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Author Topic: Air problems  (Read 6855 times)
compedgemarine
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« Reply #30 on: September 13, 2008, 08:35:00 AM »

OK so now we know there are a variety of issues. first question, how long have you owned this bus? Have you ever replaced the compressor? If not then I would guess that it was changed prior to your ownership. that is the same problem I had with the Kenworth. Just like mine it is possible the compressor was change or repaired (probably the reason for RTV in the system) and they didnt clean out the system. Like Jerry and the others said, just replace the governor and flush the lines and service the dryer. all this assuming you are sure the compressor is not pumping out oil. the biggest problem with the MCI having the dryer in the front is that there is 35 feet of hose that could have a lot of oil and crap laying in it so you will need to unhook it at each end and flush it good. the hydraulic shops us a line cleaner which is basically a foam plug that is soaked in cleaner and pushed through the line with air pressure.
good luck.
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luvrbus
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« Reply #31 on: September 13, 2008, 09:45:44 AM »

That foam for cleaning is called a poly pig when you are buying one fwiw. how does a air dryer work being 35ft from the compressor I have been told by shops that it should be no more than 10ft from the compressor fact or fiction anyone know for sure
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compedgemarine
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« Reply #32 on: September 13, 2008, 10:23:05 AM »

I have been told the same thing but most all MCIs have the dryer around the front axle I believe. someone smarter than me will have to figure out the right answer but I cant believe they would do it all these years if it was a problem. I have an Eagle and mine is behind the drive axle so it is about a six foot hose. seems to work ok there.
steve
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John316
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« Reply #33 on: September 13, 2008, 11:13:36 AM »

Quantum500

I forgot to mention, that you might also want to check your shop air. Sometimes the shop compressors are full of water and other foreign material. I'm not sure if you have had the air hooked up much, but that could explain some of the water in the lines.

God bless,

John

P.S. luverbus we have had some issues with the dryer being 40 feet from the compressor. If the compressor makes much condensation  and it sits in that main line the line can freeze easier. In addition the main line to the dryer is copper, which splits when it freezes. MCI also makes a heater boot to go on the output from the dryer to prevent freeze ups in that elbow (of course that's provided that your dryer isn't functioning properly and is letting water through).    

« Last Edit: September 13, 2008, 11:15:46 AM by John316 » Logged

MCI 1995 DL3. DD S60 with a Allison B500.
quantum500
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« Reply #34 on: September 13, 2008, 06:48:24 PM »

If you read all my previous posts I got the dryer to purge with shop air hooked up to the purge line.  I have had the bus for almost a year.  The previous owner told me when I bought it that to get the parking brake to release you must first hit the brakes....it doesn't do that anymore.  Could it be that this problem has persisted through 2 owners?  I have not replaced the compressor, if it does need attention I will probably rebuild it myself if I can find a good deal on parts.  My shop air is very clean I do a fair amount of painting and wouldn't risk contamination in my paint.  I did find this deal for all you guys with the an old dryer, you can thank me later.   Grin  http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWAX:BIN&item=380047884121
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compedgemarine
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« Reply #35 on: September 13, 2008, 07:11:11 PM »

dont know about MCIs but my Eagle has a brake interlock. you release the brakes then apply 100psi to the service brakes to release them. if yours has this also and it has quit functioning you may want to check with someone to ensure that is wont interfere with any other part of the system. if the compressor has never been changed then there is a good chance it is fading and pumping oil into the system.
good luck.
steve
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Sojourner
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« Reply #36 on: September 13, 2008, 09:58:21 PM »

I have been told the same thing but most all MCIs have the dryer around the front axle I believe. someone smarter than me will have to figure out the right answer but I cant believe they would do it all these years if it was a problem. I have an Eagle and mine is behind the drive axle so it is about a six foot hose. seems to work ok there.
steve


There a reason for AD-2 being in front to allow compressor's line to cooled before dyer to maximize moisture removal via automatic purge.

Read the Bendix Compressor Guide and you will find it suggest at least 15 feet or more.
http://www.todaystrucking.com/images/BendixCompressor%20TroubleshootBW1971.pdf

quantum500...do the free checking first and read the above link about "The Bendix® BASIC test should be the definitive method for judging excessive oil fouling/oil passing." to learn if your compressor is good or bad.

BTW...sign of no oil coating from relay exhaust mean no oil in diaphram. Which no problem but to get dryer AD-2 apart to replace oiled soaked desiccant beads for new one. The instruction is in the Bendix AD1_AD-2 link in my first post.

And replace D-2 governor with open..clear thru no leak lines and I believe will you be fine.

And don't do AD-2 servicing yet until your sure compressor oil consumption is OK.

FWIW

Sojourn for Christ, Gerald
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quantum500
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« Reply #37 on: September 13, 2008, 11:35:37 PM »

dont know about MCIs but my Eagle has a brake interlock. you release the brakes then apply 100psi to the service brakes to release them. if yours has this also and it has quit functioning you may want to check with someone to ensure that is wont interfere with any other part of the system. if the compressor has never been changed then there is a good chance it is fading and pumping oil into the system.
good luck.
steve

Thats a thought.
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luvrbus
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« Reply #38 on: September 14, 2008, 04:32:19 AM »

Jerry, my AD-2 Bendix service manual under service data #sd-08-2403 page 15 it calls for 6ft min on 2 cylinder compressors and 10ft for 1 cylinder compressors no reference to the max length fwiw
« Last Edit: September 14, 2008, 04:52:27 AM by luvrbus » Logged
buswarrior
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« Reply #39 on: September 15, 2008, 09:07:47 AM »

Good grief!

Quantum, you say you've been using the "drain daily" drain in the engine compartment regularly and getting pretty much nothing out of it. The compressor is fine. If it was worn out and pumping oil, you would be getting the first load of oil here, and all over your pants, and you aren't.

Regarding the use of the term "ping tank" MCI calls the small tank after the air compressor a "Discharge Muffler" and it is the first place to catch and drain the moisture from the humidity that has been squeezed out of the intake air.

My air drier contamination theory: Besides simply deteriorating over years of neglect, the air drier may have been hastened to this condition. In an effort to prevent air system freezing, introducing brake alcohol into the air system in the wrong place, (ahead of the air drier) will quickly destroy the desiccant in the air drier, turning it into a mud, which then escapes its containment and plugs up the proper functioning of the purge valve. The normal and small amount of oil that makes it to the air drier may make the mud appear to be heavily oil contaminated. Maybe some previous owner or driver has done this prior to your ownership. Pumping the alcohol in through the drain in the engine room is popularly the way this dastardly deed is accomplished. (Note, if you are a northern busnut, and don't have an air drier, this is an easy and ok way to introduce alcohol to the system) Once ruined, it is only a matter of running time for the purge valve to fail and then over time, the cavity in the air drier fills with a mixture of desiccant mud, oil and moisture. Getting goo out the Safety Valve suggests the cavity has filled somewhat, eh?

If you want to, the drier may be successfully returned to functioning with a clean out, desiccant replacement and replacing the purge valve instead of cleaning it is good preventive maintenance. Don't skimp by buying one without the built in heater. You never know when the winds from up here will blow to down there.... And run the fused power line, if you don't have one already.

However, as noted, updating to a more modern air drier has advantages for quick parts acquisition. As for the parts counter guy saying parts are hard to come by for the AD1 and AD2, no, the parts are readily available to order, daily demand for them is down, as they are getting to be quite few and far between out on the road commercially, and he has chosen, for good reason, to not stock stuff that doesn't move.

When choosing a new drier, be sure that you are getting one that is rated for the big air flow requirements of a bus air system. The air drier can only "dry out" so much air on each pumping cycle before it is saturated.

As noted, just go buy a new governor. Again, good preventive maintenance and it isn't worth your time to fool with a rebuild kit.

In air brake circles, the device to prevent a pressurized vessel from damage if due to some failure the pressure climbs beyond the rating of the vessel is called a "Safety Valve". Some slang terms include pop-off valve, blow-off valve. A Pressure Protection valve is the proper name for the device that blocks air from filling the accessory parts of the air system in order to direct the compressor's full efforts at the brake tanks, "protecting" the brake part of the air system from any failure in the accessories.

The Safety Valve may very well have been doing its job properly. If the air drier's condition was blocking the flow of air into the system, the pressure in the line from the compressor to the blockage was quite able to surpass 150 lbs, and the Safety Valve released the excess pressure to protect it from bursting. However, the Safety Valve has very small passages in it, a sealing surface and depending on age, a metal spring, which will now be polluted with stuff which may effect its operation in the future, so again for preventive maintenance, it would be good to purchase a replacement.

By placing the air drier way up there, MCI's air driers enjoy a long service life. Heat in the incoming air charge is hard on the desiccant. MCI is able to get a considerable drop in heat over that distance.
There is no way to have the bus functional and have the airline from the compressor to the air drier filled with enough water to split it under freezing. The Discharge Muffler has been built strong enough to withstand a certain amount of abuse in this area. Remember, MCI is from Winnipeg....

As for cleaning lines, if this line of thought is close to the condition your coach is in, the relatively short line from the air drier to the wet tank, and the wet tank itself, should be the only places that may be contaminated sufficiently to require a little cleaning.

From the air drier, blow toward the wet tank, and see what comes out the drain valve. If you like, feed it a little water, enough to get the level in the tank a little above the drain and see what comes out. Maybe leave it sit for awhile. Don't use any solvents or other chemicals that would be harmful to the internals of your air valves. Rubber, plastic, metal sealing surfaces...

The signal line for the governor goes back to the wet tank, but up high, so I doubt there is any crap in it. With the wet tank drain open, give it a little shot of air before you attach it. The other line goes to the air drier to signal the purge valve, be sure to take it apart at the drier end first and give it a little shot.

Whew!

happy coaching!
buswarrior
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quantum500
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« Reply #40 on: September 15, 2008, 10:01:04 AM »

Thanks for the detailed message!  I appreciate it.
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luvrbus
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« Reply #41 on: September 15, 2008, 10:26:01 AM »

Q500, if you get a excess of water most of the time it is not condensation but a bad compressor.I replace my compressor 4 years and with the new one I had water every day in my tanks that wasn't there before the problem we found out was the head was leaking on the compressor. At the Bendix school in Phoenix the instructor told the class that a AD 2 dryer was the best dryers Bendix ever built the new dryer AD-IS was made because the older units did too good of a job drying the air causing problems with the new auto shift transmissions o-ring failures and fwiw I live in the middel of nowhere and the local NAPA store has had every part I ever needed for my AD-2 dryer
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rusty
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« Reply #42 on: September 15, 2008, 12:38:17 PM »

  Clifford The Bendix manual tells you to but the air dryer no more than 10 feet from the compressor and down hill for same.
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luvrbus
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« Reply #43 on: September 15, 2008, 01:22:08 PM »

Wayne, what page is that on, I knew it was in the manual and the instructor told us the same ( was awake then) that is why I asked  when 35ft was mention but I could not find it
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rusty
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« Reply #44 on: September 15, 2008, 02:51:17 PM »

  Clifford After looking at the manual I may have to retract my statement. On page 9 of the Air Brake handbook they talk about line size and lengths. 15 feet is as long as they talk about and that is 3/4 line. In my notes of the class I have written 10 feet max. Something must have been said I am no good at making thing up. It does talk about the distance between the compressor and the governor. Thats not an issue with most of us as the govenor is mounted at the compressor. I will have to ask Jim maybe he will remember what they where talking about. They do say the hose must run down hill to the dryer, and they talk abut insulation to proct for freezing.
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