Likely air leak locations

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Likely air leak locations

March 02, 2019, 06:53:50 pm

The air pressure on our 93 GV goes from full to empty in about an hour after killing the engine. We just spent 3 weeks at MOT having several things repaired, the air leak was supposed to be one of them. The air bags do hold air much better than they did but the tank pressure still leaks like a sieve and I'm trying to locate the source of the leak. The throttle started make a slight hiss a while back but today on our way to Eureka Springs it really started leaking while being depressed. So there's one leak and I'm hoping that I will be able to remove the throttle assembly some how and repair that leak while we're here. I have crawled around the coach but haven't been able to locate any other leaks. Is there any specific places that are more prone to leakage?

Thanks,
Tyler and Hannah

Re: Likely air leak locations

Reply #1 – March 02, 2019, 07:06:56 pm

Kiddie bubbles are your friend.

That size leak should be easy to find.

Yes, it could be several smaller leaks, but if it bubbles it is bad.

Re: Likely air leak locations

Reply #2 – March 02, 2019, 07:23:03 pm

Do you have a step cover? The control under our steps started leaking bad on a trip.

Re: Likely air leak locations

Reply #3 – March 02, 2019, 07:26:36 pm

That's what I thought as well. I figured that a leak that substantial could be heard and have spayed a lot of what I can access easily with soap and water but with no luck. I will continue the search! Haha

Re: Likely air leak locations

Reply #4 – March 02, 2019, 07:28:45 pm

We do have an air controlled step and I have not checked it! That will be the next place I check! Thank you

Re: Likely air leak locations

Reply #5 – March 02, 2019, 08:10:51 pm

Quote from: The Soft Boulders – March 02, 2019, 07:28:45 pm

We do have an air controlled step and I have not checked it! That will be the next place I check! Thank you

It might only leak when closed, open, or both. So check both

Re: Likely air leak locations

Reply #6 – March 02, 2019, 08:13:31 pm

Tyler,

Here is a link to the info you need for the treadle valve leak you are talking about. Williams Controls WM453109 Air Throttle Valve

You could have the check valves or related piping on your air tanks leaking air back into the air dryer. Here is a link to one of Chucks air leak repairs that may help you out.Air Tank Valves R&R Chuck is the go to guy when you have an air leak on a early 90's GV. When he sees this thread he will chime in.

Here is another thread that may help you out. Wet Tank Air Leak Fixed (Accidentally)

Pamela & Mike

Re: Likely air leak locations

Reply #7 – March 02, 2019, 08:30:55 pm

I like this stuff for leak detection.
Amazon.com: Snoop Leak 8OZ-SNOOP Snoop Leak Detector, 8 oz.: Industrial &...

It is a never ending quest. Kind of a game we all play. Sooner or later you get the really big ones and then get used to the small ones. Check the pressure protection valves on each of the two tanks. Mine both leak, I have replacements when I get to it. I also have a right rear ride height valve with a slow leak too. Replacements in my spare parts tub for when it becomes more annoying. Same with check valves. Sooner or later they all leak.

Prioritize. Fix what needs fixing now that prevents fun.

Re: Likely air leak locations

Reply #8 – March 02, 2019, 08:53:07 pm

I use this for air and refrigerant leaks, bid blue

Re: Likely air leak locations

Reply #9 – March 02, 2019, 11:11:59 pm

Tyler,

Those threads that Pam/Mike linked (above) have some good info in them. I have been poking around my air system for 5 years looking for leaks. I still haven't found all of them. Like most members, I've got our coach to where I can live with it, and that's good enough for me.

Do you have the air system schematic for your coach? It is very helpful in understanding the flow of air through the system.

Besides all the places mentioned in my old threads, here's some places you might check when you get a bottle of soap solution. Any air pressure regulator is suspect - they all seem to leak eventually. You should have one up at the front of your coach, just in front of the two air tanks. There is one under the steps that controls pressure to the step cylinders. The Bendix cruise control and air throttle assembly mounted on a plate on the engine compartment wall has several components that might leak. Another place where I had a leak was the parking brake control. I rebuilt it:

Bendix PP-1 Repair Kit.

Re: Likely air leak locations

Reply #10 – March 02, 2019, 11:47:03 pm

Thanks so much to everyone for the responses! I hate to admit it but I'm really out of my element with this coach. Things continue to go wrong at such a pace that I cant keep up. Add on top of that my lack of knowledge and not having a place to actually work on it only compounds my anxiety. The guys at the shop replaced 3 solenoids on the back six pack and the entire assembly for the front along with the petcocks for the tanks. They also fixed some other leaks in the system that they found. I'm a bit at a loss because they gave us the impression that we were good to go. That's neither here nor there now but if they couldn't find it I'm not sure how I'm supposed ha! We will read through all of the information that everyone provided and keep trying to chip away at it. We don't have a choice but to. Thanks again to everyone, we'd be totally lost if it wasn't for the people on this forum.

Re: Likely air leak locations

Reply #11 – March 02, 2019, 11:54:28 pm

I know it seems overwhelming at first, but you will work through it. I had absolutely zero knowledge of a diesel motorhome with air brakes when we bought ours. Had to learn it all 100% from scratch. This Forum helps a lot. For any question you have, try to use the search function and pull up appropriate old threads. More than likely there will at least be helpful information, if not the exact answer. If you search and don't find what you need, then ask! We'll help all we can.

Re: Likely air leak locations

Reply #12 – March 03, 2019, 06:59:33 am

Chasing air leaks is ongoing project. Look at it as a regular maintenance issue.

Re: Likely air leak locations

Reply #13 – March 03, 2019, 07:16:43 am

I'm like Chuck, when I first started researching motorhomes, I couldn't even spell diesel let alone know what other systems would be involved. Have I felt overwhelmed? Yes many times. But with the help of this forum and its search capacity, the great people willing to help with their time and advice and learning about my coach, I have come to enjoy figuring out how to fix and/or improve various items on my coach. In time you will undoubtedly look back and with a sense of pride say "That wasn't so bad, or I know where that problem is and how to fix it."

It is all just a learning curve which is part of the adventure. Yes, I hope to avoid some of the adventures ahead, but they will come and with everyone's help, I'm certain that it will become just another one for the records. When you do locate where your major leaks are, be sure to post what you find so that some other newbie (as we all were once) will find your advice and be able to resolve his/her issue.

Larry

Re: Likely air leak locations

Reply #14 – March 03, 2019, 10:34:43 am

Tho it seems like a slight hiss, the throttle leak may be enough to dump that much. My park brake hisses ever so slightly and when it does the tank drops quickly.
Chasing air loss should be considered a hobby , eternal job.etc. IMHO

Re: Likely air leak locations

Reply #15 – March 03, 2019, 11:07:53 am

On the throttle make sure you check all the air line connections.
Cylinders for the air step check the shafts that come out of cylinder for O ring leaks.
Tank check valves, all of them can cause leak back and I have replaced all 3 of them.
I found the check valve on my air dryer (main line to wet tank) was installed back to front so fixed that. That was first time in Nac after that I rebuild my own now.
Just some ideas.
JohnH

Re: Likely air leak locations

Reply #16 – March 04, 2019, 10:57:42 pm

My wife absolutely loves our Foretravel and can't wait to move in full time. I, on the other hand, am often overwhelmed by it. Were it not for this forum I would have bailed. On the other hand, drove back from Albuquerque last month in horrible winds and the exceptional road manners of a Foretravel were on display. I thought it was a little windy, opened the door to get some fuel and the wind nearly sent me flying through the parking lot. I had to use two hands to open and close door while bracing myself and still struggled to control the door. No problem driving. I try to remember this whenever I'm baffled by the air system, fuel system, and electrical system.

Re: Likely air leak locations

Reply #17 – March 04, 2019, 11:16:58 pm

Lots of little ones add up. Be patient!

Everyone is right, step is the 1st one. many tech's miss that one.

Re: Likely air leak locations

Reply #18 – March 05, 2019, 07:36:40 am

Went ahead and ordered the throttle rebuild kit chuck linked in his post. It was really dumping the air while using the throttle and has me concerned for safety. I also noticed for the first time that there are two needles on our air gauge. The white needle is perfectly aligned with the red as to make it nearly invisible. I'm not sure if the gauge is broken or if something else is going on but the two have never separated since we've had it.

Re: Likely air leak locations

Reply #19 – March 05, 2019, 07:56:18 am

My wife and I love the coach but at the same time i have to beware of the law of diminishing returns, as there are issues with it that are beyond the reasonable possibility of repair. That is the greatest source of my anxiety. It's a fine line to walk because there is absolutely no way to recoup the money we've invested already let alone the amount it will continue to cost to maintain. Now that it's our only residence though, not maintaining isn't an option.

Re: Likely air leak locations

Reply #20 – March 05, 2019, 08:02:25 am

Quote from: The Soft Boulders – March 05, 2019, 07:36:40 am

I also noticed for the first time that there are two needles on our air gauge. The white needle is perfectly aligned with the red as to make it nearly invisible. I'm not sure if the gauge is broken or if something else is going on but the two have never separated since we've had it.

One needle is for the front air tank pressure and the other is for the rear air tank pressure. It isn't broken as the 2 needles work on separate air feed lines.

Mike

Re: Likely air leak locations

Reply #21 – March 05, 2019, 08:36:44 am

Quote from: The Soft Boulders – March 05, 2019, 07:36:40 am

The white needle is perfectly aligned with the red as to make it nearly invisible. I'm not sure if the gauge is broken or if something else is going on but the two have never separated since we've had it.

Tyler,

The double needle air gauge is common to the older GVs. As Mike says, two separate air lines to the back of the gauge. One needle shows "front" air tank pressure - other needle shows "rear" air tank pressure. Both of these tanks, despite confusing names, are located under the nose of your coach behind the front bumper. On my coach, the red needle = front tank, and white = rear tank.

Although it is possible that both needles are always showing exactly the same pressure, I would say this is very unusual. Personally, I would like to verify the fact that both needles are, in fact, registering actual tank pressure. This can be done with a fairly easy test, but of course first you need to get your air system to the point that it will hold pressure for a reasonable amount of time (like overnight).

When you are ready to try it, see my next post for the test procedure.

Re: Likely air leak locations

Reply #22 – March 05, 2019, 08:58:39 am

Testing components of the coach air system can be fairly simple. To do so, it is most helpful to have the air system schematic for your coach. Without it, working on the system is very difficult. Try this test to check some of the important parts of system.

1. Run engine until air compressor cut-out pressure is achieved. Shut off engine. The entire air system is now at the same pressure.

2. Check (record) the reading on both dash air pressure gauges (or both needles, if single dash gauge).

3. Open the water drain valve on the WET tank (see air system schematic), and allow pressure to bleed off to zero.
3a. What came out of drain valve? Dry air is good. Water, or oily grey "mud", or dry white powder is not so good. Time to service dryer.

4. Check (record) the reading on both dash air pressure gauges (needles).

5. If both dash gauges read the same pressure in step #2 and step #4, then the inlet check valves on the respective tanks are good.
Clarification: With "good" check valves, the "front" and "rear" air tanks should not lose any pressure when you drain the wet tank.

6. If either, or both, of the dash gauges lost pressure between step #2 and step #4, the inlet check valve on the respective tank is bad, and should be rebuilt or replaced.

7. Locate your FRONT air tank (see air system schematic), open water drain valve, bleed off pressure to zero. (See note 3a above)

8. Check dash air gauge(s). One gauge(needle) should now show zero pressure - this is your FRONT tank gauge. Other should still read the same as step 4.

9. Locate your REAR air tank (see air system schematic), open water drain valve, bleed off pressure to zero. (See note 3a above)

10. The remaining dash gauge (needle) should now show zero. This is your REAR tank gauge.

Re: Likely air leak locations

Reply #23 – March 05, 2019, 10:46:06 am

I found the schematic and parts list with the treadle valve on it.

Re: Likely air leak locations

Reply #24 – March 05, 2019, 10:54:25 am

That air diagram is very helpful. See the numbers on the air lines? There are paper labels taped to all the OEM air lines - use them to help you find and identify the other valves and components. The physical location of things on the coach do not necessarily correspond to the position on the diagram, but you can get in the ballpark by tracing the air lines.

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