FRONT AIRBAGS

[bluevost]

Good morning POGgers,

The following comments relate to my (all) solid axle coach vintage 1994 chassis.

Since returning from OKC I have done some reseach regarding original air bags and the replacements called out by Prevost. The original bag was Goodyear 1R11-096 (Prevost #63-0126), no longer available from Goodyear. See the link below to view the spec sheet.

http://www.truckcomponentsonline.com...96_p_1157.html

Prevost is now installing Goodyear 1R11-244 (Prevost #63-0259) as replacements. The above link will get you to the spec sheet for this bag also, use the search tool. One important thing to know is that when looking at the bag from above, the air fitting and the stud are at the 3 and 9 o'clock position. When flipping the bag upside down, the bottom studs are at the 12 and 6 o'clock position. This is key. Although the spec sheet for the 1R11-244 shows the bottom studs at 3 and 9 o'clock, they come at 12 and 6, so I'm told.

Now to the issue of front end lift. As I have stated earlier, I have not been able to lift the front of the bus enough to get level even in a campground, since the air bag swap. Why?? The spec sheets show the exact same amount of travel for both bags. To make a long story short, IT ISN'T THE BAGS. It's our old friend Norgren. That's right. At Mira Loma yesterday, Luis replaced the Norgren valve between the front wheels, and the smaller Norgren on the bulkhead in the bottom compartment. Both of them were original to the '94 chassis. Now I have 7 inches of lift from ride heigth. It must of been coincidental between the air bag swap (Mar. 2008) and the Norgren valve starting to fail.

My apologies to Bill Jensen of Prevost. I put a "chop block" on him at OKC. But he was right all along. I am satisfied that this is the correct replacement bag for my coach.

Ken

[Sid Tuls]

Hey Good morning Ken, Glad to hear about the good comments @ Mira Loma I was there last week to replace both of my windshields and have a level 2 service done. I've been very pleased with their work. Scott who also is a POG member is always ready to answer any questons that I have and believe me I always have some. I also dont do any of my own work but feel much better when they put my bus up on the lift and take a look under it with a mechanic. They can spot things that I would miss anyway.

[BrianE]

Hi Ken, Glad your lift issue has been resolved. The way I understand the confusion concerning correct airbag application however never did lie with Bill Jensen or any of the tech support staff. When the 126 bag was discontinued there was an initial discrepancy in the parts department between airbag part numbers and their application to bus serial numbers. The issue has been resolved due in part to input from customers and the willingness of Prevost tech support to listen and have the discrepancy corrected.

[rickdesilva]

Ken
Its great that you figured out the problem. You wire brushed Bill pretty good at the seminar. Its a great feeling when you can figure out one of those irritating problems. For safety I would just keep Buster away from your coach.....unless he's serving cocktails.

[Jon Wehrenberg]

Ken,

Can you please be more specific as to the Norgren problem. This is an apples and oranges situation so we need to clarify how an owner can determine if he has an air bag issue or one related to valving.

As I read your post I was led to believe you could raise your coach to the ride height manually, but not beyond. That would be an air bag issue. But if what you are saying is you cannot raise your front at all, except by going to the driving or ride position, then it is an issue related to the Norgren valves.

Do I have your issue properly interpreted?

[bluevost]

Jon,

It seems air pressure was the issue. There was enough (barely) to raise the front of the bus to ride height, but not enough to raise the bus for leveling. Luis mentioned a build up of moisture over time could have been the culprit. The Norgren valve had no problem dumping air, but would not let enough air pressure pass to raise the bus. Does that make sense to you??

Ken

[Jon Wehrenberg]

Ken and others reading this:

If the opening in the Norgren was only big enough to allow one molecule at a time to pass through it, given enough time the air pressure of the air bags would eventually equal the air system pressure.

I surmise the Norgren was in fact capable of opening to allow air to pass in sufficient amounts so the bus was able to come all the way up to its fully extended height within a reasonable period of time. I further surmise Ken was either impatient (I doubt that) or there was a real problem which we will now never know.

When the bus is asked to rise fully on the front axle two of the solenoids on the rear steer compartment are energized and the air flowing through them (one of them anyway) shifts the Norgren valve from being closed to opening a path from the aux system pressure to the air bag. I will agree if it does not open fully a smaller volume of air will flow through the Norgren per minute, but at some point the air in the air bags will equal aux system pressure and the front air bags will be fully extended. I never heard Ken say the bus would go beyond ride height.

If the five port Norgren does not open then nothing happens. It will not even come up to ride height. My guess to explain the issue is one side of the Norgren may have been water logged and it created a hydraulic lock preventing the Norgen from functioning in the manual direction. It obviously shifted and opened in the direction that brought the ride height valves in play.

A water logged valve likely is corroded so replacement is a correct recommendation. That water logging comes from a failure to drain and maintain the air system on the bus, a situation made worse on the aux air side.

Now to play devil's advocate.......that does not explain why many others are having problems getting their coaches to the fully raised height. I doubt that all are the result of a bad Norgren or bad solenoid valves. This may be a mystery we cannot ever solve unless we knew precisely what happened when the controls were set to raise the front and exactly what parts Prevost changed to make the front raise.

Just so everyone is very clear on this, our air bags will raise in proportion to the amount of air pressure in the bags. If the section of the coach to be raised has more weight then the air bags will need more pressure than a similar coach that has less weight in the same area. The only thing that will allow a coach to raise with lower pressure is a larger diameter air bag.

If a coach needs to come up to its fully raised position it will do so as long as two conditions are met. First, there has to be a flow path. If the valve fully opens then air can flow faster and the pressure will rise quicker and the coach will come to its fully extended height. If the valve only partially opens, no matter how small the aperature, it will still come to the fully extended height, only it will take longer for that to occur.

As a reference point, my front air bags will fully extend if my system pressure is around 110 PSI, and they will be at ride height somewhere around 100 PSI. The rears take less pressure to fully extend. Any pressures above what it takes to get full extension is excess. Someday I am going to set up a means to monitor air bag pressures just for information gathering purposes.

[Ray Davis]

Given that the way you raise a bag is to select with the Level-Low and then manually press and hold the UP switch, it's most likely that this was only done for a few seconds, to maybe 20 seconds or so?

So, IF the Norgren was indeed slow, then this would give the symptom of not being able to rise above ride height?

Ray

[gmcbuffalo]

How can we check our sluggist noregen systems to eliminate the possiblility of water logging? Is this a matter of disconnecting a air line and letting air blow out?
GregM

[Jon Wehrenberg]

Moisture can enter our bus brake and auxiliary air systems via humidity in the air compressed by the engine driven compressor.

To prevent that moisture laden air from getting beyond the first compressed air tank we must maintain the dryer element. As long as the dessicant in the air dryer is maintained it traps moisture and what little oil passes the compressor. If any moisture and oil passes the dryer it is supposed to be captured in the first compressed air tank in the system referred to as the "wet" tank.

Coming from the other direction, the auxiliary air compressor can also introduce moisture into the system. Most coaches are equipped with some form of moisture trap to catch this moisture. The aux air supply will not introduce air or moisture into the braking portions of the air system. Both the engine driven compressor and the aux compressor can and do introduce air and moisture into the aux system so maintenance of the air system is the only way to prevent moisture from collecting in amounts capable of creating a hydraulic lock on the Norgrens or corroding the interior smooth surfaces of the valves.

Maintenance consists of replacing the air dryer cartridge or element as often as necessary. Generally when moisture is seen in the wet tank along with some oil contamination in a higher than normal quantity it is time to change the element. I change mine every two years, but someone using the coach more often or in high humidity conditions or whose compressor is passing some oil may need more frequent changes.

The next step in maintenance is to drain all pressure in all tanks draining all moisture out at that time and checking to insure each tank in series maintains pressure to verify the system check and protection valves are functioning as intended.

The final step is draining the aux system water trap.

I drain my tanks every 5000 to 6000 miles and so far I get very little moisture from them. Perhaps I collect a table spoon or two, total.

If sufficient moisture has collected in the suspension system valves I suspect they can be drained by removing every hose or fitting, but I also suspect the moisture has corroded the valves so they will leak and the bus will get the leans. It is a whole lot easier and cheaper to maintain the air system in our buses than it is to try to reverse the problems trapped moisture and cause. For those who operate in sub freezing temperatures moisture in the brake or aux systems can create major problems.