Will not air up

edvanland · January 27, 2018, 08:44:37 AM

I have a MCI 7 with a 8V92 and Allison 740 trans. Have been getting a weird sound from the air dryer area. Sounds like the noise made when air is forced through a thin space, I know that doesn't help much. Started that in Quartzsite but would still air up. Washed the engine yesterday and adjusted the brakes again. Now it will not get past 60 pounds and hearing a air leak. Ran out of time yesterday so will get under it again today and try to find the air leak. Geoff said it sounds like the air drier and hoping it isn't the compressor. Will find out which air dryer I have today. Waiting for the temp to rise.
ED

lostagain · January 27, 2018, 09:18:40 AM

Ed it just wants you to stay longer...

Once under there, you should be able to find where the leak is, if it is audible like you say. Good luck. You know I would help you if I was there.

JC

edvanland · January 27, 2018, 10:34:14 AM

Thanks JC I am going to hook up my compressor to it and then get my jack under it put blocks under the wheels and do all the safety precautions and see if I can find the air leak.

luvrbus · January 27, 2018, 10:45:10 AM

Probably the purge valve on the dryer stuck

Dave5Cs · January 27, 2018, 10:45:25 AM

Ed check the bottom of your airdryer in the middle and if it is coming from there hit it with some WD=40 and tap with a stick and maybe it will close up. Sometime the purge valve sticks open. Had it happen to mine. If you have the long cylinder hanging off the front wall of the wheel well it is an AD2 Air dryer. The purge valve on the bottom where there is a rubber disk can be replaced from NAPA or truck stop. it just unscrews with a socket. If you pull the bottom off be careful to unplug the wire to the heater first.

sorry clifford must of been typing at the same time. At least he isn't on a Flatbed yet.

buswarrior · January 27, 2018, 01:26:55 PM

When you buy a replacement purge valve, make sure it has a heating element, and match the voltage of your coach.

How cold is it? Does your purge valve heater have power to it?

If it sticks once... time for some preventive maintenance, desicant and purge valve, you won't need to think about it again for many busnut years!

Happy coaching!
Buswarrior

edvanland · January 27, 2018, 02:28:23 PM

One leak is a hose, think I can get the dag gum thing off, no. There should be a swivel on one end, nope. Took one of the hose nuts loose and looks like it is some kind of fitting where it should come loose. Looks like a compression fitting. To late today to do anything because the parts house is closed. Will try again next week. Did not see a drain on the bottom of the air dryer and not heating element. I will check that out better tomorrow. I got the bus back on the ground and now have it inside the garage with the door shut, so when I get the hose off or find out what ever else I need I don't have to worry about getting it all the way back in the garage. Any other suggestions would be appreciated. It is a Bendix air dryer with a replaceable canister. Will tackle it more next week and of course will all so call Luke.

luvrbus · January 27, 2018, 02:38:11 PM

A hose on the DD-3 can ?

Dave5Cs · January 27, 2018, 06:14:40 PM

The purge valve if it is ad2 will just unscrew without the heater. The heater is the rectangle box molded into the bottom next to the purge valve with one wire on a bolt coming out of it with a little nut on it. Only has to be removed if you take the whole bottom off to replace the Dessicant cartridge up in it.

If it is in fact a replaceable Canister then it might be an AD9 with the 10 small bolts that you have to take off and also the strap to take it out of the harness it is in. Be careful of the Lines on either of those they can and will snap if you are to hard on them and they come through the floor and are very hard to replace.

Ed also there is a Pressure release valve at that same area depending which you have that is a brass valve like on a compressor when they get to much air they will stay opened until it get down to normal.

You have an airbag filter that is just to the rear or the airdryer that is as big as a fist with a drain valve on it. These are all up front in the wheel well area.
Ed it might be a shorter AD4 also. Here is the manual for the air system on a MC9 which is similar to yours. It show both.

http://buses101.com/PDF_Files/MCI%209%20Maint%20Manual%20in%20PDF%20format/MC-9%20-%20Maint%20Manual%20Section%204.pdf

edvanland · January 29, 2018, 08:02:42 AM

Thanks all. I do have a Bendix standard AD-9 Air dryer and also the manual with the diagram of the air system. Will get back at it. Tried to take off one of the air lines and could not get it to unscrew all the way. The air lines are fairly new and look almost new. They are rubber and look like it is a compression fitting just can not get the line out of the fitting on the valve. Any suggestions.

lostagain · January 29, 2018, 08:09:13 AM

You could cut it with an angle grinder or reciprocating saw, and have a new one made up.

JC

buswarrior · January 29, 2018, 08:12:10 AM

You really want to get the air schematic for your serial number MC7.

MC7 is single circuit brakes, MC9 is dual circuit. Designation of tanks and locations all changed.

Not sure about the MC7, but the MC8 had 8 different air schematics, depending on when it was made, and to which State's old safety standards, from before FMVSS 121 in 1975.

Nothing worse than learning your coach wrong, and having to go back and re-learn!!

Happy coaching!
Buswarrior

Dave5Cs · January 29, 2018, 08:16:22 AM

Why did they do the MC 7 single circuit. My 5C is dual. Thats interesting

lostagain · January 29, 2018, 08:43:11 AM

Dave, MC7s are 10 years older than 5Cs.

JC

sledhead · January 29, 2018, 12:56:17 PM

try some soap and water in a spray bottle to lube up the fittings and it will help to seal when you put it back together

dave