Airpack pooped out, who's got one? Help?

[HeadWizard]

There I was, trying to park the Deuce and the brake pedal goes to the floor. Much testing and we discover the airpack is not holding pressure.

Disassembled the unit and its pretty clean. Probably can get by with a rebuild kit, but a new unit would work also. Mine is a NEWER style unit.

Any and all help is appreciated.

Don

 

[houdel]

RE: Airpack pooped out, who

With or without air pressure, the brake pedal should not go to the floor. That was the whole point of the air assist, you would still have brakes if you lost air pressure. Sounds like you are either losing brake fluid someplace or your M/C is shot.

Prior to this problem with the airpack, did your brake pedal go to the floor on a cold start before air pressure built up in the system? Have you checked your brake fluid level? You may very well have an airpack leak, but if the brake pedal is going to the floor I'd suspect a hydraulic problem, not a pneumatic problem. It may be that your airpack has been leaking for some time but your M/C decided to take a sudden puke.

Check TM 9-2320-361-20, page 8-26 for the internal leakage test. Note - you vehicle may NOT have the line (3) and adapter (5) in instruction a.2; this is the vent line on the top of the M/C fill cap. Mine has just a simple vent fitting on top of the fill cap.

 

[HeadWizard]

Very good point.

I did the M/C leakdown test as indicated by the TM and the M/C is holding pressure. When I attempted to bleed the M/C, I got out air (under pressure) and fluid without depressing the pedal. I assumed that the airpack was bypassing and just pushing out air from the compressed air source. I went so far as to block off the output from the airpack (hydraulics) to the truck and re-test the M/C leakdown test. Pedal went to the floor. Would not bleed to a firm pedal, fluid full.

Prior to all this nonsense, I bled all the wheel cylinders and got lots of clean fluid out, no air. Did this using the gravity bleed method because I could not get a firm pedal. There are no obvious leaks, there are no non-obvious leaks.

Very possibly my diagnosis is faulty as I do not have a complete and full understanding on how the airpack is to function - it's been know to happen - but I am a shop owner and ASE Master Tech.

Again - any help from the more informed is appreciated.

Tired and late for dinner. Bye.

 

[acetomatoco]

Remember there is a hydraulic bleeder valve on the air pak too... ACE

 

[littlebob]

Make sure to post your findings when you get it figured out. I haven't done my brakes yet. I bought new M/C rebuilt airpac and new wheel cylinders. Before I started taking it apart the braking was very poor, I think it was a combination of all of the above. It was losing fluid and really didn't stop anywhere near what Mcinfantry's did when he let me drive his.
littlebob

 

[HeadWizard]

10-4 on posting a fix when I figure this out. The only bleed valve that I can find on the system (other than the wheel cylinders) is on the airpack unit. No bleeder on the master itself. Seems strange - maybe I'm just blind.

Are there any exploded view diagrams anywhere of the hydraulic flow thru the master and airpack unit? Operational diagrams, anything?

Anyone know if the rebuild pack works on both the new and old units?

Got a wedding Saturday and family stuff Sunday. Looks like Monday before any further progress on my end.

Oh - forgot to mention that this problem is on my 73 AMGE M35A2C and not on Shorty - not that it matters.

 

[houdel]

There is no bleeder on the M/C. You bleed the M/C, line between the M/C and airpack, and the hydraulic portion of the airpack through a bleeder on the top of the hydraulic head on the airpack.

The -34P TM does not give a breakdown of the AHU, so either it was not serviced at the DSU/GSU level, or there is a separate service manual for it (I tried LOGSA but could not get connected today), or it was sent elsewhere for service, or was simply replaced and the old one discarded. Since there are repair kits available for the AHU they must have been serviced somewhere.

If you are getting air when you attempted to bleed the M/C (I assume your air system was pressurized), I can only GUESS there is a leak between the air and hydraulic sides of the AHU. IF that WERE the case, brake fluid would leak into the air chamber when you applied the brakes, and air would leak into the hydraulic lines when you tried bleeding the M/C. Only a guess though!

 

[HeadWizard]

Thanks for the info. That's the only place I found the bleed it.

Your thoughts that I should be getting fluid into the air cylinder was the same thing I thought should be happening - but it's not. Very confusing.

I'm going to clean the unit, hone the unit and reassemble it. I'm then going to start from scratch and reverify and test everything. Maybe then I'll find where I screwed up.

Don

 

[houdel]

Looks like you are down to step 9(b)!