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Author Topic: Air Leaks 4104  (Read 1176 times)
4104SoFl
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« on: November 13, 2013, 07:17:17 AM »

When I fill the air tank that is below the driver seat with the shops air compressor the air gauge will read 120 and the air bags will fill up. The brakes will not release. I have to crank the bus up and build air pressure. When I build air pressure in this manner I can only get about 75 lbs on the gauge. There is a leak some where in the rear axle area. It will leak down to about 35 lbs then hold. The leak in the back stops. Any ideas?
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Orville Meyer
Loxahatchee, FL
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RJ
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« Reply #1 on: November 13, 2013, 07:59:23 AM »

NAME? -*

There are check valves in the system that only allow air to flow one way, so you cannot totally fill all the air tanks from the front.

Try filling the coach's air system from the engine compartment with your shop air and then report back to us what happens.

FWIW & HTH. . .

 Wink


* - Please take a minute to fill out your profile so that you have a signature line at the bottom of your posts similar to mine below.  Simply click on Profile in the above menu tabs, then click on the Forum Profile Info tab in the LH menu and follow the prompts.  By doing so we can better refer you to local parts and service sources, plus you might discover that there's a busnut nearby who's willing to share. 
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RJ Long
PD4106-2784 No More
Fresno CA
4104SoFl
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« Reply #2 on: November 13, 2013, 08:02:18 AM »

RJ do you want my full name. I not hiding from anyone.
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Orville Meyer
Loxahatchee, FL
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chessie4905
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« Reply #3 on: November 13, 2013, 08:25:34 AM »

   General location; at least the state you reside in. I always filled mine from that tank. What kind of parking brakes do you have? DD3's or Maxi's?
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GMC h8h 649#028
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« Reply #4 on: November 13, 2013, 10:38:13 AM »

OK RJ aired the system from the back by the motor. 120 LBS. As soon as I stop air it up the gauge began to fall. There is an air leak by the rear wheels, but it not much. Is it possible that the air compressor can only produce about 75 lbs of pressure? Is this a sign that the compressor is shot?
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Orville Meyer
Loxahatchee, FL
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gus
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« Reply #5 on: November 13, 2013, 11:59:05 AM »

If your air bags stay up your leak is in the brake system. They use a separate Auxiliary system at the front tank. If the air bags leak down a leveling valve or connection is probably leaking, they do that a lot.

If the leak is at the left rear wheel and the bags stay up you probably have a leak in the wet tank just aft of the wheel or in an air line from the tank. This tank is notorious for rusting out. It is well hidden up high forward of the firewall! The drain valve at the bottom of this tank is also bad to leak.

There is also a check valve just forward of the compressor muffler. If it fails the air will leak down.

First solve the leak problem then check the comp. It is probably good.

4104 is designed for only 102 psi in the system so 120 will only cause more leaks.

4104s don't have spring or Maxi's unless added on.
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PD4107-152
PD4104-1274
Ash Flat, AR
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« Reply #6 on: November 13, 2013, 02:30:35 PM »

"The brakes won't release."
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GMC h8h 649#028
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4104SoFl
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« Reply #7 on: November 13, 2013, 02:57:13 PM »

Brakes will release. Compressor will pump to about 75 Lbs. I can move the bus. Air leaks seems (SEEMS) to be coming from the air brake canister itself. I did pull it and replaced the diaphragms. It had two and has two air lines running too it. I do not know what kind of brakes they are. Mr. Bonagura from US Coach says he sure they are not D3, because they do not have three lines. These have two. I replaced those diaphragms a few month back. I believe that a good strong compressor would pump to 105 even with this small of a leak. I could be wrong. Any thought or comments would be welcome.
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Orville Meyer
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luvrbus
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« Reply #8 on: November 13, 2013, 03:07:54 PM »

Could be the compressor is set to kickout at 75 lbs have you tried to set the governor ? also if the compressor has a air filter mounted on it check and be sure it is clean with a bad filter they will not pump up

good luck
« Last Edit: November 13, 2013, 03:24:08 PM by luvrbus » Logged

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« Reply #9 on: November 13, 2013, 04:21:27 PM »

You say you replaced the diaphragms. When you did this did you have part numbers for the chambers to get the right diaphragms?
If you had a part # off a chamber it would tell you what chambers you have.

Also a good way to find the leak is to leave the shop air hooked to it while listening and spraying bubble solution on air lines, brake chambers and anywhere else that could be leaking.
Grin  BK  Grin
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luvrbus
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« Reply #10 on: November 13, 2013, 04:25:21 PM »

I wonder what he has for brakes? most spring brakes are sealed to keep you out of harms way with the spring
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robertglines1
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« Reply #11 on: November 13, 2013, 04:35:33 PM »

If the sealing surface for the diaphragms was rough or dirty=  when new ones were installed the new ones would leak also---rite?   worth a re-check with soap bubbles?   
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Bob@Judy  98 XLE prevost with 3 slides --Home done---last one! SW INdiana
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« Reply #12 on: November 13, 2013, 04:49:31 PM »

Clifford & Bob I agree with both of you!

I know for the longest time (until I got brave enough to actually split 1 apart) a DD3 I was scared to death it would be loaded with a spring big enough to flip a bus!

I had years ago seen a spring from a regular "spring break" chamber go through half of a cinder block and drop down inside the wall of a shop.
Never saw the reason to split one open again after that since they are cheap enough to replace instead of someone losing their head trying to say $30-40.
Grin  BK  Grin
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4104SoFl
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« Reply #13 on: November 14, 2013, 02:19:14 AM »

Thanks for all the help. I had to move the bus of the concrete pad and bring my 28' trailer up. It needs brakes and some other work. I will haul it to GA with the 1 ton dodge for Thanksgiving. Taking some furniture up there to kin folks. I will be back on the bus in December. Thanks Again
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Orville Meyer
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« Reply #14 on: November 14, 2013, 05:12:52 AM »

   Did you have to use a threaded tool to seat the emergency spring before separating the halves to replace the diaphragms?
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GMC h8h 649#028
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« Reply #15 on: November 14, 2013, 08:53:32 AM »

Yes I did
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Orville Meyer
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« Reply #16 on: November 14, 2013, 03:05:37 PM »

   Probably at least a couple of things. Did you replace the diaphragms to correct this problem initially? Did the brakes work ok for awhile after you repaired the chambers? If not, you obviously reassembled them with wrong or incorrectly installed diaphragms, or have a reversed hose or hole in one, or another issue instead of a leaking chamber,etc. If so, I would check the valve at the rear tank first, then the tank for a leak. Since you say it stops at 35psi, it sounds like that em. brake valve, but you'll need to SAFELY get under there and check it out. Who knows what kind of plumbing was added to install the maxi-chambers.
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GMC h8h 649#028
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'53 4104. Roadworthy but rough around the edges.


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« Reply #17 on: November 17, 2013, 03:43:21 AM »

look at the diagrams/explanations in the shop manual they explain location and functions of air lines and wet/dry tanks.  Agree with Gus rear wet tank probably scrap.  Had to change all 3 tanks on my 04 when I got it.
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Oonrahnjay
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« Reply #18 on: November 17, 2013, 01:07:28 PM »

    The "gold standard" is the soap bubble test, but I've found that using a stethoscope (or a 3 foot long piece of 1/4" DOT tube) is a good way to track down areas where you need to apply soap.  The sound test won't work on tiny, slow leaks but if it's a leak big enough to cause your system to act oddly, you'll be able to hear enough to point you towards likely problems.
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Bruce H; Wallace (near Wilmington) NC
1976 Daimler (British) Double-Decker Bus; 34' long
6-cyl, 4-stroke, Leyland O-680 engine

(New Email -- brucebearnc@ (theGoogle gmail place) .com)
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