Need help with an air leak

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Need help with an air leak

February 03, 2020, 06:24:26 pm

My coach sat in heated storage without exercise for 3 months. As a rule we try to get it out once a month but I've hurt my back and am scheduled for fusion next month.

Last week we started it up to take it out for a couple of hours. It took longer than normal to air up and for the air dryer to purge. Once it did I backed it out, foot on the brake. At that point the low pressure alarm went off, both tanks dropped to 60 pounds and the brakes got mushy. I managed to stop, took it out of gear and applied the parking brake. Again, it took a while to air up and purge. Once it did I put it back in the garage and parked it.

I found a good mobile diesel truck mechanic to come change the D2 Governor. The old one rattled to I expected this was a good fix. My D2 is set for 125PSI as was the old one.

We tried again today. Once aired up I press the brake all the way down. The air dropped a little then stopped. I then pumped the brakes and the pressure on both tanks dropped like a rock to 60 pounds. I feel that if I continued the tanks would have dropped to zero.

I aired back up and shut the engine off. I walked around the coach listening for an obvious leak and didn't hear anything.

Unfortunately with my back injury I have limited mobility. I can't get under there and crawl around.

Any suggestions from the experts would be greatly appreciated! Where should I start?

Thanks all,
Jeff

Edited to add: Leveling is not effected. The coach stays up.

Re: Need help with an air leak

Reply #1 – February 03, 2020, 06:36:37 pm

Get another person to listen outside while coach is running, especially near the air dryer and go from there, can you somehow make
sure he put the D2 on correctly.

Re: Need help with an air leak

Reply #2 – February 03, 2020, 06:45:48 pm

See page 8, "Test Air Leakage Rate".

"Test Air Leakage Rate. With a fully-charged air system (typically 125 psi), turn off the engine, release the parking brake, and time the air pressure drop. The loss rate should be less than two psi in one minute for single vehicles and less than three psi in one minute for combination vehicles. Then apply 90 psi or more with the brake pedal. After the initial pressure drop, if the air pressure falls more than three psi in one minute for single vehicles (more than four psi for combination vehicles), the air loss rate is too much. Check for air leaks and fix before driving the vehicle. Otherwise, you could lose your brakes while driving.
Check Air Compressor Governor Cut-in and Cut-out Pressures. Pumping by the air compressor should start at about 100 psi and stop at about 125 psi. (Check manufacturer's specifications.) Run the engine at a fast idle. The air governor should cut-out the air compressor at about the manufacturer's specified pressure. The air pressure shown by your gauge(s) will stop rising. With the engine idling, step on and off the brake to reduce the air tank pressure. The compressor should cut-in at about the manufacturer's specified cut-in pressure. The pressure should begin to rise."

I also found this useful, "The In Cab Air Brake Test".

The In-Cab Airbrake Test | Layover.com

Re: Need help with an air leak

Reply #3 – February 03, 2020, 07:41:19 pm

No, what he is describing is NOT normal. If this only occurs when the service brake is applied, there may be a bad diaphragm in one of the brake chambers or bad air line going to one of them.

But, both gauges dropping at the same time due to a massive air leak-- wonder if a check valve is also suspect?

Re: Need help with an air leak

Reply #4 – February 03, 2020, 07:41:36 pm

Quote from: Jack L – February 03, 2020, 06:45:48 pm

What you describe, may be normal.

I don't understand this statement. Jeff's coach is not acting "normal" when he says:

"Once aired up I press the brake all the way down. The air dropped a little then stopped. I then pumped the brakes and the pressure on both tanks dropped like a rock to 60 pounds. I feel that if I continued the tanks would have dropped to zero."

The pressure should not drop like a rock to 60 psi. The air compressor should cut in at about 90-100 psi and recharge the air tanks.

It sounds to me like the new D2 was not installed correctly, and/or is not properly sensing the wet tank (RES) pressure. I would suggest some more experimentation to determine at exactly what pressure the air compressor is cutting in and out. Jeff knows from past experience how his air compressor should work, and what readings are "normal" on the dash air pressure gauges.

Re: Need help with an air leak

Reply #5 – February 03, 2020, 09:11:00 pm

From what I read if he steps on the brake pedal and holds it the pressure stops dropping. When he pumps the brakes continuously it drops. If a diaphragm or airline is bad it would drop while holding the pedal down. The compressor will not keep up at idle if you keep pumping the brakes. Jeff needs to get the pressure up and hold the brake, it should drop a little then come back up while he holds the brake pedal. Next when the pressure is up count how many times and in how short a period he is pumping the pedal. A relay valve would be more suspect to me.

Re: Need help with an air leak

Reply #6 – February 03, 2020, 09:28:24 pm

Thanks Craneman, I'll give it a try.

Re: Need help with an air leak

Reply #7 – February 03, 2020, 10:23:58 pm

Have someone go to each wheel while you push the brake pedal . The leak is post pedal , could be the pedal itself if both tanks show pressure loss .

Re: Need help with an air leak

Reply #8 – February 03, 2020, 10:34:41 pm

Thanks Mike

Re: Need help with an air leak

Reply #9 – February 04, 2020, 11:50:55 am

Just a thought. What about ice in the air lines. Is it cold were you are?

Re: Need help with an air leak

Reply #10 – February 04, 2020, 12:00:36 pm

Quote from: Big Al – February 04, 2020, 11:50:55 am

Just a thought. What about ice in the air lines. Is it cold were you are?

We are in heated storage to no ice.

Re: Need help with an air leak

Reply #11 – February 06, 2020, 08:41:31 am

Jeff, any updates on the leak?

Re: Need help with an air leak

Reply #12 – February 06, 2020, 08:46:51 am

Not yet Craneman. I ordered trailer hitch/safety stands that arrive today. I hope to head to storage tomorrow with a friend that will pump the brakes while I look for the leak. I also want to find the D2 on my DD 6V92 to see if that was installed correctly. I have old one, I want to compare and make sure correct ports were used on the replacement.

At least, this is the plan, depending on my back.

Re: Need help with an air leak

Reply #13 – February 06, 2020, 09:02:48 am

If you start it up and don't touch the brakes does the governor shut off the air compressor and dump air through the drier at 125 psi? if so it is working properly.

Re: Need help with an air leak

Reply #14 – February 06, 2020, 09:04:11 am

Quote from: Jeff & Sandy – February 06, 2020, 08:46:51 am

I also want to find the D2 on my DD 6V92 to see if that was installed correctly.

The air line from the wet tank goes to one of the bottom ports. The air line going to your air compressor goes to one of the middle ports. Top port is exhaust.

Haldex D2 Governor Service Data

Re: Need help with an air leak

Reply #15 – February 06, 2020, 09:28:24 am

Quote from: Chuck & Jeannie – February 06, 2020, 09:04:11 am

The air line from the wet tank goes to one of the bottom ports. The air line going to your air compressor goes to one of the middle ports. Top port is exhaust.

Haldex D2 Governor Service Data

Thanks Chuck. Is it possible to connect incorrectly?

Re: Need help with an air leak

Reply #16 – February 06, 2020, 09:37:49 am

Yes, but it will not function if the lines are hooked up wrong. It only controls the cut in and cut out of the compressor. Nothing to do with the brakes.

Re: Need help with an air leak

Reply #17 – February 06, 2020, 09:59:18 am

X2 what the other Chuck said.

If the 2 air lines were swapped at the D2, it would not function at all.

I think in that case your air compressor would never receive the "unload" signal, and would continue to compress air until something let go.

Hopefully it would be the safety relief valve on your wet tank at around 150 psi.

Re: Need help with an air leak

Reply #18 – March 04, 2020, 01:32:26 pm

Just to circle back it wasn't the D2 (replaced it) and it's not the brakes. We couldn't find any air leaks in the brake system today.

The Mechanic feels the issue is that the compressor (original) is taking too long to air the coach up or the braided air line from the compressor to the air dryer is bad.

I was losing air when pumping the brakes until the emergency brake deployed at around 40PSI. The coach would air back up slowly, eventually to 125PSI and the air dryer purges as designed.

When driving about a mile around a large, flat parking lot today, using the brakes to make the turns PSI didn't get above 70 PSI until I parked it and waited a while.

The mechanic will make another house call to replace the braided air hose next week. If that doesn't solve the issue he will replace the compressor.

Edited to add, the braided hose does look crimped at the compressor connection.

I do like this guy and he has a great reputation and has a very busy Deisel shop here in town. He doesn't want to take my money until it's completely resolved. He charged me $80 to replace the D2. He wouldn't accept any payment today. He traveled an hour each way and spent two hours under the coach.

Re: Need help with an air leak

Reply #19 – March 04, 2020, 01:43:41 pm

Quote from: Jeff & Sandy – March 04, 2020, 01:32:26 pm

Quote from: Jeff & Sandy – March 04, 2020, 01:32:26 pm
The mechanic will make another house call to replace the braided air hose next week.

Sounds like you have a solid mechanic. Hard to find guys like that. Sorry you are having issues and can get them resolved quickly.

When the mechanic does replace the braided hose, can you get a part number to share? It looks like a teflon lined hose. I do not need one now, but like to be prepared.

Re: Need help with an air leak

Reply #20 – March 04, 2020, 01:48:32 pm

Will do, DayDreamer. It should be next week.

Re: Need help with an air leak

Reply #21 – March 04, 2020, 04:57:01 pm

Quote from: wolfe10 – February 03, 2020, 07:41:19 pm

But, both gauges dropping at the same time due to a massive air leak-- wonder if a check valve is also suspect?

When I was at the Granvention last October I was told by Mark Crick that he spends a lot of time repairing or replacing check valves that are leaking and most people do not test for leaking check valves.

Re: Need help with an air leak

Reply #22 – March 04, 2020, 05:13:26 pm

We 'checked'. There are no air leaks in the brake system.

Mark and his family are awesome. We met his parents as well. We met last year, he did some work on my coach in South Dakota

Re: Need help with an air leak

Reply #23 – March 04, 2020, 10:15:26 pm

Quote from: turbojack – March 04, 2020, 04:57:01 pm

When I was at the Granvention last October I was told by Mark Crick that he spends a lot of time repairing or replacing check valves that are leaking and most people do not test for leaking check valves.

Does anybody have a good strategy for testing the check valves?

Since both service tanks on our coach will drain when the wet tank is drained via the water drain, I am assuming the check valve on the inlet to the service tanks has failed. I intend to replace them and will see if the service tanks hold air when the wet tank is drained. Is this a good way to test the service tank inlet check valves?

Any thoughts on how to test the wet tank inlet check valve, the shuttle valves on the service tanks, and the pressure protection valves on the service tanks? Any more of them?

Re: Need help with an air leak

Reply #24 – March 04, 2020, 10:31:18 pm

Quote from: DayDreamer – March 04, 2020, 10:15:26 pm

1. Since both service tanks on our coach will drain when the wet tank is drained via the water drain, I am assuming the check valve on the inlet to the service tanks has failed. Is this a good way to test the service tank inlet check valves?

2. Any thoughts on how to test the wet tank inlet check valve?

3. the shuttle valves on the service tanks?

4. the pressure protection valves on the service tanks?

1. Yes. What you did is the gold standard test for those check valves. They have failed. Either clean them & reuse, or replace them.

2. No. If in doubt, take it off and inspect it. If condition is doubtful, replace it.

3. No. If in doubt, take them off and inspect them. If condition is doubtful, replace them.

4. It is possible to check the protection valves by doing the following:
a. Pressure up the wet tank to about 100 psi.
b. Open (disconnect) one of the air lines downstream of the protection valve on one of the brake tanks.
c. While the air pressure is escaping from the open line, watch the pressure gauge for that tank.
d. If the protection valve is working properly, the pressure in that tank will stop decreasing at about 50-60 psi and hold.
e. If the pressure in the tank keeps falling to zero, that protection valve has failed.
f. Then do the same test for the protection valve on the other brake tank, starting from Step A above.

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