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Author Topic: need some help with air leak  (Read 2161 times)
BRUISER
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« on: March 10, 2013, 05:03:21 AM »

I finally figured out where the air leak is coming from on my bus..

if you look at pic below it is coming from the black thing in the middle.. yesterday when under bus I had my hand on it and the black area is rubber and is easily movable, looks like a release valve or something.. does anyone know exactly what that does and can it be fixed or do I need to replace entire blue thing?

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iMPAKS.com
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1983 MCI MC-9
Steve102C3
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« Reply #1 on: March 10, 2013, 07:14:44 AM »

If I'm not mistaken, that is a brake valve (E-10 maybe?). I replaced mine because it was leaking there also.

It still leaked afterward.

Turns out this leaking may indicate a bad brake diaphragm.

On my bus it looks like one or both drive axle brakes (brake cans) need to be repaired. That is my next big project.

If you search my name for posts, you can find a discussion on troubleshooting.

Hope this helps.

Steve
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Steve
1989 MCI 102C3
SW Arkansas
robertglines1
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« Reply #2 on: March 10, 2013, 07:21:22 AM »

Your parking brake was still applied?  No service brakes applied?  Bob
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Bob@Judy  98 XLE prevost with 3 slides --Home done---last one! SW INdiana
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« Reply #3 on: March 10, 2013, 08:57:19 AM »

As mentioned, I believe that that valve will exhaust air from an internal system leak like a bad diaphragm.
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« Reply #4 on: March 10, 2013, 08:58:13 AM »

yes bus is parked with parking brake applied.. bus will not air up over 80psi
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iMPAKS.com
Raleigh, NC
1983 MCI MC-9
Cary and Don
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« Reply #5 on: March 10, 2013, 11:26:10 AM »

If you suspect that the relay valve is the problem,  you can take out those four screws you see in the bottom.  The interior parts can be removed and cleaned.  There is a chance there is some crud in there causing the leak.  Dump all your air first and chuck your wheels.  Put blocks under the body so it can't come down on you. If it leaks really bad when applying the service brakes,  it's most likely a diaphragm in a chamber.  They are pretty easy to change yourself.

As for not airing up past 80lbs.  Does the compressor cut out or does it just not go past that even if the compressor is pumping?  If the compressor is still pumping,  I would suspect a very major leak in the auxiliary air system.  The valve for that opens somewhere between 65 and 80lbs.

Don and Cary
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1973 05 Eagle
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Dave5Cs
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« Reply #6 on: March 10, 2013, 12:56:49 PM »

That is the E-8 Rely Valve. Like above check your brake diaphragm in the rear by carefully clamping each air line to the brake can off to see if the leak stops. If it does then it is a brake diaphragm. If not it is probably the valve. It can be rebuilt but for the price just get a new one. It will last as long as you have the bus most likely. I just replaced mine about 58.00 NAPA Grin

Dave5Cs
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« Reply #7 on: March 10, 2013, 02:12:58 PM »

Do you have the part number ?
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iMPAKS.com
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1983 MCI MC-9
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1979 MCI MC5Cs 6V-71 HT-740 Allison, Roseville, CA




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« Reply #8 on: March 10, 2013, 02:21:30 PM »

Rear brake Relay Valve - R-8 on a 5C
Page 4.1101 March, 1981 Parts manual

4R-11-1

Might check with your supplier to see if there has been an upgrade for the MC 9
Looks the same in the picture with the same amount of hoses etc.

You might also check your regular next to it and your inversion valve. I replace all just in case.

Dave5Cs
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Cary and Don
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« Reply #9 on: March 10, 2013, 05:37:24 PM »

There is a chance that there isn't anything wrong with the valve.  I would make sure it isn't something else first.  Those are a bear to change.  We chased a leak on that valve only to find out we had two leaks from someplace else that showed up at the valve.  It doesn't look all that old in the picture.  The little rubber is even still there.

Don and Cary
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buswarrior
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« Reply #10 on: March 10, 2013, 05:59:43 PM »


As noted, don't go changing parts until the diagnosis has been properly done.

None of us appreciate when the auto mechanic throws parts at our cars as a diagnostic effort, why would we throw parts at the coach?

Confirm or deny that the brake chambers are bleeding air back and out the exhaust on that relay valve.

The black rubber disc is to keep the insects out of the valve internals. Beware the mud building wasps, no disc, they'll plug it solid inside and you get functionality trouble with the service brakes. I've seen them plug 1/4 turn drain valves on tanks and opening the valve won't blow the nest out. Solid as cement those nests.

The exhaust is normally open on a relay valve, so any air in the service portion of the chamber can escape, but if any air leaks into the service side from the parking side, it shows as a leaking relay valve.

Relay valves are also capable of leaking internally on their own, as they are supplied with tank pressure for their job of applying the associated brake chambers when signaled pneumatically by the brake pedal.

And pay attention those with spring brakes, you can get the same symptoms, not just the DD3. A spring chamber can leak down the shaft seal into the service portion. The DD3, it will be the parking diaphragm leaking through.

happy coaching!
buswarrior

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« Reply #11 on: March 12, 2013, 08:48:39 AM »

so been getting dirty laying on the ground under bus with not much luck..

I have read threw the manuals and the pictures are terrible..I can not find any other leaks and to be honest I can not see any other issues with brakes etc.. it does make sense that it is related to brakes, because I rev'ed up bus and it aired up and once I released the parking brake the bus could hold air pressure find and would actually air up to the point the front air regulator would let air out once it had full air..

so it is related to brake system..

so what should I look at directly? do you have any pics of areas to look at ? thanks
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iMPAKS.com
Raleigh, NC
1983 MCI MC-9
Lin
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« Reply #12 on: March 12, 2013, 10:02:01 AM »

Okay, if I have this right, it only leaks when the parking brakes are applied.  As I understand it, that would point to a bad parking brake diaphragm on a DD3.  Do you have DD3's?
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« Reply #13 on: March 12, 2013, 10:48:04 AM »

yes only when parking brakes applied and yes DD-3
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iMPAKS.com
Raleigh, NC
1983 MCI MC-9
Cary and Don
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« Reply #14 on: March 12, 2013, 11:39:06 AM »

Might want to check the park brake push/pull valve also. It feeds the air to the parking diaphram.

Those diaphrams are so easy to change.  If you have any questions as to their age,  why not just change them out?  Half hour each.  It's so much easier to do at home than on the road someplace.  You can't believe how much air lose you can fix changing them even if there doesn't seem to anything wrong with them.

Don and Cary
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