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Bus Discussion => Bus Topics ( click here for quick start! ) => Topic started by: GnarlyBus on April 06, 2019, 03:43:14 PM
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We're on the road heading north and after lunch the bus won't air up. This issue happened this morning but seemed to go away and start normally after I messed with the parking brake push-pull valve. I figured that I hadn't set it correctly the night before but here we are again.
The air bags are still full from when we parked, but the bus doesn't build air on the dash gauge (maybe very slowly). I can hear air coming from between the front wheels. Maybe louder from the passenger side. I checked the air dryer and it's not the problem.
It seems like something is stuck open but I'm not sure what or how to reach it.
What can I do next? Thanks!
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Turn wheels all the way one way, check both sides, turn all the way the other way to improve access.
Keep looking, listening and feeling around.
Everyone is just going to start listing all the parts under the front end, still won't find YOUR leak...
Happy coaching!
Buswarrior
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It is totally the air dryer stuck open at the bottom. I thought something much smaller under the drivers seat was the air dryer.
Any tricks to make it close so I can get on the road?
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Used search and found that I can tap it closed and service it later? Here's a pic. Tap the brass piece at the bottom?
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I cleaned it all up. I also noticed the air dryer heater connection was broken (maybe by me when pulling the boot off) so I repaired that. How does the heater work? How do I "turn it on"?
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It comes on with the ignition.>>>Dan
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Thanks! I'm back up and airing up! See y'all down the road! Scheduling an air dryer rebuild/purchase tonight!
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I got to where I needed tonight. Whenever I stopped the bus, the purge valve would open for a minute or two before closing again. After looking at pictures online (see attached) I realized I'm missing a rubber stopper on the purge valve. How is it even stopping leaking if this is gone?
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That is just an air deflector. The purge valve is behind that. What generally happens is people don't maintane their air dryer each year or two and all the crap come through it and water then the stuff gets blown out the end when the psi reaches 120 and stuff gets stuck in the port on the bottom and won't allow it to close some even get rust in there because their heater is not working. Some work when you turn your heater on and it gets to a certain temp. :)
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Glad you're functional.
Check the schematic, most of that era, the air drier heater was powered by the coach heat switch, an inline fuse holder on the wire with a glass fuse in it tucked into bottom of the outside under driver's window electric panel.
Unwittingly, busnuts tear out the coach HVAC, never turn on the switch in the cold, and no power to the air drier. Seated coach with air leaks, left idling in the winter with the coach heat turned off to keep the engine temp up would freeze up its drier too.
The heater has its own thermostat, nothing for you to do, except confirm there's power to it.
The rubber disc is to keep the critters from getting in, and let the blast of purge get out. Mud daubers and those small wasps that use mud to lay their eggs in small places are the devil for a sitting air system...
Good that you are planning service soon, air driers don't get better by themselves, and the tapping trick only works for so long...
Happy coaching!
Buswarrior
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Thanks for the note on the heater wire. I was wondering about that. I read a thread where it talked about the wire being powered by the HVAC system which is totally gone from my bus. I'll check power to it and look for that 3A glass fuse tomorrow. Just in case I need to run a new wire, it's 24v, right?
I'm glad the deflector isn't crucial. Once I get it on the road, it purges at 120 and kicks back in at around 90. So does that rule out issues with the governor/hoses from there?
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The cycle sounds fine. I think you've found your issue.
Yes, the purge valve heater is 24 volts, and be sure to remind your service technician, as 12 volt heaters predominate out in our mostly 12 volt world. You need the right one put back in!
When checking that wire to the air drier, don't fool yourself that it has no power, if you haven't got the coach into the proper configuration to give it power.
HVAC won't turn on until low air goes out, and alternator starts charging. I can't remember if the air drier wire is connected before or after that big relay.
Happy coaching!
Buswarrior
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If you have the correct sized wrench (I used a small pipe wrench) you can remove the purge valve, clean it up, lubricate the O-rings a bit and it might keep working for a while. You can also buy a rebuild kit, and replace the soft parts for a proper fix. The kit is Bendix part number 287053N for an AD2 purge valve kit. The correct sequence of events is this: Air governor is in cut-in mode, air system is filling, air signal from governor to purge valve is zero PSI. System fills to cut-out pressure, governor switches to cut-out mode, governor sends a line (90 psi at that point) pressure signal to the compressor and to the purge valve. Air pressure opens the purge valve, exhausts the air inside the air dryer, and holds the purge valve open until cut-in and the cycle starts again. The normal failure mode is the purge valve sticks open when the air governs switches to the next fill cycle, it ignores the high pressure signal and does not close. Hitting it with a stick jars it loose. If it does it once, it will do it again, so at least clean/lubricate it.
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I installed a switch on the dash to turn the dryer purge valve heater on or off. I like manual things. To test the heater, the temperature has to be below freezing so the thermostat turns it on, regardless of how it is powered upstream.
JC
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I went ahead and wired it to ignition this morning with a fuse. Starting the bus up soon. Hope to be rolling down the road again today.
I appreciate all the responses!
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Started up the bus and it leaked out of the purge valve. The tapping trick didn't work. :(
So I removed the shield to get these pictures.
I think I'm gonna try to pull off the valve (don't have a socket or crescent wrench that big) and clean it.
I found a remain heater on there. Also found a tag that says 12v 60w. So the heater has been replaced with a 12v? Guess I'll rewire it.
Any other tricks than tapping it to get me down the road?
Can I remove the purge valve without removing the whole end cap?
Also, the governor was pushing air out the exhaust port the whole time while the bus was trying to air up. Is that normal?
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Pulled apart the purge valve and nothing seemed wrong with it. Plenty spring left and the o-rings look good. I lived them up and put it back together. The stopper looked to be in great shape.
So maybe instead of sticking open, its being told to stay open by a faulty governor???
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You could try cleaning the D2 governor or if you have the right fittings you could bypass the air dryer for now with a piece of hose. In other words connect the incoming (at the bottom)and the out going ( at the top) temporarily just make sure you drain the tanks regularly. I have had mine like that for 2 years with no problems but I don't live in cold country.
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I guess I was a little early in calling this thread solved. I thought it was a simple sticky purge valve as that is where the air is gushing out.
What could cause the air dryer purge valve to be forced open when trying to air up the bus (works perfect when it does air up and go down the road)? It's not "sticking" or frozen, it's being forced open at the wrong time.
The purge valve is open and flowing when the bus is at 30 psi trying to air up.
It almost seems like the governor is in cut out mode and is redirecting the air to the dryer purge valve.
We've been moving down the road slowly trying to get as far as we can each day because we don't know when it's gonna decide to work again.
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Do you know how long ago the dryer was last serviced? How about the governor?
You should go to a truck parts store and buy a new governor, and a kit for the dryer that includes the desiccant cartridge and the purge valve with the heater and replace everything. That is routine preventive maintenance that should be done on a regular schedule. You will then have a fresh base line to run off of for the future. I would not carry on just by band-aiding an important system like the air system. You will find the overhaul directions on the Bendix web site. The parts are quite cheap, because they are made by the thousands for truckers and bus companies.
JC
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These items have not been serviced in the 4 years I've had the bus. The air system is kind of the last area I'm learning. We don't drive the bus much.
I'll be replacing he governor sms dong an overhaul on the air dryer when we arrive in Oregon in a few days.
Just trying to better understand my issue so I don't get stuck somewhere in the next few days. I've read the air dryer and governor manuals in the last two days and am now reading the compressor.
Thanks.
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My bet is still the purge valve needing a kit. If the governor was at fault, it would be unloading the compressor at the same time - and 30 psi is probably not enough air pressure to either unload the compressor or open the purge valve. The mere fact that the compressor can build air and cuts out at 120 is pretty decent proof that the governor is working properly.
If you take the dust cover off the purge valve you can press direct on the valve to force it firmly closed, to see if that makes any difference to air leaking out.
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... I'll be replacing he governor sms dong an overhaul on the air dryer when we arrive in Oregon in a few days.
Just trying to better understand my issue so I don't get stuck somewhere in the next few days. ...
Someone earlier described how to completely bypass the dryer, and -- for a few days on a "get you home" basis -- I'd be leaning that way. As described, just bypass the dryer with a piece of 1/2", or maybe 3/4" DOT hose* (and would the pressure line from the governor have to be blocked off???).
Good luck with it. It seems to me that a new governor (or a good rebuilt one) and dryer rebuild with solve this for you but you'll have to do what you have to do to get to Oregon first.
* 3/4" hose is not trusted a lot these days, but IMO if you have some that's undamaged, you might as well use it in the main air feed side, at least on a temp basis.
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My bet is still the purge valve needing a kit. If the governor was at fault, it would be unloading the compressor at the same time - and 30 psi is probably not enough air pressure to either unload the compressor or open the purge valve. The mere fact that the compressor can build air and cuts out at 120 is pretty decent proof that the governor is working properly.
If you take the dust cover off the purge valve you can press direct on the valve to force it firmly closed, to see if that makes any difference to air leaking out.
I removed the dust cover and pushed it closed. The bus aired right up. It's definitely the purge valve sticking.
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The purge valve's natural state is to be closed. It takes an air pressure signal from the governor to trigger opening, and the resulting purge.
You will likely find it easier to disconnect and plug the signal line, than trying to disconnect both main lines, and then somehow connect them together, all without destroying the ability to put it all back together.
The purge valve will just stay shut, and then you can return it to service once parts are available.
Don't be running around with a compromised air system... stopping is kinda important...
Happy coaching!
Buswarrior
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Oh, have you been draining the discharge muffler every day? Down the back, curb side engine access, "Drain Daily" mounted to the back of the tag axle wheel well?
And you'll have to put some special effort into getting the wet tank drained, once this excitement comes to an end to return your air system to dry.
Or you get to scream next winter about brakes stuck on...
Happy coaching!
Buswarrior
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BW has a great idea, disconnect the air line coming out of the center port of the air govenor ( the hose connection between the two mounting ports) and plug it, I think a 1/4 pipe plug. Simple access through the door on the floor, probably under the bed. That will simply disable the air dryer. Push the purge valve closed, should be good to go. What has probably happened is the O-ring around the top of the valve is sticky, not lubricated with correct silicon grease, or the internal spring has failed or lost sufficient tension. The kit comes with new O-rings, a new valve head, a new spring and the correct grease. And a few other parts.
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Made it to our spot in Oregon!
So I have two weeks to do my repairs and maintenance.
I undid the control hose at the end cap of the air dryer and pushed the purge valve closed. My attempt at plugging the control line didn't work so it was open. Started up the bus and it aired up to 130 and stayed within 2-3 of that. When I pumped the brakes down to 80 to test, the psi built back up quickly.
So I made my way to Oregon. Kinda weird to me that it stayed at 130 the whole way (except when braking). Is that what you'd expect from an undone control line? Did I just male rd compressor run the whole time without a cutout?
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Yeah, sounds like it ran the whole way.
Get it all fixed up, and forget about it...
Drain everything!
Happy coaching!
Buswarrior
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The open control line means that the unloader valves in the air compressor never got pressure, so the compressor simply ran for the duration, always pumping air. You are lucky, I think, that it didn't rise to 150 psi and blow the safety release valve. It really should have. You lost all control over the air compressor by disabling the air governor.
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The leak out the control line kept it to 130 more than likely.
So long as it still pumps, and it likely does, this isn't much different abuse than a transit operation or one of those blower units on a truck...
Don't do it again!
Happy coaching!
Buswarrior
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... I undid the control hose at the end cap of the air dryer and pushed the purge valve closed. My attempt at plugging the control line didn't work so it was open. ...
Did you have a 1/4 in. pipe plug? A while ago, I sat down an put together an emergency kit for my bus. It has 1/4 in., 3/8 in., 1/2 in. plugs, same for caps, at least one DOT compression fitting with a male threaded end for any brake line on my bus, same with a female threaded end, female joining sleeve for 1/4 - 1/2 in., male double joining nipple in all sizes, many adapters with one size female and one size male, etc. And much more. I think we should all carry some basics like this (as well as dryer rebuild kits, extra 150 pound blow-off valves, etc.) You never know what you might need on the road and you'll probably need much of these items when you're working in your shop -- just remember to note what you're using and replace them.
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Great advice on carrying a kit of extra parts that might not feel extra when you're driving through northern Nevada and the nearest hardware store is 2+ hours away!
Here's what I've ordered so far:
Bendix AD-2 Purge Valve Kit 287053 - two of them!
Bendix AD-2 Dessicant Kit 286718 - two of them!
Bendix Governor 275491X - Gonna swap mine out
Bendix Governor Rebuild Kit 276121 - I want to open up my current governor and rebuild it so I have a better understanding of it.
1/4" Brass Flare Plug - 10
I'm adding various other plugs, caps and fittings from Oonrahnjay's list as well.
I'm also working on adding a ball valve to that control line coming off the governor that goes to the purge valve just in case I ever have this problem again...which I know I shouldn't with proper maintenance but it would make me feel better knowing it was on there.
Getting jacks and cribbing set up in the next week and gonna open the tanks up to get the water out.
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A2 upper check spring and ball valve kit. It is in the big nut at the top fitting. :)
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Those governors come with female hex pipe plugs. Get a set of allen wrenches. Harbor Freight has them in a pack that each one swings out similiar to a pocket knife.
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And remember who has to take it apart next time...
As applicable, pipe dope, teflon tape, anti-seize, lubricate, clean threads, proper wrenches vs adjustable bolt rounders...
A busnut is his own worst enemy or friend...
Happy coaching!
Buswarrior
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A2 upper check spring and ball valve kit. It is in the big nut at the top fitting. :)
Thanks! I ordered one just now.
One thing I have going for me is a solid amount of tools. Plenty of Allen wrenches, flare wrenches, 6-pointers, etc.
I did have to use channel lock pliers to get the 2" purge valve housing off. Not really ideal as it needs to be really tight on there. Both times I put it back on I had to go back and tighten it further. So I ordered a socket for it.
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To save me measuring, what size socket is it? I want to order one too - I used a pipe wrench on mind, also not ideal.
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To save me measuring, what size socket is it? I want to order one too - I used a pipe wrench on mind, also not ideal.
I read on this helpful thread over at WOG (https://www.wanderlodgeownersgroup.com/forums/showthread.php?t=23533) that it was 2" (on a picture in page 2) so that's what I ordered but in the next day or two I should be under there again and can throw a caliper on it to be sure.
I found a 2" socket on Amazon for $8 prime.
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Next time put some anti-seize or plumbers grease on it and it will go back on easier.
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To save me measuring, what size socket is it? I want to order one too - I used a pipe wrench on mind, also not ideal.
Definitely 2" socket. Checked it just now.
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Man, I have learned a ton about coach air systems and brakes this last week. Lots of great videos on YouTube but I've realized I should be been way more on top of this stuff. It really isn't that hard to drain air tanks (especially with the pull cord valves I'm adding) or get under the bus (when properly crib bed).
I've been busy. I got the governor changed out. When I did, I added a schraeder valve on the unloader port and a ball valve to the control line heading to the air dryer. This should allow me to test the unloader valves on the compressor with the engine off. It will also allow me to test the purge valve on the air dryer and shut off the control line if I ever need to in the future. With proper maintenance I'm sure it's unlikely I'll ever have this sticky purge valve issue again.
I rebuilt the dessicant cartridge for the AD-2 air dryer I have. When I opened it up, there was what I would consider to be a lot of oil in there. Not just in the oil catch brass part but in the dessicant. I would guess maybe a half cup. This really freaked me out but I suppose running the compressor for 7 hrs with the control line off like I did meant it ran the whole time without a break. The next time I fire up the bus I'm going to pull the discharge line off and hold cardboard 6" from the hole to check for oil splatter. How much oil is too much?
I rebuilt the air dryer purge valve and tested the heater. The end cover goes black on tomorrow.
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The heater in air driers is controlled by a thermostat in the drier they come on around 38F
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Yep, left it outside overnight and ohmed it in the morning. Right around 2 ohms.
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Dessicant doesn't like oil. If you continue to get oil there, consider replacing compressor.
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The discharge muffler on an MC9 should catch "normal" amounts of oil. So long as you "Drain Daily" ... only a really bad compressor will get oil to the drier.
The desicant will withstand a little, since oil mist is a reality of operation. But a soaking will render the "desicant" function useless.
What are you getting out of the "Drain Daily"?
Happy coaching!
Buswarrior
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This is the drain daily rear discharge muffler, right? Does it purge on it's own at all? It does have some wet oil slobber evidence.
This is the rear tank drain as well, right?
I'm installing pull cords on my front tanks later and the under driver tank is easy. Expecting lots of junk to come out of the front tanks today and then I can monitor them in the future and see how much is making it past the dryer.
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At least first time, open tank drains and leave them open at least overnight to completely drain any oil / residue.
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Fired up the bus today and the bus air is working properly again! The air dryer is purging properly again.
I drained the tanks for about 30 seconds each for the first time ever and nothing but a short burst of moisture left the wet tank. Other tanks were just air. Adding pull lanyards so I can be on top of draining these every time.
Thanks everybody for the help!
Also, I added a psi gauge near the discharge muffler to make sure the compressor was cycling.
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Thanks for leading the way. I'll be following up on my own system later.
Jim
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This is the drain daily rear discharge muffler, right? Does it purge on it's own at all? It does have some wet oil slobber evidence.
This is the rear tank drain as well, right?
I'm installing pull cords on my front tanks later and the under driver tank is easy. Expecting lots of junk to come out of the front tanks today and then I can monitor them in the future and see how much is making it past the dryer.
Manual valve. Feel free to replace that one pictured with something that has a handle.
Mind your shoes and pant legs, there's likely going to be a big mess blasted out of there.
No, it isn't connected to the rear tank. It is inline to the air drier.
happy coaching!
buswarrior