not holding air

[stevet903]

Do you know when it was last serviced? (Prevost recommends every year). If you don't you probably should put new desiccant while you are there as well as the parts you need.  You can do it on the bus, I dumped the air from the tags and removed the tag wheel to get better access.  The end cover comes off the bottom, 3 bolts and a snap ring, and you can either replace it with a reman cover or put whatever new parts that it needs while on the bench.  You must drain all the air out of the system - if you don't the cover will launch with 100psi or so behind it!!  Of course, block the coach up while working under it....

Here's an exploded diagram - http://www.prevostcar.com/DB/services/bbs/eng/Mi04-12.pdf

[robertglines1]

I would remove and clean ..then you can use shop air to test it...maybe even paint if it is rusted. good cleaning could even solve problem....like Steve said be careful....

[eddiepotts]

I went out to work on the governor this morning before I messed with the dryer. I read that this could be a problem to cause the purge valve to blow. I disconnected the line and started the bus to see if the purge line had constant air. what I found was it was not blowing but a hole worn through the braided air line coming off compressor. could this be my problem. I also read that a major airleak could do it but not sure if it meant before or after dryer. I know I need a new air line but can't get one until Tuesday when the truck parts house opens. Just trying to find the fix as I go to learn the cause before I just rebuild the whole system and knot know what the problem was. Thanks.

[robertglines1]

try splice in it that could diangnose problem just cut leak out and splice...have done it...bob

[eddiepotts]

Good idea Bob. I will try that. Does the purge valve blow at start up for a few seconds until it reaches pressure normally?

[robertglines1]

don't know about valve ...my temp splice has been in for 3 yrs now..oops

[JackConrad]

Good idea Bob. I will try that. Does the purge valve blow at start up for a few seconds until it reaches pressure normally?

Mine does not.  No air from the dryer till air compressor kick off at about 125 PSI.  Jack

[bevans6]

When the governor signals the air dryer to open the purge valve, it stays open until the governor tells it to close when it starts providing air again.  The governor controls the purge valve.  There is a check valve between the air dryer and the wet tank.  The check valve prevents air from escaping from the wet tank when the purge valve is open, and allows air to pass into the wet tank when the pressure from the compressor exceeds that inside the wet tank.

Brian

[eddiepotts]

I changed purge vale and canister. valve kit $13 and canister was $25 through NAPA. There is an $18 core so take it with you if parts house not close. I did find the main braided air line had a hole in it along with the line from the governor. $85 for the big one and $48 for the small one. It all is good now but this weekend I will be pulling the air tanks to clean out. The dryer was so packed with dirt and grime I don't think it had ever purged before the valve split. The top of the canister was even blown open with desiccant everywhere. I had no idea that I ever had a problem. If I would not have lost air I would have never even looked at it not knowing anything about it. The breaks worked fine as far as I know. It is the only bus I have ever driven. I am going to go to the electronic store here and buy some plastic wire loom to cover the hoses so I do not have to worry about them rubbing any more. I think I will spend the most time and money cleaning the street in front of my house where years of goop has fallen all over it. Yes I am one of those neighbors. Do all my work in the street. It keeps my driveway clean.

[bevans6]

I once painted a car in the street - in front of my friends house!  His curb was blue for years.   

Brian

[bobofthenorth]

I am going to go to the electronic store here and buy some plastic wire loom to cover the hoses so I do not have to worry about them rubbing any more.

Last spring when we had the bus in my buddy's shop he sent me underneath with a flashlight to look for rubbing hoses.  He found one that had worn the rubber off so we replaced it and I found one that had a collection of non-DOT fittings that we replaced as well.  I took a handful of nylon ties and snugged a few others up where it looked like they might rub someday.  It was a good lesson for me - something else to watch for while I am under there with a grease gun.  I'm a firm believer that everybody should grease their own equipment, regardless of what other work they do on it.  The simple act of crawling between grease zerks gives you a good opportunity to look closely at everything along the way.

[bevans6]

It's interesting that for commercial vehicles, checking for rubbing hoses is part of the DOT daily inspection, and checking for rubbing hoses on the under-chassis of a bus in commercial service is 30 days or 10,000 km (up here anyway).  We should be doing such an inspection at least once in a while...

Brian

[eddiepotts]

I agree. I would have never done it until now that I have had to buy a hose. I think for pennys a foot I will have all hoses covered in plastic covers soon.

[DaveG]

Not that hoses should be rubbing against anything, but if they do...keep some old radiator hose and garden hose handy, along with some zipties.

[buswarrior]

Plastic covers only take a little longer to rub through...

Anything that touches anything must be SECURED TIGHTLY against movement.

Good quality plastic zip ties, and the mentioned pieces of old rad hose cut up to put in between for a cushion.

happy coaching!
buswarrior