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Air Leak


dandick66
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I’m looking for some advice on where to start looking for an air leak.  Here are my symptoms and readings.

With parking brake on:  compressor cuts off at 115.  Pressure starts dropping as follows: 110 - 8 seconds, 105 - 21 seconds, holds at 104 for over 2 minutes and 30 seconds, so I pushed brake several times to get compressor to kick back in.

With parking brake off: compressor cuts off at 115.  Pressure starts dropping as follows: 110 - 9 seconds, 105 - 20 seconds, 102 - 51 seconds, 101 - 1 min 2 seconds, 99 - 1 min 30 seconds, 98 - 1 min 50 seconds, 97 - 2 min 1 second, 96 - 2 min 15 seconds.  Compressor cuts back on at 95 and shuts offf at 115 (37 seconds).

parking brake off, depressing service brake.  Compressor cuts off at 115:  102 - 5 seconds, 90 - 15 seconds, 85 - 23 seconds, 80 - 32 seconds, 75 - 36 seconds.

I’m not sure where to start looking.  I know I need to get some soapy water, but I don’t think I need to be looking at the air suspension.  Any ideas are appreciated.

Dan D, 2012 Diplomat 43DFT  

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I would say shut it off, have someone stand on the brake while you go around and listen. With this sort of a leak from the braking system you should be able to locate the area to investigate closer? Maybe listen around the brake pedal area first.

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23 hours ago, Dr4Film said:

In case you don't have this Air Brake Test procedure I have attached it for people to use.

Good luck in looking for your problem. If it were me I would take it to a trusted truck repair service shop for them to troubleshoot and repair. Air brakes are critical so they need to be in tip-top condition.

Air Brake System Test.pdf 237.47 kB · 3 downloads

Richard,

May i have your permission to share the Air Brake Test  pdf  with another site membership i am a member of?

Thank You

Paul A

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1 hour ago, Paul A. said:

Richard,

May i have your permission to share the Air Brake Test  pdf  with another site membership i am a member of?

Thank You

Paul A

Absolutely Paul. It's there to help people make sure their critical air brake system is working correctly. This trip from Florida to western NY I took some routes that were new to me which had some awful steep grades both up and down.  Sure glad my brakes worked great as they were much needed on some of these rolling grades in West Virginia and PA.

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On 7/19/2020 at 5:15 PM, Dr4Film said:

In case you don't have this Air Brake Test procedure I have attached it for people to use.

Good luck in looking for your problem. If it were me I would take it to a trusted truck repair service shop for them to troubleshoot and repair. Air brakes are critical so they need to be in tip-top condition.

Air Brake System Test.pdf 237.47 kB · 10 downloads

Thanks for the file.  It appears my unit is failing both the static and applied brake tests. Unfortunately, I am having difficulty getting accurate pressure readings.  My dash has gauges for both the front and rear tanks, but they only register when the ignition is on.  I have a feeling they are electric gauges with some type of transducer for reading the pressure.  I will try to look at them today.  Here in Virginia, we are in a heat wave for the past 2 weeks and the foreseeable future.  It has been in the mid 90’s!  
 

I do have front and rear tanks readings available (digital display) from my Medallion instrumentation.  The problem is, it only works when the engine is running, and if the pressure is low, it alarms and flashes between “Front Air Low” and “Rear Air Low”.  Once they build up pressure he display will indicate the pressures.  I was thinking about installing a mechanical gauge and was considering installing two Viair 90087 gauges.  I’m thinking that I would need some type of adapter, and “T” into the fron and rear hoses.  Has anyone here done anything like that (successfully)?
 

I received the attached file from REV yesterday.  It reads like a real schematic and I was impressed they had it and sent it to me.  The print is pretty small , but I will try to figure it out.  Note: I also submitted the file to the Downloads section so it should be available for all.

Dan D

18623342_B (Schematic Pneumatics DEKA 43ft) Model (1).pdf

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I don't know why the electric gauges would be a problem, most newer OTR trucks use them and the ignition is supposed to be ON for the air brake test. Otherwise you would not even hear the buzzer. And your diagram shows the transducers too. Other than knowing that the tanks are full prior to looking for a leak, you don't need them for this activity. Just my opinion...

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On 7/20/2020 at 6:22 PM, Dr4Film said:

Absolutely Paul. It's there to help people make sure their critical air brake system is working correctly. This trip from Florida to western NY I took some routes that were new to me which had some awful steep grades both up and down.  Sure glad my brakes worked great as they were much needed on some of these rolling grades in West Virginia and PA.

 

On 7/21/2020 at 11:39 AM, Ivan K said:

I don't know why the electric gauges would be a problem, most newer OTR trucks use them and the ignition is supposed to be ON for the air brake test. Otherwise you would not even hear the buzzer. And your diagram shows the transducers too. Other than knowing that the tanks are full prior to looking for a leak, you don't need them for this activity. Just my opinion...

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31ED8FAC-1BBD-41D1-A426-04F7F715FD67.jpeg

If you look at the photos, you can see that the gauges are not real user friendly.  There is no way, you could determine a 2 PSI drop in one minute.  It would be tough to tell a 30 or 40 PSI drop.

i just went out and started it up and let the compressor cut off, then I shut down the engine and had my wife mash and hold the brake.  I could not hear any leaking/hissing, so I guess I’ll be looking for a truck shop.  There is a commercial bus garage near me.  Maybe they will look at it.

Dan

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Your initial 10 psi loss after purge is normal for a meritor Wabco SS1200 dryer.  The regeneration valve opens and uses this tank air to prepare the desicant filter (dry's out the beads), for the next cycle. Usually stays open for 15-20 seconds or so. Fairly low flow of air. 

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I had 3 fittings on my front air tank leaking.  You could hear one and soapy water found the other 2. My pressure would hold for brake tests, but I'd be at zero overnight.  Replaced those 3 fittings and now all is well. 

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I did find a small leak at the “mini tank” and fixed it.  I’m still trying to understand how the entire system works.  I’ve read a lot, but I don’t think I fully understand it.

Here’s what I know/think.  The air compressor feeds the dryer.  The dryer feeds the front tank and the front tank feeds the rear tank and what I call the mini tank.  It’s the one that has the small electric compressor connected to it.  I know there are check valves and valves to prevent the pressure from dropping too far so that the brakes don’t work.  When I discovered the leak at the mini tank, I opened the drain valve on it and it seemed like it took a long time to drain for such a small tank.  What I discovered was that when I opened the mini tank drain, it drained the mini tank, but it also took air from the front and rear tanks and lowered their pressure to 65 PSI.  
 

I did stop by the bus garage last week.  When I explained the symptoms to the service manager, he immediately said I had a leaking brake chamber.  He said they could look at it,  but I’d be at the “back of the line”, as they have to keep their buses running and normally only work on their own stuff.  I’ll check with him again this week to see when/if is a good time to bring my coach in.   Something I wondered about over the weekend... when I push the brake pedal, both front and rear tanks drop pressure pretty much equally.  If I had a bad brake chamber, wouldn’t I see the front or rear tank drop pressure first?

Dan D 

2012 Diplomat 43DFT 
 

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I agree with your thinking. The pressure drop stops because your pressure protection valve kick in to preserve air for your vital system, brakes. I would look for a leak in auxiliaries, add on systems like step cover, horns, vacuum generator, leveling and such. It helps to have air plumbing diagram and know what's feeding what past the PPV. These could be the smaller lines. Check valves are not always totally stopping a backflow either.

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10 minutes ago, Ivan K said:

I agree with your thinking. The pressure drop stops because your pressure protection valve kick in to preserve air for your vital system, brakes. I would look for a leak in auxiliaries, add on systems like step cover, horns, vacuum generator, leveling and such. It helps to have air plumbing diagram and know what's feeding what past the PPV. These could be the smaller lines. Check valves are not always totally stopping a backflow either.

Thanks for the reply, but if I had a leak in the auxiliaries wouldn’t the pressure drop at a steady rate?  Mine loses a little, but it loses a lot when the brake pedal is pushed.  I did get the schematic from REV.  It is in an earlier post.

Do you know if I could safely clamp off the line going to the rear tank for troubleshooting purposes?  I don’t want to damage the air line and I’ve looked online and couldn’t find an answer yet.

Dan D, 2012 Diplomat 43DFT 

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Pressure drops significantly every time you hit the brakes but should not drop more than 3 psi from that initial drop in one minute while standing on the brake. Don't know about clamping a line but if you don't need it in the picture, it can be removed from the front tank and plug the tank. Just be super careful, it was mentioned many times earlier about the coach dropping down on someone... no air in tanks, suspension supported and such.

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1 hour ago, dandick66 said:

I did find a small leak at the “mini tank” and fixed it.  I’m still trying to understand how the entire system works.  I’ve read a lot, but I don’t think I fully understand it.

Here’s what I know/think.  The air compressor feeds the dryer.  The dryer feeds the front tank and the front tank feeds the rear tank and what I call the mini tank.  It’s the one that has the small electric compressor connected to it.  I know there are check valves and valves to prevent the pressure from dropping too far so that the brakes don’t work.  When I discovered the leak at the mini tank, I opened the drain valve on it and it seemed like it took a long time to drain for such a small tank.  What I discovered was that when I opened the mini tank drain, it drained the mini tank, but it also took air from the front and rear tanks and lowered their pressure to 65 PSI. 

Dan D 

2012 Diplomat 43DFT 
 

The air goes from the air dryer to the Wet Side of the front tank then to dry side of the front tank then finally to the rear tank. That is so the rear tank will not have any water in it as that one is used for the rear air brakes plus the spring  emergency brakes. The front tank services most of the accessories such as horn, step cover, dash vent controls, etc. s well as the front air bags and air brakes. The rear tank services the rear air bags, air brakes and spring brakes.

 

Edited by Dr4Film
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  • 1 month later...

UPDATE AS OF 04 SEP

I took the coach to a shop that works on buses.  They found 2 brake hoses were leaking (front passenger side and rear drivers side drive axle). These are the large hoses that run from the brake relay valves to the brake chambers.  They also replaced the governor.  Total cost for parts and 4 hours labor was $467.  The governor was only $20, the brake hoses were about $15 per foot.  I brought the coach home and it leaked down enough overnight that the low pressure alarms came on.  I took it back to them and they had it a few days and said the new governor was leaking so they replaced it and the next new one leaked, too.  So they ordered a Haldex governor and it works fine. He said I might still have a leak in the suspension system but he didn’t have any info on the leveling system computer (I told him I didn’t think it had a computer in the leveling system).  He said he had done everything he could and I’d need to take it to someone who knows about the leveling system.  Fortunately, he didn’t charge me for the additional work. 
 

I noticed that my auxiliary compressor fuse keeps blowing, so I don’t know what’s going on with that.  I sprayed soapy water all around the auxiliary compressor and tank and have a few leaks.  I don’t know if they are leaking enough to lose about 70PSI overnight, but I’ll find out.  It looks like the auxiliary compressor and tank are on a bracket that I can unbolt and remove both components.  I’ve ordered some fittings and plugs, so when they arrive I’m going to plug the lines and isolate the suspension and air horn from the rest of the air system.  I’ll run it up until the compressor cuts off and see if it holds air overnight.  While I have the auxiliary compressor out, I’ll figure out if the compressor is shot or not and I’ll fix the leaks I found.  One of the leaks appears to be from the bottom of the small tank. It looks to be some kind of pop off valve as it has a small ring in n the bottom and is spring loaded.  
 

I’ll update this when I get the parts and get some troubleshooting completed l. Ideas and/or suggestions are welcome.  By the way, leveling system is Power Gear/Valid VTL01K049

Dan D, 2012 Diplomat 43DFT

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Man, thats tough.  Sorry to hear about all the troubles.  If you haven't checked it, check you emergency brake fitting at the pull out knob too.  Mine had a minor leak there, but enough to be aggravating.  I didn't know til I had it out of the dash. 

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22 hours ago, Steven P said:

Man, thats tough.  Sorry to hear about all the troubles.  If you haven't checked it, check you emergency brake fitting at the pull out knob too.  Mine had a minor leak there, but enough to be aggravating.  I didn't know til I had it out of the dash. 

Thanks.  I think I’ll be able to see the fitting if I remove the top dash pad.  I will check it out once I get all my fittings together.

When I started the coach the other day it had very close to zero PSI in both tanks.  Now I’m wondering if I still have leaks in the brake system, too.  I thought the PPV was supposed to stop airflow in the direction of the suspension when the tank pressure drops to about 75 PSI.  It’s really tough to find accurate descriptions and information on how the system is supposed to work.

Dan D, 2012 Diplomat 43DFT 

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Mine would leak out overnight and was leaking from the swivel fittings at the tank. By AM, I'd have zero pressure.  Fixed those and now it only loses maybe 30lbs? overnight.  I can live w that.  Have you done a brake check to make sure your brakes fall within the correct parameters?

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4 hours ago, Steven P said:

Mine would leak out overnight and was leaking from the swivel fittings at the tank. By AM, I'd have zero pressure.  Fixed those and now it only loses maybe 30lbs? overnight.  I can live w that.  Have you done a brake check to make sure your brakes fall within the correct parameters?

I did the brake check and it passed.  This was after they replaced the 2 hoses.  Also, the service manager at the bus garage told me he sprayed the soap mixture all over the tanks and fittings.  I have no reason to think that he didn’t check everything he could think of.  However, like I said before, he did tell me that there might be something leaking in the suspension system.  I don’t think he knew where the auxiliary compressor and tank were located on the coach.  My fittings and hoses are supposed to be here late next week.  Once I get them, I’m going to isolate the air suspension and horn and see if  the leaks go away or leased.  I also picked up a dual needle pressure gauge.  That should give me much better resolution so I can have a better idea of how much air is leaking out.  

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My air pressure would leak down over night too.  I leak checked and only found a few very small leaks.  I level manually and usually leave the front a little higher than the back so rain would drain to the rear.  I realized that the rear leveling solenoids were never being energized.  So I manually bumped the up and down arrows a few times on the rear as well as the side solenoids.  I do this routinely when parking, and my pressure stays up for weeks.  04 Windsor

 

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There are many good suggestions here.  I would add that my "elusive" leak turned out being from my treadle valve (brake pedal valve) area.  I will never know if it was the treadle valve itself or just the push-to-connect (PTC) hose fittings, because it was such a bitch to get to that I replaced the treadle valve, all its PTC fittings and hoses at the same time.

I have also had significant leaks from the parking brake valve and from ALL Pressure Protection Valves (PPV).  It has been a long, time-consuming process (not very expensive for just the parts) but now the suspension will stay at ride height for weeks and the coach tank pressures take almost a month to decline to 30 PSI.

I have had better luck simply renewing all connections than chasing leaks with liquid soap.  Most of the PTC fittings have enough extra tubing that you can release the tubing from the fitting, cut it off past where the seal rode and reconnect.  Be sure you cut the tubing off squarely on the end and use nothing but a razor blade to cut it cleanly.  NEVER cut it by using dikes (side-cutting, plier-like tool).  You release the tubing from the connector by PUSHING the release collar inward toward the fitting.  After inserting the newly-cut tubing, pull the release collar away from the fitting, then give the tubing a good tug to be sure the inner collet has gripped it tightly.

As Ivan said, you can sometimes hear a leak, even a small one, if things are very quiet.

Good luck!

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We should all meet somewhere and have a air-leak party.   I’m in the same boat, my tanks emptying overnight.    I’ve heard the parking break leaking, I can torque the know and not hear it anymore.    I know that doesn’t mean it’s not leaking. 
 

I keep a supply of o-rings and o-ring ointment for the HWH air leveling solenoids in the coach, is there a better replacement for them?
 

The last leak I fixed was on the tag axel soleniod, Push to connect fittings had lost its springiness.  
 

Good luck chairing leaks.

 

Granville Barker

05 Dynasty

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My fittings and plugs arrived yesterday, so I will start troubleshooting soon.  I was wondering about PPV’s.  I understand if one is leaking, you could see the leak with bubbles or hear it.  But, is it possible for the valve to be defective internally where it would allow air to flow all the time?  If so, is there any way to test it?
 

Also, Please look at the attached drawing and parts list.  Can someone tell me what item E8 “VALVE RELAY 2 WAY CHECK” is?  How can a check valve be 2 way?  Also, item O6 “VALVE PRESSURE PROTECT “, the parts list indicates a quantity of 1, but if you look at the drawing, you will see there is 1 on the front tank and 2 on the rear tank.  Lastly, please look at sheet 3.  Towards the bottom of the sheet is the drawing of the air dryer assembly.  But look at the top of the sheet (above the air dryer drawing) and it lists item J2 “DRYER AIR, BENDIX”.  Are there 2 air dryers,  or is there some other drying device that I should be looking for?

Thanks,

Dan D, 2012 Diplomat 43DFT 

18623342_B (Schematic Pneumatics DEKA 43ft) Model (1).pdf

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