Air Valve Between Rear Duals

Glennman · April 04, 2021, 08:42:26 PM

The air valve (the one with about 7 air lines attached to it) between the rear duals on my '74 MCI is dumping air out of the diaphragm at the bottom of the valve assembly. I'm unable to tell if it dumps while the bus is running due to engine noise, but when I shut it off, it dumps air so fast that everything drains (air gauge goes to zero) within a couple of minutes. It also takes a long time to air up enough for the breaks to release, so that is telling me that it is probably leaking all the time.

I noticed there are 4 Phillips head screws at the bottom that removes the bottom of the assembly (the rubber dust cover diaphragm).

Do people get those rebuilt, or do I need to replace the entire unit (?). As usual, any help is appreciated! I'm putting some time into my '74 since I can't get my '02 going!

luvrbus · April 05, 2021, 04:31:50 AM

That is the brake relay they come off to rebuild and you are better off just buying a exchange unit

chessie4905 · April 05, 2021, 06:20:18 AM

Check the air line hoses coming from our DD3 brake chambers. (3) hoses to each. Could be from leaking diaphragm in one of them. Just disconnect one hose at a time and see if leak is coming from them instead.
If it is the brake valve, should be an R-6.

https://www.amazon.com/brake-replaces-Bendix-279952-H-30280/dp/B07N6PP8HG

ol713 · April 05, 2021, 09:39:42 AM

Hi;;

Call LUke @Cjoach service. He has them rebuilt (exchange) Had mine changed out

about two years ago. Just note which hose goes where.

Good luck Merle

Lucas = = (856) 794-3104

Glennman · April 05, 2021, 12:25:20 PM

Quote from: chessie4905 on April 05, 2021, 06:20:18 AM
Check the air line hoses coming from our DD3 brake chambers. (3) hoses to each. Could be from leaking diaphragm in one of them. Just disconnect one hose at a time and see if leak is coming from them instead.
If it is the brake valve, should be an R-6.

https://www.amazon.com/brake-replaces-Bendix-279952-H-30280/dp/B07N6PP8HG

Ok, so it looks like it could be one of two devices with problems. One, the valve assembly itself, the other the brake chamber.

Pardon my ignorance, and I know that brakes are a very serious matter, but is it the case that those hoses will not have air in them unless the canister diaphragm is faulty? In other words, it seems to me that if the system is charged, then air will come out whether there is a diaphragm issue or not.

Obviously I need an education on air systems, but I'm hoping I can at least troubleshoot it. Thanks.

hogi6123 · April 05, 2021, 02:24:45 PM

You need the air diagram for your bus.

In my experience, air shouldn't be coming out any of the ports unless it is actively being released, such as letting up on the brake pedal.

Also in my experience, the actual problem may or may not be the particular valve where the air is coming out, it could be a diaphragm in one of the other valves or brakes.

With the air diagram and a little thought and experimentation, it's not hard to figure out where the problem lies.

buswarrior · April 05, 2021, 08:29:38 PM

The one with the octupus is the inversion valve. It is in charge of the parking brake, note 4 of the 6 lines to the pair of DD3 chambers come out of it.

Does this leak happen with the parking brake released? Block the wheels, run bus, release brakes, shut bus off with parking brake released and investigate.

It is good preventive maintenance to renew the inversion valve, the last commercial operator surely did not do any.

Make VERY sure you know exactly which line goes to where... top to bottom, the inversion valve has levels of cavities, you will note both of the rear most lines from the chambers attach to the same "level" of the inversion valve, and so on.

Happy coaching!
Buswarrior

Glennman · April 12, 2021, 07:43:53 PM

Quote from: buswarrior on April 05, 2021, 08:29:38 PM

Does this leak happen with the parking brake released? Block the wheels, run bus, release brakes, shut bus off with parking brake released and investigate.

So I fired up the bus tonight to air it up enough to release the break, etc., as you suggested, and now the air is spewing so bad it barely aired up to about 10 psi. I even had to shut it off with the air shutter.

So now I guess it is the process of elimination? Replacing parts until I get to the right one? I'll start with the valve, then if that doesn't do it, its the break canisters, and so on.

Dave5Cs · April 12, 2021, 08:54:29 PM

Pinch off the supply hose to the brake camber and if it stops at the E8 valve at the rear wall on the ceiling of the wheel well in the middle then it is the camber thats bad. If it is leaking at the camber then iti is the E8 relay valve. The inversion valve is cheap and probably never replaced.

buswarrior · April 12, 2021, 10:32:32 PM

Where was this giant leak blowing out of?

That is a huge leak.

This is an opportunity to refurbish the lot and then forget about it for a decade or more... inversion valve, the airlines, DD3 diaphragms and a fresh relay valve, and that's the thing back to new back there?

Happy coaching!
Buswarrior

hogi6123 · April 14, 2021, 07:57:38 AM

Quote from: Glennman on April 12, 2021, 07:43:53 PM
So now I guess it is the process of elimination? Replacing parts until I get to the right one? I'll start with the valve, then if that doesn't do it, its the break canisters, and so on.

I wouldn't just start replacing parts, I would check them first. But that valve is the most likely offender.

I would hook up an external shop compressor to the bus if possible. Make the bus safe to crawl underneath: blocks to keep it from rolling and settling.

You have DD3 brakes? Most likely. Disconnect all the hoses to the DD3 brakes. On my bus it was easy to do at the brakes with a few wrenches.

If I remember correctly:
With parking brakes on and service brakes off, there should be two ports/hoses on the valve with pressure, one to each DD3 brake can. If there are more, the valve seals are bad and need to be replaced.

If there are only two ports with air escaping, connect those two back up. If the air is now coming out of any part of the valve, its seals are bad.

If the air is coming out of any of the disconnected ports/hoses from the brakes, a brake diaphragm is bad.

Glennman · April 23, 2021, 12:39:34 PM

I just ordered a new relay valve from Luke at US Coach. The old one's base disintegrated when I started taking the bolts off that attaches it to the frame. So, even if that isn't the problem, I will be replacing it anyway. A good measure I think. After that, if the air continues to bleed off, I'll go into to brake chambers and replace the diaphragms as needed. Thanks everyone for your help on this.

Glennman · April 27, 2021, 09:20:29 PM

So, I just received the new air relay valve. It only has a single 3/8" NPT inlet for "supply". This would apparently be where I'm supposed to connect the (2) 3/4" air lines. Doesn't seem too likely. I'll be looking into this tomorrow. Should I expect to have to adapt a unit that is not an exact replica, or are these a common item, and I merely received the wrong one???

chessie4905 · April 28, 2021, 04:36:44 AM

Is it an R6 or R8? The R6 are available with two different port sizes. You received the one with the smaller ports. Return it for the other one.
Did your old valve have an aluminum tag on it? The correct number will be stamped on it. You can download the Bendix brake component catalog. It lists all their brake system components, and port sizes, orientation, etc, and Bendix part number for each one in remanufactured or new. This catalog should be kept with your shop manuals, etc.
Or you can get the correct one from Luke at U.S. Coach in New Berlin, N.J. Call him, he ships.
If you google bendix relay valve, a pdf catalog will come up as a choice.

Glennman · April 28, 2021, 01:02:56 PM

The one I got was from Luke. I sent him a picture, but no part numbers. I'll check for the tag and part numbers this time, and in the meantime, I'll download the Bendix catalogue. The part that concerns me (besides not having the right unit) would be if I had to redo all those lines back there to fit some new configuration of connections. Sounds like I have more work to do (not that there was ever any less work to do!). Thanks.