Air Pressure Drop?

[Jon Wehrenberg]

Jon,

My 95, on a 94 chassis, dumps the tag axle on loss of aux air. I have traced the pneumatic drawings for my coach and think I know the reason.

On the passenger side-rear, accessible through the access door in front of the chassis battery access door, a pneumatic cluster in located. This manifold is sourced by the aux air system. Through a 24 volt relay I think (Have not checked out that portion of the logic yet) is controlled by the Allison Transmission (After obtaining a speed of 15 or greater, the 24 volt relay is activated, routing supply air to the Norgren), air is routed to the supply of a Norgren that controls the tag release. When air pressure is loss on the aux system, supply is lost to the Norgren controlling the tag, and air is released from the tag through the loss of aux pressure, via the Norgren supply. I have looked at this in detail and this could be worthy of a seminar. It is so simple it is complicated.


Your statement that pilot air is de-energized (with the key off) to the Norgrens is correct for the front and rear duals. It get tricky on the tag axle logic.

The tag axle dump upon loss of aux air will happen on a 94 chassis (It does on mine.)


Hector

If I am correct, that is the system that is tied into the stabilizators to prevent the tag from lifting above a certain speed.

If that is the case there are very few of us who have that system still enabled. To the best of my knowledge you, Jim C and I have that system. Prevost has been disabling the system.

[Yankee802]

First, I'm not sure I understand how that bubbler thing detects air leaks, but I can find air leaks REAL fast with dish soap and a spray bottle, and it's cheap and easy.

Second, I guess my coach is of the vintage that does not have the lock in the airbags to keep them level. If my aux tank goes to zero, my bus is on the ground. I discovered this when a friend showed me how to bleed the aux air tank of water, man it was RED, almost like blood spraying out of that valve. I'll endavor to do that once a month. Also, my coach will ever so slowly sink down, albeit level, over a week or so. I haven't checked the air brakes, but after reading this thread, I'll do Jon's test. I have noticed that after almost a month sitting, when I start her up for her montly run, the air pressure in the dash guages are in the 60ish pound range, if memory serves.

Geoff

[Jon Wehrenberg]

Geoff,

Soapy water is only one method of finding leaks. When you get into chasing leaks you will find other methods are required due to the nature of where leaks can occur, a lot of locations requiring sophisticated devices because the leaks are internal.