Air leak questions again

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Air leak questions again

November 02, 2013, 10:52:08 pm

I know this is an old topic to most but I need a bit of guidance.
I am slowly finding and fixing some leaks and have started under the front end. All leaks I think are fixed in lines coming off the 2 tanks, and am sure there are some in the rear section,but, first a question.
My gauges show a drop in pressure equally on both so does this mean that the one way valves on both tanks are leaking back to each? I did have some good leaks at the foot brake but fixed all those at line connections but could it be internal?? Has anyone had that on similar year?
My air bags do not change in weeks but can there be an air leak in either manifold for them regardless?
Can the 12v compressor line be suspect. I do not leave the auto switch on so it never runs.
What has the majority of you found to be the main causes of air loss. I loose pressure down to 30lbs overnight !!!
Thanks
John H

Re: Air leak questions again

Reply #1 – November 03, 2013, 08:19:51 am

my leaks were at the air compressor fittings.

Re: Air leak questions again

Reply #2 – November 03, 2013, 08:24:50 am

My system loses pressure down to 30lbs overnight and it doesn't bother me at all. There is no effect on over-the-road or parked performance. I believe that all air system connections leak, it's just a matter of degree. You can spend your life chasing leaks and spend your money replacing components, or just enjoy your coach.

Re: Air leak questions again

Reply #3 – November 03, 2013, 08:43:46 am

John, when I started chasing leaks one thing I kept overlooking were the dump air valves at the front and rear wheel wells. When I finally thought to soap them up all three valves in the front were leaking. My gauges were dropping at the same rate too. Replaced them all with good brass valves from a heavy truck parts store.

On edit: I have also had leaks at the at the 12v compressor desiccant filter and blowoff valve just behind it.

Dean

Re: Air leak questions again

Reply #4 – November 03, 2013, 08:47:51 am

The manifold and its' connections. If repairs have been made to the system, go back and give them a going over. Anything bleeding off in the dash area (yellow air button, etc..)? Replaced one on my Pete in 8 years (fwiw). Bleed valves. Small squirt bottle of soapy water can be a tool.
Good hearing & patience. pc

Re: Air leak questions again

Reply #5 – November 03, 2013, 08:51:29 am

Oh, and another one that was hard to find was the Hadley horn relay under the dash.

D

Re: Air leak questions again

Reply #6 – November 03, 2013, 10:41:55 am

John:

Your 12V compressor should have a one-way check valve to isolate the compressor. I replaced my 22 year old check valve at the compressor and that improved my bleed down alot. Now my pressure drops to approx 60 psi (both needles) overnight and then slowly goes down from there. After a week it will show about 30 psi. I'm happy with that.

Re: Air leak questions again

Reply #7 – November 03, 2013, 11:02:30 am

I had what appeared to be several leaks and could not find them. Finally Foretravel found that the bowls that collect water were leaking air and had tiny cracks. Removed bowl at awning box and did not replace, the one at the aux compressor replaced but I might consider removing it also as I never see water in it. Now my air will stay up above 90 psi for about
for 4 to 5 days. My aux compressor seldom comes on and if it does it will run for about 5 minutes and cut off. Good luck DAN

Re: Air leak questions again

Reply #8 – November 03, 2013, 12:08:23 pm

John,

Have you checked your parking brake control knob? Mine would leak when I twisted it around and would leak down overnight. I learned from Wyatt on his post how to repair it easily. If you pull it out there should be a serial no. on it for either replacement or repair. I completely repaired mine with an inexpensive kit that has both "O" rings made by Haldex Midland. Heavy Duty Truck Parts Online, Medium Duty, Light Duty - FinditParts There also is a 60psi pressure valve which is on a "T" connecting the air lines cluster under the steering column. The bubble test showed it leaking so I took it off and tightened the small bolts up and that seemed to have stopped it. Now it will lose about 10 psi a day and hold at 60 for quite a while. I can live with that.

Jerry aka Murph

Re: Air leak questions again

Reply #9 – November 03, 2013, 12:55:35 pm

As soon as the weather got cold I developed a bad air leak through the purge valve on my Bendix AD-4 air dryer. I just rebuilt the AD-4 at the end of the Summer, including the purge valve, check valve, O rings, and desiccant cartridge, and it was working better than ever until the weather got cold. Now my air system leaks down on both gauges and the electric compressor starts about every three hours, or more if the weather is really cold. I'm not sure what the connection is with the temperature. Maybe the rubber contracts as the temperature falls. For a long time I wasn't sure where the leak was, but once the weather got cold enough the leak got louder and I could hear the air hissing out of the purge valve. I got under there yesterday and confirmed it with a bottle of soap suds. I need to get a wood block or another heavy duty bottle jack to hold the suspension up when I release the air pressure. If I can find a suitable wood block I'll replace the purge valve today. If not I'll replace it next weekend... You might want to check your air dryer for a leaking purge valve. It happens often I'm told, and it apparently doesn't matter if you just installed a new purge valve recently.

Those of you who are familiar with rebuilding the Bendix air dryer, can I just remove and replace the bottom part of the purge valve to stop the leak or do I need to remove the end cover and replace the purge piston and the small O ring? I think I'm gonna try just replacing the bottom part of the valve from outside first to see if that stops the leak. According to the drawing it looks like the coil spring on the inside pulls the purge valve closed. It looks like the purge piston on the inside defeats the coil spring when air pressure gets high enough causing the purge valve to release a blast of air out the exhaust hose. If I can't get the leak to stop by replacing the purge valve from outside I'll have to remove the end cover to get to the inside. I don't want to remove the whole air dryer again. It's in a very difficult location on my coach. Most of the work is getting the air dryer out and back in again. Rebuilding the air dryer only takes a few minutes once you get it out.

Re: Air leak questions again

Reply #10 – November 03, 2013, 01:00:05 pm

Thanks for all your input, I will go out and do some looking. Thanks also for e-mails too guys.
John H

Re: Air leak questions again

Reply #11 – November 04, 2013, 11:58:10 am

Quote from: RRadio – November 03, 2013, 12:55:35 pm

I need to get a wood block or another heavy duty bottle jack to hold the suspension up when I release the air pressure.

I believe most of us have a set of blocks to place between the suspension members after it has been raised, when we go under the coach. I use 2 1/2" water pipe cut to about 11.5". Square steel tube with 3/8 wall thickness is better as it will not roll around when stowed. Wood will work, but would recommend 4 x 4 oak or other good hardwood not something that splits easily. The blocks go near the air bags for those that are wondering about that.

Re: Air leak questions again

Reply #12 – November 04, 2013, 03:11:20 pm

Slowly but surely I am getting rid of leaks. Changed both dry tank check valves although they were in good shape but did see a possible blow by mark on one diaphragm. Silly question coming next-- which air gauge serves which dry tank as I now have the lower gauge holding better than top and that will give me an idea of lines and devices to look for any leaks on that one system.
Thanks
John H

Re: Air leak questions again

Reply #13 – November 04, 2013, 04:07:18 pm

Sure is Dave, so now I have changed the oil and filters (simple from below) and able to do a thorough check of everything with out being a contortionist. Going to do a full clean up of engine exterior and tranny after finishing the greasing after lunch. To me this Pit has already paid for itself just in the fact I am now satisfied with the complete underbody and drivetrain after being able to do a full check of it all. Much better than having someone tell you it all looks good!!
One thing surprises me though and it is the fact that a lot of valves, check valves etc are in some crazy places to get to, why did they not put them in a safe lower location and just run longer air lines from them. Would make sense to me, especially if you do not have access to a pit or hoist.?? It would have made replacement or repair a lot cheaper and easier, even for FOT!!
Gotta get back while the sun is shining outside.
John H
ps- do you know which gauge serves which tank on a 2000 295. I could just turn the coach around and bleed down one tank but want to leave it the way it is right now so I can complete all the jobs.

Re: Air leak questions again

Reply #14 – November 04, 2013, 06:17:37 pm

and the gold waches go to --Pamela and Mike, and, Bill Chaplin for their suggestions to take off and check the "one way check valves" going into tanks.
Mine were looking good but I messed one up so got a new "generic" one and the pressure on tank gauges has held solid for 2 hrs at 120psi. I have not taken the wet tank one off or the inline one from Air Dryer so will do in morning. I want to see what happens then to pressures overnight.
My pit is almost paid for already with labour saved!!!
John H

Re: Air leak questions again

Reply #15 – November 04, 2013, 08:16:23 pm

John,

Mike said that finding those internal air leaks are the hardest to locate.

Pamela & Mike

Re: Air leak questions again

Reply #16 – November 04, 2013, 09:43:21 pm

Would a stethoscope be able to detect air leaks through the check valves without taking anything apart?

My air leak turned out to be the pneumatic temperature sensor on the back of the passenger side cylinder head which controls the radiator fan clutch. I have the rear radiator and the fan has a pneumatic clutch that's controlled by the temperature sensor. I realize your coach doesn't have a pneumatic fan clutch but other readers may benefit from this information. I called Foretravel today and was told they've never seen one of those go bad before and they don't have them in stock. I called Stewart & Stevenson, the Detroit Diesel service center, but they don't have one either. I'll have to search for the part. The sensor still works as far as I know and the leak isn't noticeable when the engine is running, but it makes my electric compressor run every 2-3 hours depending on how cold the weather is. I put a wood block near the airbags to hold the suspension up and shut off the breaker for the electric air compressor for now.

Re: Air leak questions again

Reply #17 – November 04, 2013, 11:42:45 pm

Pam and Mike, the only thing I am thinking is regarding those check valves, that when they were leaking ( obviously they were) then the air going back in the system must have been exiting (leaking) somewhere otherwise it would not have depleted. Or have I got it wrong??
I still do not know which tank is connected to which gauge. I have a feeling I read somewhere which is which but cannot find it. Once I have done all the things in engine end I will turn it around and open one of the tanks drains and that will tell me.
John H

Re: Air leak questions again

Reply #18 – November 04, 2013, 11:45:39 pm

Guess the top gauge is the front, bottom one the rear?

On my U225, I had two needles on one gauge, a white and red, forgot which was which now that the coach is sold.

Wish I had your beautiful pit near by.

Re: Air leak questions again

Reply #19 – November 05, 2013, 08:14:41 am

John,

If the check valves are leaking as you have found the air can escape out via:
1.The blow down on the bottom of the dryer if it isn't sealing properly
2.It can come back through the governor and escape through the valve unloader on the compressor
3.If the discharge check valve is leaking on the dryer it could back up and leak out through the compressor valves. (real remote possibility)

On another note on our '97 the front tank is the top gage and the bottom gage is the rear tank. (not the wet tank)

Pamela & Mike

Re: Air leak questions again

Reply #20 – November 05, 2013, 12:12:58 pm

That is funny (strange) in that I replaced the front tank check valve with a new one and the pressure is at 50psi (16 hrs later) and the rear tank valve I took off and cleaned up (they only had 1 valve-but ordered 2 more-so I can replace all) and that gauge reads 120psi still-NO LOSS in 16 hrs???
Hmmm? So I will look at schematics and try figure out what is served by this front tank and check all that out. I am still going to replace both valves when they arrive wednesday, but I would have thought it would be other way around, new-good old (cleaned up) not so good?
Thanks
JohnH

Re: Air leak questions again

Reply #21 – November 05, 2013, 01:05:58 pm

John, are you using schematic B-2254? On it there are only a few lines that are ONLY supplied by the front tank (slide cover, tank drain, Line 55 to regulator and front manifold, & line 63 which splits to front ABS valves and treadle valve).
The front and rear tanks each have two check valves and one protection valve, I replaced all of those and after cleaning and bench testing found a couple worth saving as spares. I also changed all of the push-to-connect fittings I dealt and that were easy to get to with to DOT compression types. Also replaced regulator to front manifold. After sitting for 7 days my dash gauges are both at 66 psi. I have identified some leaks along line 27 that supplies the rear manifolds, but haven't had time to chase them yet. Let us know what you find.
Regards, Dick

Re: Air leak questions again

Reply #22 – November 05, 2013, 03:19:15 pm

Dick mine is B 2036 so I gather that the different year has different #s.
I will look and see what it covers. I have no slide to worry about.
It will be cold under there now as we had a touch of snow last night but now gone here at Lake level but still in hills. Think I will put a heater in the pit with me!!!
John H

Re: Air leak questions again

Reply #23 – November 05, 2013, 08:03:22 pm

Well today back under and do some more checking.
Decided to take off the Dryer as I have had a full service kit for months and as it was last done in Oct 2010 at FOT so it was time. I was surprised how clean and dry it all was and although the filters looked good for a while longer I decided do it now. So, after changing everything out I put it back to work on the Outlet air connection and change the parts for the check valve. It was here that I got a shock, the seat and spring had been installed backwards so this "check valve" had not been doing the job for all that time !!! I have not aired up the system yet as am waiting for another tank check valve to arrive before I start it up. No wonder I have had problems holding air these last few years. The seat on this part was absolutely new AND the spring had wrapped itself around this seat. I will wait till I run the engine tomorrow before emailing FOT as want to make sure all is ok now. I will send them a copy of invoice too.
Here is picture of seat showing it has never done anything
John H

Re: Air leak questions again

Reply #24 – November 05, 2013, 09:41:11 pm

John,

Looks like you have found one of your major leaks. Now you see how hard it is to find a leak that is internal, you can't leave any stone unturned.

Pamela & Mike

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