M939A2 (M923A2) wheel valve rebuild

[Alexsha]

So the parts came in and I had the time to rebuild my wheel valve that wouldn't stay shut. I had taken the valve apart before and cleaned it, but it just wouldn't stay shut and when the CTIS stopped inflating, it immediately began deflating back to the QRV. Annoying to say the least. So here's my adventure in pictures!

 

[Alexsha]

You can definitely see the difference between the old and new diaphragms. If your CTIS valve is leaking, replace the diaphragm first. There's not much that can actually break the valve body. You just need to check the center nut for corrosion. Also, the new spring was a bit longer, probably because it's new, but maybe pulling out old springs can help.

I wish I had taken a before picture of the valve body. There was a LOT of gunk in there. I had to use a brass brush to clean it out.

With these rebuild my CTIS is inflating the tires just fine and they're holding air. The last issue I'm seeing is that even when full (62psi) the CTIS will go into an inflation cycle for quite some time before the highway light goes solid. It stays that way for a couple minutes then it goes back into inflation. The tires don't seem to be airing down and letting the truck sit, the pressure stays. With the CTIS running there's a bit of air coming out the front QRV duckbill. I'm wondering if I'll be rebuilding/replacing that next.

 

[MtnSnow]

Nicely done Alex

 

[todds112]

Amazing how simple they are inside. Thanks for the pics.

 

[Alexsha]

Some things to note:
1. The o-ring that seals the connection to the tire stem is worth replacing. I did not but will do so later.
2. The steel tube coming from the hub that attaches to the wheel valve is actually 2 pieces. I cleaned the rust out of the connection with steel wool. There was a slight air leak after reconnecting it. I used some plumbers goop and it sealed right up.
3. When you unbolt the wheel valve top, it might stick... and then shoot across the room because of the spring. Be aware.

 

[Alexsha]

Reading through the ctis troubleshooting guide, it seems that air should not come out the qrv at all except during a deflate. I would imagine as the system inflates, if one of the 3 axles is at pressure before the others, air would be released at that valve. Is that the case or not?

 

[Suprman]

In theory all 6 tires are connected so air in will go to the lowest tire. The pressure sensor could be off slightly. I think the system wants to see around 65 psi at highway pressure. It will continue to do pressure checks every 15 minutes or so automatically. If your tires don't leak down just unplug the control and when you want to use it again you can plug it back in. With the truck off of course. The pressure check gets annoying. You could also have a few small leaks on the fill lines so when it does the pressure check it sees a few psi less than it should. When filling its sending a steady feed of air so the little bit leaking here and there dosnt really affect filling.

 

[Alexsha]

Unplugging it is not an option. It must work. Such is my nature.

So, I should get out the soapy water and check all the lines and connections from the PCU to the QRVs and from the QRVs to the wheels. Basically everything between the PCU and wheel valves.

Would enough small leaks on the fill side cause it to check more often than 15 minutes? Basically it gets up to pressure, the light goes solid, and within about 2 minutes, it checks again and starts filling again.

 

[Suprman]

Doing a pressure check on 15-20 minute intervals is normal. There are 2 styles of controllers. One that the lights are always on with the truck and one that the lights are only on when the light switch is on. The second being newer and I believe it has a newer program. In my experience the newer controller works a bit better. I unplug my controller because the continuous pressure check is annoying and I have no need for it.

 

[98G]

Was that the mid right valve you rebuilt?

 

[Alexsha]

Was that the mid right valve you rebuilt?

No. It was the driver side front. I found that 2 of the 3 solenoids were dead in the PCU, so the ctis was never actually coming on and filling. Once those were replaced the ctis would come on, but once the truck was shut down the front driver tire would deflate to 20 psi or so before the wheel valve could close.

 

[todds112]

No. It was the driver side front. I found that 2 of the 3 solenoids were dead in the PCU, so the ctis was never actually coming on and filling. Once those were replaced the ctis would come on, but once the truck was shut down the front driver tire would deflate to 20 psi or so before the wheel valve could close.

How did you replace the solenoids? Where did you get the new ones?

 

[Alexsha]

How did you replace the solenoids? Where did you get the new ones?

That deserves it's own thread. Let me look through the invoices and do a write up. I forgot to take pictures, but it's pretty straightforward.

 

[Alexsha]

Here's a write up:

http://www.steelsoldiers.com/showthread.php?137569-M939A2-CTIS-PCU-solenoid-replacement&p=1693141