Chasing Air Leaks

[dalej]

Just to add a bit, I was adjusting the brakes after I was done with the seal job. When I released the air in the brakes, took it off park brake. I heard a leak in the air line. It was the line that feeds the drive axle to keep the spring from setting the brake in case you loose air. It had to be leaking for a while, just can't hear it while you driving down the road.

I don't think I have ever checked for leaks with the park brake off.

Learned somthing else today.

[Joe Cannarozzi]

Dale

A 3 part process.

First you need to get the thing to hold air with parking brakes set.

When you get to that point then you can release the parking brakes and listen and watch the guages. This would be the emergency air leaks your now listening for.

Last but not least with the parking brake released and no leaks, step on the brake pedal and hold to listen for service air leaking.

The maxis on the drive axle have 2 lines going to them 1 is emergency air and the other is service air. The tag has only 1 line supplying it, service air only.

Chasing emergency leaks and service leaks are reletivly easy to find and fix. Getting the bus to hold air in general is the tough one. You can't really begin to check for emergency leaks(brakes released) until you first get the system tight enough to be able to tell that the loss of air, if any, with the parking brake released, is from an emergency source and not just a leak in general.

[Jon Wehrenberg]

For those of you with manual slack adjusters (and you know who you are!) if you are under the bus greasing it, why aren't you also adjusting your brakes each time?

If you were doing that you would have your emergency brake off every time, and would have early detection of a leak.

Now that I have preached....I have automatic slack adjusters and I do not release my emergency brake and look for leaks as often as I should.

[Joe Cannarozzi]

Heck Jon we have auto adjusters on our 86 how far back do you have to go?

[dalej]

He was talking to me, I should have known better.

[Jon Wehrenberg]

I think Joe has had his slack adjusters changed if he has automatics.

All I know is my 87 had manual adjustment. I don't know what year the automatic slack adjusters were first installed.

I have to be careful picking on Dale. I want a friend that can tell me how to get my wife to break down my wheels and polish them.

[BrianE]

Just before leaving home in February, in an effort to correct a slight right lean, I discovered a leaking 5 port Norgren in the right rear leveling position. When I replaced the valve the leans didn't get any better but the lure of the highway won out and off we went. Since then I have rolled around under the bus, in the dirt, and replaced both the primary air tank check valve and the rear brake quick release valve, both of which were leaking and neither of which were contributing to the leans. Enough was enough so we squared off the corner heading towards Kerrville and spent 3 days at Prevost in Fort Worth.

At first it was discouraging to see the "experts" going through the same soapy water trouble shooting routine that I had been exercising time after time with no results. I was dismayed to see they didn't use any kind of listening device, ultrasonic or otherwise. The Fort Worth folks told me they were not aware that ultrasonic leak detectors even existed! Prematurely, I then jumped to the conclusion that the decision not to use listening gear was an attempt to prolong the trouble shooting process. My first reaction to this assumption was to write a scathing commentary about these guys to my POG buddies. Luckily good sense prevailed and before getting out the poison pen I called Bill Jensen, Service Manager of the MH division who, after giving me a very informative air leak trouble shooting lesson, agreed to order an ultrasonic leak detector for the Fort Worth shop. In less than an hour David Jacoby, the Fort Worth Manager informed me he had an Amprobe (thanks Jon) ultrasonic detector on its way.

Bottom line of the whole experience however is that leaks were detected in two airbags using soapy water, leaks that I had completely missed. The leaks were found by guys that do it every day and unlike an amateur like me, know where and how to look. I also picked up a number of tips on finding leaks, such as raising the tags in order to eliminate them from the puzzle and that internal leaks in Norgren valves usually vent to the atmosphere if you know where to look.

In conclusion, I need to apologize to the Prevost folks for jumping to conclusions. I also need to thank them for only charging me for six hours labor when I know they spent over 10 hours on the problem. At $92.00 an hour its pretty easy for us to be critical of Prevost maintenance and to avoid them if possible. I for one, won't hesitate to use them in the future when I get in over my head. I'm only sorry that they don't have a northwest location.

[Jon Wehrenberg]

Brian has made some excellent points. Because of the huge number of potential places for leakage in our coaches there is no single way to find leaks. I hope Brian is willing to share in greater detail some of the techniques.

When I have to start chasing leaks I will first rely on my ears. I just get it as quiet as possible in the garage and air up the coach and its systems and start listening. If I think I hear something I use my stethoscope, first with the funnel on the end and then with the long probe.

I also use soapy solutions whenever I am in the area of a leak I can hear.

But not all leaks can be pinpointed using a stethoscope or soapy solutions. That is when the ultrasonic leak detector comes into play.

When we deal with leaks at POG III it will be easier to understand why some leaks are almost impossible to find. I have sympathy for the Prevost techs because I have screwed with leak detection on Liberty coaches for 17 years and I still do not understand exactly how the system works or how many places I need to look when the leak is making the coach lean a specific way. The Prevost techs deal with every different converter's systems and they often lack an understanding not only of the system, but the age or condition of the very components that are part of it.

[Just Plain Jeff]

Per Jon: -->I have sympathy for the Prevost techs<--

(Cue the Halleujiah Chorus!)

Anyway.

I've posted this somewhere before, or not, having senior CRS.

About six years ago we had an air failure while in Maine. Went to Prevost at St. Nicolas, company service facility.

They have made a rolling air-system diagnostic machine. It puts air into the bus, measures air resistance (lotsa dials) and a spider of hoses. They pull the original build plans from the coach by VIN as some vary. Then they have a protocol of Level-Low operations, engine on/engine off, etc. They nailed our air leak in about 15 minutes of checking. It was a valve in front of the D/N 50 box.

After watching that experience, and being aware that I had no clue what they were talking about, I have asked a number of other Prevost facilities about the device and they are unaware of it, and don't seem to be that interested in finding out.

This would be a good POG project. If Fast Roger is up for it, he and I will make one.

The one at St. Nicolas, of course, is made from stainless steel, rivets and no slide-outs.

Good stuff.

[Joe Cannarozzi]

Here are the air relays for the tag axle that I found bubbling at the flange for the diaphrams on them. Left hand, right hand, both the same valve.

My Bus 128.jpg

I'm sitting up inbetween the rear-end and the tag, looking at the drivers side. I believe that these regulate the air pressure for the tag air bags and it exhausts here when you dump it.

The new one is leaking, much less but at the same place. I tightened the phillips screws as much as I dare. I'll try to bench test the other new one first. The old one had loose flange screws too and Ill tighten them and bench test it too, might be able to seal it up. It would be a good addition to central spares.

My Bus 123.jpg