| Author | Message | ||
| Randy Davidson (Rdavidson)
Registered Member Username: Rdavidson Post Number: 8 Registered: 7-2006 Posted From: 69.19.14.44 Rating: N/A |
In other posts air suspension leaks have been discussed at length. "Find the leaks" is commonly the correct answer. Well, I'm still looking. My '93 H3-40 will hold it's air for about 2 hrs and then, in less than 3 seconds, dump all the auxilary air until it is resting on the stops. This bus is equipped with Kneeling, Hi-bouy and Lo-bouy. I've always thought that there is a pressure-spring valve that is held tight while pressure is high and then dumps when the pressure drops. I've assumed that I had a leak somewhere causing this valve to "pop off" after 2 hours or so. I've never found that leak. Resently, it has been suggested that this bus was "designed" to dump its air after a period (and they would not override this feature sighting lawyer bs). So, my questions are: 1) are there other's with this "feature"? When I press "kneel" the front can dump in about the same 3 seconds. Same with Lo-bouy for all the bags. 2) if this IS a feature, what was running through the engineer's head? 3) a feature of this type could be electric in nature and therefore "unpluggable"? I have dabooks and I don't see this feature. 4) if it is NOT a feature and I DO have a leak, again, what's this valve for? See 2. Thanks for your ideas, Randy P.S. Oh, and if someone HAS fixed this -- what did you do? | ||
| Buswarrior (Buswarrior)
Registered Member Username: Buswarrior Post Number: 1287 Registered: 12-2000 Posted From: 76.68.135.71  Rating: N/A |
Hello Randy. I'm inclined to agree with your interpretation of that line of BS. Prevost did NOT design your bus to behave this way. You need to know what the air pressure in the tank that feeds the suspension is doing leading up to this "dumping" event. You can make up a temporary connection via the tank drain fitting to install a gauge where the dash gauges are leaving you blind. Beware, the dash gauges may or may not be telling you what you need to know, there are check valves plumbed in, leaving parts of the air system to do all manner of leaking without you being aware. Does your model show two or three readings on the dash? This sounds like a flawed valve or a previous owner has installed or removed the wrong part from the suspension plumbing. The functionality of your model year's kneeling and hi/low boy valving also must be understood. If the presence of air pressure is part of how they operate, loss of pressure will trigger malfunction. Is the kneeling/hi/low boy system good old analog or via the computer on the '93? The earlier attempts at kneeling and hi/low boy caused a lot of trouble for the commercial fleets, there may be upgrades that were not done to your coach. If the check valve function of the levelling valves has failed/been removed/isn't featured, it is possible for a set of fairly good suspension bellows to suddenly empty backwards into the already drained away aux tank, when the bellows have seeped enough for the levelling valve to call for more air. There's a reason, we just have to find it. happy coaching! buswarrior | ||
| Randy Davidson (Rdavidson)
Registered Member Username: Rdavidson Post Number: 9 Registered: 7-2006 Posted From: 69.19.14.33 Rating: N/A |
Thanks for your input Buswarrior. In answer to your questions: 1) I have two dial air guages that are mechanically connected to the primary and secondary braking systems. They do not dump like the auxilary tanks do and give me no information as you suspect. 2) I believe the kneeling/hi/lo functions are NOT part of the DEC II. There are switches that appear to me to go directly to solenoids. The lo-bouy lever actually activates a valve directly under the panel with air hoses directly connected (no wiring at all). 3) I replaced my leveling valves (3x) some time ago chasing this leak down. They had no effect but was worth the effort. However, I have not checked to see if the check valves in the lines are in the right places per the book. Either way, the aux air dumps directly to atmosphere with quite a loud hiss. It's not going back into the tanks. I had ALL of the dump valves and operating connections under the bus replaced at Ft. Worth Prevost (for major $$$, never again). That did nothing but reinforce the meaning of DIY. I have a new drier as well. There are many excuses for not being able to chase this down but my primary hurdle is that I have no ramps, pit, or lift to easily follow the lines per the book. And, it seems, I can't ever hire it done. I have two Auxilary tanks. Both have manual drain valves (I've seen them). I was planning to replace them with something that would allow me to open them from the side of the bus rather than going under. That would be the time to install a Tee of sorts to guage the pressure as well. Thanks for those ideas and encouragement, Randy | ||
| Lyle Kent (Lylekent)
Registered Member Username: Lylekent Post Number: 1 Registered: 5-2008 Posted From: 69.107.130.246 Rating: N/A |
Hi There, Just a thought...... In busses that only monitor the front and rear brake tanks such as yours as I have found it very useful to intsall an "accessory" air gauge on the dash (as more modern prevosts have) to monitor that pressure easily as the bus sits or while rolling down the road. Depending on check valves I have done this right from the air seat. It helps in diagnosing many air problems. Do we know where exactly the air is being exhausted from? Is the air dryer doing this? I assume its from the levelling valves themselves? Be cautious installing pull cords to drain air tanks on busses with hi-lo's becuase they can dump your air when you might not want it due to coach level etc. Make sure you have enough slack. As and old-school-drain-all-your- tanks- daily guy I did this on modern coaches and later regretted it. Good Luck Lyle | ||
| larry currier (Larryc)
Registered Member Username: Larryc Post Number: 169 Registered: 2-2007 Posted From: 207.200.116.13 Rating: N/A |
I don't know how old your air bags are but they do require replacement as needed. Normally an in service truck with air suspension will rust out the bottom steel base of the air bag closest to the wet tank about every 6 or 7 years. I would start spraying soapy water around until I found the problem. Get a pit. | ||
| Tony LEE (T_lee)
Registered Member Username: T_lee Post Number: 30 Registered: 11-2007 Posted From: 84.157.129.26 Rating: N/A |
"I was planning to replace them with something that would allow me to open them from the side of the bus rather than going under." Standard drain release valve - male thread to screw into the tank and has a toggle with SS wire attached so you can remotely operate it manually. Run the wires through saddled water hose to the nearest wheel-well as they do with the MCIs |