Short Air Pack- 3 Leak Questions

[ckid]

If anyone has input on this, I'm all ears. Rebuilt my short air pack a couple of months ago using the guide @silverstate55 wrote up on these forums for the short style, bled the brakes, have run the truck a few times checking other systems.

This weekend I noticed a drip around the O-ring where the air can joins the hydraulic side. Pulled the air pack and also found brake fluid in the air pack vent line. Took the whole thing apart and there was actually less fluid in the air can than in the vent line– just enough to cause a few drips when I poured it out. The vent lined had enough in it to pour out in a little stream- maybe a tablespoon worth?

Checked my cups- all turned the correct way. The only cup I didn't replace during the original rebuild was the one in the fluid side of the aluminum assembly the goes on the pushrod. It's the one that's pinned in, and there was no replacement in the kit (same as per the instructions I was following).



My first thought was this cup was leaking fluid into the air can– except there was very little fluid in the can, and more in the vent line. Plus, the cup doesn't look torn or seem too dried out.

Then I found a little corrosion I had missed inside the slave cylinder housing where the lower piston sits. Enough to make the cylinder wall a little rough.



So my second thought is maybe the corrosion was preventing the cups on the lower piston from sealing, allowing the fluid to leak by it from the fluid chamber and into the slave cylinder housing, and when the brakes were applied the air carried some of that fluid into my air can. This made more sense because there was, again, more fluid in the vent line than in the air can.

All of that to ask 3 questions.

1) Does my thinking about the leak source make sense (leaking past the lower slave cylinder piston), or am I missing something?

2) Can the pinned-in cup in the aluminum piece be replaced? Looks like I could pull it out through the center hole, gently fold a new one and put it in. But I don't want to try it and find out I was wrong. If it can be replaced, does anyone know a part #? It isn't included in any of the rebuild kits best I can tell.

3) Regarding the big O-ring where the air can bolts to the hydraulic side... should it not seal better? Seems like there's no contact of the air can on the O-ring, and if fluid can leak by, then how the heck is it sealing against any air? The new O-ring was the same size as the old one best I could tell when I did the rebuild. Would it be worth finding a little thicker O-ring?

Thanks in advance for any insights!

 

[Barrman]

I think you are on the right track with the corrosion. How pliable where your "new" cups you put in? If they were a bit dry and crusty that could also be an issue.

 

[ckid]

New cups felt good and pliable. I don't think they're the problem, although I have no way of knowing for sure.

 

[Mullaney]

If anyone has input on this, I'm all ears. Rebuilt my short air pack a couple of months ago using the guide @silverstate55 wrote up on these forums for the short style, bled the brakes, have run the truck a few times checking other systems.

This weekend I noticed a drip around the O-ring where the air can joins the hydraulic side. Pulled the air pack and also found brake fluid in the air pack vent line. Took the whole thing apart and there was actually less fluid in the air can than in the vent line– just enough to cause a few drips when I poured it out. The vent lined had enough in it to pour out in a little stream- maybe a tablespoon worth?

Checked my cups- all turned the correct way. The only cup I didn't replace during the original rebuild was the one in the fluid side of the aluminum assembly the goes on the pushrod. It's the one that's pinned in, and there was no replacement in the kit (same as per the instructions I was following).

View attachment 859783

My first thought was this cup was leaking fluid into the air can– except there was very little fluid in the can, and more in the vent line. Plus, the cup doesn't look torn or seem too dried out.

Then I found a little corrosion I had missed inside the slave cylinder housing where the lower piston sits. Enough to make the cylinder wall a little rough.

View attachment 859788

So my second thought is maybe the corrosion was preventing the cups on the lower piston from sealing, allowing the fluid to leak by it from the fluid chamber and into the slave cylinder housing, and when the brakes were applied the air carried some of that fluid into my air can. This made more sense because there was, again, more fluid in the vent line than in the air can.

All of that to ask 3 questions.

1) Does my thinking about the leak source make sense (leaking past the lower slave cylinder piston), or am I missing something?

2) Can the pinned-in cup in the aluminum piece be replaced? Looks like I could pull it out through the center hole, gently fold a new one and put it in. But I don't want to try it and find out I was wrong. If it can be replaced, does anyone know a part #? It isn't included in any of the rebuild kits best I can tell.

3) Regarding the big O-ring where the air can bolts to the hydraulic side... should it not seal better? Seems like there's no contact of the air can on the O-ring, and if fluid can leak by, then how the heck is it sealing against any air? The new O-ring was the same size as the old one best I could tell when I did the rebuild. Would it be worth finding a little thicker O-ring?

Thanks in advance for any insights!

.
I can't help but think the corrosion in the barrel. Thicker o-ring might also be to your detriment if it is pinched when you install it. A little bit of silicon lube might be beneficial...

 

[ckid]

Good point about the O-ring getting pinched. I'm just surprised it doesn't seem to really make much of a seal to begin with. I did put silicon lube on the other cups and O-rings, but not that big one on the air can. I'll make a point to add some on reinstall.

 

[rustystud]

That seal is replaceable. You need to use a small pick with a hook on the end to peel it out. There are many companies that sell this "square" type O-ring. Go to your local NAPA store with it and they should be able to match it up. Better yet, if you have an actual O-ring seal company near you they can match it up exactly. I bought an actual "square O-ring" seal kit from my local seal company. Their out there, you just have to look. As far as the corrosion goes, clean it up as best you can and go with a harder "Durometer" O-ring.

 

[Mullaney]

That seal is replaceable. You need to use a small pick with a hook on the end to peel it out. There are many companies that sell this "square" type O-ring. Go to your local NAPA store with it and they should be able to match it up. Better yet, if you have an actual O-ring seal company near you they can match it up exactly. I bought an actual "square O-ring" seal kit from my local seal company. Their out there, you just have to look. As far as the corrosion goes, clean it up as best you can and go with a harder "Durometer" O-ring.

.
Some folks call that 4 sided ring a "Quad Ring". Might be useful to use that term when dealing with o-ring suppliers. A hydraulic shop may have those harder durometer rings and they definitely understand quad rings.

 

[ckid]

Thanks @rustystud , good to know it can be removed. Figured I'd change everything possible while I'm back in there, even if it's not a seal that comes in the kits. Seems like the cylinder wall cleaned up nice and smooth with a little #0000 steel wool, so hopefully that solves that issue.

@Mullaney , good info on the Quad Ring. We have a hydraulic shop over in Asheville, so I'll start with them.

 

[rustystud]

.
Some folks call that 4 sided ring a "Quad Ring". Might be useful to use that term when dealing with o-ring suppliers. A hydraulic shop may have those harder durometer rings and they definitely understand quad rings.

Good thing you remembered the actual name ! That will definitely help. I've forgotten so many things lately it is getting ridicules .

 

[Mullaney]

Good thing you remembered the actual name ! That will definitely help. I've forgotten so many things lately it is getting ridicules .

.
I completely understand that!

Worst part for me is trying to give driving directions. Third street with the big oak tree on the corner, down one street, turn at the ugly pink house, up the hill and turn left.

Then they ask "What is the street name and number so I can plug it into my GPS?".

I have no idea.

 

[rustystud]

.
I completely understand that!

Worst part for me is trying to give driving directions. Third street with the big oak tree on the corner, down one street, turn at the ugly pink house, up the hill and turn left.

Then they ask "What is the street name and number so I can plug it into my GPS?".

I have no idea.

I know what you mean ! You look like a fool when they say "you don't know the street number ? " and you have to say "no I forgot " .