lino
Member
- 148
- 2
- 18
- Location
- Wake Forest, NC
Hey All,
I need a sanity check. I think...
So I have a USAF deuce with the dual circuit brakes. I recently rebuilt two short airpacks and replaced the two that were in there. I also replaced the MC, with one from Peashooter. Functionally the same, but has remote reservoir and integrated bias switch.
(if this post belongs in the deuce modification section for that reason, I apologize)
I had a heck of a time getting the MC bled. I probably should have bench bled it, but without an integrated reservoir, that was tricky too, and since the airpack bleeders were close, I bled it from those.
The lines between the MC and the airpacks are also new.
So after running about 3 gallons of BFS thru it (some recycled since it was thru new components) I thought I was good. No more bubbles. I should clarify that while using a power bleeder, I also cycled the pedal (convenient from below on these trucks!) so that I could urge all the air out of the system.
I still had a two pump pedal when done. First pump got to about 1/3 from floor. It could lock the brakes like that too. Second pump was about 2/3 from floor, and much firmer. Wait about 5 sec and you were back at "first pump" levels.
So, I talked with Peashooter and on his advice (and being reminded about a post I'd read), I tried "reverse" bleeding by using a vacuum pump on the MC reservoir and back feeding fluid thru a primed bleeder line and bottle at both airpacks. Even more air came out.
I did have an issue on the right (front) airpack side because the vacuum necessary to pull the fluid back was enough to draw air from around the bleed nipple threads. So I reset the works on that one. Started over, replaced the bleed nipple, was very careful how much vacuum I applied - and I started over.
After all that, I re-bled the whole system, per TM. First airpacks, then rear-rear, then rear-front, then front. I pulled almost a quart thru at each location, just to be sure. No bubbles.
And I still have two pump brakes.
First pump gets very solid about 1/3 left (or 2/3 of way to floor). Haven't test driven yet, but I suspect it will lock everything up. Second pump is much higher, about 2/3 travel left when it firms (or 1/3 of way to floor). Within about 5 sec, it's back to "first pump" status.
My intuition tells me that this can only be air in the line. Am I nuts?
Is this normal?
Can someone recommend something else to try?
Is this OK?
(as it is, I feel like I'm insane - doing the same thing over and over and expecting a different result)
Any help, comments or recommendations would be greatly appreciated!
Thanks!
ciao
lino
Oh, and I have some other possibly relevant notes:
*While test driving, when I stomp on the brakes then release, it feels like they remain on for a brief moment longer. Parked, the brake lights support this too. They stay on briefly (less than one sec) after I let go. Only after a hard push. Light push has immediate release.
*Vent lines on air pack function fine. I also disconnected vents at airpack and had same function.
*Pedal linkage has 1/8" free play before engaging MC
*MC reservoir vent is free flowing and not clogged.
*When I push pedal, there is a whoosh, and I can see air pressure gauge drop slightly.
*When I release, there is a whoosh from the vent hose.
*MC vent is separate from airpack air vent.
*It's too subtle to feel with my foot, but when I pull the pedal with my hand from below, I can feel pressure build, then something moves (in airpack), motion gets easier, then air starts to whoosh.
* Airpacks were lubed with GP grease on air side and silicone grease and BFS on fluid side when I rebuilt. - possibly I should add some air tool oil to airlines upstream of airpack.
*Airtanks are bled until no more water comes out each time engine is run.
Thanks again!
I need a sanity check. I think...
So I have a USAF deuce with the dual circuit brakes. I recently rebuilt two short airpacks and replaced the two that were in there. I also replaced the MC, with one from Peashooter. Functionally the same, but has remote reservoir and integrated bias switch.
(if this post belongs in the deuce modification section for that reason, I apologize)
I had a heck of a time getting the MC bled. I probably should have bench bled it, but without an integrated reservoir, that was tricky too, and since the airpack bleeders were close, I bled it from those.
The lines between the MC and the airpacks are also new.
So after running about 3 gallons of BFS thru it (some recycled since it was thru new components) I thought I was good. No more bubbles. I should clarify that while using a power bleeder, I also cycled the pedal (convenient from below on these trucks!) so that I could urge all the air out of the system.
I still had a two pump pedal when done. First pump got to about 1/3 from floor. It could lock the brakes like that too. Second pump was about 2/3 from floor, and much firmer. Wait about 5 sec and you were back at "first pump" levels.
So, I talked with Peashooter and on his advice (and being reminded about a post I'd read), I tried "reverse" bleeding by using a vacuum pump on the MC reservoir and back feeding fluid thru a primed bleeder line and bottle at both airpacks. Even more air came out.
I did have an issue on the right (front) airpack side because the vacuum necessary to pull the fluid back was enough to draw air from around the bleed nipple threads. So I reset the works on that one. Started over, replaced the bleed nipple, was very careful how much vacuum I applied - and I started over.
After all that, I re-bled the whole system, per TM. First airpacks, then rear-rear, then rear-front, then front. I pulled almost a quart thru at each location, just to be sure. No bubbles.
And I still have two pump brakes.
First pump gets very solid about 1/3 left (or 2/3 of way to floor). Haven't test driven yet, but I suspect it will lock everything up. Second pump is much higher, about 2/3 travel left when it firms (or 1/3 of way to floor). Within about 5 sec, it's back to "first pump" status.
My intuition tells me that this can only be air in the line. Am I nuts?
Is this normal?
Can someone recommend something else to try?
Is this OK?
(as it is, I feel like I'm insane - doing the same thing over and over and expecting a different result)
Any help, comments or recommendations would be greatly appreciated!
Thanks!
ciao
lino
Oh, and I have some other possibly relevant notes:
*While test driving, when I stomp on the brakes then release, it feels like they remain on for a brief moment longer. Parked, the brake lights support this too. They stay on briefly (less than one sec) after I let go. Only after a hard push. Light push has immediate release.
*Vent lines on air pack function fine. I also disconnected vents at airpack and had same function.
*Pedal linkage has 1/8" free play before engaging MC
*MC reservoir vent is free flowing and not clogged.
*When I push pedal, there is a whoosh, and I can see air pressure gauge drop slightly.
*When I release, there is a whoosh from the vent hose.
*MC vent is separate from airpack air vent.
*It's too subtle to feel with my foot, but when I pull the pedal with my hand from below, I can feel pressure build, then something moves (in airpack), motion gets easier, then air starts to whoosh.
* Airpacks were lubed with GP grease on air side and silicone grease and BFS on fluid side when I rebuilt. - possibly I should add some air tool oil to airlines upstream of airpack.
*Airtanks are bled until no more water comes out each time engine is run.
Thanks again!
