This post is for BAC members with SMC-era coaches with air-over-hydraulic brakes. I've had my Beaver for 4+ years and have been accustomed to the fact that by morning the pressure in both my air tanks was significantly below operating levels. I've asked several shops to look for leaks and no one was able to find any. The coach drove fine and the compressor would cycle on and off with a frequency that depended on how "undulating" the road surface was and how much air the airbags were using while staying level. Sinec I didn't know anything different this is what I accepted as normal.
Last week I asked Iron Horse RV to bleed the hydraulic brake system and refill with fresh fluid. Since the MH is 15 years old and I have no record of this ever being done I decide this was a smart maintenance item to do. After the system was refilled and was being tested a major leak in the air pressure side of the system became apparent. The source of the problem turned out to be the air valve located beneath the brake pedal which had blown an O-ring. It's a difficult thing to get to and has like 9 air lines going to it so removing and replacing is not a fast procedure.
Once we examined the valve it was apparent that it probably had had a slow leak for quite a while until it finally ruptured the O-ring. In fact, with the new valve in place the air pressure in both tanks stays virtually constant overnight. While driving air is still used for leveling but, on the average, the compressor cycles on less often.
If anyone else is experiencing symptoms similar to what I have described you would be well advised to consider this as a possible cause. We were very lucky that the system failed while at a shop since the consequences of such a failed valve would be loss of all air pressure to the brakes and air bags.
The valve is an E-6 Coreless Valve P/N BEN-OR286171X for which I was charged ~$92.
