GMC Air-pak parts needed

[M221Jimmy]

Hi everyone,

I am in the process of completely repairing/replacing the brakes on my 1953 M221 tractor. I have most of it done and the hoses are sourced and on the way thanks to the sticky post "G749 parts list"

Coming to the issue at hand, I have my air-pak disassembled and a 5-ton rebuild kit is on the way but I am looking for the power piston assembly (thread in housing and piston) out of a 5-ton air-pak. I have read the rebuilt thread on here and it looks like that will be all I will need to complete this project.

I would be interested in at least one power piston assembly if anyone has one they would sell. (I could use a 2nd assembly for another truck in the future if there is a supply of these).

Thank you...

 

[DUUANE]

I dont have any myself..and im sure someone on the list will have more options. I have purchased with success from Oshkosh equipment, erick's truck parts and big mike's. The Idaho motor pool is good as well..hope this helps.

Good luck.

 

[SCM35A2]

I've bought just bout all my brake parts including my air pack rebuild kit from Big Mike's Motor Pool & have been pleased with everything.

 

[Valley Rock]

I have two boosters laying here, one from a 68 Deuce and one from a late 50s M62, are the GMC ones unique ?

 

[M221Jimmy]

From reading the sticky post on the air pak rebuilt nearly everything is the same except the diameter of the power piston. The 5ton rebuilt kits (which I have bought and is headed my way) has the bigger diameter cups. I would like to put the 5ton piston and housing in my air pak so rebuilding will be a little easier in the future. I can get a piston and cup from classic and exotic restorations but I would have to have a machine shop bore out my housing a bit which I really didn't want to do.

I'm not sure what all trucks use that bigger piston assembly. Are yours assembled or parts units?

 

[M221Jimmy]

Thanks a bunch!!!! I'll give them a call in the morning and see what they have to offer.

 

[USMC 00-08]

A couple years ago we started a discussion on the power piston, but progress has been slow. I had machined one out of 304 stainless and 1944MB and I finally tested it out in his M211 over the Memorial Day weekend during an approximately 120 mile round trip from Big Timber to Bozeman, Montana. It worked very well in city driving as well as through mountain passes. Here is a link to that discussion.

https://www.steelsoldiers.com/showthread.php?166715-G749-Airpak-power-piston-conversion

I need to figure up what these would cost to make and also find time to slip them in between regular production.

 

[M221Jimmy]

I ended up getting the new piston and seals from Classic and Exotic Restorations out of Michigan. I had a local machine shop bore and hone the housing to 1.000 in. and it went together very well...I'm impressed but they are pricey ($110 for the piston, 4 seals and snap ring). The machine shop charged $30 to bore it out and re-cut the snap-ring grove.

I just ordered their stainless steel air pak cylinder bore as mine was badly pitted. It was another $210 but that should take care of everything in need for my air pak.