M1078 CTIS Air Down Problem

[PhilM]

The front passenger side tire on my 1995 M1078 has ben airing down to flat when parked for several days. It airs up to the Highway CTIS setting when running. Now the drivers side tire has also started airing down to flat when parked for a few days. I haven't checked the hoses yet, but I assumed it was a bad air-wheel-valve. Is it logical that both front air-wheel valves to need replacement? Or should I look elsewhere in the system? Any thoughts from those who know this CTIS system would be really appreciated. It becoming a royal PIA!
Thanks!
Phil

 

[NDT]

Open the wheel valves and clean the seating surface and check for crud. Bubble test the hose and stem with Mr Bubble and a paint brush.

 

[Ronmar]

To confirm the wheel valve, fill the tire, Remove the banjo and tape a rubber glove over the banjo fitting on the end of the hose. If the valve leaks the glove will inflate...

do you have kneeling valves? At the opposite end of the wheel valve/hose assy from where the glove is attached, there is a elbow that connects to the wheel air pipe. on the front they put ones with a slotted screw head designed to act as a pressure reg and release the air down to a set low pressure when the screw head is turned. This was for use with the hydraulic suspension compression system for aircraft loading/transport. These valves often fail and leak...

 

[PhilM]

To confirm the wheel valve, fill the tire, Remove the banjo and tape a rubber glove over the banjo fitting on the end of the hose. If the valve leaks the glove will inflate...

do you have kneeling valves? At the opposite end of the wheel valve/hose assy from where the glove is attached, there is a elbow that connects to the wheel air pipe. on the front they put ones with a slotted screw head designed to act as a pressure reg and release the air down to a set low pressure when the screw head is turned. This was for use with the hydraulic suspension compression system for aircraft loading/transport. These valves often fail and leak...

Thanks: I'll try that and see what I learn!

 

[tennmogger]

Another common leak is where the kneeling valve (which Ron mentioned) screws on to the skinny end of the stem from the wheel. That joint has delicate threads and a tiny internal o-ring. The kneeling valve is heavy and puts a lot force on the end of the stem as it is whipped around while driving. The joint is hard to check, being out of view behind the kneeling valve and hard to get soapy water on.

If you take off the kneeling valve you can screw a Schrader stem valve into the tire stem and eliminate the CTIS stuff. Note that the end of the stem can become swedged to smaller size by the kneeling valve wallowing around on it and the end might need to be opened a tiny amount (drill bit by hand) for the Schrader valve to fit.

Your tire deflation could be simply leaky tires or the wheels internal o-ring.

 

[PhilM]

Another common leak is where the kneeling valve (which Ron mentioned) screws on to the skinny end of the stem from the wheel. That joint has delicate threads and a tiny internal o-ring. The kneeling valve is heavy and puts a lot force on the end of the stem as it is whipped around while driving. The joint is hard to check, being out of view behind the kneeling valve and hard to get soapy water on.

If you take off the kneeling valve you can screw a Schrader stem valve into the tire stem and eliminate the CTIS stuff. Note that the end of the stem can become swedged to smaller size by the kneeling valve wallowing around on it and the end might need to be opened a tiny amount (drill bit by hand) for the Schrader valve to fit.

Your tire deflation could be simply leaky tires or the wheels internal o-ring.

Thanks!