Air Bag Replacement

[dale farley]

I brought my bus home today to do some maintenance. As I had discussed in a previous thread, I had a significant leak in my right tag axle air bag. It took about 1/1/2 hour to replace it, because I wasn't really sure about the procedure. But I got it done and everything seems to be fine with the installation.

The bus still drops on the right side when I turn it off. Before removing the tag wheel, I placed 4" of plywood under all 4 of the drive wheels, so it would be off the ground a little. I then placed 2 jacks under the right side and jacked it up enough to make sure the bus wouldn't come down too low with me under it when I drained all the air. Every time I turn off the bus, I hear what sounds like air traveling through a pipe. It is very audible in the area where the front drive air bag and ride height valve are located (see attached picture). I have checked every fitting with soap, my ultrasonic leak detector and a hose (cheap stethoscope), and I can't find a leak. As the bus drops on that side, the noise subsides.

Now that I am out from under the bus, I am wondering if this could be caused by the fact that I still have the right side of the bus jacked up a little bit? The wheels are not off the ground, but it is sitting on the jacks. Could the ride heigth valve be trying to level the right side or does that valve even work when the bus is shut off?

I would go back out and let the jacks down, but it is dark and cold, and I have to jack the bus up again Monday so I can change the Air Dryer cartridge. Sorry for the long post.

[Orren Zook]

Roadrunner,

The leveling valve you show in the picture is mechanical, and would continue to seek level even when the ignition is turned off. If so, check the little hose at the top of the valve (there should be three ports on the side where the leveling arm is) to see if it is exhausting air when you hear the sound described. You've got a couple of variables too, 4" of wood under the drive axle and the right side of the coach jacked up, both of which should cause the leveling valves to operate seeking to level the bus.

Make sure you watch for pinch points while you're under the coach checking this.

[dalej]

Dale if you start jacking on the bus you will let old air out of the valves but new air won't replace it until
the key is in the on position. As you can see in the photo the leveling valve goes through a solenoid that
is run off the 24v, so the key has to be on. Hope this helps....we have this thread somewhere on this site.

[Joe Cannarozzi]

Roadrunner, sounds like that is exactly what is going on. When that ride-height valve begins to function 2 things happen. First there is a delay built in. Second it will adjust very long and slowly. As previously suggested you'll feel the air coming out the exhaust port, a short small tube hooked up to nothing.

[Jon Wehrenberg]

Roadrunner....sorry to disagree with our fine associates, but the ride height valve that was pictured WILL NOT FUNCTION WITH THE KEY OFF.

I have emphasized this before but it needs repeating. Each converter has their own way of handling the leveling of our coaches so we cannot get too specific here, however I have never seen or heard of any Prevost with a level low system that had functioning RIDE HEIGHT valves with the key off.

We can get into a discussion of the general procedures for isolating a leak that allows a coach to lean, but first I wanted to correct the misconception.

However....if that valve leaks it is possible for the coach to lean. If it is leaking the air will escape from the six inch plastic exhaust tube as Joe points out. He also point out about the time delay so be very careful before you put yourself in harms way to insure the coach cannot drop no matter what happens.

[Jon Wehrenberg]

Dale you are correct but if you look closely at the photo I think it is a Norgren valve controlling the air supply to the ride height valve. Depending on the converter it might be pneumatic.

[Joe Cannarozzi]

That ride hight valve Will let air out of that corrisponding corner with the ignition off. I just went out and disconnected the linkage arm to check it and I got Air to exhaust and there is no key in the ignition.

I know there is an electric solonoid that isolates things when the ignition is off and I'm sure that I can not raise that corner with the ignition off but it can be lowered with the ignition off. So if the frame was jacked higher than normal ride height while servicing it that ride hight valve on our bus under those conditions, would allow air out with the ignition off.

One disclamer is that our bus does not incorporate these norgrin valves. Don't know the first thing about them.

[Jon Wehrenberg]

Joe,

My second paragraph above emphasizes that different converters did different things and on this forum we discussed your coach IS different. The fact that you do not have the Norgren valves I think separates you from most if not all other coaches on the forum.

If the ride height valves continued to function with the key off, then the minute you leveled your coach and turned off the key, the valves would be trying to bring the coach to the position dictated by the ride height valves, and I don't even think your coach does that.

We can only make broad statements about leveling unless the posters have specific converter information and knowledge and it is clear their topic is related to not only a specific converter, but in some cases a model year or coach style. For example my Elegant Lady may be different than a Classic of the same year.

[rfoster]

Roadrunner: As Jon had mentioned we have changed all 8, yea 8 of the air bags on our two coaches. His did great. Mine is still laying down in front overnight. Jon checked with his new hi tech ultrasonic leak detector and in less than 30 seconds located a Norgren valve in front steering compartment leaking past the spool inside the valve (no way to detect with bubbles). I have not replaced it has yet (still working for a living or for the gov't) but will at my first opportunity. This doesn't fix your coach but may give you a bit of satisfaction in knowing chit happens to the best of us. I did have an air bag leak on the left front due to age, a pinhole had developed ,it was time to replace them all, I was in hopes that would cure the problem of the leans. A work still in progress.

[dale farley]

At first, I didn't think I had Norgren valves, but I have since verified that I do. As shown in the picture, there are two different Norgrens in my steering compartment.

Jon, I am not sure if there is a Norgren in the area with my ride valve. I assume you are talking about the valve that appears, in the picture, to be on top of the ride valve. I was thinking that was an integral part of the ride height valve, but I don't know. The only other component I see is what appears to be a small manifold on the right side of the picture.

I hope to solve this puzzle tomorrow if it stops raining. I will check to see if I get the same noise again, then I wil remove the jacks and see it it repeats itself. I am hoping it will go away.

[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.

[dale farley]

Jon, I "think" I am doing what I should be, but there are still many more things about the bus that I don't know than those that I do know. My bus has a switch with four positions. If I stop on uneven ground and want to level the bus, I raise/lower the Right Side, Left Side, the Front, then turn the switch back to the Drive position. The instructions specify that you turn the switch back to Drive after leveling the bus. Any time I am on the road, the switch is in the Drive position. I hope this is what you are referring to.

In all the scenarios I have described above, the switch has been in the Drive position. Since the bus is on relatively level ground, I have not been going to the other 3 switch positions, but only letting the bus come to "level" in the Drive position. Each time I have started the bus, let it exhaust at the air dryer, and then turned off the ignition without moving the switch from the Drive position. As it is sitting now, the bubble shows the bus is level,and the height has not changed in the last 4 hours.

[Jon Wehrenberg]

Dale, it sounds like you are doing things right, and if it continues to sit where you left it, it also sounds like it is leak free.

I'll have to remember in the context of describing the switch position for travel to include the "drive" position. In my Liberty it is the "road" position and I once drove a coach that had the correct travel position labeled "automatic".

There are things you can observe. I think your photo showed an auxiliary system pressure gauge. It is possible for that to drop to a very low pressure, while the air bags continue to hold pressure to keep the bus level. The reason I point that out is that on some coaches if the aux. air pressure drops below around 30 PSI, some valves will open and dump air in one or more of the air bags. That does not mean the air bags or some parts of the leveling system are leaking, but it does mean there is an aux system leak that needs to be addressed. Some coaches have had a fix to eliminate that problem and others never had the problem depending on the converter or year of the shell.

[dale farley]

Jon,

I am not sure about the relationship of my air gages. My manual says the two gages on my dash are Primary and Secondary Air System gages. I assume the one in my steering compartment is for my auxillary system for such things as the air slide over the steps, air operated seat, etc. I see that my auxillary gage currently reads 85 lbs and the two dash gages read about 110.

I have not seen anything that tells me what the difference is between the Primary and Secondary air systems. Is the Secondary just a backup for the Primary. I do not have a 12V or 110V auxillary pump in my steering compartment and have not determined if I need one.

[Jon Wehrenberg]

The dash gauges relate to your braking system air pressure.

The steering compartment gauge is auxiliary air and that deals with things like your driver's seat, floor slide, belt tensioners, pocket doors, bed lift, generator air bags and your bus suspension system.

Each of the gauges can be used in part to isolate problems. Your aux air system will not be charged with air until your primary and secondary systems reach a certain pressure, around 70 to 75 PSI. All three systems when charged from the bus air compressor will reach the same maximum pressure, usually around 120 to 130. If you have an aux compressor that maintains aux system air pressure when parked it may not reach that max pressure, but will be enough to maintain the generator air bags and the floor slide for example.

How fast they leak and how often the compressor cycles is an indicator of the system condition. If you think it is confusing welcome to the club. Our club is large and not very exclusive. The primary and secondary systems are reasonably straightforward, but the aux systems are the converters domain and they can be complex and troublesome.

[dale farley]

Jon, Good info. I assume I don't have an auxillary compressor because I don't see one in the steering compartment. Also, I assume I don't have a gage that tells me the pressure in my air bag system.

I hope to receive an AD-2 air dryer cartridge from Prevost today, so I can change mine since I don't know when it was last serviced. Is there anything special I need to know before I pull the dryer apart? They also sent me a thermostat rebuild kit for the thermostat on the bottom of the dryer. I am not sure if I need to rebuild that or not. I didn't request the kit, they just acted like it is a normal procedure when changing the cartridge.

[Jon Wehrenberg]

Dale,

Try this link to learn a little more about the dryer.

http://bendix.com/bendix/troubleshooting/jump.do;jsessionid=DA7FC51A95B1C462E5E57808820A522 B.bendix1?target=airdryers-LandingPage

I haven't replaced or rebuilt a thermostat. I have replaced the element on the dryer that has the cartridge drop from the bottom and the spin on type. Neither one is a real problem. Be careful under that bus.

[dale farley]

After replacing the air bag, leveling the bus and leaving it alone for 24 hours, I see it has dropped about 1/8". I assume this is not enough to be considered a problem?

[BrianE]

Jon.

Thanks for posting the Bendix link, I added it to my bookmarks. I have been experiencing an intermittent noise that occurs just as the air system is reaching pressure and the compressor is about to shut off. It is a long drawn-out sound that JDUB would be proud to claim as his own. :eek: Doesn't always occur and the system seems to operate normally otherwise any ideas? Thanks to all.

BrianE
94Liberty XL

[JIM CHALOUPKA]

If it doesn't smell don't worry about it. :rolleyes:

RATING: -10

[Jon Wehrenberg]

A small drop like 1/8" is something some on this forum wish was the case with their coaches. I'm not even sure that would necessarily indicate a leak although it probably does.

I forgot to respond to the question about pressure in the air bags. Our air bag pressure is not important to know. It varies as we go down the road. If we are straight and level it is possible for each corner to have different pressures because the bags are only pressurized enough to raise the coach body to the ride height. Whatever that pressure is is determined by the ride height valves, which are not regulating pressure per se, but are measuring the body height via the lever arm on the valve.

As you start driving around a curve, centrifugal force makes the body want to lean. (I'll ignore the time delay feature here) As the body leans the lever arm moves and the ride height valves start to add air on the outside of the curve to counteract the lean in that direction, while the valvres on the inside of the curve are allowing air bag air to escape, lowering the pressure and the air bags which have extended to cause the coach to lean

If we were to monitor pressure in the air bags it would not be a big deal, but as we drove we would see constantly varying values.

To add to the variation, there would be other factors, such as someone moving about in the bus, transfering water from the fresh side of the coach to the waste side, and the use of fuel or addition of fuel or cargo.

[bill&jody]

i seem to remember from a conversation with lester that there is a check valve between brake air and aux air. aux can be pressurized by brake air but not vice versa. for example (again, according to lester) if you need hi pressure 100+ air in your aux tank to, say, pump up a tire, you will quickly exhaust the aux air and it will not pump up unless you pump down your brake air. on the way back up, the brake air will pressurize the aux.

maybe i have some of the quotes from lester wrong or backward, but i think i accruately remember the "pump down the brakes to charge the aux" conversation.

anybody got thoughts on this?

incidently, i just noticed a small line of bubles on the port side tag bag while underneath doing soap bubble testing. one other thing is my port side drive bag is smaller and newer than the other 5. prevost elgin sez they are the same part number. i suspect some hammer mechanic may have slipped something in to appease the previous owner's scheduling constraints. unfortunately, i don't have a place to do all the bag work - TGO frowns on major maint on their sites - not sure if thats good or bad.

[truk4u]

Wild Bill,

You got it right.. The brake tanks are going to get air first and then the aux. The problem is, lets say your trying to get to 100 lbs on the tire. Your engine compressor is set up to probably kick in the compressor at 90 lbs and kick it off at 120 lbs (dryer exhausts). So if your trying to pump up a tire from 90 lbs to 100 lbs, you can't get the compressor to kick on because it's not below 90 lbs. You can pump the brakes to bleed down the brake tanks and that will kick on the compressor and then quickly start filling your tire. The downside to this is some will continue to pump allowing you to fill the tire to the 100 lbs and others will reach the 120 and kick off, leaving you with only about 20 lbs in the aux to finish the job. The aux tank doesn't have nearly the volume of the tire and the next thing you know, your holding a hose that isn't doing anything. So you can start the process all over again.

Mine has a aux tank gauge in the steering bay, so I can watch the gauge and when there isn't enough pressure to continue, I just let air out of the hose until the compressor kicks back in and start the whole process again.

I probably haven't explained this well, it's easier to show and tell. I have the same problem at home, my shop compressor doesn't hold enough air vloume to get me where I need to be, so I have to let air out of the hose to once again start the sequence all over again. Ya I know, I need a bigger compressor!:rolleyes:

Just ask Jon when you see him at your mini rally, he probably carriers an extra compressor just for tires.:D

[lewpopp]

Even tho my aux tank shows I have 120#, I have a hell-of-a-time getting from 90# to !00#. It takes forever and that isn't where I want to be.

I need a better way to get up to 110# easily.

[bill&jody]

t4u - nope, you've explained it crystal clearly. (crystaly clear ?) yep, i carry a small craftsman compressor that gets me the 120 psi i need. i don't keep tires at 120, altho the book calls for (as i recall) 110 based on load.
i understand whutcher sayin, and i understand lew's lament - if i depended on the aux pump to get a tire from 0 to 100, or 50 for that matter, the tire would expire from the 5 year rule before it'd get up to pressure. i'm almost thnking i'd like to plumb in the ac compressor to the dc line for when 120ac is avail. it would run for 20,30 seconds, and it'd all be over. as it is, my aux runs 5,6 cycles to get from 75 to 105 (gauge in steering room). whats another 60 pounds.

wmm

[BrianE]

Just finished servicing the bus for our early departure to POG III. Replaced the AD-2 dryer element, aux air element, replaced a leaking Norgren and determined it's time to replace some air bags. Does anyone have a source and/or cross over part numbers from Prevost to commercial air bags?

I also created what appears to be an internal leak as I can't find it with soapy water that causes right side (yes, I replaced the right rear 5 port Norgren) leans on both road and coach leveling systems. Jon, looks like I might need your ultra-sonic. Source would be appreciated. :(
______________
94 Liberty XL

[Jon Wehrenberg]

Brian,

Easy to get cross over. First, get hold of Prevost in Elgin (parts) and get the correct Prevost numbers for your coach. Your vintage and length has some choices on the front axle because at that time Prevost was offering a smaller air bag, but made available a larger one. They will verify by serial number. I have had great luck talking to Charlie Kailor, and he is detailed enough to pick the right one. He can provide the trade numbers for your air bags also.

I did a web search and could not beat the Prevost prices when I bought mine. He also offered a discount because I bought more than two, and I think the closest I came to what I paid Prevost was about $50 more. Prevost also delivered them the next day out of Nashville with no shipping charge.

Just a guess here, but I learned from another POG member that a lean as you describe may be from the tag axle Norgren. If you can't find it with soapy water, plug the exhaust and see if that affects it. If you can't find it that way then the quick method is the ultrasonic leak detector.

I found a leak detector like mine at www.grainger.com and it is an Amprobe ultrasonic leak detector. A web search will turn up other suppliers that might be cheaper. Avoid Contractor Books. They were my source and they lied to me. I paid $322.00 with the noise generator because I will also use it to check my plane cabin for leaks using the noise generator, but on the bus you can do without that.

Good luck. The leans will drive you nuts.

[bill&jody]

jon, et al-
when climbing around under my "home" with your amprobe, i noticed that air was escaping from the bottom of my air dryer after shutting down the engine. i'd guess air leaked out of the dryer for, say, 5 min or so (the sniffer heard it - or rather, i heard it via the sniffer). after that, it stopped. just fyi, the dryer was serviced at k.robertson last march.

is that to be expected?

wmm

[BrianE]

Many thanks Jon. It's good to know Prevost is competitive in SOME things. Will get them coming Monday. Based on your thoughts tried dumping the tag, still leans. I might have gotten a bad Norgren. Will shop for a leak detector next.
______________
94 Liberty XL

[mikedee]

I purchase an air doubler to inflate tires. Takes a given amount of 100 psi air and makes a lesser amount of 200 PSI air. It has a regulator and a couple gauges for input pressure and exhaust pressure. I set the output at 150 psi and it inflates front tires to 116 very easily. Fits in the palm of our hand, just like the 3 one hundred dollar bills it cost ($287.00)

Mike & Dee

[gmcbuffalo]

MikeDee
Where did you get the air doubler?
GregM

[Jon Wehrenberg]

WMM,

Never having had a problem with a dryer I haven't had the opportunity to pull one apart. At the end of a cycle on both my coaches each dryer would spit a little air and then shut off. I presume that is to purge collected moisture.

Play around on this site to get further information.

http://bendix.com/bendix/troubleshooting/jump.do;jsessionid=9DFCFCFB4F3CD2F98365DD649465E80 7.bendix1?target=airdryers-LandingPage

If Joe is out there I suspect he can offer advice.

[ken&ellen]

Jon, I would like to get your opinion on having the air bags replaced. Since we have moved to Savannah, GA we are only a few hours North of Prevost, Liberty, & etc. Here in the Savannah area we have a multitude of large truck repair companies and I am sure they replace air bags on these large sleeper cabs on a regular basis. I no longer have a facility or the equipment to do heavy work......so doing it on my own is not an option. Your thoughts. Thanks. Ken & Ellen

[Joe Cannarozzi]

Bill if the dryer is loosing air for minutes after a purge at the end of cycle something is going south. 179 bucks for a rebuilt on exchange. You can rebuild it yourself for 79 bucks for the dissident and o-rings but then have to buy the heating element seperate and its a little harder to do and I don't remember the cost of that off the top of my head. I, for the first time, rebuilt my own on the bus and IMHO, think the way to go is just pull it for a rebuilt replacement. Much easier and quicker and the cost difference is minimal. Also I pulled my Tag tire and it was a breeze and I know you can-not but it is still dooable with-out. Your call.

Ken IMHO it is a question of cost verses confidence. If Prevost is 20 bucks an hour more but you are not sure about the truck garage I think I'd spend the extra money. On the other hand this is not rocket sience and if you feel confident with another service center give them the job but double check the bags they are using and tell them ahead of time you are bringing your squirt bottle with soapy water when you pick it up.

Finding a good truck service center you can trust, is closer to home and is less expensive is also a quest worth making.

Ya think I would stay buisy doing mobile bus service?

[BrianE]

Bill, I second Joe's advice. I just finished overhauling the Bendix AD2 dryer in our bus. Did it without removing the tag wheel and it would have been a lot easier if I had. Don't have a big impact wrench though. By the time I got it apart it would have been easier and not much more expensive to just exchange it. Next time its due I will install a Wabco System Saver 1200. www.meritorwabco.com. It is much later technology, will fit in the same location and has an easy to change spin on element. After '94 Prevost changed to the AD9 Dryer but it would be a bear to retrofit on an earlier bus.

________________
94 Liberty XL

[Jon Wehrenberg]

Ken,

I wish I could endorse Prevost, but unless you get an iron clad price quote I would be afraid. I have been in communication with two from this site whose recent Prevost air bag experience has left them frustrated.

Let me arm you with some simple information. It relates to my recent 45' experience, and I think the 40' is a little different. To easily replace the air bags you need to access them. That involves removing the steer tires, the outer drive tires and the tag tires. The tags do not have to come off, but it makes work easier. You also have to remove the drive axle front fender liners.

Allow time for that. We are not talking a lot. The front air bag fittings are inaccessible, so to remove the front air bags CUT the air hose at the fitting. Throw away the compression fitting. To remove the bags the bus must be blocked at its highest, or lifted at the support points so the axles hang. All 8 bags have three 3/4" nuts and larger nuts at the air fitting. Once removed (along with the air hose fittings) the bags are out. Allow 30 minutes for the removal of each bag.

The fronts need some new air fittings. Re-use the 1/2 Ell, and add a 4 1/2" X 1/2" nipple and a 1/2" female pipe to compression fitting. Recut the front hose to fit. All other fittings are reuseable. PREVOST IS NOW DOING THIS BECAUSE THE ORIGINAL DESIGN IS UNWORKABLE.

Replacement of the air bags takes 1/2 hour. Then you have the additional time required to replace the fender liners and tires.

My guess is 10 man hours, the air bags, and a few plumbing parts. You can buy the airbags yourself from Prevost. In the quantity you will buy you will spend around $140 apiece, maybe a little more, maybe less.

Whoever does the job will need to get under the coach for the tag or rear drive air bag fitting (I forget which), and you may have to pull a shock on the drive axle for your 40 foot, but that only takes a few minutes. All the rest of the work is done from the outside. A pit is nice, but I have done two while sitting on the floor so wherever you take it does not need lifts or a pit.

If you consider Prevost, which I recommend, I would make them reduce the cost to writing and I would not be shy about telling them how long it will take and why. I will stand behind what I wrote above and would have no problem proving it.