Airpak not releasing

[wcolt45]

Anybody have the understanding of how these airpaks work that may point me to a specific part,piece to look at as to why its not releasing the fluid back to the m/c?

 

[bugei]

here is a link to the old discussion about the error in the tm.

http://www.steelsoldiers.com/deuce/7623-airpack-rebuild-warning.html

 

[rlwm211]

My guess, and this is just a guess, is that the hydraulic brake piston that operates the air valve piston in the Compensator in your AirPack is sticking and not allowing the fluid past and back to the master cylinder.

This is the small piston that is installed directly opposite of the air valve and presses against the airvalve piston and the spring of the air valve piston pushes the hydraulic piston back to the "off" position.

I always hone the bore for the smaller hysdraulic Compensator piston. In all hydraulic brake system work, cleanliness as well as smoothness are the order of the day and it only takes a tiny bit of anything to prevent things from working properly.

My suggestion is to remove the airpack and "review" your work looking for a problem that would prevent the brake fluid to return to the master.

The air pack is a simple machine and as long as the bores are clean, the air cylinders and piston bores are smooth it all should work.

RL

 

[Squirt-Truck]

211 is correct. the slave cylinder in the air-pack is not returning fully, either is binding or is being blocked by ???.
If the air piston to rod connection is not the proper length then the slave can not return past the bleed hole and relieve the pressure to the MC.

Does your air-pack not have two bleeders? One for the pilot line and one for the service line??

 

[wcolt45]

no,just one bleeder,i have tore down on my bench now looking for the problem,the large piston in can is very hard to move ,should it be that tight?i remember it was hard to get started during the rebuild, and what did you use to hone the small air valve piston bore?

 

[wcolt45]

carefully inspected the bore of small air piston and there is some pitting there that i didnt catch before,may be the problem,i imagine even light pitting couldnt be good,not super bad but cant be honed smooth

 

[wcolt45]

where would the second bleeder be located?i have the oid type airpak.

 

[Squirt-Truck]

Big piston (ALL) pistons should move freely. I use a cylinder hone for the air piston bore, a brake hones for the small pistons. The little air piston gets a fine honing with a dowel rod and fine crocus cloth.

Be sure of the clearances, return stroke, the service fluid side of the slave cylinder MUST return past the bleed port easily. Otherwise the fluid can not relieve. Does your air-pack have a back pressure valve in the slave connection to the service line? These can also be a problem.

 

[whyme]

hey if you come to a point where where your current pack cannot be fixed do to the pitting let me know. i might be able to help.

 

[flyxpl]

I had this problem when getting a recovered truck with no brakes going . When I had the brakes half A$$ed working with some air still in the system It would take time for the pressure to bleed off after the brake was released. Once I put the power bleeder on and gave the brakes a good bleeding it quit doing it.

 

[wcolt45]

i had to give the big piston a good tug with visegrips attached to get it out of the can,i did hone the cans bore ,it looked good before and still does,the new cup made it tight,the only other threaded hole in the airpak ,besides bleeder is a thin hex plug kinda under the bleeder that reveales the end of the small piston

 

[rlwm211]

The air piston cylinder can be cleaned with emery cloth. Be sure to lubricate it with air tool oil before assembly and it does not hurt to prelube the piston rod and the seal on the air piston itself.

You can hone the compensator hydraulic bore quite a bit as it does not act with the high pressure the slave cylinder bore does in the air pack so the seals will compensate.

Everything on the air side should be well lubed including the felt on the air control piston in the air valve.

Use BFS for lubricating all of the parts that come in contact with the brake fluid.

I say all of this acknowledging that you probably did lube everything, but I just wanted to be sure.

RL

 

[wcolt45]

I did lube well,deciding to get another rebuild kit and try again,try to reuse what i have ,or soak it up and buy a new airpak.what a headache!!

 

[rlwm211]

I pondered this last night after I shut down the computer and it occiurred to me that what you said points to the problem; i.e. the Air piston does not move freely in the cannister.

I suggest that the problem is the air piston not returning all the way causing the slave piston to not return to the position where it allows fluid to return to the master.

Chances are that the piston returns to a different location on every application so it varies as to where it stops.

I would carefully take the airpack apart, use fine emery cloth polish the large air cannister and hone the other bores so they are in good condition. Smooth, little or no discolored metal. Discoloration is corrosion. You do not need a new kit if you do this carefully.

Put the airpack together and be certain the air piston moves freely and will return properly. The spring in front of the piston in the slave bore of the hydraulic side is there merely to keep the piston against the piston rod of the air piston and is not intended to return the entire assembly to a resting position.

Hope this helps

RL

 

[wcolt45]

thats probably it!!the new cup that was in my rebuild kit for the large air piston is why its so tight,looks like leather or something similar and very stiff,any ideas in how to make it more plyable?

 

[doghead]

Soak it in BFS for a while.

 

[wcolt45]

also is it recommended during reassembly to use some tyye of sealer,gasket maker on the gaskets

 

[doghead]

I do not use any sealant on the gaskets.

 

[rlwm211]

I would not use gasket sealer. If you need to, lightly sand the flat metal surfaces to smooth them so they seal properly. The areas where is high pressure do not rely on gaskets to preserve pressure, and the rest is pretty much low pressure of the air system.

If the round ring gasket for the Air piston cover is too small, soak it in warm water for a few minutes. It is made of rawhide and will return to original size.

The quality of the rebuild will be determined by the care in which you place your preparation of the bores. When I rebuild an airpack, I spend more time by a factor of about 5 on the slave bore, compensator bore and the air piston bores than I do everything else combined. If they are smooth and perfect, then everything will assemble nicely and work properly.

Be sure to prelube the air piston cannister walls with Airtool oil.

RL

 

[scrapdaddy]

Man, you guys know some chit! I'm saving all of this. Thanks