G749 Airpak power piston conversion

[USMC 00-08]

I have been thinking about machining some power pistons for the G749 airpak that are the same size as the 5 ton power pistons so that we can use the 5 ton airpak rebuild kit. Is there any interest from any of you in having one of these?

The 5 ton power piston appears to me that it is made out of chrome plated carbon steel. This chrome plating looks like it is flaking off.


I was thinking of making some out of 304 stainless. Does anyone see why this would not work or know of a better material to use?


I have done this conversion in my airpak using a good piston out of an M809 series airpak as mentioned in the below thread and it works great. All of the 5 ton rebuild kit was used with the exception of 2 unneeded seals in that kit.

http://www.steelsoldiers.com/showthread.php?70703-M220-AirPak-rebuild

The cost of doing this has not been figured up yet, but was wondering if there was any other interest in these parts before I make any. I can't imaging the parts costing more than buying an old 5 ton airpak just to take the piston out of.

For those of you that don't know, the G749 power piston is slightly smaller on the internal piece and no one has been able to find new seals for it.

Please let me know your thoughts.

 

[SturmTyger380]

I'm in! I have three trucks so would spring for 5 sets to fix the trucks and have spares.

 

[99nouns]

Contact simp5782 he had those seals custom made, I am sure you guys can pull a good product together.

 

[02smokemaker]

I'm in for one!

 

[1944mb]

I'd be in for at least 2-3

 

[USMC 00-08]

Looks like we have enough interest in some of these. I will start figuring out material cost, etc. One thing I don't know is if stainless will react negatively with the aluminum housing these power pistons thread into. I don't think it will be an issue, but I want to research it a little more. I want this to be trouble free for all of us, while creating a part that we can use over and over if needed.

If anyone knows if aluminum and stainless react negatively with each other, please let me know.

 

[99nouns]

Looks like we have enough interest in some of these. I will start figuring out material cost, etc. One thing I don't know is if stainless will react negatively with the aluminum housing these power pistons thread into. I don't think it will be an issue, but I want to research it a little more. I want this to be trouble free for all of us, while creating a part that we can use over and over if needed.

If anyone knows if aluminum and stainless react negatively with each other, please let me know.

Sometimes ago I was looking into bolting an aluminum something to something and looking for a right bolt to use and I was told what ever you do, do not use stainless steel, best ones are the zinc plated hardened steel if you will not be removing it often, because removing several times will cause the zinc wear off and that's bad if humidity gets in there, I cant remember the details but aluminum also shrinks and expands up to 10% under changing temperatures.

I hope someone else can get more technical on this.

 

[USMC 00-08]

Good info. I definitely want to research this out before I make any. Maybe chrome plated carbon steel is our only option.

 

[SturmTyger380]

I did a little searching around. Do we know what kind of Aluminum the housing is cast out of?

What I found: if stainless steel and aluminum are in contact and moisture is present, the aluminum will sacrifice (corrode). Brake fluid can suspend moisture. Maybe that's why they were plated?

Metal reactions list - This list is in the order of reactivity and the farther apart two metals are from each other the more corrosion will happen.
--------------------------------------------
Magnesium
Mg alloy AZ-31B
Mg alloy HK-31A
Zinc (hot-dip, die cast, or plated)
Beryllium (hot pressed)
Al 7072 clad on 7075
Al 2014-T3
Al 1160-H14
Al 7079-T6
Cadmium (plated)
Uranium
Al 218 (die cast)
Al 5052-0
Al 5052-H12
Al 5456-0, H353
Al 5052-H32
Al 1100-0
Al 3003-H25
Al 6061-T6
Al A360 (die cast)
Al 7075-T6
Al 6061-0
Indium
Al 2014-0
Al 2024-T4
Al 5052-H16
Tin (plated)
Stainless steel 430 (active)
Lead
Steel 1010
Iron (cast)
Copper (plated, cast, or wrought)
Nickel (plated)
Chromium (Plated)
Tantalum
AM350 (active)
Stainless steel 310 (active)
Stainless steel 301 (active)
Stainless steel 304 (active)
Stainless steel 430 (active)
Stainless steel 410 (active)
Stainless steel 17-7PH (active)
Tungsten
Niobium (columbium) 1% Zr
Brass, Yellow, 268
Uranium 8% Mo.
Brass, Naval, 464
Yellow Brass
Muntz Metal 280
Brass (plated)
Nickel-silver (18% Ni)
Stainless steel 316L (active)
Bronze 220
Copper 110
Red Brass
Stainless steel 347 (active)
Molybdenum, Commercial pure
Copper-nickel 715
Admiralty brass
Stainless steel 202 (active)
Bronze, Phosphor 534 (B-1)
Monel 400
Stainless steel 201 (active)
Carpenter 20 (active)
Stainless steel 321 (active)
Stainless steel 316 (active)
Stainless steel 309 (active)
Stainless steel 17-7PH (passive)
Silicone Bronze 655
Stainless steel 304 (passive)
Stainless steel 301 (passive)
Stainless steel 321 (passive)
Stainless steel 201 (passive)
Stainless steel 286 (passive)
Stainless steel 316L (passive)
AM355 (active)
Stainless steel 202 (passive)
Carpenter 20 (passive)
AM355 (passive)
A286 (passive)
Titanium 5A1, 2.5 Sn
Titanium 13V, 11Cr, 3Al (annealed)
Titanium 6Al, 4V (solution treated and aged)
Titanium 6Al, 4V (anneal)
Titanium 8Mn
Titanium 13V, 11Cr 3Al (solution heat treated and aged)
Titanium 75A
AM350 (passive)
Silver
Gold
Graphite

 

[USMC 00-08]

I've not been able to find out what kind of aluminum yet. That part is included in the 5 ton rebuild kit. I think it is cast aluminum.

 

[USMC 00-08]

Speaking with the engineers at work today, they think that 304 stainless in an aluminum housing "should not be a serious issue in regards to corrosion". They did say that the aluminum would corrode before the stainless does. They could not see any problem with this combination in a brake system when exposed to DOT 3 or Dot 5. They did not really seem to think highly of chrome plated carbon steel.

The aluminum housing that the piston threads into is included in the rebuild kits and is replaced every time. I can't imagine the housing failing before anything else.

What do you guys think?

 

[SturmTyger380]

True the housing gets replaced. And I have no idea on that list what the difference is if you are 5 or 10 metals away from Aluminum.

I would go for it if it makes it easier to have made.

 

[99nouns]

You know it makes sense, because in my case it was a fastener and there was a great pressure being applied and I think the concern was aluminum being cracked at fastning points. In your case it is just a moving piston and it is sealed by rubber, so even a little corrosion would not make any differance.

I guess you got a green light.

Dont I love engeenering.

 

[USMC 00-08]

I can use other metals. I just want to use whatever everyone is most comfortable with since this is an unknown for all of us. Also would like to be able to reuse the piston assembly.

 

[USMC 00-08]

I was wrong about the aluminum housing being replaced. It is the front of the housing that is replaced.


Here is a better view of the housing and the replacement part. This is an airpak I rebuilt with the 5 ton kit. It's the one on my truck right now. I found and used an original M809 series power piston that did not have chrome flaking off of it.

 

[rustystud]

Stainless will not harm or cause any problems with the aluminum. I worked building "Seine" winches at Kolstrand Marine for the Alaskan fishing fleet out of Seattle for a decade. All the later winches where made from aluminum and all the fasteners "had" to be stainless steel. These winches where exposed to the worst possible environment "the open sea" !!! In fact all our products that where made out of aluminum had to have stainless steel fasteners.

 

[1944mb]

Id say go for it, this would be a good step forward to keeping these trucks rolling if we'd be able to rebuild the airpak easier without having to find a 5 ton airpak to rob parts out of

 

[USMC 00-08]

Stainless will not harm or cause any problems with the aluminum. I worked building "Seine" winches at Kolstrand Marine for the Alaskan fishing fleet out of Seattle for a decade. All the later winches where made from aluminum and all the fasteners "had" to be stainless steel. These winches where exposed to the worst possible environment "the open sea" !!! In fact all our products that where made out of aluminum had to have stainless steel fasteners.

What kind of stainless did you use or find worked best?

 

[rustystud]

What kind of stainless did you use or find worked best?

316 is best for the harsh environment but 304 works OK. 304 is stronger too.

 

[USMC 00-08]

I'll start pricing material and then let everyone decide what stainless we want.