Haven't found info on a rebuild kit for Wabco 461-315-161-0 treadle valve yet. Several local auto parts places and a big truck repair place don't find reference to any kit. The big-trucks guy speculated the treadle valve is critical enough that a new, certified, valve might be all that is available.
Anyway, I took apart the treadle valve again, cleaned again, and got it working fine. The guts look like new, o-rings pliable, and face seals just fine. I had just found a tiny pile of sand in there and one chunk caught in a face seal. That's what dumped my air.
Here are some notes if you suspect trouble with the treadle valve. First, the vent for it is in the center of the front of the truck, in front of the radiator, and you can reach it if you take off the grill and reach upward. It vents downward. But, reaching it won't help a bit!
Physically tracing the source of the hose to that 'leak' is impossible....can't to it, it's back behind the heater. Just know that that vent comes from the treadle valve. The hose to the vent comes off the treadle valve on it's rear, the side nearest the driver, and nearest to the steering column. The thin-walled vent hose is a press fit, and can be removed by hand. Pull the hose off and now the vent is right there under the steering column where you can hear it. If you heard air escaping up front, you will heard it there at the treadle valve.
This is where the swoosh of air comes from when the brakes are dumped.
A leak through the treadle manifests as air coming out that vent. As air flows there then air will be flowing through the brake controller on the dash. It can sound like the (yellow knobbed) control is leaking.
The leak can be on either of the two circuits, front or rear, and it can make a huge difference on repair effort as to which is leaking. My initial leak was on the rearward section and that is the tough one to work on, but it can be done without removal.
Testing which section is leaking: First, a numbering convention is needed. There are four tubes coming out the left side of the treadle valve. As you look at them from standing beside the drivers floorboard, I called them 1, 2, 3, 4, just as read from top left to lower right.
1 and 2 are input hoses and have truck air on them. If you remove the lower two, 3 and 4, those go to the brakes and have zero pressure if not actuated. If pressure is coming out of either of those hoses (hose side) it's feedback from the brake system, and something leaking elsewhere, not the treadle.
If there's air coming out of the ports 3 or 4 then the treadle valve is leaking. My initial failure was air leaking out of port 3 (caused by the gravel in the face seal). My second failure was leakage coming out of port 4, the other face valve leaking.
If your leak is out number 4 then removal of just the most accessible half of the treadle valve is required. Disconnect the pressure sensor, take out 4 bolts holding the two halves of the treadle valve together, and work it loose. Note o-ring seal.
Take apart this half of the assembly with retainer clip pliers, being ready for strong spring pressure(!!!). Disassemble, clean out junk, lube, and reassemble.
It's a good idea to remove both hoses 1 and 2, build truck air, and let those hoses blow all the crud out of the lines before reattaching everything.
That how I got my brakes going.
