brock
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- Orange, CA
A number of weeks ago I had a thread about an air leak on my 1987 M923A2 that was shut down. This post is addressing the points discussed from that thread.
The symptom was a hissing sound coming from the intake stack and rapid air loss of the secondary air system. After much searching around the truck I was able to isolate the leak to the treadle valve under the dash. A stethescope was used to verify the leak was coming from the secondary braking system supply port and leaving through the exhaust port to the stack.
I ordered a replacement from Those Military Guys. Id like to add a couple of notes regarding the replacement treadle valve I bought:
The air pressure release port was not tapped for the -A2 configuration trucks with the Wet kit (uppermost port on the back of the valve). I had to tap the hole with a 1/2" NPT tap.
It is important to note that the replacement treadle valve came with a retaining plate that held the plunger assembly in place, not allowing the O-ring to pop out of place. Leave this on when attaching the pedal assembly on the valve, without the retaining plate the o-ring is at risk of being damaged.
After installation of the new valve the leak has gone away and braking effort has been significantly reduced. Total installation time took about 4 hours and was very straight forward.
If you are experiencing an air leak and cant seem to find it, take a look at your treadle valve.
I hope this post helps.
Thanks.
The symptom was a hissing sound coming from the intake stack and rapid air loss of the secondary air system. After much searching around the truck I was able to isolate the leak to the treadle valve under the dash. A stethescope was used to verify the leak was coming from the secondary braking system supply port and leaving through the exhaust port to the stack.
I ordered a replacement from Those Military Guys. Id like to add a couple of notes regarding the replacement treadle valve I bought:
The air pressure release port was not tapped for the -A2 configuration trucks with the Wet kit (uppermost port on the back of the valve). I had to tap the hole with a 1/2" NPT tap.
It is important to note that the replacement treadle valve came with a retaining plate that held the plunger assembly in place, not allowing the O-ring to pop out of place. Leave this on when attaching the pedal assembly on the valve, without the retaining plate the o-ring is at risk of being damaged.
After installation of the new valve the leak has gone away and braking effort has been significantly reduced. Total installation time took about 4 hours and was very straight forward.
If you are experiencing an air leak and cant seem to find it, take a look at your treadle valve.
I hope this post helps.
Thanks.