Air bags leaking down on one side of bus

[chessie4905]

My 4905 has held air for almost 6 months.

[chessie4905]

The air bag system is separated from air brake systems by valves and checkvalves. If the leveling system is tight, the bags will stay inflated, even though the air in rest of systems leaks out. The leveling valves have built in check valves to keep have pressurized. Generally, the front air bags (4) are controlled by one leveling valve. The rear airbags, have two leveling valves, each controls bags (2) per side. So, if you have a leak, it can be: bag/s keaking, leveling valve/s leaking, or lines to have from leveling valves.You can have one more more leaks at the same time. Also on older MIC and GMC's the bags are attached at the top to hollow long rectangular air beams. The idea was that the hollow beams contained additional compressed air volume to provide a compliant ride. However time and corrosion and dust over the years caused leaks in the beams which were very difficult and expensive to repair. Someone devised plates that mounted between top of bag and bottom of beam to deal with this. The air volume is definitely less and makes the ride firmer, so they say. On the older busses, you can't isolate bag from beam as far as which is most likely leaking, so most will replace all 4 bags and install the block off plates at the same time. The coach could oscillate some over bumps if you only did one side (2). You may get lucky and it is just a leaking line, but I doubt it. Like carries all the parts. Btw, the block off plates have gone up in price significantly in past few years. They are anodized aluminum and 1/4 or 5/16 thick.

[goutoe]

I do have a hydraulic leveling system that helps keep the weight off of the suspension, but the right side bags go down overnight the left side stays aired up between uses, even if my dash gauges drop to zero, somehow the leveler valves hold the bags full or at least partially full for some time.

[chessie4905]

Leveling valves have built in valves that won't allow leak back unless lever move  (due to suspension change in height) opens to admit or release air. If it opens to admit air and air pressure in supply line is less than pressure in bag, then air will go out of the bag back into air source line till either pressures equalize or bag deflates partially or completely. So either bag of line from leveling valve is leaking or leveling valve is defective.

[chessie4905]

Yes Geoff, I am also confused;too much to do a reply to him. More info needed.

[Templar52]

Sometime,the little valve inside the leveling valve is simply not there. Or at the wrong position. Poeple often remove this tiny valve and simply do not installed back in place. You have to check carefully to see this valve.
The close circuit of air in the rear and front suspension is create with thoses little bycicle tube valve.