I rebuilt my Airpack only to have it fail from water and corrosion again...

RangerDave

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The step by step airpack rebuilds I have noodled were very useful threads and I thank you all for the time to have done it! I rebuilt my Master Cylinder and Air Pack last year and much to my chagrin, the remote brake fluid reservoir started lowering and the brakes started fading.... only a 100 miles or so on the truck and only warming it up and "exercising" the brakes from time to time as it sits... So, I pulled it and rebuilt it - again -thinking I flipped a seal or something, but I found that was not the case...

So, the burning question that I have, "where does all of the crap in the air lines come from and how can I prevent more crap from getting into the airpack to ruin my seals and corroding the surfaces????"

Because when I opened it up, I was horrified at the amount of rust and gunk from the water migration into the air pack - not to mention the pitting from water sitting in some of the chambers... The two worst places (chambers) were where the "J" tube enters the rear of the airpack and the small stainless? piston with the two gaskets (brake fluid side that pushes against the larger brass piston that controls the air valving).

Two possibly significant notes about what I did...
1. I failed to blow out the air lines leading to and away from the airpack - my bad
2. I flushed the old dot 5 out with denatured alcohol as some had recommended doing and then purged that out with new dot 5... - is it possible that some of that denatured alcohol could have pooled around the airpack seal where the stainless double piston cup is, because it didn't get properly flushed out and collecting water and causing those seals to fail? I was just flabbergasted at how much corrosion had happened from last year and virtually no use...

I also have an alcohol evaporator plumbed into the side of the air compressor to help with the water problems...

PS: Although I am not against doing the work to search for all of the forum posts and notes about "how to fix" my stuff, searching for those helpful threads and finding what you need can be an onerous task if you are starting from scratch. I have looked and read for days at a time, only to have someone else finally ask the same question and then get flamed for "not knowing how to search". So, I am timid about being that "one" when posting.... Maybe it already exists and it is my "inadequacy" of not being able to search the forum using the "right" words, but I think it would be helpful (especially as the forum threads grow with membership and knowledge) to have up in the sticky, specific sections that seem to get a lot of views (because of need). In stead of having one person post a "how to" in the sticky with 9 pages of "thank yous" - A "how to" that has links in it to as many threads in the forum to link all of the same info together. Like having a sticky on "Brake System Airpack" as a general topic for instance, and have a real good step by step rebuild and having as many of the links the other 18 threads that contain critical information for its care, maintenance and other oddities that you might come across in overhauling, trouble shooting, or field repairing posted inside the sticky thread by members who have either posted the info or found the info from other members. Close up pictures that are not blurry would be great too. So instead of the pages and pages of thank yous with a post here and there with any helpful information, only a summary post of what you will find once you click the link in the thread... I have seen this in threads where someone has a question and then gets flamed, only to have someone else "find" said posts and then give those links to the person searching for the info and problem solved... I have almost done this several times to help preempt the forum search blues, but didn't want to step on anyones toes. End Rant.

Thanks Again for all your comments - I put on my welding gloves, so flame away!!! ;-)
 

gimpyrobb

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Get one of the alcohol bottles for the compressor intake or a compressed air conditioner from an A3.
 

RangerDave

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Thanks for the thoughts on air dryers and filters.

It was above freezing today so I was able to check all of the lines that lead to the airpack. Nothing. Dry as a bone. Between the alcohol evaporator and the wet/dry tank combo, no moisture or gunk....

So, now I am to believe that the denatured alcohol was the culprit... I guess I didn't do a good enough job bleeding it out and it pooled around the seal and collected moisture - causing the seal to fail...

So it's off to install and bleed the brake lines...
 

doghead

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Do you drain your air tanks regularly?

Have you inspected or rebuilt your wheel cylinders? (how did you determine the brake fluid loss was in the air-pack?)
 

RangerDave

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Dang..... Got it installed, bled and had an immediate hard pedal... I guess something went wrong again.... everything seemed to function and move properly when in the shop, so something is stuck inside...

Yes, I do drain the airtanks regularly. I probably check once every 2-3 hours when I'm working the woodlot. I had no water purge out of it today after sitting and the alcohol evaporator is functioning properly.

I know the wheel cylinders need attention and may leak a bit, but the brake fluid was on both sides of the air can big piston and blowing out the air vent tube in the engine compartment....

When I crack the air vent, where you put in air tool oil, I can hear the brakes release. So something inside the airpack is stuck and not releasing the air...

What should I be looking for when I crack this thing open again??? I have to figure out what I did wrong...
 

RangerDave

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I may have a lead... I'll have to try and adjust the pushrod leading to the Master Cylinder to see if it is not allowing the MC to fully release the vent ...

"That didn't fix it either. At least with the brake adjustment all 6 wheels were heating up evenly, where prior they were heating unevenly. But with the bleeding workaround, travelled all the way from Franklin, Virginia to Cedar Park, Texas stopping every 30 to 55 minutes along the way to dump a tablespoon or so of fluid to keep the creeping pressure below the shoe/drum contact point.

The pressure at which the brakes start to drag seemed to be around 30 psi. This is below the threshold for the Brakesmart display so I had to figure this out from meter readings. After each bleeding the pressure read zero. After any brake application my pressure read maybe 15 psi, and from there it would slowly creep up till the brakes started dragging.

I read on the internet that once a shoe starts to drag, the heat warms the brake fluid in that wheel cylinder which causes it to expand, which makes the shoe drag harder, increasing the heat which increases the pressure, etc. until the fluid starts boiling or until a cylinder seal fails.

In Cedar Park, Texas, where the Comfort Inn there has a Texas shaped waffle iron, in an effort to delay our mornings departure in the hope that the light rain would clear up shortly, I finally discovered the real cause of my $6000+ problem - the master cylinder pushrod was mis-rigged.

The fact that the brake pedal gets harder (pushes back more and more) as you drive indicates that there is pressure pushing back against the master cylinder piston. Where does this pressure come from? It can come from the expanding oil or from the air pack piston pushing fluid out of the air pack. When the air pack piston moves, it works like a second master cylinder, working the wheel cylinders this also pushing back on the actual master cylinder, which is felt on the brake pedal.

But how can the air pack push back on the brake pedal? Well as long as the brake pedal is being pushed by your foot, or by the pushrod being adjusted too long, the air pack piston can push back against it just fine.

But at the very end of its travel, the master cylinder does one more thing that even after I had read through it several times it didn't really click how important it was... At the end of its travel, the master cylinder vents the brake line fluid back into its reservoir. Zero psig. No significant pressure can develope on the brake line with the vent port open.

So if the pedal's released and the pushrod is not too long, the master cylinder will be pushed back by any back pressure (as well as its internal spring) until the vent port is opened, dumping any pressure to the reservoir. With no pressure on the master cylinder side and residual pressure on the wheel cylinder side the air pack piston will be moved full brakes released."
 

doghead

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So something inside the airpack is stuck and not releasing the air...
The compensator valve controls the air flow to the air cannister piston.

It sounds like this is where your problem may be.


It is important that the little holes in the bottom of the master cylinder resivour, are not plugged. Pedal adjustment is critical.
 
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RangerDave

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I rebuilt the Master Cylinder at the same time last year with the Airpack. It may be possible that something got in there to clog the vent hole after the rebuild.

When I pulled the plug on the back of the large air can, where you put air tool oil, the main release of air released the brakes, but there was still a constant flow of air coming out - suggesting that something internal was not releasing and being kept open... The back pressure from the MC pushrod and pedal adjustment perhaps holding/pushing the compensator valve partially open... I'll have to check it out tomorrow when we have some light... Thanks!
 

RangerDave

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Well the brake pedal wasn't the culprit.

I am guessing that the remote reservoir gasket/baffle seal is the culprit. When I pulled the cap off of the reservoir I got an immediate intake of air and the rubber baffle was deformed from pressure. Hmmm... I figured using an old clutch tank would have had an adequate amount of breather play in it, but I guess not. I ran it for a while with no gasket and only the cap with the hole in the top and now I have a normal feeling pedal!!! Amazing how only a little thing can make a huge difference.... Now to just find either an old axle, or hydraulic breather vent to thread into the top of the remote reservoir to let it breath. If I was really thinking about fording, I'd vent it to the Air Cleaner. Thanks all!!
 
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