM »

Tightening was not the answer. I can turn it forever. What I need to know now is this something I need to remove from the bus or can I rebuild it in place. It is the Bendix ad-2.
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stevet903
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« Reply #15 on: May 25, 2010, 07:56:53 PM »

Do you know when it was last serviced? (Prevost recommends every year). If you don't you probably should put new desiccant while you are there as well as the parts you need.  You can do it on the bus, I dumped the air from the tags and removed the tag wheel to get better access.  The end cover comes off the bottom, 3 bolts and a snap ring, and you can either replace it with a reman cover or put whatever new parts that it needs while on the bench.  You must drain all the air out of the system - if you don't the cover will launch with 100psi or so behind it!!  Of course, block the coach up while working under it....

Here's an exploded diagram - http://www.prevostcar.com/DB/services/bbs/eng/Mi04-12.pdf
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robertglines1
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« Reply #16 on: May 26, 2010, 05:20:00 AM »

I would remove and clean ..then you can use shop air to test it...maybe even paint if it is rusted. good cleaning could even solve problem....like Steve said be careful....
« Last Edit: May 26, 2010, 05:23:07 AM by robertglines1 » Logged

Bob@Judy  98 XLE prevost with 3 slides --Home done---last one! SW INdiana
eddiepotts
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« Reply #17 on: May 29, 2010, 12:14:41 PM »

I went out to work on the governor this morning before I messed with the dryer. I read that this could be a problem to cause the purge valve to blow. I disconnected the line and started the bus to see if the purge line had constant air. what I found was it was not blowing but a hole worn through the braided air line coming off compressor. could this be my problem. I also read that a major airleak could do it but not sure if it meant before or after dryer. I know I need a new air line but can't get one until Tuesday when the truck parts house opens. Just trying to find the fix as I go to learn the cause before I just rebuild the whole system and knot know what the problem was. Thanks.
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robertglines1
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« Reply #18 on: May 29, 2010, 12:26:16 PM »

try splice in it that could diangnose problem just cut leak out and splice...have done it...bob
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Bob@Judy  98 XLE prevost with 3 slides --Home done---last one! SW INdiana
eddiepotts
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« Reply #19 on: May 29, 2010, 12:30:29 PM »

Good idea Bob. I will try that. Does the purge valve blow at start up for a few seconds until it reaches pressure normally?
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robertglines1
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« Reply #20 on: May 29, 2010, 12:34:52 PM »

don't know about valve ...my temp splice has been in for 3 yrs now..oops
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Bob@Judy  98 XLE prevost with 3 slides --Home done---last one! SW INdiana
JackConrad
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« Reply #21 on: May 29, 2010, 02:57:21 PM »

Good idea Bob. I will try that. Does the purge valve blow at start up for a few seconds until it reaches pressure normally?

Mine does not.  No air from the dryer till air compressor kick off at about 125 PSI.  Jack
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« Reply #22 on: May 29, 2010, 03:56:51 PM »

When the governor signals the air dryer to open the purge valve, it stays open until the governor tells it to close when it starts providing air again.  The governor controls the purge valve.  There is a check valve between the air dryer and the wet tank.  The check valve prevents air from escaping from the wet tank when the purge valve is open, and allows air to pass into the wet tank when the pressure from the compressor exceeds that inside the wet tank.

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
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« Reply #23 on: June 10, 2010, 05:22:50 PM »

I changed purge vale and canister. valve kit $13 and canister was $25 through NAPA. There is an $18 core so take it with you if parts house not close. I did find the main braided air line had a hole in it along with the line from the governor. $85 for the big one and $48 for the small one. It all is good now but this weekend I will be pulling the air tanks to clean out. The dryer was so packed with dirt and grime I don't think it had ever purged before the valve split. The top of the canister was even blown open with desiccant everywhere. I had no idea that I ever had a problem. If I would not have lost air I would have never even looked at it not knowing anything about it. The breaks worked fine as far as I know. It is the only bus I have ever driven. I am going to go to the electronic store here and buy some plastic wire loom to cover the hoses so I do not have to worry about them rubbing any more. I think I will spend the most time and money cleaning the street in front of my house where years of goop has fallen all over it. Yes I am one of those neighbors. Do all my work in the street. It keeps my driveway clean. Grin
« Last Edit: June 10, 2010, 05:25:19 PM by eddiepotts » Logged
bevans6
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« Reply #24 on: June 11, 2010, 05:29:55 AM »

I once painted a car in the street - in front of my friends house!  His curb was blue for years.   Shocked

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
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1978 Lola T440 Formula Ford
1972 NTM MK-4 B/SR
bobofthenorth
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« Reply #25 on: June 11, 2010, 06:04:27 AM »

I am going to go to the electronic store here and buy some plastic wire loom to cover the hoses so I do not have to worry about them rubbing any more.

Last spring when we had the bus in my buddy's shop he sent me underneath with a flashlight to look for rubbing hoses.  He found one that had worn the rubber off so we replaced it and I found one that had a collection of non-DOT fittings that we replaced as well.  I took a handful of nylon ties and snugged a few others up where it looked like they might rub someday.  It was a good lesson for me - something else to watch for while I am under there with a grease gun.  I'm a firm believer that everybody should grease their own equipment, regardless of what other work they do on it.  The simple act of crawling between grease zerks gives you a good opportunity to look closely at everything along the way.
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R.J.(Bob) Evans
1981 Prevost 8-92, 10 spd
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« Reply #26 on: June 11, 2010, 12:09:33 PM »

It's interesting that for commercial vehicles, checking for rubbing hoses is part of the DOT daily inspection, and checking for rubbing hoses on the under-chassis of a bus in commercial service is 30 days or 10,000 km (up here anyway).  We should be doing such an inspection at least once in a while...

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
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1978 Lola T440 Formula Ford
1972 NTM MK-4 B/SR
eddiepotts
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« Reply #27 on: June 11, 2010, 12:57:15 PM »

I agree. I would have never done it until now that I have had to buy a hose. I think for pennys a foot I will have all hoses covered in plastic covers soon.
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DaveG
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« Reply #28 on: June 11, 2010, 04:18:07 PM »

Not that hoses should be rubbing against anything, but if they do...keep some old radiator hose and garden hose handy, along with some zipties.
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« Reply #29 on: June 12, 2010, 07:47:06 AM »

Plastic covers only take a little longer to rub through...

Anything that touches anything must be SECURED TIGHTLY against movement.

Good quality plastic zip ties, and the mentioned pieces of old rad hose cut up to put in between for a cushion.

happy coaching!
buswarrior
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eddiepotts
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« Reply #30 on: June 18, 2010, 08:48:42 AM »

I think I can finally post a pic of what the inside of my dryer cover looked like at the purge valve. no telling how long it was never attended to.

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txjeff
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« Reply #31 on: June 18, 2010, 09:02:05 AM »

thats nasty..........I guess I better service mine since the PO didnt look at stuff like that. I see you got the pics to post....

jeff
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« Reply #32 on: June 18, 2010, 09:07:13 AM »

I went to the test area and tried. It's about time Grin
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buswarrior
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« Reply #33 on: June 19, 2010, 07:34:21 PM »

Now the only concern is did the current compressor pump that in there, or the one before?

Monitor what is being blown out the exhaust on the air drier, this is a fine warning that the compressor may be pumping oil.

All part of the restoration efforts!

happy coaching!
buswarrior

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