The Nitro

Pulled the kidney valve all apart which is the one that changed air leak sound from flap on other valve when I hit it with hammer and it all looked ok except for a small bent rusty almost broken fine wire spring and rubber flap valve in the “con” port. Very rustly and corroded inside this port and suspecting the flap not sealing properly behind spring. (No idea if that port is linked to the problem or not) orings seemed ok in the rest of valve. will replace both valves I think and see.

The valve that I just showed apart has the 2 discharge ports and they go down to T pieces which then feed the 4 cans ports marked “spring brakes” so I’ve been calling it the park brake valve but didnt know the exact name for it. The first valve I replaced when this problem started at start of thread (one with leak out bottom flap and green hose on cap marked “signal” has its 2 discharge ports leading to T pieces that feed the 4 cans ports marked “service brake” so I was calling that leaking one the service brake valve as pushing brake pedal sends air down green signal line into the top of cap of that valve

Good to know thanks.

The check valve up in cap isnt real good either.

Might of found the problem. The big oring on park brake valve is buggered. That would let air from par brake go past and directly into yellow hose leading to service brake and out the flap. Never mind the other stuff Joey, thats just a nosecone, supersonic De larval nozzle, altimeter and dual deployment with redundancy backup parachutes ejection system I’m building for my rocket 😂

Rang the local truck parts guy and sent him pics of both valves and hes got em in stock. Ones called a kidney valve he said but wasnt sure exactly what it does Haha. Anyway the yellow hose thats leaking into service brake valve from spring brake/park brake valve is called the equalization port from what I can tell. He said its a couple hundred bucks for the 2 new valves so thats good hes got em if I need em. Truck needs to be on the Rd again by the weekend to deliver about 50 tonne of cow feed to a bloke that needs some.

The leak happens with trailer connected or disconnected so I think its on truck side but the trailer cans do need replacing after I fix the truck. The comment about dash brake valves could be relevent still as that red button for trailer brakes would not have been touched/pulled for perhaps 10 years as previous owner didnt have a trailer on it. Ive been using that button so if its somehow connected to engine off or on or feeds the park brake valve or the unknown valve i showed with green and blue and orange lines then we might be onto something. I will dissasemble the park valve and unknown valve and look in them tonight after work if i can

I can plumb my air compressor into wet tank somehow and see. Theres a coupler coming out of wet tank that was probably used to pump tyres in the past. I’m listening to everyones replies and picking out the logical ideas to check and try that fit in with my own understanding of how things might work. I’m not rushing off to parts store for every idea I hear online but at the same time I know theres a lot smarter guys here that me with more experience. The cans on trailer are looking very old, I can see inside peep hole the rubber is perrished a bit (still work) and the cans on trailer are 20/24 same as on truck. The new cans i bought will go on trailer instead when i find my problem on truck. So no loss there as trailer definitely needs new cans anyway. The problem will be found one way or another but taking it to truck mechanic is not happening. I couldnt sleep at night letting another bloke find this simple air leak it would make me feel useless hahaha

its my first truck mate, I didnt even know what a treadle valve or any valve at all on the truck was for untill a few months ago when I bought the truck. I’m a truck green horn. But I do like the challenge of learning how things work and trying to fix them. I’d be entirely lost without this website as its here where im getting help to fix all the problems I’ve found so far. The truck leaks down overnight while park brakes are on. A little comes out from cab air bag valve and a little from dryer valve and a little from rear airbag height valve. this leaking service brake valve is intermittent. Sometimes it leaks for 20 seconds then stops then sometimes it leaks continuous and the leak is significant that the compressor cant deliver more than 8 on dash guage where it is usually at 9.5 while its not leaking. I bought 2 new cans hoping it might be the inner seal on a can like was suggested. Removing all 4 can hoses (service brake side) while valve was leaking revealed the cans are not the problem as the air is coming from yellow hose and not cans. When its not leaking theres no air coming out yellow hose from park beake valve. So Turned my attention and hammer to that park brake valve and the one upstream from it. I have no understanding of how the circuits works and even less of the dash pull push buttons for brakes. But the problem started after I bought the trailer a month ago or whenever it was and started hooking trailer up and mucking about with trailer brake release knob in dash. Coincidence of not i do not know yet

Truck has only been back on rd for a few months after a couple years sitting. It had all sorts of air leaks when i bought it. One in axle diff lock, governor valve, air hoses, service brake valve, air seat hose fittings, a buggered check valve at wet tank, the treadle valve, etc. slowly getting it all fixed as things pop up. We will get there, but this one is taking a bit of time to track down. Appreciating the help for sure.

Air pressure governor valve is new and i backed it off slightly from where it was set by factory. Air gauge reads 9.5 in dash. I dont know if thats too high still and its causing problems but truck was running fine and the leak just appeared randomly

I might need to find an air diagram somewhere to try understand how the entire brake system works and see if that yellow hose is supposed to have air coming out of it from park brake valve to service brake can lines or not. I would of thought the air is meant to go up yellow line to park brake valve instead to tell park brake valve that service brakes are on. I have no clue really but the yellow hose is where the leak is coming from. It seems to just come into service brake valve and dump out the flap at bottom.

The duck quacking type sound is almost telling me there is some sort of spring involved in the fault

There is a red button on dash in cab to push in to release trailer brakes next to the yellow one and it looks to be run through some sort of brake away safety air valve at rear of truck and the connection of air lines to trailer is via a double port flat face coupler where you pull a spring lever and it pinches them together. I will have a look at trailer brake hoses on truck side and try figure out how that works or how thd air gets there. the service brake valve is the one that leaks out bottom flap. It takes signal by foot brake via small green hose on top and sends air to both black hoses to cans service ports. The yellow hose is t into one of service brake ports at the valve and looks like its supposed to get pressured up the same as service brakes and heads over to park brake valve. (Not sure why) but while the leak is present the air is coming back from yellow hose park brake valve. I think its not supposed to do that. So im guessing either the park brake valve is leaking or the other one with orange hose in front of it. The leak doesnt sound like plain leak like if you had a hole in a tyre, it sounds more like a duck quacking over and over

Just started truck again and the leak is stopped again. No amount of hitting valves with hammer can invoke it. Guess I will drain tanks and keep trying to get it to leak again. I’ve saved probably $600 in labour soo far trying to find it so thats good hahaha.

This is the valve that feeds the service brakes on both rear axles via the black hoses and has the air leaking out bottom. The air is leaking to the black service lines rather than leaking back from the service brake lines. I removed the yellow hose and air is coming out of it and going into the valve and leaking directly out bottom flap. i followed yellow hose and it comes from this valve shown below on other side of frame that feeds the park brakes on cans. I tried hitting this valve with hammer and it didnt seem to change the big leak still coming from service brake valve. i followed orange lines on this park brake valve towards cab and find this valve shown below: When I hit this valve with hammer the leak changes a lot. Im not sure what this valve does but its looking like it might be the problem. Unless its even farther upstream from this one I have no idea but thinking I might try buying a new one of these and see.?

Ok guys, made some progress. Yes the truck wheels are chokked up nicely. So I just started truck again and its leaking bigtime again. It wont even build up maximum air pressure because of that leaking flap on bottom of valve i showed. So I removed all 4 service brake lines off cans and none of them have air leaking out from cans. Hmmm but the leak is still roaring out from that valve. it appears its not the cans inner seal at fault.

Just watched video that was posted about how to set pushrod length. Made sense to me. Thanks

I can use the allen head bolt in the caliper to set the brakes to 90 degrees after new cans are on yep.

I’m now starting to think I need to try remove all 4 cans and check the stickout length of them to eye from the mounting face uncaged and see if the 2 new cans i bought allow enough threads to end up with the same length. If so... i just wind the eye down on new cans to same length as old ones. Chop excess thread off and lock nut up and re install. Is this right?

I might try taking a can off truck and see how it looks once its at its fully extended length like the new one is and it may work afterall. Mechanics are on $180 an hr here so If I can figure this stuff out via this forum and my pictures I post it will surely help me out.

I was thinking the 90 degrees would also be maximum leverage and not sure why the rego guy has tightened the brakes that much. I also felt he adjusted brakes a bit short as I had adjusted them all to 90 degrees myself prior to taking truck in for rego inspection but didnt question him as he is the guy passing it for rego/ mechanic and I’m just a back yarder learning best i can as I go along.

The brakes in box are uncaged. Ahhhh I see. what Mark T just said just clicked for me. In other words the brakes are fully on in the boxed cans. If I were to remove my old brake can I am now suspecting its rod will also stick out more than it is now on truck its just that the brake adjustment is preventing it. yes your right I’m new to trucks and havn’t understood how it all works. But learning as I go with this forum help. Its making sense now. I was forgetting the rod in my can on truck is so short as the caliper is stopping it going to its full extended range like the new one in box is showing. I’m now thinking I may have to leave brake hoses connected with brakes released to remove can or else insert the caging bolt to get the pressure off the eye to remove pin. I think I’m learning something guys. Haha. Appreciating the help for sure.

Thanks for the help mate. I will buy 4 new cans and see if that fixes it. I will keep trying to get it to leak again today but seems the cans are the best place to look from all advice here so far. thanks guys