Air wont build up bleeds off thru intake

[aztec]

931-a2 wont build up air pressure can hear air escaping in intake stack wont hardly build 80 lbs shut off and bleeds out thru intake right away.. Help PLEASE

 

[74M35A2]

I think this one is an air brake part, possibly located just behind front bumper. Simp knows this system somewhat decently. He'll be along here in a minute....

 

[aztec]

Thanks

 

[simp5782]

First make sure that your transfer case handle switch is not stuck pushed in. This can allow air to bypass the interlock solenoid and vent out. If your problem stops, report back, if nothing changes move on to making sure your brake pedal is releasing all the way back up. If it is fine. With it running, open the drivers rear glad hand and see if you have air escaping that is bypassing the brake pedal valve. If yes, report back and we can chase it. If no pressure is there. Crawl under the truck and close off the valve that Is on top of the wet tank on the truck. It has 2. One on front. One on the top middle. Close the top middle and see if your primary air gauge builds more pressure and the air escaping sound goes away. If no. Report back and we can chase that issue. If the primary builds air pressure Then reopen the secondary shut off valve and go to the front of the truck There is a small drop down plate with 4 or 5 air lines on it in front of the front axle below the radiator. Scrape paint from the lines and remove the white line from the valve. This is usually the bottom drivers side line. If you have air coming from the valve on that port, you have a bad Q2 valve.

If you have air coming from the line side you removed then that next
Step is to start at the brake pedal vent and work your way back. Report back after you have followed these diagnostic procedures. I can make a video If needed.

 

[aztec]

xfer sw good brake pedal up no air glad hand closed valve on top of tank no change other primary stays at zero secondary wont go above 80 long time air coming out intake

 

[aztec]

352-322-0692

 

[simp5782]

Ok so with the secondary valve closed the secondary tank holds air and does not bleed off.

This indicates a primary side bleed and nothing on the secondary to include the Q2 valve. However we want to make sure so on the front Q2 valve vent line and see if you have air coming from the line side. If yes, move on to the treadle valve vent line. This is the very top air line on the treadle valve in the engine bay to the inside of your Protective control box. Remove the top line and see if you have air pressure from the valve side or the line side. This will be a large Horton jacket hose with 7/8" JIC fittings. Make sure both valves are open on the wet tank first. If air is coming from the valve side. Replace the brake pedal valve if air is on the line side move on to Chock the wheels while parked on flat ground. Release the parking brake. After releasing the brake see if your secondary tank drops air pressure. It shouldn't. Take a spray bottle with soapy water and spray around the spring brake cans on the front axle first. Then work your way to the Right rear. Report back on which one you see bubbles on. IF you have no bubbles at all. Let me know and I can tell you how to isolate which cans it could be. More than likely it is a spring brake diaphragm

 

[aztec]

secondary does bleed off wont build past 80

 

[aztec]

constant air leak into intake

 

[simp5782]

Ok. If you closed the valve it can't build air pressure so it should be at 0 or holding what it's got and not bleeding off. So zero or holding pressure on the secondary with it closed. The primary Is not building air at all then with the primary valve solely open either.

 

[aztec]

tried to drive brakes are locked wow truck worked perfect before filter change

 

[simp5782]

Well If the tanks dont have air then nothing gets to the spring tank via the secondary or primary tanks therefore there is no air for the brakes to release. I am uploading a video on the checking procedure now.

Did you remove the vent line from the Q2 valve to see if you had air on the valve or the air line side. Do this with both tank valves open.

If you have a source for accessory air then hook up a gladhand to the rear emergency side and use a home air compressor to charge the system so you can hear for air leaks as well.

 

[simp5782]

https://youtu.be/QyIEZVQfnLk

 

[aztec]

where is the lineal valve

 

[aztec]

no air at q2

 

[simp5782]

There are 2. One is what the parking brake activates. the other is on the transfer case front where the shift rod linkage is and is activated by the large washer.

The emergency brake linear valve can bypass air if it faults. Simply remove which ever one is the vent line in the cab on the rear of it. Look under it for which port the white line goes to. Typically the middle port

The transfer case linear valve only gets air with the wet tank above 60 psi. There is no gauge for the wet tank. You can close off both primary and secondary air valves off the wet tank and see if you still have air from the intake. This shows either a stuck interlock cylinder or transfer case linear valve bypassing to vent they the stack.

 

[simp5782]

no air at q2

Do you have air coming from the line side at the Q2 that comes from the frame rail? If yes or no go up to the vent line off the pedal valve on the firewall. If no then you are definitely dealing with the Pressure protection side of the truck

 

[aztec]

parking brake lineal is blowing by air stops when I engage parking brake primary and secondary pump up to 135 and hold but now I cannot get spring breaks to release

 

[simp5782]

Bypass the linear valve and go to a push pull type valve. You have a spot in front of the shifter with that hole in the spacer bracket for the valve to be mounted. You can push the dashboard black button to override the spring brakes

https://youtu.be/ELcWO5Q2A1w

 

[aztec]

my truck is a 931-a2 tractor wirh a spring break over ride on dash push to over ride nothing happens