Air pack rebuilding question

[acesneights1]

IIRC, the TM is incorrect. It shows a seal being installed backward. It has been ages since I did one but have done 10+ of them. I had the same issue with the first due to the TM directions. I think Recovery4x4 was the one that turned me on to the issue, maybe he will see this and post up.

yes, that is my understanding. I used this from a posting here.

 

[acesneights1]

Ace, are you working on a new(short) style or old(long) style air pack?

Old. Long style

 

[acesneights1]

I have to dissemble it again but I believe this spring was missing when we disassembled it and I did not put one back in for that reason and must have missed it when I looked at this diagram. I wonder if this would be causing it. It's possible this was rebuilt already once and it was not put back. The symptom I'm having is the symptom that prompted us to try and rebuild it in the first place.

 

[acesneights1]

View attachment 674242View attachment 674243

Picture one shows how cruddy the hydraulic valve bore can get. Picture two shows the two styles of piston. They both have two seals on them.

I did replace the shaft seal and the hydraulic valve was actually pretty clean but I will re inspect it.
really the whole unit was very clean inside except for a little crud on the air piston itself.

 

[rustystud]

I have to dissemble it again but I believe this spring was missing when we disassembled it and I did not put one back in for that reason and must have missed it when I looked at this diagram. I wonder if this would be causing it. It's possible this was rebuilt already once and it was not put back. The symptom I'm having is the symptom that prompted us to try and rebuild it in the first place.

That spring allows the piston to return to the brake "off" position. Also this small hole at the top of the piston bore needs to be open to allow the piston to return properly. With it plugged it creates a vacuum on the piston which will hold it in the apply position.

 

[JDToumanian]

View attachment 674240View attachment 674241

That 'O' ring in the aluminum shaft collar is just one way hydraulic fluid can enter the air chamber. The other way is through the hydraulic actuating piston which controls air pressure. If that seal is bad or the walls rusted it will cause a hydraulic leak into the air chamber.

Is that a John Deere air pack?

 

[acesneights1]

Well, the spring was in place and not the issue. I checked all the cups and seals again and nothing looked improperly installed.
we need this truck for a fundraiser in a month so for now aborting the rebuild. Another member loaned us a used one until we can find another one or figure out what is wrong with this one. I may build a test bench. Taking it on and off the truck to test is a Royal PIA and waste of expensive fluid.

 

[rustystud]

Is that a John Deere air pack?

No. It was off a Deuce.

 

[silverstate55]

This is an excellent post. However I just rebuilt one and am still getting brake fluid out of the vent. I took it back apart to check all the cups and make sure they were installed correctly and they were. The bore in the hydraulic side looked good. The bore on the air chamber had a few pits in it. I honed it as best I could. I don't hear air leaking when brake is applied and held but could air be leaking by the air piston and then pressurizing the hydraulics and causing brake fluid to come back into the front side of the air chamber ?
we took this unit apart twice to no avail. Any ideas ?

Same thing just happened to me. I've rebuilt several long & short Air Packs with no issues; this one I rebuilt a year ago on a friend's truck, along with master cylinder & every wheel cylinder....I also added a remote reservoir on the firewall. It has been working fine for about 9 or 10 months, but recently started blowing brake fluid out of the firewall vent. I removed it & rebuilt it once again today (following Bjorn's instructions from his MVM article to a "T" and triple-checking orientations of seals, etc....). I did notice some unusual grooves in the large piston shell, so I spent over 2 hours honing it out as smooth and consistent as I could. All the rubber & felt seals were undamaged & seemed to have nice tight fits. I re-installed it and bled it first, then bled all 6 wheel cylinders. Beautiful purple DOT5 was flowing from every bleeder, bubble-free....but I did notice that I was going through a lot more brake fluid than normal, about 2 quarts' worth. Alarm bells started ringing, but I pressed on.

No no leaks were noted, so after cleaning up the brake-bleeding exercise I fired the truck up and built up air pressure. After which I noticed a steady dripping of brake fluid from between the large piston shell & slave cylinder. No problem, I thought, I'll just tighten up the two bolts on the compensator body, which necessitated the removal of the J-pipe & its adapter. As soon as I loosened the J-pipe, brake fluid started dripping out. As this was an air fitting, I didn't think that there should be any brake fluid in it. The J-pipe was filled with brake fluid & so was rear of large piston shell. I snugged down the three bolts securing the compensator body to slave cylinder, reinstalled the J-pipe, and the leak appeared to be resolved. Or so I foolishly thought.

Started truck again & built up air pressure, and now there were two gushing leaks on Air-Pak....I thought something must be stuck, so I depressed the brake pedal a couple of times. The pedal was very soft & went right to the floor each time.

About 1-1/2 quarts of brake fluid shot out of the firewall vent, all over engine compartment & passenger-side frame rail, all down my driveway. I shut everything down and spent about 45 minutes trying to clean up all the spilled brake fluid. So I'm down one Air-Pak and almost a gallon of DOT5. I guess I really am stupid, I have no idea what went wrong, and am resigned to trying to find a new Air-Pak as well as another gallon of DOT5.

Am I really this dumb, or is the Air-Pak just too far gone to rebuild? What went wrong? I triple-checked everything and took my time as I re-assembled everything.....

Thanks in advance for any help/advice, or for just confirming how stupid I really am.

 

[rustystud]

Same thing just happened to me. I've rebuilt several long & short Air Packs with no issues; this one I rebuilt a year ago on a friend's truck, along with master cylinder & every wheel cylinder....I also added a remote reservoir on the firewall. It has been working fine for about 9 or 10 months, but recently started blowing brake fluid out of the firewall vent. I removed it & rebuilt it once again today (following Bjorn's instructions from his MVM article to a "T" and triple-checking orientations of seals, etc....). I did notice some unusual grooves in the large piston shell, so I spent over 2 hours honing it out as smooth and consistent as I could. All the rubber & felt seals were undamaged & seemed to have nice tight fits. I re-installed it and bled it first, then bled all 6 wheel cylinders. Beautiful purple DOT5 was flowing from every bleeder, bubble-free....but I did notice that I was going through a lot more brake fluid than normal, about 2 quarts' worth. Alarm bells started ringing, but I pressed on.

No no leaks were noted, so after cleaning up the brake-bleeding exercise I fired the truck up and built up air pressure. After which I noticed a steady dripping of brake fluid from between the large piston shell & slave cylinder. No problem, I thought, I'll just tighten up the two bolts on the compensator body, which necessitated the removal of the J-pipe & its adapter. As soon as I loosened the J-pipe, brake fluid started dripping out. As this was an air fitting, I didn't think that there should be any brake fluid in it. The J-pipe was filled with brake fluid & so was rear of large piston shell. I snugged down the three bolts securing the compensator body to slave cylinder, reinstalled the J-pipe, and the leak appeared to be resolved. Or so I foolishly thought.

Started truck again & built up air pressure, and now there were two gushing leaks on Air-Pak....I thought something must be stuck, so I depressed the brake pedal a couple of times. The pedal was very soft & went right to the floor each time.

About 1-1/2 quarts of brake fluid shot out of the firewall vent, all over engine compartment & passenger-side frame rail, all down my driveway. I shut everything down and spent about 45 minutes trying to clean up all the spilled brake fluid. So I'm down one Air-Pak and almost a gallon of DOT5. I guess I really am stupid, I have no idea what went wrong, and am resigned to trying to find a new Air-Pak as well as another gallon of DOT5.

Am I really this dumb, or is the Air-Pak just too far gone to rebuild? What went wrong? I triple-checked everything and took my time as I re-assembled everything.....

Thanks in advance for any help/advice, or for just confirming how stupid I really am.

Sounds like your "power" piston (I don't remember it's technical name right now) seals are leaking. That is the small piston that "pushes" the air valve open. That allows the large boost piston to apply. If the seals here leak, it will send brake fluid out the air bleed line which used to go to the air filter.