09-12-2017, 09:03 AM
Yeah Bill, to have 4 things fail at the same time seems highly unlikely. And as you say, even if the HCV's failed they should only allow air to leak if the travel solenoids leak when they are supposed to be shut. The HCV's could be leaking SUPPLY air all the time but that should not effect the air bags whenever the TRAVEL solenoids are closed.
Let me think this through out loud. The air bags have relatively high pressure in them +90psi in my 93 single axle coach. So, if the rear is dropping, that air pressure needs to be leaking to some place that is lower in pressure, either the atmosphere or to the SUPPLY tank if it is less than 90psi. We believe the bags themselves and the lines to them are not leaking because there are times when they hold up just fine. The thing that stands between the air bags and the places of lower pressure is the 6 pack. So, let's take the solenoids one at a time.
The "Raise" solenoids, if leaking, could drop the rear, but only if the SUPPLY tank was less then 90psi and would tend to raise the rear if much above 90psi. The raising part doesn't seem to be happening so we can rule that out.
The "lower" solenoids, if leaking, would drop the rear in all the time and would be compensated by either the HCV's in the "travel" mode or by the "raise" solenoids when activated. We can test if that is happening by applying soap bubbles to the vents at the 6-pack. This failure seems unlikely since I think you described no dropping occurred when going from "travel" to "off" at the control panel. Still, since soap is cheap and easy it's worth verifying.
The "travel" solenoids, if leaking, would drop the rear only if the HCV is either above its set height or if it was below its set height and the SUPPLY tank is less than 90psi and air would then go backwards into that tank. One other way to test this besides pulling the travel air lines at the 6-pack would be to dump the rear a bit, go to the "off" mode on the control panel and ensure that the SUPPLY tank stays above 100psi. If the "travel" solenoids are leaking the rear should slowly rise as the HCV tries to get back to its set height.
The added conundrum is that both sides seem to be dropping at about the same rate so whatever leaks exist must be nearly identical, not likely due to wear or holes.
I'm beginning to fear that all these tests will prove negative and we have a logically impossible problem. If that is the case, I'm looking in the wrong place, because all these problems are ultimately logical. Hmmm. Where else might I look. The only other support of the rear of the coach is the tag axle. I don't have one so that has just now entered my thinking. So, now I'm thinking I would put a pressure gauge on either of the lines from the 6-pack to air bags and know for sure the dropping is due to lowering pressure in the air bags. If the pressure is dropping I really need to put my thinking cap on tight. If the pressure is NOT dropping then I would start looking to the tag axle suspension system. Geez, I love my "simple" system.
Bill, sorry I can't be more definitive, but given that you seem to have a logically impossible problem .....
Let me think this through out loud. The air bags have relatively high pressure in them +90psi in my 93 single axle coach. So, if the rear is dropping, that air pressure needs to be leaking to some place that is lower in pressure, either the atmosphere or to the SUPPLY tank if it is less than 90psi. We believe the bags themselves and the lines to them are not leaking because there are times when they hold up just fine. The thing that stands between the air bags and the places of lower pressure is the 6 pack. So, let's take the solenoids one at a time.
The "Raise" solenoids, if leaking, could drop the rear, but only if the SUPPLY tank was less then 90psi and would tend to raise the rear if much above 90psi. The raising part doesn't seem to be happening so we can rule that out.
The "lower" solenoids, if leaking, would drop the rear in all the time and would be compensated by either the HCV's in the "travel" mode or by the "raise" solenoids when activated. We can test if that is happening by applying soap bubbles to the vents at the 6-pack. This failure seems unlikely since I think you described no dropping occurred when going from "travel" to "off" at the control panel. Still, since soap is cheap and easy it's worth verifying.
The "travel" solenoids, if leaking, would drop the rear only if the HCV is either above its set height or if it was below its set height and the SUPPLY tank is less than 90psi and air would then go backwards into that tank. One other way to test this besides pulling the travel air lines at the 6-pack would be to dump the rear a bit, go to the "off" mode on the control panel and ensure that the SUPPLY tank stays above 100psi. If the "travel" solenoids are leaking the rear should slowly rise as the HCV tries to get back to its set height.
The added conundrum is that both sides seem to be dropping at about the same rate so whatever leaks exist must be nearly identical, not likely due to wear or holes.
I'm beginning to fear that all these tests will prove negative and we have a logically impossible problem. If that is the case, I'm looking in the wrong place, because all these problems are ultimately logical. Hmmm. Where else might I look. The only other support of the rear of the coach is the tag axle. I don't have one so that has just now entered my thinking. So, now I'm thinking I would put a pressure gauge on either of the lines from the 6-pack to air bags and know for sure the dropping is due to lowering pressure in the air bags. If the pressure is dropping I really need to put my thinking cap on tight. If the pressure is NOT dropping then I would start looking to the tag axle suspension system. Geez, I love my "simple" system.
Bill, sorry I can't be more definitive, but given that you seem to have a logically impossible problem .....
Jon Kabbe
1993 coach 337 with Civic towed