2019 LT Air Leak at Front Relay Valve

I am trying to figure out what is causing my air leak. It is very audible when the service brake is pressed. It makes no difference if the park brake is engaged or not. I have located two relay valves on the truck. One is under the 5th wheel area and the one in question is located under the driver door area near the battery box. All the air lines going to it are orange. The relay valve is an R-14 type. The leak is coming from the balance/quick exhaust port on the top not the normal exhaust on the bottom.

I have done some tracing on the service line to figure out where it is routed. From the relay valve it goes to another valve mounted further back under the cab. I'll call this the mystery valve as it is very hard to see and buried by cable looms of wiring, air lines, etc. The mystery valve seems to be straight through. I don't feel any 3rd air ports, though, there might be an electrical connector (this is all based off my memory and I could be wrong). From the mystery valve it goes back to the treadle valve on the firewall. All the lines are 3/8 so that seems to be a signal line.

So I think this valve is used for front brakes because of the color of the lines and location. Can anyone confirm? This WABCO general troubleshooting document seems to be the closest/most accurate for my truck.

I have read general suggestions on troubleshooting air brakes/relave valve issues and two common themes seem to be issues with a Quick Release valve and internally leaking brake chambers. I have been unable to locate a QR valve for the front though I can find two on the rear. Also, the steer axles have Type 24 chambers so I am not sure how a leaky brake chamber can backfeed if there isn't a park brake involved.

I had some training on air brakes as a heavy truck mechanic in the Army but my knowledge is sort of basic and we didn't have all the modern ABS and anti compounding to deal with. Can anyone give some general guidance on troubleshooting? Many thanks in advance!

 

I did some more digging. There are 3 lines connected to the mystery valve not 2 as I originally stated. The valve is either a Wabco differential brake valve or a Wabco 3/2 way solenoid valve. (Page 29 & 30 of the PDF ) The markings on the paint are in terrible shape so it's really hard to get the numbers. I also got a much better idea of the line routing so now the picture is becoming more clear to me. See my updated plumbing drawing (Int'l partial brake ckt). I can blow into port 1 on the Wabco valve and air comes out port 2 sending it to the balance exhaust port on the R-14 relay valve. I presume that air should be sent to port 3 in normal operation and port 2 as required according to pulses sent on the electrical connection to control the valve.

 

@Heavyd that drawing is incredibly helpful. Thanks for sending! I am glad to see it matches my crude hand drawing. Part #2 Traction solenoid valve would seem to be the logical culprit based on my symptoms. I did a check with my meter and the solenoid measures about 8 ohms. I suppose I could also check for voltage on the connection but maybe that voltage is only present when needed?

Anyhow, it seems logical that the valve has failed. I don't think it should always dump air to the R14 balance exhaust port. Would you agree?

I did a part lookup using OnCommand and the part number from International is 3567224C1. I wasn't initially able to find (the more universal) Service Part Number.
However, a little more searching for P/N 3567224C1 yielded a hit from Wabco with a part number of 4721708670.

Now let's see what that little bugger is gonna cost... Prices are all over the place on this one.

 

@JB7 Thanks for the comments. I think we are saying the same thing.

Yes, that is the value I got.

I removed the supply air at #2 C and no longer hear the leak at #15. Like I said in my previous post, if I blow through the valve at C, air flows from C to D. I tested this by pressing the brakes and I can feel air at D every time I press.
I can also see the logic for doing it your way.
Also, the leak always/only happens when I press my service brake (if there is air in the system) regardless of park brake position on the dash.

Yeah, I am not seeing any evidence of that. No codes or warning lights.

I'll double check the chambers and see what they do. That's a good point. I'll also wait and see if Heavyd has any additional input. This part isn't cheap so the cost of a manual with procedures might be worth it. At the end of the day I am trying to be sure I am diagnosing correctly. I personally hate guessing and I acknowledge what you said. Right now it is just a logical (slightly educated) hunch.

 

I followed up this afternoon after work.
I confirmed that the Wabco solenoid valve is getting 12v at the electrical connector when the truck key turns on. So the valve is capable of getting electrical signal. After that, the computer controls on or off so I shouldn't condemn it.

OK, I see why I was confused and going the wrong way with my logic. My understanding changed based on two different drawings for the R14 valve.
The R14 w Passage Way drawing clearly shows that that service port air acts on the piston and moves it down. This in turn opens the valve and supplies air to the delivery ports. The delivery ports supply air to the brake chambers and cause them to move.

The drawing that had me confused was R14 no Passage Way Shown. I was interpreting the drawing literally as shown and thinking air was getting routed out the exhaust because it had nowhere else to go. I should have read more carefully. The dialogue explains the operation of the valve even though the picture doesn't depict the flow as well as the other.

I didn't see any movement on the brakes chambers when I pressed the service brakes. I presume there must be internal leakage in the relay valve and should be rebuilt or replaced. I just got a spare valve this evening that I can swap in to test. Fingers crossed...

 

Thanks Heavyd
Your commentary lines up very closely with my understanding plus the new things I just figured out about R14. The only area we differ is on the cover for the R14. My understanding is that the valve has an exhaust port on top. I have not heard of them leaking through the material but I suppose anything is possible. I just haven't experienced that before. Plus, there can be minor differences depending on who made the part and how it is used in circuit.

I did take out the R14 valve at one point and performed a general inspection. I didn't find any obviously broken plastic on the piston or bad o rings. That's what caused me to suggest that there could be some internal leakage. Maybe the O rings look ok but not good enough to allow air to be delivered to the chambers or the piston is sticking. JB7 had a good suggestion to watch what happens when applying the brakes. Anyway, we both agree that R14 should be replaced. I'll report back when I get R14 changed out.

Thanks to both of you!