[77newell]

The total tire to road traction available on the tag axle has to be considerably less than the drive axle - half the tires and a lower air bag pressure. To compensate for this difference one or both of two things must be designed into the system. the brakes would have a smaller braking area and/or the force applied to actuate the brakes must be lower. A lower actuation force could come from either a smaller brake "can" or from lower actuating air pressure. Additionally, if we are to maintain optimal braking effectiveness, as the air bag pressure is changed there must be some way to adjust the braking force or we either lose some potential additional braking effort with higher tab axle air bag pressures or we slide the tag wheels with reduced tag axle air bag pressures.

SO, are the the brake drums the same size on the tag and drive axles, are the "cans" the same size on the two axles, what difference is there to between the two relay valves controlling the respective brakes. Given the evidence thus far, I'm wondering if the relay valve for the tag brakes is either messed up or is the wrong one. Just thinking out loud here in cold wet Michigan.