I have an air leak

David Anderson · April 04, 2011, 06:50:41 PM

I was driving through Oklahoma and noticed my air was cycling about every 90 seconds. I stopped and checked for leaks but couldn't hear anything. I drove a bit farther and it seems to slow for a while then continued about every 90 seconds. We spent the night in Miami OK and I checked the next morning while parked. I could not get it to leak down. Drove for a while and it started again. It only leaks while driving, not any when the parking brake is engaged. We made it to our destination and I started the bus this morning, aired it up, released the brake, it never leaked a drop. I tried cycling the service brakes, cycling the parking brake. It held pressure like normal. I left the parking brake released, turned of the bus and after 4 hours it had about 65psi left. That's about normal for me in the past.

What am I missing? I crawled under the coach and sprayed all the relay valves with soap and got no bubbles. Could it be the governor at high rpm? I don't have a clue.

We are in Bethany MO for 2 weeks then on to Washington MO for our Katy bike trail trip. I'd like to get this figured out before we leave.

David

niles500 · April 04, 2011, 07:23:09 PM

If you have an Air Dryer it might be that or possibly the unloaders in your comp. need rebuilt - HTH

luvrbus · April 04, 2011, 08:10:46 PM

Could be one of automatic tank drains David you just installed a new compressor did you not

good luck

David Anderson · April 05, 2011, 06:22:49 PM

Quote from: luvrbus on April 04, 2011, 08:10:46 PM
Could be one of automatic tank drains David you just installed a new compressor did you not

good luck

I didn't know I had an automatic tank drain. If so, how does it work, and yes a new compressor last fall. Also a new air dryer back in December. I can't duplicate the problem while stopped even with the parking brake off.

David

buswarrior · April 05, 2011, 06:49:34 PM

It is possible to have had some bit of junk stick in an exhaust, and then it happened to finally blow out.

What style of parking brake do you have?

I'd take it out for a drive to be sure this isn't a dynamic issue that sitting still hides it.

happy coaching!
buswarrior

Busted Knuckle · April 05, 2011, 08:10:58 PM

It's not coming from the passenger seat is it?

Jest checking, I'll run & hide now!

BK

niles500 · April 05, 2011, 11:02:33 PM

With all that new info I'm now in the ballpark of new governor (but I'm not a wrench - just a parts replacer) - FWIW

P.S. - Have you had it out since replacing the air dryer in December?

brando4905 · April 06, 2011, 05:16:07 AM

Do you have an air throttle? Just a guess. I had a problem with mine leaking air while accelerating last year, had Luke replace it, all's well now.

luvrbus · April 06, 2011, 07:58:07 AM

David, if your's haven't been removed Eagle have automatic drains (looks like a relay with no lines) on every tank,sometimes they leak at high pressure,low pressure or vibration will cause leaks driving the one on the tank buy the drop box is bad about leaking because of it's location getting all the road junk.
Not hard to rebuild David just 4 bolts and Jefferson has the kits,I always kept mine even with the guys here saying toss the automatic drains mine never gave me a problem

good luck

scenicruiser997 · April 06, 2011, 08:08:05 AM

David, I just went through the same thing. I rebuilt the air throttle only to find that was not the case.
When I was running down the road it too was cycling pretty fast, but when I pulled over, set the parking brake, I could not hear anything. But when I parked the bus and chocked the wheels and released the parking brake, you could hear the air rushing out of somewhere behing the rear wheels. It had me fooled at first thinking it was a DD3 Brake Can leaking, but after pulling the passenger side tires off, you could hear it coming from the Inversion Valve. The TR-2 Inversion Valve was leaking. Just replaced it and that fixed the problem. Aaron just south of Tulsa, OK.

luvrbus · April 06, 2011, 09:21:08 AM

Never saw a inversion valve on a model 10 with spring brakes before ?

good luck

rv_safetyman · April 06, 2011, 03:23:00 PM

David, you and I both have Houston Metro buses. Mine had mechanical drain valves on each tank - not automatic.

Jim

norwest AL · April 06, 2011, 04:02:37 PM

I had this same problem on my kenworth constant cycling.i figured out that when the compresser unloaded, air was leaking backwards into the compresser. Check the first tank for a stuck check valve.

David Anderson · April 06, 2011, 06:28:31 PM

Lots of replies. Thanks for the help. One other piece of info. Both gauges are dropping simultaneously. I think check valve (48 in the manual, Figure 12-10) must not be working. I need to diagnose that. If I air up the bus and open the towing air supply tee and let the wet tank drain its air, shouldn't the front tank and the aux tank stay charged? I've read the book a couple of times, but my lack of practical experience with the system is a shortcoming.

I won't drive the bus again until Apr 16. I'm hemmed in by 32 RV's right now at the jobsite. This is the biggest crew I've worked with and we will raise 70' trusses to the walls on the building tomorrow. That is also the longest truss I've ever laid up too. Should be lots of cameras out here tomorrow. I plan on driving the bus to Washington MO on the 16th. I'll have time to stop, chock the bus and search for a leak if it replicates itself again.

My manual shows a DV2 auto drain valve on the rear tank. Jim says we don't have one. I took a mirror and shined a light behind the mud shield on the bottom of the rear brake tank and only found a manual drain. Unless it is somewhere else, I don't have one.

I don't have an air throttle.. I don't show an inversion valve in my Eagle manual.

David

buswarrior · April 06, 2011, 06:50:40 PM

Hello David.

What year is your coach?

With two gauges, I'll assume you have a dual air system, and comments from other Eagle owners suggest you don't have DD3 parking brakes.

Assuming correct functioning, if both tanks are dropping, it could be a parking circuit problem, and we need to see the schematic for how the auxiliary get's its air supply.

A failed check valve should not cause a loss of air by itself, it would only allow the air from somewhere else in the system to drain when it wasn't supposed to.

Leaking spring brake relay valve, or spring brake chamber? Again, some migrating junk someplace that subsequently moved, or something sticking and then moving/sealing properly for the moment?

What is this "towing air supply tee" and was it engaged/operative at the time, where is it plumbed, what protects the coach from its failure and what was attached to it?

You should be able to air up the coach, and then drain the wet tank, and the front and rear tanks should stay fully aired up. Depending on where your auxiliary is fed from, and what protection it has, will determine whether it should be staying aired up or not too.

You should further be able to drain the front or back and the other stays fully aired up.

Depending on where the aux is plumbed, and its protection, you should be able to drain it and the other tanks not empty, either at all, or below some set point.

Keep feeding us info, we'll get to the bottom of this!

happy coaching!
buswarrior