[Archived]

Mike,

If you drained as much water from the air system as you describe you may end up being our resident air system expert because you have to go through it line by line, valve by valve, and system by system until you have reversed the damage done by moisture. I hate that your coach has issues but I believe you have only scratched the surface.

Within your coach air system will be various check and protection valves. Their purpose is to limit air flow until your primary, then secondary, then auxiliary air systems are satisfied with pressure. In other words no air will flow into the auxiliary system until the brake systems have at least 75 PSI. To do that the protection valves need to sense pressure and then open to permit air flow. I can envision valves that will not function as intended due to rust or crud in them. The only cure is to follow the air flow as shown on the pneumatic diagrams for the coach and insure the lines and tanks are dry and the valves are functioning.

http://prevostparts.volvo.com/technicalpublications/en/manuel.asp

The link above will get you to your pneumatic diagram.

The extent of your problem concerns me because of the number of devices that rely on air to function properly and if they have been exposed to water or even moisture to a small extent can need repair or replacement. I would first isolate the brake systems and get those dry and working. My immediate concern would be the various protection valves and the foot treadle. If the air dryer was rusted I would be especially concerned with rust on the brake chambers.

Once I was comfortable the brake systems were dry and functioning I would bring the aux air systems on line and my greatest concern would be damage done to the leveling valves. It sounds like a seated coach so it may not have the level low system but it could have ride height valves as well as other suspension system valves adversely affected.

As a note your system should have a compressor cut out pressure of 120 to 125 and a cut in 20 PSI less than the cut out. If you can block out everything downstream from the wet tank and get it cycling as required with the pressures needed, then you can move downstream one tank at a time, methodically sorting out the systems.

Good luck. There are many resources for help. Don’t be shy about asking for help and advice here. There are occasions when we even can give correct answers.

[Archived]

Thanks Jon, I had thought that is what I may have to do. The coach was a one owner trade in to Prevost from a tour company out of Knoxville. I bought the coach knowing it needed engine repair. Water was in the oil. $98000 later after repairs from a local Detroit Dealer the motor is running great. Drove it home 50 miles, air system working fine then out of nowhere this happens. Had I known the air system had never been serviced by the previous owner I would have had that done as well. There has been 430 miles put on the coach since I bought it, Most of that was towing! As Bubba Gump should say “Buses are like a box of chocolates, You never know what you’re gonna get”. Thanks for the advice I will keep you posted on the outcome.

[JIM]

What is very important right now is for you to prevent further damage and to make certain your entire air system works as designed. The coach is built with a number of protections so any catastrophic air system failure does not take away all of your braking and lock up the spring brakes. To do that from beginning to end the coach has various valves. Not a single one has to function as intended for you to use the coach normally, but when something goes wrong such as a serious air leak you will rely on those protections so you don’t find yourself in the fast lane somewhere with the brakes locked up.

As a general comment I find the generic components used in the pneumatic system to be relatively cheap and readily available. Almost all the valves for example, such as relay valves are Bendix valves that any truck supply house or Prevost has in stock.

One comment………never ever get under your coach unless it is supported at the chassis support points. This is especially true if you are working on the pneumatic system which includes the suspension. Hydraulic jacks are not safe because they too can fail. Make sure the support is strong and adequate for the weight involved.

[Archived]

You will learn the system : you really need to know it. When you go to the prevost car site use the last letter in your serial number plus the last four didgets (unit number) will give you coach specific info. When you put new air drier in did you get line back to air compressor (small) governer installed also. Do you have shop air? if so can system be pumped up with shop air? Sometimes on seated coach air system this will release a stuck check valve and help figure out where problem is. As others have said don’t rely on air bags to hold coach up with you under there. The shop air will also help figure out compressor/govenor or air system problem. Give me a call if you like I am a home builder and have done a 89XL seated coach. 812 449 8263 Ver cell. Bob

[Bob]

Tank inside lower door left front under drivers window. drain it. If you don’t get anything out of it make sure drain is open (not plugged by rust or crud). Blue air lines are your suspension system.

[David]

As usual Bob gives great advice. One thing I have learned however is that while it likely left the Prevost Car factory with properly color coded air lines, do not place yourself at risk by assuming all subsequent mechanics that might have had to replace an air line observed the color coding.

[Bob]

Hey Bob, Thanks,good to hear from you! OK, been out working on the coach today. Nothing on the Prevost drawings match my system. ie: it shows the governor hose from the res. port goes to the wet tank. Mine goes from the wet tank (Green Line) to a filter then a junction block and splits to serve the governor, engine stop and fast idle cylinders. After making sure my hoses were clear with shop air I took the filter apart and crud was in it not to mention the filter looked like someone had just wrapped twine around the metal baffle to make a filter rather than replace it. This may explain the compressor stopping to pump air @ 50 psi if it is not getting pressure back from the wet tank. So far the lines I’ve checked seem to be OK. A little nasty but clear. Gonna drop the wet tank and clean it out next. Yes, I did some experimenting with shop air and it did fill the system including the suspension. Was running the motor to see if it would unclog whatever is blocking the lines but it never did. As soon as I shut the engine down I heard air blowoff between the Tag and Drive axle. After being under it today I found a valve in between the Drive axle brake cannister and the primary tank (feeds both Drive axle brakes, also another just like it that did the same for the tag brakes) it had a round rubber disc at the bottom that looked like air had blown off the road dirt that had accumalated over the years. The other one for the tag axle seemed to be alright because the road dirt was still on it. After the wet tank cleaning I will check it to see if it has malfunctioned. The primary tank seems to be OK, drained it today and a mist of water came out which seemed to be normal. I will keep you all posted on the outcome of this adventure! Any thoughts or advice is greatly appreciated!

[Archived]

Jon, You’re absolutely right! Made that mistake 20 years ago with a residential electrical circuit. Had gone to replace the transformer in a HVAC unit. Shut it off at the service switch in the HVAC closet and then was nailed by electricity. Turns out the service tech before me was to lazy to replace the switch so he shut it off at the electical panel went back and wired the switch wires direct and left the old switch in the box. Never assume anything!

[Archived]

not exhausting out between axles as long as shop air is hooked up? I’m going to reread your whole post. All govenor has to do is sense when system pressure is obtained where it is being measured.

[Mike]

Is there a yellow line going to it on top? By the way prevost parts is the best price for the correct part and quickest delivery for brake parts.

[David]

Not exhausting air as long as air is hooked up. Not sure about the yellow line, there was so much grime. I will check tommorrow. You’re right about Prevost parts … I talked with Roger Anderson to find replacement seals for the engine stop and fast idle air cylinders yesterday @ 3:00pm. They arrived at my door this afternoon at 4:00pm. Talk about good service and knowledge. Roger knew exactly what I was asking for. He must have been our age because I had talked to a younger guy that morning that didn’t have a clue. He sent me the drawing of the of the air cylinders for the belt tension. Told me to contact Detroit Prevost didn’t handle that part. After hours with WW Williams and sending a pic they didn’t make that part and told me to call MCI. Go Figure, Guess it’s all in who you talk to!