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IFS Concern
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Hey Al,
I just noticed your comment about the Konis and ride height. I just put new Konis on the front of mine, and Jon says he thinks thats the reason the front end won’t come up much. What exactly did you do, or have them do, to adjust your ride height?
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After reading 4-15-13 post from Prevost about they don’t recommend lowering coach for long periods on air bags, I wonder if Prevost work centers can ever get the leaks fixed they work on so your bus doesn’t leak down and hit the stops. Having had mine in twice since the first of year (Ft Worth and Houston) still hits the bottom after a couple days.They have had total leeway from me on cost, over replacing every and anything they think is suspect. They have replaced all bags, and majority of valves. Maybe next time they will replace all air lines. My bus barn will be ready and wired in a week or two and will block up and look myself. Oh yeah, these trips have run in the thousands. Rant over!
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I hope others agree with me.
I have changed several sets of air bags and Norgren valves over the years on my coaches and have assisted other owners doing the same thing. I have never succeeded in putting the coach back together so it is leak free.
There are so many fittings involved, so many potential places for air leaks, and the possibility the new parts themselves can leak that I have had to chase leaks until the coach suspension would not leak down. While I would be upset if I was paying Prevost or any other shop serious money to correct the leans, I can understand just how difficult it is to reach perfection.
Rule number one is to never re-use the push in fittings. They work great once. They simplify assembly. But over time as the seal ages it becomes a leak point. Demand that every single fitting that is part of the suspension be DOT compression fittings. And go one step further and demand whoever tightens the compression nut on the tube that he understands there is a specification regarding how many turns of the nut constitute “tight”.
The suspension can be leak tested one section at a time. Don’t move to the next section until the first has been leak tested. On almost all of our coaches we can pressurize the front, the left rear and the right rear independent of one another using the level low. It takes time, lights, mirrors and multiple ways to check for leaks but it has to be done. Sticking to one section at a time sharpens the focus. And no matter how careful I have tried to be I have come into the garage the next day and seen the coach lean over requiring me to recheck everything I thought I had done right.
Bottom line………..plan on the time it takes to do the job once, and then the time it takes to let it sit to verify it will not lean. When setting it up for a check do not raise the coach all the way up. Allow it to come to the driving height and use that as the benchmark for determining if the coach is leaking down. The rationale is to avoid over inflating the air bags. Unless the coach is unusually heavy the pressure in the air bags to bring them to ride height is much less than the bus system pressure. In my previous coach about 95 to 100 PSI brought the front to driving height and somewhere around 75 PSI put the rear at driving height. If the coach is raised all the way up it might take some more pressure but maybe not full air system pressure. But we tend to raise it and keep pressurizing the air bags. That means it will not lean until all the pressure above the needed pressure is leaked out. But if you start with just enough pressure to bring it to driving height, every drop of air that leaks out causes a minute drop in height so the leans become apparent faster.
And if you ever have the suspension system replaced (air bags and Norgrens) and it is returned to you leak free buy that mechanic a gift. He deserves it.
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Karl,
I have Koni’s on the front of mine and although slow, trying to get the front raised takes time. It helps if you dump the tag and I need full air pressure to make it happen. Not sure if the Koni’s have any effect, they were on the bus when I bought it.
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Karl, I have had 3 types of shocks on my bus front axle.
Original Prevost shocks, one was leaking so the replacement was Koni. Adjustment was set to firm ride which was recommended by Prevost and Marathon. In my opinion this was to stiff a ride. It did in fact eliminate the bounce while driving after hitting uneven sections of the roadway.
Next came Roadking custom made for my bus. At first they seemed to be an improvement over the Koni. After going on a trip that had really rough roads I felt the suspension was not smoothing out the harsh bumps.
Went back to the Koni shocks with setting at smooth ride. This is the setting that Koni sets from the factory. At this point I’am very satisfied with the smooth ride with Koni all around, set on lowest setting.
This is my second RV with Koni shocks. Our CC Affinity had Koni which were set at one turn to firm on front axle.
I have checked full extension of both OEM Prevost shock and Koni which were the same. With all my shocks trial and error I have never noticed any restriction while raising or lowering.
My opinion on Koni is……..a better ride and worth the cost of replacement.
The adjustment to your ride height is done by moving a shaft up or down that is attached to the air valve in the center of the front axle. Any adjustment of the valve should only be done on a level surface allowing more or less air to enter the air bag. I believe from my memory the air bag suggested height is at 11 or 12 inches. I do not have access to my notes but will check the exact measure of the front bags.
With access to a pit, one can safely adjust ride height without any fear of the bus falling on you. It also allows trial and error checking the adjustment by raising and lowering the suspension.
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I have Konis on the front and no problem raising the front above ride height.
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I have never had a coach that would keep the air bags inflated more than a few days including my present Prevost.
If this is damaging to the bags , what is the cure other than starting the coach every 3 days?
Wave
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I think a lot of the boys have air compressors on board and tied into system. I don’t with my conversion. One of the guys will enlighten you to how they do it. Mine has gotten better since the temps have warmed up but when it was cold it would drop in a day or two.
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Wave and Glen,
Prevost standard for “leak free” with respect to the suspension and the leans is three days. If it stays level for three days before leaning or dropping in the front it is deemed acceptable. I presume their standard hasn’t changed.
Having said that you can get a coach to sit at ride height or a level position for weeks if not months if you eliminate the leaks in the Norgrens, the air bags, and the fittings. This applies to all coaches made since the logic on the suspension was changed in the mid nineties. Prior to that you not only had to keep the suspension leak free, the aux air system had to be as well because this discussion presumes you are not running the aux compressor and the leveling system.
The first step to getting the coach leak free is the most basic. Verify the fittings and the air bags are not leaking and soapy water, patience and a mirror are the tools needed. The only problem with air bags is you can use bubbles to verify the top crimp is not leaking, but you have no way of verifying the bottom “can” crimp to the rubber is not leaking because you cannot get at it with soapy water, nor can you see it.
Verifying the Norgren valves are not leaking is not always possible with soapy water. If it leaks out the end caps that can be seen, but if it leaks through you have to chase its path up to the front Norgren valves, meaning you want a pneumatic diagram in hand to follow the paths.
I know of at least 2 new air bags that leaked. I bench tested a Norgren and found it leaked. So every component besides the multitude of connections has to be verified as leak free. Installing new parts that have been tested and found leak free is often easier than looking for leaks as the coaches age because of the time it takes to look everything over.
The final way to find leaks is to use Hector’s Tennessee (sorry, Texas) bubbler that he has described in one of his articles. By using the bubbler every leak in every component can be isolated but you need to use a pneumatic diagram as a guide and you need a variety of fittings to connect to the various lines in the system.
But above all, get rid of the push in connectors. Karl and I just completed his coach and two of the push in connectors had to be reused until replacement compression fittings could be found and those two leaked out of all the other fittings we installed.
To pay someone to squirt soapy water on your coach fittings is expensive. If there is any way possible for you to do it yourself such as asking the local truck service company to let you have an hour over their pit not only helps you get an understanding of the system, but it will save you a lot of money.
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Jon is absolutely correct in saying that you can get your bus to stay level for weeks, even months on end. Our Liberty (since sold) has remained rock solid level for months (knock on wood) while spending the winter in Florida. As far as I’m concerned, it might as well be indefinite. A big help is warm temperatures. Cold weather will definitely test your system and will allow any flaws to be dramaticly evident.
But, it didn’t just happen. It took a LOT of work searching for leaks with a solution called Big Blue leak detection fluid. It’s manufactured to detect microscopic leaks in hospital oxygen systems…..and it isn’t cheap.
As an aside, one of the biggest culprits I found contributing to my leaks were the air tank drain cocks. I suggest that you seriously consider replacing all of them with new when you replace the air springs. I also found brand spanking new Norgren valves that leaked. Now THAT was frustrating….
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I have an auxiliary compressor . Does that keep the bags inflated ? If so I cannot see that on the primary or secondary gauges.
Wave
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Thanks so much guys for the info. Yeah had bags , norgen valves, leveling valves or ride height valves, and other components replaced. Electrician is finishing up my 50’x 60′ shop as we speak and will take a look myself. Should have poured slab for a walk in pit when doing slab. Hindsight right?!
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Wave,
I cannot answer your question because for an aux compressor to be able to keep the coach air bags inflated it depends on the pressure settings on the compressor and the pressure required to keep the air bags filled so the coach will not lean.
If you depend on an aux compressor and an automatic leveling feature to keep a coach with a leaky suspension level you are going to wear out a lot of compressors and worse, you will start introducing moisture into the aux system unless you are very careful about maintaining the aux system spitters or water traps.
Most coaches do not display aux pressure on the dash. Some owners have added a gauge, and I have added pressure gauges on my last two coaches to read aux air, but the gauges were in the steer compartment bay. My XLII does have a dash display of aux pressure but the key needs to be on for me to get an accurate reading. The one in the steer compartment I can read any time.
Don’t use a band aid fix, but instead get the suspension air tight.
Having said that you can spend serious money doing that if you drive a bus into a service center and tell the guys to find all the leaks and fix them. Most shops will spend hours looking for leaks (on your dime) and then hours more replacing valves, fittings and air bags. Or you can learn how to diagnose the specific location of the leaks and limit your efforts or theirs to dealing with the leaks in a given section of the coach. Too complex to fully explain in a post but with an understanding of your suspension pneumatics you can limit places to look for leaks.
After spending hours making coaches leak free (that’s a lie and really never happens) I am convinced the easiest and cheapest way to prevent the leans is to consider any air bag or Norgren valve as having served its purpose when it is 10 years old and replacing them. No chasing of leaks. I spend my time being very careful with the assembly and making sure the fittings are compression fittings, and the threaded portions have good thread dope (my preference) or teflon tape. I do my own work so my costs are time and parts. If you choose to renew the suspension to eliminate the leans by taking the coach to a shop, get quotes. There are alternatives to Prevost that are reasonable and quality conscious. Just make sure they know Prevost coaches. Most RV places haven’t a clue.
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I will turn the aux. compressor off except to place tension on fan belts before starting. Just to be clear, my coach does
not lean after a month of setting but I note the primary and secondary air gauges go down after a few days.
Wave
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Wave, Good information.
For those who are not yet familiar with how our coach air systems are plumbed and what the gauges tell us, here is a brief overview.
We have three air systems, primary and secondary brake circuits, and an auxiliary air circuit or system. All coaches show the primary and secondary brake circuit pressures on the dash. In addition low pressure in those circuits will trigger audible and visual alarms. When parked there is no pressure to the brake chambers and the parking brake is actually a very heavy spring that is holding the brake. If the gauges on those circuits drop it is not because there is an air leak associated with either the service brakes or the emergency brakes. The loss of pressure could be a bad or open valve on the air tanks, it could be a leak at the foot treadle or any number of other places such as at a relay valve. The two brake circuits should hold pressure for a very long time as in months, but it is not unusual when they drop after a short period of time such as over a few days. You definitely do not want them to drop in a matter of hours.
The auxiliary system can be large and complex and if we have leaks that is where they are likely to be found. Everything other than brakes will be on the aux air system. Prevost will have its suspension on the aux system. It will have the door lock, belt tensioners, and even air to the transmission retarder. The converter will also tap into the aux air system and everything from the floor slide to the generator air bags, and a multitude of other devices can be aux air powered.
At the very least, as owners and drivers all of us should know and understand how to do a DOT brake system check. That is the single most important part of the pneumatic system and a basic understanding of the air brake system will be very valuable.
Here are a few usually misunderstood conceptions about our air systems:
We do not need any air pressure anywhere in our coach to prevent our coach from leaning or dropping. Since the mid nineties when Prevost changed the operating logic air is locked into the suspensions when the key is off. If the coach leans, the leak is within a specific part of the suspension.
The aux compressor will not provide air to the brake system.
The coach has protection and check valves so that a catastophic failure of an aux system hose or device will not disable the brakes. However they are mechanical and it your responsibility as an owner to insure they are functioning.
Even if you properly maintain your brake system air dryer, and insure the tanks do not contain moisture, if you run your aux compressor frequently you have to insure its moisture traps or spitters are drained and working. Aux compressor air does not go through the coach air dryer.
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