Finding air brake leak

[jlynn37064]

I have a leak somewhere around the rear axels. I can hear it, but I'm having a hard time finding it. I'm going to spray bubble solution, but I don't want to mess up any electrical under there. I replaced the Relay Valve, but that wasn't this cause. The chambers aren't leaking. I've sprayed them with soapy water and no bubbles. 

It's a 2006 Beaver Patriot Thunder with Cat C-13.  

I've ran through the DOT test. I definitely have a leak when the air brake is off and the service brake is applied. It leaks very rapidly. I thought it was the Relay Valve so I replaced it, but nothing changed. While under the rig, my wife pressed the brakes and I can hear air running through lines, but it's like having my head in a bucket. The air noise seems to be bouncing off the under carriage. I want to spray the soapy solution, but I see a lot of electrical connects.  You help is appreciated. 

 

[Ivan K]

I personally wouldn't worry when it comes to connectors on air valves, these should be waterproof anyway but potentially leaking air too. Just like oil pressure sensor might leak oil through its connector. I would direct the stream away from for instance sixpack connectors if unprotected. Stream is sometimes better for me than wide spray pattern as I can shoot it from a distance.

[Jdw12345]

So are you saying that when your wife applies the service brakes with the parking brake released you hear the air leak?

 If so, you might have an air leak on the service side of the brake canister, there’s what’s called a pancake in the canister that can fail and leak when the service brakes are applied, sometimes a broken emergency spring can break and cause the leak.

 So, block the wheels so the coach can not roll, air up the coach and have your wife release the parking brake, wait for a minute and then have her set the parking brake, if you hear any type of clunking noise you possibly might have a broken spring on the emergency side of brake canister, if you hear anything other than air rushing through the brake lines there’s a chance of a bad or worn brake chamber.

 If you need to replace a brake canister get a complete canister, don’t purchase what’s called a “piggyback” that’s just the emergency side of the canister, I would stay away from less expensive brand canister’s, we’re talking about your brakes here!  MGM brand is possibly what’s on your coach and a very good brand, they should cost you about 150 bucks for a complete canister, they are available at any heavy duty truck dealers, Peterbilt, Kenworth, Freightliner, possibly NAPA etc. 

If you have a tag axle it’s possible that you could have a leaking pancake on the service brake on the tag axle, the tag axle does not have a emergency side to the canister, only a service side. The pancake is serviceable but can be kinda of a pain to deal with the clamp on it, but it’s certainly possible to do.

        

Now, if you are comfortable with changing the canister out, just google it and watch some videos, if not by all means take it to a trk shop and have them do it, it’s only about a 45 minute job to change out a brake canister. Make sure if you do the work that you get the air hoses back on the canister on the correct port, there’s two air lines going to each canister on the drive axle, one for the parking brake, ie emergency side, and one going to the service side. 
If you do have a bad break canister I would recommend changing out both of them, again, we’re talking about your brakes! You will have to back the brakes off manually to do this job and you’ll have to cut the 
 

 If you go to a parts house to purchase the parts they will most likely ask you what size you need, I’m 99% positive that you’ll need what’s called a 30-30 with a 2 1/2” stroke, it has to do with the size of the chambers and the stroke.

 

 I put a couple of links down below for reference. If you google a 30-30 brake canister you’ll be able to find all kinds for sale, anywhere from 45-50 bucks on up, the choice is yours. After making a living in the trucking business some things are not worth taking the cheapest route, brakes are not one of them, IMO.

 

 After all of that, it’s possibly you may only need to replace a brake line or fitting!

 If you changed out a brake valve I’m assuming you are not to afraid of working on your coach or have some degree of mechanical confidence!

One last item, if you change out your brake canister, by all means, do not get curious and cut the band that holds the canister together!  There’s a spring in there that is extremely dangerous!

https://www.fleetpride.com/parts/air-system/chambers/spring-brake-chamber/mgm-brakes-spring-brake-chamber-3430051?cclcl=en_US

https://www.googleadservices.com/pagead/aclk?sa=L&ai=DChcSEwiBtPakjL39AhWwyZQJHU9fCkEYABAHGgJ5bQ&ae=2&ohost=www.google.com&cid=CAESbOD2FVn_QsdM0g2w6UPu0K0ExzACVMUBpxS3x1Om6o8sR0MApjsEHxIoYz-NAFOQ8K9hwp04HMAufamii11ZKQPH22p0zzqBZbnjcEmZLPHU0STwT55rq2JXFZepm4A2DFVOPJQNIbb5gxfmjA&sig=AOD64_152bD8N0zEz4oMOtg9hzfTOWiqow&ctype=5&q=&ved=2ahUKEwjts-6kjL39AhWRnGoFHR9oAKMQ5bgDKAB6BAgDEBY&adurl=

[jlynn37064]

7 hours ago, Ivan K said:

I personally wouldn't worry when it comes to connectors on air valves, these should be waterproof anyway but potentially leaking air too. Just like oil pressure sensor might leak oil through its connector. I would direct the stream away from for instance sixpack connectors if unprotected. Stream is sometimes better for me than wide spray pattern as I can shoot it from a distance.

Thanks Ivan

1 hour ago, Jdw12345 said:

So are you saying that when your wife applies the service brakes with the parking brake released you hear the air leak?

 If so, you might have an air leak on the service side of the brake canister, there’s what’s called a pancake in the canister that can fail and leak when the service brakes are applied, sometimes a broken emergency spring can break and cause the leak.

 So, block the wheels so the coach can not roll, air up the coach and have your wife release the parking brake, wait for a minute and then have her set the parking brake, if you hear any type of clunking noise you possibly might have a broken spring on the emergency side of brake canister, if you hear anything other than air rushing through the brake lines there’s a chance of a bad or worn brake chamber.

 If you need to replace a brake canister get a complete canister, don’t purchase what’s called a “piggyback” that’s just the emergency side of the canister, I would stay away from less expensive brand canister’s, we’re talking about your brakes here!  MGM brand is possibly what’s on your coach and a very good brand, they should cost you about 150 bucks for a complete canister, they are available at any heavy duty truck dealers, Peterbilt, Kenworth, Freightliner, possibly NAPA etc. 

If you have a tag axle it’s possible that you could have a leaking pancake on the service brake on the tag axle, the tag axle does not have a emergency side to the canister, only a service side. The pancake is serviceable but can be kinda of a pain to deal with the clamp on it, but it’s certainly possible to do.

        

Now, if you are comfortable with changing the canister out, just google it and watch some videos, if not by all means take it to a trk shop and have them do it, it’s only about a 45 minute job to change out a brake canister. Make sure if you do the work that you get the air hoses back on the canister on the correct port, there’s two air lines going to each canister on the drive axle, one for the parking brake, ie emergency side, and one going to the service side. 
If you do have a bad break canister I would recommend changing out both of them, again, we’re talking about your brakes! You will have to back the brakes off manually to do this job and you’ll have to cut the 
 

 If you go to a parts house to purchase the parts they will most likely ask you what size you need, I’m 99% positive that you’ll need what’s called a 30-30 with a 2 1/2” stroke, it has to do with the size of the chambers and the stroke.

 

 I put a couple of links down below for reference. If you google a 30-30 brake canister you’ll be able to find all kinds for sale, anywhere from 45-50 bucks on up, the choice is yours. After making a living in the trucking business some things are not worth taking the cheapest route, brakes are not one of them, IMO.

 

 After all of that, it’s possibly you may only need to replace a brake line or fitting!

 If you changed out a brake valve I’m assuming you are not to afraid of working on your coach or have some degree of mechanical confidence!

One last item, if you change out your brake canister, by all means, do not get curious and cut the band that holds the canister together!  There’s a spring in there that is extremely dangerous!

https://www.fleetpride.com/parts/air-system/chambers/spring-brake-chamber/mgm-brakes-spring-brake-chamber-3430051?cclcl=en_US

https://www.googleadservices.com/pagead/aclk?sa=L&ai=DChcSEwiBtPakjL39AhWwyZQJHU9fCkEYABAHGgJ5bQ&ae=2&ohost=www.google.com&cid=CAESbOD2FVn_QsdM0g2w6UPu0K0ExzACVMUBpxS3x1Om6o8sR0MApjsEHxIoYz-NAFOQ8K9hwp04HMAufamii11ZKQPH22p0zzqBZbnjcEmZLPHU0STwT55rq2JXFZepm4A2DFVOPJQNIbb5gxfmjA&sig=AOD64_152bD8N0zEz4oMOtg9hzfTOWiqow&ctype=5&q=&ved=2ahUKEwjts-6kjL39AhWRnGoFHR9oAKMQ5bgDKAB6BAgDEBY&adurl=

Thanks Jeff. 

I've sprayed soapy water on the brake cannisters and see no bubbling. I will test the parking brake to see if there are any noises from the chambers.  

My brake cannisters face outward. They compress the calipers. I've seen several videos where they connect to a level that is connected to the brakes. Mine aren't like that on the drive axel. 

[Jdw12345]

I see, you have disk brakes on the drive axle, I didn’t realize that vintage of coaches use disks, sorry about the long response for a drum brake configuration!

[jacwjames]

When I had air leaks I started spraying soapy water and eventually found all my PPV's leaking.  

Best thing I did when I started working on it was to make 6 ramps out of 2X10's cut 42, 36, 30. 24"  stacked and screwed together with a block added at the back to prevent backing off.  This gave me 6" of lift so I could crawl under the rig safely, plus when the air is completely dropped there was enough room to work under the rig. 

[jlynn37064]

Thanks Jim. I did make ramps for the rear. There was no way I was going under there without getting it higher off the ground. 

[Bruce S]

I have watched YouTube videos on Ultrasonic leak detectors which are supposed to locate any air leak you have in your system.  Though a good one is not cheap I think in the long run they would pay for themselves in avoided labour/parts costs.  Does anyone on this site have one of these devices and what experiences did they have with them?  I have been pondering purchasing one for about a year now...

[Ivan K]

If you can hear it, it most likely won't detect it. I tried one that was returnable, not the most expensive one but it was useless for my leaks. I stick with bubbly water but maybe there are some that detect wider frequency range.

[96 EVO]

Usually if you can hear air leaking, you can feel it.

If you have a patient wife, have her pump the brakes repeatedly, while you feel every line, connection.

Obviously, take every safety precaution so the coach can't move or lower on you!

[Larry Maida]

I thought i had an air leak. Parking, after the brakes set I would hear it while setting up. Then I got suspicious. So I did a basic brake test every tractor trailer driver does every day. I released the parking brake with engine runnng but in neutral. Then I pressed the brake pretty hard, you need to use up 20-25/lbs and HOLD. Watch your air gauge. If after a short wait you start building air not loosing it you dont have an air leak in your brakes. Mine turned out to be the air bags bleeding off as coach settled down on jacks. Good luck!

Edited March 4, 2023 by Larry Maida

[96 EVO]

That won't work!

Your compressor can fill your tanks much faster than most air leaks!

Here's the actual test for leaking brake lines / cans........

@ Full Charge Shut off Motor  Listen for Air Leaks  Make Full Brake Application for 1 min pressure must not drop > 3 PSI

Edited March 4, 2023 by 96 EVO

[Larry Maida]

Really I drove rigs for years. From car carriers to oil tankers. It works just hold down brake hard enough to use up a decent amount of air. 

[jlynn37064]

On 3/2/2023 at 5:25 AM, Jdw12345 said:

So are you saying that when your wife applies the service brakes with the parking brake released you hear the air leak?

 If so, you might have an air leak on the service side of the brake canister, there’s what’s called a pancake in the canister that can fail and leak when the service brakes are applied, sometimes a broken emergency spring can break and cause the leak.

 So, block the wheels so the coach can not roll, air up the coach and have your wife release the parking brake, wait for a minute and then have her set the parking brake, if you hear any type of clunking noise you possibly might have a broken spring on the emergency side of brake canister, if you hear anything other than air rushing through the brake lines there’s a chance of a bad or worn brake chamber.

 If you need to replace a brake canister get a complete canister, don’t purchase what’s called a “piggyback” that’s just the emergency side of the canister, I would stay away from less expensive brand canister’s, we’re talking about your brakes here!  MGM brand is possibly what’s on your coach and a very good brand, they should cost you about 150 bucks for a complete canister, they are available at any heavy duty truck dealers, Peterbilt, Kenworth, Freightliner, possibly NAPA etc. 

If you have a tag axle it’s possible that you could have a leaking pancake on the service brake on the tag axle, the tag axle does not have a emergency side to the canister, only a service side. The pancake is serviceable but can be kinda of a pain to deal with the clamp on it, but it’s certainly possible to do.

        

Now, if you are comfortable with changing the canister out, just google it and watch some videos, if not by all means take it to a trk shop and have them do it, it’s only about a 45 minute job to change out a brake canister. Make sure if you do the work that you get the air hoses back on the canister on the correct port, there’s two air lines going to each canister on the drive axle, one for the parking brake, ie emergency side, and one going to the service side. 
If you do have a bad break canister I would recommend changing out both of them, again, we’re talking about your brakes! You will have to back the brakes off manually to do this job and you’ll have to cut the 
 

 If you go to a parts house to purchase the parts they will most likely ask you what size you need, I’m 99% positive that you’ll need what’s called a 30-30 with a 2 1/2” stroke, it has to do with the size of the chambers and the stroke.

 

 I put a couple of links down below for reference. If you google a 30-30 brake canister you’ll be able to find all kinds for sale, anywhere from 45-50 bucks on up, the choice is yours. After making a living in the trucking business some things are not worth taking the cheapest route, brakes are not one of them, IMO.

 

 After all of that, it’s possibly you may only need to replace a brake line or fitting!

 If you changed out a brake valve I’m assuming you are not to afraid of working on your coach or have some degree of mechanical confidence!

One last item, if you change out your brake canister, by all means, do not get curious and cut the band that holds the canister together!  There’s a spring in there that is extremely dangerous!

https://www.fleetpride.com/parts/air-system/chambers/spring-brake-chamber/mgm-brakes-spring-brake-chamber-3430051?cclcl=en_US

https://www.googleadservices.com/pagead/aclk?sa=L&ai=DChcSEwiBtPakjL39AhWwyZQJHU9fCkEYABAHGgJ5bQ&ae=2&ohost=www.google.com&cid=CAESbOD2FVn_QsdM0g2w6UPu0K0ExzACVMUBpxS3x1Om6o8sR0MApjsEHxIoYz-NAFOQ8K9hwp04HMAufamii11ZKQPH22p0zzqBZbnjcEmZLPHU0STwT55rq2JXFZepm4A2DFVOPJQNIbb5gxfmjA&sig=AOD64_152bD8N0zEz4oMOtg9hzfTOWiqow&ctype=5&q=&ved=2ahUKEwjts-6kjL39AhWRnGoFHR9oAKMQ5bgDKAB6BAgDEBY&adurl=

Thanks Jeff. 

I've sprayed soapy water on the brake cannisters and see no bubbling. I will test the parking brake to see if there are any noises from the chambers.  

My brake cannisters face outward. They compress the calipers. I've seen several videos where they connect to a level that is connected to the brakes. Mine aren't like that on the drive axel. 

Thanks for responding. I definitely have a leak. When applying the brakes with the engine off, my tanks drop 60 - 70 PSI within a minute.  We were backing into a site and the brakes would not hold the rig. We had to apply the parking brake and allow air to build up. I have plenty of air for a hard stop, but constant application of the brake causes PSI to drop. 

[jacwjames]

In 2021, as I was getting my rig ready to travel after years of sitting, I did a bleed down test.  I charged the system to full pressure and shut it off and walked away, it took almost a week for the air to bleed down enough for the alarm to sound when I turned on the key.  This is what I was use to so I thought all was good.

Took one long trip June-July without a problem.  I then took a trip in Nov and parked/camped one night and in the AM, when I turned the key the low air alarm went off, I thought hmmmm ?????????????  But continued my trip and every night the air would bleed down so when I was parked for several days I decided to take a quick look, and started spraying soapy water.  Didn't take long to see the problem, all 4 of my Pressure Protection Valves were leaking, one much worse then the others.  The rig could easily keep up while driving and even passed the air brake test so I continued my trip.  Then when I was at a national park and stopped at the visitor center to look at the display and went back to the rig after ~45 minutes the alarm went off, I lost almost all the air pressure. 

That's when I decided to head home and fix the leaks.  Not really that difficult and cost to replace all the PPV's and other fittings was less then $200. 

Out of curiosity I took the PPV's apart, every one of them had severe corrosion.  Not sure why, never had a problem with my air dryer, no water in system.  But when I did some research the installation document for a PPV showed that they were originally stalled upside down.  There is a weep hole that is suppose to be pointing down so when it was originally pointed up any moisture in the valve would stay and probably caused the corrosion.  Attached is a picture of the PPV taken apart, all the white stuff is corrosion on the spring.  My guess is that as the PPV was being worked small flakes of the stuff would flake off and cause the diaphragm to leak. 

 

[Jdw12345]

My coach leaks down enough overnight that the low pressure alarm will go off in the morning, I don’t really worry too much about it, would I like to have less air leaks, yes, I have been under my coach a couple of times looking for them. I think a misconception some people might have is that they don’t want to wear out the air compressor because of excessive running of the air compressor, for those that might not know, your air compressor is indeed running all the time, the only difference is that the air governor is controlling if the air coming from the air compressor fills the reservoir tanks or just dumps to the atmosphere, these compressors are not like the air compressor you might have in your shop/garage that actually run as needed, the compressor on your engine is always running, they are gear driven off a accessary drive on the engine. 

Edited March 5, 2023 by Jdw12345

[jlynn37064]

3 hours ago, jacwjames said:

In 2021, as I was getting my rig ready to travel after years of sitting, I did a bleed down test.  I charged the system to full pressure and shut it off and walked away, it took almost a week for the air to bleed down enough for the alarm to sound when I turned on the key.  This is what I was use to so I thought all was good.

Took one long trip June-July without a problem.  I then took a trip in Nov and parked/camped one night and in the AM, when I turned the key the low air alarm went off, I thought hmmmm ?????????????  But continued my trip and every night the air would bleed down so when I was parked for several days I decided to take a quick look, and started spraying soapy water.  Didn't take long to see the problem, all 4 of my Pressure Protection Valves were leaking, one much worse then the others.  The rig could easily keep up while driving and even passed the air brake test so I continued my trip.  Then when I was at a national park and stopped at the visitor center to look at the display and went back to the rig after ~45 minutes the alarm went off, I lost almost all the air pressure. 

That's when I decided to head home and fix the leaks.  Not really that difficult and cost to replace all the PPV's and other fittings was less then $200. 

Out of curiosity I took the PPV's apart, every one of them had severe corrosion.  Not sure why, never had a problem with my air dryer, no water in system.  But when I did some research the installation document for a PPV showed that they were originally stalled upside down.  There is a weep hole that is suppose to be pointing down so when it was originally pointed up any moisture in the valve would stay and probably caused the corrosion.  Attached is a picture of the PPV taken apart, all the white stuff is corrosion on the spring.  My guess is that as the PPV was being worked small flakes of the stuff would flake off and cause the diaphragm to leak. 

 

Jim, thanks. I’ll see if I can locate these on my rig and give them the soapy water treatment. I’d love for that to be my problem and to just replace them 

[96 EVO]

If a leaking PPV is causing your issues, the tanks will drain down without even applying your service brakes.

No PPV's in the service brake system.

[Frank McElroy]

On 3/4/2023 at 5:19 PM, 96 EVO said:

That won't work!

Your compressor can fill your tanks much faster than most air leaks!

Here's the actual test for leaking brake lines / cans........

@ Full Charge Shut off Motor  Listen for Air Leaks  Make Full Brake Application for 1 min pressure must not drop > 3 PSI

Ben you are absolutely correct.  DOT regs, call for engine off, parking brake off, full brake application and for 1 min, pressure must not drop >3PSI.  On my coach I get <3 PSI pressure drop in over 10 minutes.

[DZZippy]

Hey all. A lot of good information and everyone is accurate in my opinion. I have spent a couple decades working on fire trucks and emergency vehicles and obviously they have air systems and in many cases, more complex than our coaches. As an emergency vehicle technician, I had to follow DOT on top of a few more stringent items required by NFPA. Regarding air systems, the DOT tests that were referenced, are accurate. However there are a couple tests by DOT that are supposed to be conducted to detect air brake leak down rates as well. Some of these have been referenced already by you folks of leak down rates with engine off and engine running vs parking brake released, etc. In addition to,  air build up within a certain amount of time to pop off pressure based on engine speed. One of the other tests that I am referring more to in my replay, has to do with the engine running, parking brakes released, and service brake applied. The air compressor should still be able to maintain and build pressure to pop off by the governor. Based on the symptom / complaint, I have a feeling that test would fail. As many have eluded to, sounds like a leak on brake application side such as a ruptured diaphragm in a chamber of any sort (parking or not) on the service brake side, relay valve, or even “sense line” coming from the treadle valve (brake pedal) that goes to one of the relay valves. Possible hoses going from really valve to the service side of the chambers as well (I have found those to be insufficient many times). On a side note, if there is a ruptured diaphragm in a chamber, strong possibility that it will not produce bubbles with a soapy solution. The leak is internal of the chamber and can vent to atmosphere without producing bubbles inside the chamber. It does have a distinctive sound though. Just my $.02

[DZZippy]

30 minutes ago, DZZippy said:

Hey all. A lot of good information and everyone is accurate in my opinion. I have spent a couple decades working on fire trucks and emergency vehicles and obviously they have air systems and in many cases, more complex than our coaches. As an emergency vehicle technician, I had to follow DOT on top of a few more stringent items required by NFPA. Regarding air systems, the DOT tests that were referenced, are accurate. However there are a couple tests by DOT that are supposed to be conducted to detect air brake leak down rates as well. Some of these have been referenced already by you folks of leak down rates with engine off and engine running vs parking brake released, etc. In addition to,  air build up within a certain amount of time to pop off pressure based on engine speed. One of the other tests that I am referring more to in my replay, has to do with the engine running, parking brakes released, and service brake applied. The air compressor should still be able to maintain and build pressure to pop off by the governor. Based on the symptom / complaint, I have a feeling that test would fail. As many have eluded to, sounds like a leak on brake application side such as a ruptured diaphragm in a chamber of any sort (parking or not) on the service brake side, relay valve, or even “sense line” coming from the treadle valve (brake pedal) that goes to one of the relay valves. Possible hoses going from really valve to the service side of the chambers as well (I have found those to be insufficient many times). On a side note, if there is a ruptured diaphragm in a chamber, strong possibility that it will not produce bubbles with a soapy solution. The leak is internal of the chamber and can vent to atmosphere without producing bubbles inside the chamber. It does have a distinctive sound though. Just my $.02

I’m not going to try and side track this thread. I can definitely provide more information on the air system(s) in general if anyone wants, but I’m sure it will bore you and cure insomnia…lol

I figure someone else may have already put info out there on it as well but have not searched our plethora of info. Just want to help stay on target with the initial complaint / symptom

[96 EVO]

1 hour ago, DZZippy said:

I’m not going to try and side track this thread. I can definitely provide more information on the air system(s) in general if anyone wants, but I’m sure it will bore you and cure insomnia…lol

 

Wouldn't be the first time for me! I nodded off during my 2nd day of air brake training!

In my defense, it had been decades since I spent 8hr days in a classroom.

[Frank McElroy]

Here is a link to an air brake pre-trip procedure we have in our files.

 

[daveyjo]

This is probably not relevant, but I had a hard to find air leak.  Turns out it was a leaky air bag.  I just had to run my hand over the bag and it was obvious.

[Tom Cherry]

do not discount the WABCO DESSICANT DRYER in the rear engine compartment.  bubble test front and reae.  thwew are two sections and two separate valves.  if it leaks, price out the cost of a new one versus a tech rebuilding it.  mine would have been more.  i bought a new one