Beware of would-be air suspension mechanics

I had a conversation this morning with a client, employed by NAPA, that is acquainted with several mechanics. He recommend 2 as being great with trucks/buses and air suspension. Shortly after ending our conversation "Mechanic Dan" called. I told him I was considering replacing all my air bags and the valving. I asked if he was familiar with the Prevost bus and their air suspension system. Ol' Dan told me he had worked on lots of these systems and they were all 'purtty much the same'. Then I asked specifically if he had worked on the Prevost system. Again his vague response was that he is a great mechanic and knows this stuff inside and out. He was willing to tackle replacement of the bags and valves. No Fear. I was still feeling uncomfortable with this guy so I asked him if he knew what a 'Norgren Valve' is. Silence on the other end of the line and finally a feeble, "no".

Needless to say ol' Dan will not be working on my bus or even getting close to it. If I had not attended the seminar (Ok Fly Guy John, Briefing, damn it a briefing) presented by Jon at Pahrump I wouldn't have known these things and may have hired a BS Mechanic that would have left my pocketbook and bus FLAT.

Thanks Jon and Hector for the great information. Score another one for the POG!!;)

I won't defend this guy because he was clearly trying to blow smoke. But if the sole objective is to replace air bags and Norgren valves the skill level required is little more than that required to remove and replace. He will not need to know what he is doing or why he is doing it.

Air bag replacement entails locating the air bag, removing an air fitting, 4 nuts, and then reversing the procedure.

Obviously there is a little more involved, such as removing some wheels and the drive axle front fender liner, but that is the jist of what is involved.

Replacing the Norgrens is the same R&R. The difference is if the guy switches an air line by mistake. He does not need to know what the air lines do, or where they go, but he sure needs to replace them on the new valve in the exact same way they came from the old valve.

When all this is done everything needs to be leak tested. No bubbles can be tolerated.

My only concern is when a mechanic characterizes himself as knowing that they are all "purty much the same". This guy can't be trusted to not make assumptions. If he gets creative with where the lines go on the Norgrens sorting things out can be a nightmare. Personally I would rather have the apprentice do the job as long as he understood the ground rules. He will be so afraid of screwing things up he will actually take the time to mark hoses, make sketches, take photos, etc. Just like chickens like me do.

A number of POG members have now one what you want Darl. Especially your closest POG neighbor. Maybe he has some recommendations. I do know Jim repaired stuff done by "professionals" as have others.

Whoever does the work, insist they support the coach. Jim Shoen has shared with me his support techniques and they are superb. Nothing less than absolute support of the coach is acceptable.

Darl: As I have recently proven you do not take your Prevost into a shop displaying a Detroit- Allison sign out front thinking they know all the mechanics and service expertise for your Prevost. Some of them cannot be trusted to do the Detroit / Allison portion of the service. This said I reccomend we take our Detroit / Allison work to a factory authorzed dealer that can be trusted. Take your chassis, suspension service to a bus specialty shop. I have found a tour bus company that does all their own maintenence on their Prevost fleet of buses and has been doing it for over 20 years. They indicated they would welcome outside service work for my Prevost. They were reccomended by a friend that ran his own bus fleet for years. The shop is in San Jose, CA.
Front end and chasis alignment should be done by experts in the heavy highway bus and truck alighnment business. I have found two very experianced such shops that did excellent alignment on my 40' Prevost. One is located in Hayward, CA and the other in Sacramento. Anyone interested in any of the above names, please contact me. The only Detroit / Alliison dealer I have had excellent experiance with is in Springfield, Oregon. They have other sister shops in Oregon.

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Originally Posted by Darl-Wilson

I had a conversation this morning with a client, employed by NAPA, that is acquainted with several mechanics. He recommend 2 as being great with trucks/buses and air suspension. Shortly after ending our conversation "Mechanic Dan" called. I told him I was considering replacing all my air bags and the valving. I asked if he was familiar with the Prevost bus and their air suspension system. Ol' Dan told me he had worked on lots of these systems and they were all 'purtty much the same'. Then I asked specifically if he had worked on the Prevost system. Again his vague response was that he is a great mechanic and knows this stuff inside and out. He was willing to tackle replacement of the bags and valves. No Fear. I was still feeling uncomfortable with this guy so I asked him if he knew what a 'Norgren Valve' is. Silence on the other end of the line and finally a feeble, "no".

Needless to say ol' Dan will not be working on my bus or even getting close to it. If I had not attended the seminar (Ok Fly Guy John, Briefing, damn it a briefing) presented by Jon at Pahrump I wouldn't have known these things and may have hired a BS Mechanic that would have left my pocketbook and bus FLAT.

Thanks Jon and Hector for the great information. Score another one for the POG!!;)

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Darl,

I thrilled to hear the presentation was beneficial. Jon and I worked on the functionality behind the scenes planning a roll out for the Sevierville Rally. He took the same seminar to Pharump and I have seen several great comments. If you get rusty and would like to refresh yourself on the functionality of the suspension, it is available for use 24/7. I have posted it on my website. Checkout the post previously posted with logon information.

http://forum.prevostownersgroup.com/...ead.php?t=2116

Thanks again for the comments. This tool would not have been developed without the assistance of Jon.

The exercise of developing the presentation has meant a higher level of understanding for myself of the complex suspension system. I'm glad it was useful.

Hector
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Jon, I totally agree with what you wrote about having someone diligent doing this work as opposed to a sloppy journeyman mechanic. I am diligent, and like you would take care to mark everything so it goes back exactly as it came apart. I hate to admit this but I have a terrible fear of two things; one is of heights and the other is being under the bus. It is amazing I can fly steep banks around a pylon in a flimsy Cessna 150 without fear but I cannot look down the side of Hoover Dam without my feet tingling. I am able to get under a vehicle like my CR-V but getting under the bus with anything less than being in a well-constructed pit is one of my greatest fears. The death of Jim Scoggins did not make this any easier. I would love to fix this suspension like Jim Shoen but I can't so I need to hire it done. I am also heeding your advice about using someone skillful and not allowing them to rip me off.

Harry, we talked about the mechanics in CA before and I would appreciate the phone of both the Hayward and Sacramento shops.

Thanks for all the help and suggestions,

Darl:cool:

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Originally Posted by dreamchasers

Darl,

I thrilled to hear the presentation was beneficial. Jon and I worked on the functionality behind the scenes planning a roll out for the Sevierville Rally. He took the same seminar to Pharump and I have seen several great comments. If you get rusty and would like to refresh yourself on the functionality of the suspension, it is available for use 24/7. I have posted it on my website. Checkout the post previously posted with logon information.

http://forum.prevostownersgroup.com/...ead.php?t=2116

Thanks again for the comments. This tool would not have been developed without the assistance of Jon.

The exercise of developing the presentation has meant a higher level of understanding for myself of the complex suspension system. I'm glad it was useful.

Hector
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Hector, I sincerely appreciate all the time you and Jon took to make this presentation. This is as professional as anything I have ever seen. I am sure the other POGers share this same sentiment. I plan to review it again before I take my bus to the shop to have this work done.

Thanks,

Darl:cool:

Darl,

I am sure Jim Shoen will echo my words. The tasks you want done are not difficult. Just so you are aware of what I would consider reasonable times you can use the following to determine if your service facility is being fair to you and themselves.

I would allow 12 hours for all the air bags. That is 1.5 hours each on average and that is ample time and includes pulling the wheels necessary to access the bags. Make certain the front air bag fittings get modified if you do not have IFS. Roger and I did his coach quite easily by adding a 4 1/2" nipple to bring the fitting towards the outside where it was easy to get a wrench on it. It requires a new straight 1/2" compression fitting and the nipple and the hose to get cut. I think we posted pictures and the procedure.

There are 3 port and 5 port valves on your coach. The critical thing to remember when changing them is they are to be leak free at all fittings (like the air bags) and this is easier said than done. Jim and I added the fittings to the new valves on the workbench instead of trying to do it while under the bus. I would guess it took me about 30 to 45 minutes per valve at the most. The fittings and hose connections have to be absolutely leak free.

My guess is 2 solid days of work and your bus should be done. They must use ample supports beneath the coach. I double up my supports and I recommend anybody that even contemplates changing air bags or Norgrens needs to do the same thing because the entire chassis is up in the air.

I am going to help Eric in about a week do the air bags on his bus. If the times are any different we will post it.

Jon,

Harry was kind enough to email me 2 companies that he recommends to do the 'leans' work. My first question after I detail what I need done will be; how many hours? I also plan to be on the scene when this work is done and to have my laptop and air card so I can access Hector's website presentation.

I am going to wait until we take our 5th-12th of July trip to Lake Shasta before contracting this work. Other than crawling under the coach is there any check or simple, temporary repair I can make to slow my leaks?

I thought not!

Thanks for all your advice.

Darl

Darl,

You are on the right path changing air bags and Norgrens.

It will cost you more in time and money to chase leaks and diagnose them than it will take to just replace the aging parts.

The key to success however is to have the mechanics verify every fitting and component is leak free. As they replace the parts in a section (Front, LH, RH) they can air up the system and soap the fittings. No bubbles! It must be bubble tight.

Give me a heads up when you will have the work done and I can be sure to be available if you run into any problems. Having Hector's program will help you understand exactly which components (and only which components) are going to contribute to problems if any show up. To prevent having to pay for shoddy and careless worksmanship I would suggest you get an agreement that you will pay for the job to be done right, but will not pay for time spent finding problems to repair the work.

Jon

Jon your comment regarding "bubble tight" reminds me of the Sevierville Seminar. Hector mentioned a bubble tight test that he used thru the years in the refineries if I remember correctly. Now that being said I don't remember all the details of the device.

Hector - can you help me out here and post a refresher of the bubble tight tester. I don't need it at present, but - but sooner or later I will.

Thanks again to both of you for an excellent presentation at Sevierville.

Related to this topic, I was at Prevost NJ for 3 days solid while they tried to track down why by bags were falling and the coach wouldn't stay level. After replacing one part after the other including the Norgren valves there was still no improvement but I got a lot of "Well, those were bad anyhow and also needed to be replaced". On day 3 or 4, I was letting myself into the coach and I heard a hissing noise. I got the so called mechanics attention to it and after further investigation, it was found that the air operated strut that works the recess floor was leaking air and that strut was defective. This was a converter item and Royal had tied it into a part of the air system that was directly tied into letting the air bags leak out and fall.

For what it's worth to the issue of problem solving and wasting money.

Jeff, did Prevost adjust your bill or replace the unneeded parts with the originals? If not, did you ask them? I know Jon and several others here would be able to troubleshoot this problem easily. I am curious, did they use a leak detector? What you posted here shows Prevost may be grossly unprofessional. I can't imagine why it would take factory mechanics so long to diagnose this condition.

With 4 bags and 5 valves (I think) how long could it take to detect a leak? Jon just posted that replacing all of these items should be no more than 12 hours. 24 hours and they still didn't find the problem. Something is wrong with this picture.

Please keep us up to date Jeff...and thanks for the post.

Darl

Just to chime in on the subject regarding Prevost service, we stopped at the Prevost Service Center in Jacksonville for a scheduled replacement of the front air bags before leaving for our summer road trip. Since our bus is quickly nearing the 10 year mark, I wanted to start replacing some of the components that typically have a life expectancy of this period. The plan was to do the front bags now and the remainders later. I also had a brake inspection scheduled

The only problem that we ran into was that when the front bags were removed, the technician took note that the brass adapters, that attach between the top of the bag and the air line, appeared to have been cross threaded when they were installed, and his recommendation was that they be replaced. Unfortunately, they were not in stock so we had them shipped over night and installed the next day.

As part of this process, a petcock that is turned off during the removal process was skipped during the final leak test and, since we spent an additional night there, this air leak wasn't discovered until the next AM. This resulted in another trip to the lift where the problem was quickly identified and the petcock replaced at no charge.

The total labor and parts for this project was at the outer limit of Jon's estimate, but still within it, so I don't feel as if I were unfairly charged.

My over-all experience there was excellent. They did find a couple of things that I was unaware of during their inspection and those corrections were made. Our technician worked diligently on our bus, took the time to answer my questions, and made a sincere effort to make sure that I had a clear understanding of what was being done and why.

Based on my one-and-only experience there, I would recommend it.

Unfortunately, the technician that worked on our bus was working his last week there, as he was moving to Kansas City. To his credit, not many employees on their last days on the job would take the time and make the effort that he did to make certain that our repairs were completed not only to my satisfaction.... but to his.

During the brake inspection, he noticed a slight leak at the driver side tag axle hub seal. Well, the seal had so little oil left that he recommended replacing the bearings as well as the seal. With the new seal in place, he must have adjusted that seal a dozen times, to make sure that it was neither too loose nor too tight. I believe he said the tolerance was 1/1000".

And he did this outside in the rain, as someone else wanted to use the lift for another customer.

Jeff et al,

I want to correct something Jeff mentioned. I do not disagree that the air cylinder for the floor slide when leaking would deplete the auxiliary air system.

However, and this is important for all to understand....with the exception of early vintage coaches (I think the key is four solenoid valves in the steer compartment and not 5 as we now commonly find) the aux air system pressure can go to zero pounds and the bus WILL NOT LOSE AIR PRESSURE IN THE AIR BAGS. This is important to understand because when someone that does not understand the suspension system screws around for several days trying to trouble shoot the system they have to justify wasting thousands of your dollars.

If your bus leans or settles down in the front the cause of that problem is isolated to the related air bags, the fittings on the air bags or Norgren valves, or the five port or three port Norgrens for that particular part of the system.

No other leak anywhere in the bus affects the suspension. Jeff got lied to to cover up an inept mechanic's inability to focus on the only parts that could have been part of the problem. Harsh words, but if anyone wants to verify it access Hector's system power point program and you will see what I am saying. Just bear in mind his system is generic and individual coaches will have minor variations.

Jon's information is correct. I had the step slide air cylinder go bad on the Liberty and it had no effect at all on the air bags. I would loose aux. air pressure in a matter of minutes but the coach stayed level. Liberty installed a needle valve on the air line to the cylinder when the coach was built, so I just closed the valve until I got the new cylinder installed.