Air Bag Replacement

[Jon Wehrenberg]

Dale,

The item on the RH side of the first picture at the top of this thread appears to be a 5 port Norgren. It is unclear, but It appears pneumatically operated. I can't see clearly but in addition to the two black air lines below the plugged port, there seems to be what looks like a pneumatic operator end cap on that valve.

It has been too many years since I got behind the drive axle fender liner on my 87, but it also had Norgrens in that location. I just can't say with any degree of certainty why you have the leans because I remember when my old bus leaned in the rear on one occasion it was a valve in the front that was the cause, yet there are so many potential places in the rear for that to happen it cannot be diagnosed over the internet and there are no end of places for you to look and listen.

BTW, I know you were kidding about your "leak detector" but I had an elusive leak in the rear engine compartment that I could hear, or thought I could hear but could not pinpoint.

I put a funnel on my stethoscope to at least isolate the general area and I was able to find a leak in the fan belt bellows on the LH side of the motor, and until I did that with the stethoscope I spent all my time looking on the RH side. There is a lot of value in simple devices.

[Jon Wehrenberg]

OK, I said black air lines, but after looking agaon at that first photo, they are really blue and that is evident at the ride height valve.

Joe, If you look at the first photo, the ride height valve air supply and exhaust lines are routed through the Norgren valve, which on a second and third look now appears to be one with dual pneumatic actuators not only controls the supply air for the air bags, but the exhaust. That is why the ride height valve in that year Marathon cannot control the coach height without some switching action from the Norgren.

[Orren Zook]

OK, I said black air lines, but after looking agaon at that first photo, they are really blue and that is evident at the ride height valve.

Joe, If you look at the first photo, the ride height valve air supply and exhaust lines are routed through the Norgren valve, which on a second and third look now appears to be one with dual pneumatic actuators not only controls the supply air for the air bags, but the exhaust. That is why the ride height valve in that year Marathon cannot control the coach height without some switching action from the Norgren.

Jon,

I also took another look at the first photo (PASO499.JPG) and see that the bottom line on the Norgren valve goes to the supply (center) port on the leveling valve, the delivery (lower) port on the leveling valve would be plumbed to the inlet of the air bag, it goes out of sight between the two lines from the Norgren and the exhaust (top) port looks to be connected to a black hose that terminates in the near center of the picture.
The mechanical nature of the valve will allow it to exhaust air to compensate for the 4" block of wood under the drive tires, the Norgren may not allow air to the leveling valve but it cannot stop it from exhausting when the valve arm is not centered. If Roadrunner can hear a volume of air, he could also probably feel it escaping at the exhaust port hose thereby eliminating that as a possible leak point.

If you click on the paper clip icon found under the Air Bag Replacement topic , the attachment pictures in this thread can be magnified for closer inspection.

[Jon Wehrenberg]

Orren,

While I understand what you are saying, what does not work in your logic is the fact that Key Off, with the air bag extended due to leveling, the coach will not have air exhaust from the ride height valve because if it did the entire leveling system would be worthless. If it does exhaust air under those circumstances there is another valve that has likely failed that is supposed to interupt that flow.

When the coach is parked with the key off the ride height valves are disabled to the extent that they neither add or exhaust air from the air bags.

It is difficult to see how Dale's Marathon is plumbed, but to the best of my knowledge when the bus has the key on, and the selector switch is in the "road" or driving position (different converters label the switches differently) the level low system valves are not functioning, and air bypasses them directly to the ride height valves. Perhaps Tom can speak about how Marathon is plumbed because I thinkhe chased some leans a while back

[dalej]

QUOTE from Jon....
"When the coach is parked with the key off the ride height valves are disabled to the extent that they neither add or exhaust air from the air bags."

Jon, the ride height valves operate manually on my bus. With the key off they will let air out if I undo the
level arm and move it down. I need the key on to raise, or let new air in the bags. When I turn on the
key switch it activates the Norgren valves letting new air flow to the ride height or leveling valves and
the bus raises. If I have my level low switch on, it turns off the Norgren valves.

[Jon Wehrenberg]

I guess I stand alone on this issue, but let me try to explain again why the ride height valves are disabled.

Presume that to level the coach the rear has to be raised. So you level the coach, and when you do that the air bags extend, and that in turn moves the arm to the exhaust position on the ride height valve.

If you move the level low switch to the "road" position after leveling with the key on, the ride height valves in the rear will exhaust air and the air bags will go down to the normal height, but if you move the level low switch to the "road" position after leveling, and then immediately turn off the key the bus will not move, even though the switch is in the "road" position.

The air supply to the air bag and the exhaust through the ride height valves are both blocked with the key off effectively disabling the function of the ride height valves. I am not saying the ride height valves will not work. They are mechanical so they will function regardless of whether the key is on or off. However the level low valving blocks air to and from the ride height valves when the key is off UNLESS THE LEVEL LOW SYSTEM IS ENGAGED IN WHICH CASE AIR MAY FLOW TO OR FROM THE RIDE HEIGHT VALVES DEPENDING ON THE LEVEL LOW SWITCH POSITIONS. I emphasize the previous because on some coaches the level low system could be operated (I think on earlier coaches) with the key off. Note also that all my remarks previous to the one in caps I made certain to say the switch was in the "road" position.

When I use the word "road" position, I mean in the normal driving position. Different converters label the switch position differently.

[dalej]

Jon I think your right. After giving the mechanics some thought ( I haven't worked on the valves for 3-4 years ) I wouldn't be able to raise the bus without air always being exausted. So it has to be running through the Norgren valves. I replaced all the valves on the bus after one had started leaking.

Put me down for a 2+ on this thread!

[Jon Wehrenberg]

Dale, et al,

Leveling systems are complex and are not uniform across the board. I have had my two Liberty systems work differently, so within converters I know they change.

What is absolutely critical when someone works on a leveling system is not so much a perfect and complete understanding, but a bullet proof way of eliminating risk. I use two jacks or blocks if they are handy, but regardless of how it is done, the owner needs to be 100% certain the bus will not move unexpectedly.

The logic of the system I described above I believe applies to all the coaches on this forum, including Joe's, but that is strictly a strong opinion and I would really like it to be verified by the bus owner before any service work or repairs are made.

[dale farley]

It is still raining, but I decided to get under the bus again to see what is really happening in my particular application. While I still had the right side jacked up about 3 inches and still had 4" of plywood under the drive wheels on both sides, I started the bus and let it reach full air position again. As soon as I shut it off, I could hear the air coming from the area of the ride height valve. I could see the arm on the valve was at an angle of about 25 degrees from being horizontal with the ground.

I removed the jacks, and the air sound stopped almost immediately, and the arm on the ride height valve was completely horizontal. I was still on the 4" of plywood on each side, so I assume this wasn't affecting the level of the bus from side to side, and therefore, had no impact on the valves.

I started the bus again and backed it off the plywood and have left it in that position for the last couple hours. So far, I have seen no change in the height on either side of the bus, so I assume my tag air bag was my problem. Before replacing the tag air bag, the right side of the bus would normally leak completely down within 5-10 minutes.

Without understanding all the technical functions of the valves, what I see is that being on the plywood doesn't impact anything because the wheels are still on the ground in a relatively level position and the pressure is relatively the same on the bags/valves on each side.

Resting on jacks on the right side was lifting the frame and changing the level position of the bus. This obviously signals the ride height valve to attempt to level the bus by letting down the right side.

So for my 93 Marathon, the valve does work even with the switch off. The switch was off in all the above scenarios except when I started the bus to air up the system each time.

What I have learned from this is to not try to diagnose a leveling problem while the bus is on jacks. Jacking up the frame on one side, changes the position and operation of the valves in a different way than placing something under the wheels does. Additionally, as discussed in one of the earlier threads, when the tag axle bags leak, they do affect the whole side of the bus, so they are obviouslsy not isolated. Thanks for everyone's input.

[Jon Wehrenberg]

Dale,

We may be cross talking and not understanding what each other is saying. But to be sure you have or don't have a problem all you have to do is either level the bus, or just park it, and if it moves or leans you have a problem, and if it sits where you left it, you do not have a problem.

I can tell you (as can many others on this site) that only the worst leaks or valve malfunctions can be located without the aid of a hearing device or soapy water.

I do not know how long you had your coach or how the switches are labeled, but you do need to be sure that when you drive the level low system is disengaged (there should be a warning light on the dash if it is not) and you are controlling the bus height with the ride height valves. I don't want you to think I am talking down to you, but do want to be sure everybody understands the bus has to be sitting properly on the suspension before driving.