No air pressure!

[Wornout Wrench]

Originally Posted by CHEESE_WAGON

I second Wornout Wrench. Probably not the best way to do it, but you could temporarily replace your drain cock valve with a fitting to which a shop-type electric compressor could be used to keep the tank(s) at pressure. If the distance were sufficient between the two, might make it a lot easier to find that leak.

Probably the easiest way to do it, figure out which one is you wet tank (its the one that the hose from the air drier will go to) go into it.
Will be a 1/4" or 3/8" NPT fitting.

[Mtrdrms]

Update:
I spent a whole lotta time today putting pressure to this system. I did it 2 ways, I pulled the air hose off of the compressor and blew air with my compressor into it. I could hear air moving through the lines and into at least one tank. Once I shut the air off, I could hear all the air leaking out of the tanks. NO sign of a leak.
I also found a Schrader valve on the rear most tank. I blew air into that and the same thing happened. Air goes in, no pressure builds.
I also found a valve on one of the front tanks but it wouldnt take any air.
My question is, where does the air leak out of when you're driving and you release the brakes? Maybe that valve is stuck open?
I swear I'm not an idiot but I cannot figure this out.

[Wornout Wrench]

No, you are not an idiot. Air leaks can be a real bugger.

A few questions:

Have you figured out where the air drier is and which one is the wet tank, that will be the tank that the air drier will supply. When you say you found a shrader valve on the one tank, I am thinking that you are on the air drier. You won't be able to get enough air flow through the schrader valve.

What kind of air hoses do you have, the plastic ones or the fabric covered ones.

How big is the air tank of the compressor that you are using to try to air up the system.

And lastly, how are you getting the air into the lines, did you build a fitting so you have a good tight connection.

I had a bunch of fittings made up so that I could just plumb straight into the system. Leaks showed up real fast but also had a big compressor to power.

On a truck air system, the compressor discharge hose has to be either copper or teflon hose for the first several feet, this is because of the high temp of the air coming out of the compressor. After the 3 or 4 feet of copper or teflon they will then go back to the fabric covered or the plastic hose. Then the hose will continue on to the air drier. Have seen this hose fail many many times. Trust me on this one, it is a bastard to change, me being not exactly tiny (5'10, 220 pounds, little bit of fat but just overall big). They will have that hose strapped into the frame rails bundled up with a bunch of other hoses and wires. If it holes, you will get no air at all.

Yes you will have lots of spaghetti to try to work your way through.

Unfortunately, I am on the other side of the continent and in a different country then you so I can't come for a visit and get you fixed up. But if I was able, the first thing I would do is identify some of the components of the air system. Figure out where your air drier is and the wet (first) tank is.
I would then verify that the hosing from compressor to air drier is good and the air drier to wet tank is good. After that was confirmed as good, move on.

Your a rear engine correct?
Did you also slide forward while listening for the air leak, it could be on one of the lines heading forward. Do these buses have a forward air tank for the front axle (anyone)

[Wornout Wrench]

http://www.busparts.com/assets/pdf-f...page-1-pdf.pdf

Here is a really basic air brake diagram, give you a bit of an idea what I am talking about .

The truck/trailers that I used to work with were 7 axle with ABS and ATC. If the ABS went out, it disabled the ATC and since they were self shifting 18 speed transmissions, it would cause grief with them too.

But the systems all work the same.

[Mtrdrms]

Originally Posted by Wornout Wrench

No, you are not an idiot. Air leaks can be a real bugger.

A few questions:

Have you figured out where the air drier is and which one is the wet tank, that will be the tank that the air drier will supply. When you say you found a shrader valve on the one tank, I am thinking that you are on the air drier. You won't be able to get enough air flow through the schrader valve.

What kind of air hoses do you have, the plastic ones or the fabric covered ones.

How big is the air tank of the compressor that you are using to try to air up the system.

And lastly, how are you getting the air into the lines, did you build a fitting so you have a good tight connection.

I had a bunch of fittings made up so that I could just plumb straight into the system. Leaks showed up real fast but also had a big compressor to power.

On a truck air system, the compressor discharge hose has to be either copper or teflon hose for the first several feet, this is because of the high temp of the air coming out of the compressor. After the 3 or 4 feet of copper or teflon they will then go back to the fabric covered or the plastic hose. Then the hose will continue on to the air drier. Have seen this hose fail many many times. Trust me on this one, it is a bastard to change, me being not exactly tiny (5'10, 220 pounds, little bit of fat but just overall big). They will have that hose strapped into the frame rails bundled up with a bunch of other hoses and wires. If it holes, you will get no air at all.

Yes you will have lots of spaghetti to try to work your way through.

Unfortunately, I am on the other side of the continent and in a different country then you so I can't come for a visit and get you fixed up. But if I was able, the first thing I would do is identify some of the components of the air system. Figure out where your air drier is and the wet (first) tank is.
I would then verify that the hosing from compressor to air drier is good and the air drier to wet tank is good. After that was confirmed as good, move on.

Your a rear engine correct?
Did you also slide forward while listening for the air leak, it could be on one of the lines heading forward. Do these buses have a forward air tank for the front axle (anyone)

Haha, Vancouver isn't exactly next door!
The lines are mostly plastic. There is a braided line off of the compressor and then it goes to copper. I found the dryer - it is over the rear axle. I believe the wet tank is on the drivers side just in front of the radiator. I have found 4 tanks. That one, and 3 in the front.

Unfortunately I am only using a 5 gallon compressor that puts out about 100 psi. I did rig up a good connection to the braided line off of the compressor but I still cant hear/ see any leak.

The only reason I think the line is ok is because o can hear a little air entering the wet tank and one of the tanks in the front. Not enough to build any pressure but I can hear air IN the tanks. Then is quickly leaves the tanks.

[Wornout Wrench]

The braided line is it stainless steel?
If it is, then that is the teflon line I am talking about. Very high temp. There is a teflon liner inside the stainless. DON'T KINK IT

So we are making progress.

Leave your little compressor connected to the braided line (compressor discharge)

The air drier will have 2 good sized air lines, one will be in, one will be out. So one from the compressor and the other one will be the one going to your wet tank.

If you can figure out which line is the supply into the wet tank, and cap it off, your little compressor will pressure it up no problem. If it can't, then your leak is between the compressor and the wet tank, so your compressor discharge lines, the air drier and the air drier to wet tank line.

If it holds then we move on to the fun stuff.

Plastic lines are prone to wear, they will get a weak spot and it will blow out. but they are easy to fix.

Are the lines different colors, they do that sometimes to ID the different systems.

I have been trying to find a diagram of a rear engine bluebird air system online, havent had much luck yet.

[Wornout Wrench]

Just reread your post.

There is one air tank at the back and 3 at the front, is that correct?

Might need someone who is familiar with bluebird to step in here.

I would suspect that the tank at the back is the supply for your rear axle, will have a relay valve on it with hoses going to the brake pots.

Just have to go make dinner.

Retired husbands work is never done. Will get back to this in a bit.

[CHEESE_WAGON]

I wonder if it might help to put some smoke into the compressor intake and see if it pushes out anywhere. I've heard of that being done to help find vacuum leaks...

[Wornout Wrench]

Okay, found some information.

The schrader valve is on the wet tank, supplied by Bluebird as a way of airing up the system on a disabled bus. So that is your wet tank.

Also found this

https://www.centralstatesbus.com/wp-...s/a3brakes.pdf

Says that it is for 1999 – 2003 Blue Bird All American Service Manual.

Gives me something to go off of.

[Mtrdrms]

Ok, thats great. The lines do appear to be blue, red and black. Throughout the bus.
So the air dryer only outputs to the wet tank and the wet tank feeds the rest of the system? If thats the case, I can block off the outlet on the wet tank and pressureize it and see if it holds.
If this sounds right, I will do this tomorrow.
Getting somewhere! Thanks!

[Mtrdrms]

I can also get you any pictures you may need to aid in your diagnosis. No problem.

[Wornout Wrench]

I just got your reply, was in the middle of typing this up.

Yes, color coded lines, if they used the same ones during repairs, it will help. Not going to venture what the code is, we had different colors.

Yes, compressor to drier to wet to other things.

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Forgetting how old this is.
So they run an AD-9 air drier. If it hasn't been changed out to something newer.

Could be the purge valve stuck?

Really have a good look/listen to the exhaust on the air drier. Get the palm of you hand and cover the exhaust up, see if it build any pressure at all on your hand.

Don't think it is it because you say you can hear air moving in the tanks, but need to check it anyways.

If there is nothing leaking at the back that you can find, then your going to have to follow the lines to the front of the bus.

Hands, ears and soapy water in a spray bottle. Soapy water doesn't work very good on larger leaks.

Old mechanics trick for soapy water, use a good shot of dish soap plus about a tablespoon of glycerin mixed in. Will give the bubbles some hang time, that is for about a quart of water. Look up bubble recipes for making bubble stuff. Anything to make the bubbles last longer and be stronger. the glycerin works good.

There will be lines going forward and coming back. Not going to be fun.

Not sure where the brake treadle (pedal)is mounted but there will be supply lines to it and also the the parking brake valve.

All potential leaks

But if the little compressor is at the back of the bus, or as far away as you can get it, you might be able to hear something,

[Wornout Wrench]

Pictures are great.
Have rebuilt machines with nothing but a photo album to go on.

I'll send you a PM with an email address

[one_eyed_jack]

Reverse-flow check valve is not holding, likely gummed-up with oil. Should be the last fitting where pressure feeds into the wet tank. Pressure is not building cause the air just keeps flowing back and forth as the piston goes up and down. ( nothing to stop air from going back ) So when you shut it down, what little has built up, flows back through the compressor and into the engine intake manifold . That would explain why you hear air moving but no discernable external leaks. Check that out.

[one_eyed_jack]

Originally Posted by one_eyed_jack

Reverse-flow check valve is not holding, likely gummed-up with oil. Should be the last fitting where pressure feeds into the wet tank. Pressure is not building cause the air just keeps flowing back and forth as the piston goes up and down. ( nothing to stop air from going back ) So when you shut it down, what little has built up, flows back through the compressor and into the engine intake manifold . That would explain why you hear air moving but no discernable external leaks. Check that out.

Let me edit this slightly. That air returning to the compressor on shutdown would seep past the piston rings into the crankcase if the exhaust popet valve is holding, which it must be if you are getting 150 lbs out of the compressor.

[Mtrdrms]

Originally Posted by one_eyed_jack

Let me edit this slightly. That air returning to the compressor on shutdown would seep past the piston rings into the crankcase if the exhaust popet valve is holding, which it must be if you are getting 150 lbs out of the compressor.

Yes but would this still be the case if disconnected the line from the compressor and pressurized it myself with a compressor.?

[Mtrdrms]

So the tank closest to the air dryer has 4 lines. I think this is the wet tank? One of the lines has this shraeder valve on it.

[Mtrdrms]

The line from the compressor appears to go to the bottom of the air dryer

[Mtrdrms]

The line from the compressor appears to go to the bottom of the air dryer

I disconnected the output from the air dryer which I believe goes to the rear air tank and it is producing good pressure with the engine running.

[Mtrdrms]

Ok, so I went to the front of the bus and disconnected an inlet and air was moving but I could easily block it with my finger. It wasn't building any pressure.

Looking toward the rear, from under the front, there is a whole host of lines and things: