MCI MC-9 suspension and accessories won't air up"

[Sc17842]

Hi all posting for a friend of mine. 

"MCI MC-9 suspension and accessories won't air up"

Hi, I have a 1983 MCI MC-9 Crusader/II ex-Greyhound. The bus starts and runs fine, but the air system doesn't air up properly. The air gage in the dash shows pressure building nicely, and the service brakes work. My issue is that there's no air to anything else on the bus. I have the low air alarm, low tag air alarm, and the not gen alarm. In addition, the compressor never unloads, and if I let it go long enough, the relief will lift at 150psi. There's no air to the wipers, HVAC, luggage door locks, entry door lock, or anything else. I even have to shut the engine off manually by pushing the shutdown lever with my finger. It's done this to me twice before and I was able to free it up by cycling the air pressure by pumping the service brakes. Unfortunately, that did not work for me this time.

Does anyone know what valve could be stuck and where to look? Is it even a stuck valve?

Does anyone have a high quality copy of the air system schematic? I can't read the one that's commonly available online.

Any help is appreciated!

-Jeremy

[blue_goose]

I have one for the 102C3 but you need to put your email address in the profile for us to send you a copy.
Jack

[Templar52]

Look like a one way valve between main and accessory tank blocked.
With a smal...very smal hammer you can tap on them to try to relese them. You can try to connect a hose from the wet tank to the accessory tank by the drain valve. It will unstruck the one way valve. If it fixed the problem,change the one way valves.
If ever you change them,purchase a very hight quality one way valve.
Alain

[Brian Evans]

Pressure protection valve opens at 60 PSI and allows air to pass from the dry tank to the rest of the system.  The control feed back to the governor is after the pressure protection valve, so you may not be getting proper control of air pressure and the air dryer may not be cycling, so be careful of that.  The PPV is located on the passenger side air tank on the rear wall of the front axle bay, it is mounted on the tank beside the air system air filter.  If you have pressure in the parking brake tank and can release the parking brake, and the air dryer is cycling and the governor is regulating pressure correctly, then the PPV is not the problem and you can look at the accessory air tank under the driver's seat.  There may be a check valve on the line to that tank, and it has a drain valve so you can check to see if it is getting air.  All of the systems you mention are fed from that tank.

Brian

[ACausey]

I would second the pressure protection valve idea.  Mine is located under a little fiberglass cover in the front bay on the passenger side. I replaced mine last summer after having similar problems.  I'll see if I can dig up the part number.

Andy

Here's the part info from my notes:

Part Type: Air Valve
System: Air
Part Name: Pressure Protection Valve
Part Description 1: PR-2 Pressure Protection Valve, 65 psi
Manufacturer: Bendix
Mfr. Part Number: 277147
Vendor: NAPA
Part Number: TWD BENOR277147X
Cost: 41.85

https://www.napaonline.com/napa/en/p/TWRBENOR277147X

[jeremymc9]

Good afternoon, everyone! Now that my account has been activated I can post an update. After my experience with being unable to air up, I suspected that the problem might be temperature related. I waited for a warm day where the temperature had been above freezing for more than 24 hours. I am delighted to report that the bus aired up just fine. I was able to drive it home that evening with no issue. I suspect that there may be a bit of moisture accumulation in the air system from sitting and the swings in temperature with the fall weather, although I don't get water out of any of my drains.

I still plan to service the air dryer, as I don't have any service records for the coach.

Does anyone have any experience with air system antifreeze? I have read conflicting reports about how safe it is for seals and airbags.

Thank you to all who responded, I have learned much about my air system in the last week, and I'm sure I still have much, much more to learn.

If anyone needs me, I'll be under my bus with a bottle of soapy water, chasing down air leaks.

Regards,

Jeremy

[buswarrior]

Have you drained the discharge muffler inside the curb side engine access door?

A valve against the back of the tag wheel fender.

It's the first place after the compressor that moisture collects and is the Achilles heel for those who don't know...

If there's moisture in there, nothing gets through, which contradicts the original post about some air gauge movement...

happy coaching!
buswarrior

[jeremymc9]

I have drained the discharge muffler location. Bone dry. My suspicion is that freezing was causing the pressure protection valve to not operate properly. Whether that was due to the valve itself freezing up or something blocking the sensing line I don't know.

[buswarrior]

Change out that PPV as a PM item.

If you need that coach functional, you can put some brake alcohol into it as a stop gap.

Do all your PM catch up, and keep everything drained, you won't need any anti-freeze next year.

I like to put a 1/4 turn valve and male air fitting into the wet tank drain, and use an outboard motor fuel line and prime bulb with the female air fitting on the hose. Pump some alcohol in and then operate the coach. Leave it in there, don't drain until you have several hundred miles on a leaky teaky, or, just leave it until spring, if you aren't going that far or just in the yard.

How much? Since you already have trouble, put most of a quart in and leave it, as above.

The alcohol laden moisture/air has to work its way through, and that takes air consumption/coach operation.

Yes, Bendix strongly discourages the use of brake alcohol in these modern times with a good air drier. See line #3

The alcohol contributes to lubrication rinsing inside valves. But, if you're frozen up, damned if you do, stuck there 'til spring if you don't?

happy coaching!
buswarrior

[jeremymc9]

Luckily, I was able to drive it home, and I don't need it to move until warmer weather, since I'm tearing out the interior. I'll make sure to service the air system well, and keep it well drained all summer.

Thanks for the great advice!

Jeremy

[brmax]

Glad to hear ya got it rollin and to the homestead!
Sure makes it nice and to take a breather knowing you can work over some of that stuff on a warmer schedule, "and not on a road somewhere" so all sounds great.
One thing I wished mci had done was raise them air tanks a bit and put the drains on the bottom where they should be, but there so low in their standard mount its likely to get a drain knocked off 
I would take the dryer off and set it on the bench to work it over this spring, checking the heater ohms for spec, and also I checked to see if voltage was at the drier when power is on as it should be.
Some can be either 12 or 24 so it may have been changed if in a bind in the past.

again great to hear the good news
Floyd

[bluesblake]

I have a similar issue  but my problem is   my air system will not go over 80lbs.   I have a threaded valve under the entry door  between 2  solenoids  that is blowing air out the entire time.     
Any ideas?   

[Brian Evans]

first, start a new thread.  It's a pain reading about someone elses 5 year old unrelated problem.  The only commonality is they are both air system problems.  Second, tell us what make, model and year bus you have so we can at least have a clue.  Third, a door opening system isn't particularly critical so cap it off, take it apart, and see what might be broken.  Get the air system and electrical schematic for the thing, and work out what should be happening, what is happening, and what the difference might be caused by.   My word, that sounded grouchy when I read it back, not meant to be, welcome to the forum

[bluesblake]

Apologies for thread etiquette.