Need help identifying an air valve and what it affects

[Tenor]

On my MCI 7 I have an air leak.  I got under it during the summer and found it but I don't know what it is called.  It is in front of the drive axle in the center.  It looks like a threaded plug (?) about a 1.25 inches wide give or take, and has a slot about 1/8 wide.  In the center is a hole and I assume there is some sort of valve behind it.  It always stays open.  There is an identical piece in the spare tire bay at the end of an air line as well. 

If you know what this piece is, please tell me.  Now, to whoever knows what this is, would it have a strong affect on air pressure during breaking?  My air falls off VERY quickly while the brakes are applied.  Air does build reasonably quickly after stopping. 

Additionally, my air assist on the clutch seems to not be assisting!  Separate issues or linked?

I have found a contractor to spray insulate my bus in the next week or to, but I need to drive the bus about an hour and a half and I want these problems licked. 

Thanks for the help everyone!

[Tony LEE]

Photo would make it easier. OR have a look at this page
http://www.anythingtruck.com/commercial/airb_bendix_valves.html
and by opening up the class that looks similar, see if you can spot it.

Maybe a safety valve if there is just one air line to it, quick-release or pressure reducing if there are two lines.

Air assist on the clutch should be supplied with full system air pressure at all times. Loosen the connection at the cylinder a couple of turns to check.
Cylinder can get gunked up inside so dismantle and clean and lubricate and refit. Cyliner comes apart by removing O-rings.

Pressure comes from the auxiliary supply which only gets air when the brake system is at least 70psi so the other fault may cause low pressure on the clutch assist.

Normally can check operation by pressing and releasing clutch pedal as the air pressure rises. Below 100psi there will be little or no assist but over 100psi the assist will kick in and you should feel a definite effect once the pedal is about half way down to the flooe.

[captain ron]

Post pictures I may have brand new what you need or a good take off

[ChuckMC9]

Disclaimer - only in the last month have I gotten to know my air system much better than before. I'm ashamed it took me this long. So I'm hardly qualified to answer, but...

If air is falling off really rapidly when you apply brakes, I'd start looking at the rear. The big drive axle brake chambers, or the valves which supply them. (all located just before and also above the drive axle)

The reason is that those chambers are supplied directly from the big dry tank thru a relay valve. They are the ones getting the most air, and the most important.

Also, brakes dropping down like that is *really* dangerous. You don't want to leave that condition unchecked. It won't even pass inspection like that.

The front condition could exist at the same time and be completely unrelated. I've had quite a few things that don't have much to do with each other that have had to be dealt with.

[Tenor]

This is the picture of the front valve(?) in the spare tire bay.  The same part in front of the drive axle is the one that leaks right out the center where the hole is.  What is this part?



Tony Lee:  Thanks for the help with the clutch.  I didn't know what air pressure was required for the air assist, but while I had it running around pressure was about 115, but at a stop, I'd drop to 70 or 80 with the brakes on and that is of course when you use a clutch the most.

[JackConrad]

Does pressure only drop drastically when the brakes are appled?  Jack

[Tenor]

Pressure is slow to come up without giving it throttle.  It will drop from 110 to 70 quickly while braking.  If air is lower than 110, it will drop lower than 70.  This is the only time it loses air, but like I said, it is slow to air up to pressure.  I was wondering if more air may escape from the mystery part during braking.  I am working on getting the local bus company (Dean Transportation) to do an inspection/repair before any further driving.  Safety first!

[tomhamrick]

Best way I have found to locate leaks in the brake system is to block the wheels, release the park brake and shut down the engine. Make a full brake application and have someone listen for air leaking. You could do the same with your clutch assist as well.
Tom Hamrick

[Lin]

I am not sure what that valve is.  I had a problem of air leaking from a central rear valve that turned out to be a relay valve which I called Luke about getting.  He said that that valve exhausts air that could be leaked elsewhere.  In my case, it was the parking brake side of one of my DD3's.  It is certainly going to be something different for you, but could be one of the chambers itself if this valve also exhausts dumped air.  With all the info you have and the picture already taken, I would guess that Luke or another such expert would be able to tell you what it is instantly; experience is an amazing resource.  Would that destroy the adventure?

[buswarrior]

Hello Tenor.

Do you have the schematics for your coach?

Try another picture angle for that part, maybe from a little further back, I don't recognize it as pictured.

You have a serious condition with your coach if it won't maintain air pressure, and it needs to be properly diagnosed and fixed.

happy coaching!
buswarrior

[akbusguy2000]

I may be wrong here, but I think the object is a manual drain valve similar to the one on the bottom of my wet tank (4106).  Put a tool of some kind in the slot and see if it will turn one way or the other.  If I'm right, it may just need to be closed.

tg

[Tenor]

Bus Warrior - I do have the schematics from the manual, and it might be a pressure release valve on a tank.  It also may be a pressure regulator gone bad.  I found some similar pictures in my parts manual, but they don't have any measurements to help confirm.  I am going to fire it up later today, shut it down, and have my wife operate the brakes while I listen.  If the ice storm doesn't hit today, I may do a quick crawl under (with bus blocked) and get another look and pictures.

Thanks for all of the help folks!  I'll post later today or tomorrow.

[Tenor]

Well, finally had a decent day to fire things up and get under the bus.  The part in question is the pressure regulator for the air leveling system.  I also found that my drivers side brake cannister is blowing huge amounts of air through the vent hole.  Looks like tomorrow I'll pull both of them and rebuild the cannister.  Thanks for the help guys!

Glenn

[Stan]

Quote  "The part in question is the pressure regulator for the air leveling system." unquote

Is this the regulator for the tag axle air bags,or something else?

Your MC-7 should have DD-3 brakes and you will likely have to order new diaphragms. They are not common at truck supply places. Large truck and equipment brake shops may have them.

[NJT5047]

FWIW, shop air could be attached to the coach in order to air it up for diagnostics.
Use dry/regulator set at about 100 lbs. between the bus and air compressor.
There's a fitting inside the RH engine service door for access. 
Using shop air allows quiet hunt for leaks. 
Be careful when working with air lines.  Never disconnect an air line when air is on the bus.  Some tanks may be flat, but you could have residual pressure in another. 
Block/chock the bus before disconnecting the drive axle DD3 slacks.   That's all that keeps the bus from rolling. 
Even with the park brake released, the DD3s will set the park brakes as pressure drops to 60 or 70 lbs.   Be prepared for that movement.
If you want to remove the slacks (prior to chamber removal), air up the bus, release the park brake, and back off the slacks.  Once the slacks are loose, bleed all the air off the bus before removing air lines.
I'm sure that you are aware of such, but don't crawl under an aired up bus.   
JR