5-ton air pack rebuild instructions?

[808pants]

Can't find 'em by searching, at least with obvious terms (i.e. "air pack rebuild"). Are there such details in a TM somewhere? If need be, I'm not terribly daunted by blazing my own trail on this...but that could also lead to days of frustration if it doesn't work right...

Also curious as to whether some users reject silicone fluid for reasons other than expense/scarcity.

--Dave

 

[crasheej]

Get a copy of TM 9-2320-260-34-2-3 volume 2 of 2 part 3 of 5 dated Dec 1980. Then go to page 12-12 that will get hte coverage you need. I've used it to do mine. Had to empervise on some of the tools. Or get a copy of the old Tm9-2320-211-35 dated Sep 1964 Starts on page 250 Hope this helps some.

 

[808pants]

EXCELLENT! I was just poking around in the confusing disarray of TM files when your reply came in, crasheej, but I'd never have had the patience to find it. Turns out I've got the 1964 file - attempting to upload now in case others need it. (Yikes - A.D.D. will strike during the 12-page rebuild process...)

 

[hndrsonj]

You can get silicone fluid for 20-35 a gallon from the dealers or ebay.

 

[808pants]

hndrsonj -

Preparing for this, I naively got just a couple of quarts off ebay for the best price I could find (twice the $20-$35/gal you have seen), thinking that was going to be more than enough to deal with one or two leaking wheel-cylinders. One quart of that fluid is now in my air-pack (also a casualty of sitting a couple of years, it seems) awaiting discovery. I may not be above using paper coffee-filters to recycle that stuff - assuming I stick with the silicone.

I once used silicone fluid in a previous-life mini-cooper, with disastrous results. On that car, the MC filler-port is quite near the radiator cap, and during a period of overheating, it seems some of the steam from these overheat sessions made its way into the breather on the brake MC filler cap - I think the overflow hose blew off and that left the port spraying right at the MC cap. Leaks in one rear wheel cylinder later led me to tear the brake hydraulics open (yet again). The flip side of the selling point that water won't mix with the silicone fluid is that if water or condensation enter the system, the water (heavier than silicone) finds its way to the lowest points, and as I saw, rusted the living #$% out of them. I was looking at orange-brown globules of water-rust mix at all such points, but with the upper surfaces untouched.

The other selling point was that silicone fluid wasn't supposed to take paint off like DOT3/4. Not only did I find this not to be true, but once soaked with silicone fluid, it's virtually impossible to clean a surface to the point where a new coating will stick.

I went back to DOT4 in the mini at that point. Miscible with water, yes...but my sense is that you'd have to have a LOT of water get in before DOT3/4 would actually corrode things as in my DOT5 horror story, so it may be a benefit that water can dissolve in the DOT3/4.

I can easily imagine a Dow-Corning sales genius convincing the military that their silicone product is far superior and a must-have for all mil vehicles - based on other than real-world evidence.

Are similar corrosion stories common with 5-tons and their cousins?

 

[hndrsonj]

Have never had any problems with DOT 5. I keep an eye out and get it when I find it cheap. My last 2 gallons wer $10 each from Tracy City TN. You can get it from www.muttparts.com for $36 a gallon or www.flmv.net relatively cheap too. There was also a guy on ebay that had around 1000 gallons and was making multi purchase discounts.

 

[808pants]

Thanks again, hndrsonj.

I strongly suspect that nothing we'd normally find in our brake systems will mix with DOT5, and have in the past recycled/filtered reclaimed fluid - I tend to believe it's good until it's spilled. My purple fluid has always ended up amber, I suspect as a dye fades - bleeding it through and discarding the amber stuff seems just a waste. Solvents or liquids that will mix with silicone appear to be rare and exotic, so in my thinking, simply looking for an interface layer in a clear jar of reclaimed solvent will tell you if any other fluids have entered the system - and you can still separate them relatively easily by decanting.

 

[808pants]

The rebuilding process is...slow. I wouldn't rebuild an air-pack again, I don't think, though the $400+ new replacement cost does give me pause. Anyone got better sources?

Turns out that the rebuilding TM (at least the one I am using) is not only half-useless because the images are so distorted as to make even the lettered-part IDs all but illegible, but also, it's written quite far out-of-sequence in some sections. I'm finding I have to improvise a lot and might have been just as well off not using a TM at all.

I'm only now finding how bad the scoring/pitting is on both the slave and air cylinders - that is, since getting the parts bead-blasted. I don't mind if the air-cylinder leaks a little past the piston when at rest (due to some pitting at the bottom of the air cylinder...or do I?) but I sure as **** don't want the fluid getting past the seals in the slave cyl...and it looks like I might have more than a few thou of honing to do if I want to get past those pits and scratches. I already think I have spent too much time and effort on this, and I'm nowhere near done.

 

[808pants]

The rebuilding process is...slow. I wouldn't rebuild an air-pack again, I don't think, though the $400+ new replacement cost does give me pause. Anyone got better sources?

Turns out that the rebuilding TM (at least the one I am using) is not only half-useless because the images are so distorted as to make even the lettered-part IDs all but illegible, but also, it's written quite far out-of-sequence in some sections. I'm finding I have to improvise a lot and might have been just as well off not using a TM at all.

I'm only now finding how bad the scoring/pitting is on both the slave and air cylinders - that is, since getting the parts bead-blasted. I don't mind if the air-cylinder leaks a little past the piston when at rest (due to some pitting at the bottom of the air cylinder...or do I?) but I sure as **** don't want the fluid getting past the seals in the slave cyl...and it looks like I might have more than a few thou of honing to do if I want to get past those pits and scratches. I already think I have spent too much time and effort on this, and I'm nowhere near done.

 

[crasheej]

Like I said the TM 9-2320-260-34-2-3 dated Dece 1980 is the one I used pages 12-12 to 12-42 is vere easy to use. If you can find one. You can check out the classifide ads for Luckybatt he has 4 34s that will teeel ,show how to fix the 800s. the only one he dosen't have is volume 2 of 2 there are like 5 volumes of this TM covers just about ever thing that you can fik, and some you may not want to get envoled with.

 

[808pants]

Like I said the TM 9-2320-260-34-2-3 dated Dece 1980 is the one I used pages 12-12 to 12-42

-

Thanks again - I found this online at
Direct support and general support ... - Google Books
(or look for google books with that TM number)

What I hadn't realized is that there would be such a vast difference in the quality of the two writeups. (I guess I changed somewhat between 1964 and 1980, too - not all for the better, though)

--Dave

 

[crasheej]

You think that that is enough info. to help?

 

[808pants]

Funny you should ask...

The one I started on may just be too far gone to rebuild - I'm thinking the air cyl might not matter as much (there are some seriously deep pits in the blind end) - but the slave cyl's pits probably would require honing beyond the specified max of 1.126". I took this one off the truck a few years ago when brakes got scary, and found that the air-cyl portion was laden with silicone fluid, so I emptied it out, bagged the pack, and kept it for someday when I would rebuild it. Meantime, I got a rebuilt, but I can't for the life of me remember where.

And that's the one I just pulled out of the truck this afternoon. Bear in mind, it's probably got less than a hundred miles on it - I used this dump-truck on less than fifty runs of just a few miles each, very near where I live, then simply left the truck parked for a few years. Apparently that's all it takes to ruin a rebuilt unit - or the rebuild wasn't so good and it was leaking the whole time. Still looks new - has a sticker that says "Fort Wayne Truck Parts and Equipment" which I assume was the rebuilder. But I can see pits in the slave cyl that I think precede my use (there's no sign of rust or dirt from the pits) - it's like they stopped honing when they thought it was OK. And like my other unit, the air-cyl portion was sloshy with amber and purple (new batch) fluid, both, along with a lot of assembly lube. I noticed the rebuilder had replaced the power piston with a simple disc that might not be a bad modification, but also dispensed with the cupped steel centralizing washer that keeps the spring concentric - that doesn't seem like a good idea. Whatever...

So here's the thing - I am lacking in info on the theory of operation of these units. Is there a TM that gives some working description? I have a sort of vague idea that MC pressure must modulate the air-cyl pressure, which amplifies foot-pressure via the pushrod into the slave cylinder's series of components...but I am not clear on how/where the MC (foot-pressure) side of the system shares fluid with the pressure-assisted side of things, nor what would happen if seals between the two sides deteriorate. I want to understand so I can check all the routes by which the fluid can enter the air cylinder, as it seems so determined to do on my (or all) such packs. When fluid leaks past the slave's seals (through pits/defects in the cyl wall), where would it go/ what effect would it have before it would work its way into the air cyl? It looks to me like it's still contained by a LOT more seals in what I would take to be the modulator area, but...I'm just making things up now. Maybe pressure forces that errant fluid into the air-cylinder?

It's hard to believe that all the fluid I found in there came through the pushrod seal - the seal looks brand new, as do all the rest of them, and the rod is smooth and undamaged. But not fully understanding the normal/abnormal movements of the fluid, I can only speculate. If the 4" diapragm were torn, it seems that would also lead into the air cyl, but it wasn't - there was only some dirty-dry stuff behind it, as I would have expected from a 45-year old air compressor.

Any ideas appreciated.

--Dave

 

[808pants]

Funny you should ask...

The one I started on may just be too far gone to rebuild - I'm thinking the air cyl might not matter as much (there are some seriously deep pits in the blind end) - but the slave cyl's pits probably would require honing beyond the specified max of 1.126". I took this one off the truck a few years ago when brakes got scary, and found that the air-cyl portion was laden with silicone fluid, so I emptied it out, bagged the pack, and kept it for someday when I would rebuild it. Meantime, I got a rebuilt, but I can't for the life of me remember where.

And that's the one I just pulled out of the truck this afternoon. Bear in mind, it's probably got less than a hundred miles on it - I used this dump-truck on less than fifty runs of just a few miles each, very near where I live, then simply left the truck parked for a few years. Apparently that's all it takes to ruin a rebuilt unit - or the rebuild wasn't so good and it was leaking the whole time. Still looks new - has a sticker that says "Fort Wayne Truck Parts and Equipment" which I assume was the rebuilder. But I can see pits in the slave cyl that I think precede my use (there's no sign of rust or dirt from the pits) - it's like they stopped honing when they thought it was OK. And like my other unit, the air-cyl portion was sloshy with amber and purple (new batch) fluid, both, along with a lot of assembly lube. I noticed the rebuilder had replaced the power piston with a simple disc that might not be a bad modification, but also dispensed with the cupped steel centralizing washer that keeps the spring concentric - that doesn't seem like a good idea. Whatever...

So here's the thing - I am lacking in info on the theory of operation of these units. Is there a TM that gives some working description? I have a sort of vague idea that MC pressure must modulate the air-cyl pressure, which amplifies foot-pressure via the pushrod into the slave cylinder's series of components...but I am not clear on how/where the MC (foot-pressure) side of the system shares fluid with the pressure-assisted side of things, nor what would happen if seals between the two sides deteriorate. I want to understand so I can check all the routes by which the fluid can enter the air cylinder, as it seems so determined to do on my (or all) such packs. When fluid leaks past the slave's seals (through pits/defects in the cyl wall), where would it go/ what effect would it have before it would work its way into the air cyl? It looks to me like it's still contained by a LOT more seals in what I would take to be the modulator area, but...I'm just making things up now. Maybe pressure forces that errant fluid into the air-cylinder?

It's hard to believe that all the fluid I found in there came through the pushrod seal - the seal looks brand new, as do all the rest of them, and the rod is smooth and undamaged. But not fully understanding the normal/abnormal movements of the fluid, I can only speculate. If the 4" diapragm were torn, it seems that would also lead into the air cyl, but it wasn't - there was only some dirty-dry stuff behind it, as I would have expected from a 45-year old air compressor.

Any ideas appreciated.

--Dave