obscure size pipe plug in Farmall C transmission

KWRB · Aug 7, 2017

I am cleaning off the transmission housing of my dad's C, preparing it for the first coat of paint. I realized I have not removed the transmission drain plug yet, and that maybe I should. It has a square recess, so I try both the 3/8 and 1/2 drive socket wrenches and no luck. I appears the square recess in this plug is 7/16". I was able to find a socket online with a 7/16" male square on it, but I was curious about the plug itself and I wanted to see if I could tell the thread size before removal by knowing the countersunk square size, so I started doing some research. So far, dead ends.

Initially, I was going to make a tool out of a 1/2" ratchet extension, but then I found these 11 Piece 3/8" Drive Pipe Plug Socket Set which tell me that indeed there are different sizes. Otherwise, there wouldn't be tools, right? So then I go looking for pipe plugs with square recesses online and I can't find anything with a square size other than 3/8" and 1/2". So, I try looking for a standard.

I have a 26th edition machinery's handbook, which is usually a pretty good resource and I cannot find anything about pipe plugs in it anywhere. I also own an old machinery's handbook from 1951, which is about the year of the tractor. I was able to find a table of pipe plug dimensions, but like everything online, it only shows 3/8" and 1/2" pipe plugs.

Is it possible that there's some homemade plug in my tractor? That wouldn't explain why there are production bits available. If it's not homemade, where could I buy a replacement plug? There must be a an old standard for dimensions. Does anyone have it?

Thanks for any insight.

Kurt

jaxs · Aug 7, 2017

I would call around to hardware,plumbing and auto parts to find 7/16 square bar stock. Use 7/16 wrench with bar to remove plug. Have a 3/8 and a 1/2 mpt plugs with square heads on hand. I wouldn't worry about recessed unless it's called for on authinic restoration.

roadhunter · Aug 8, 2017

I'd take a cheap 1/2 extension and grind it down to the size necessary and get it removed. Take less than 5 minutes.

KWRB · Aug 8, 2017

jaxs said:
I would call around to hardware, plumbing and auto parts to find 7/16 square bar stock. Use 7/16 wrench with bar to remove plug. Have a 3/8 and a 1/2 mpt plugs with square heads on hand. I wouldn't worry about recessed unless it's called for on authentic restoration.

If it's not authentic, I'm off the hook entirely. Unfortunately, I cannot see the thing in the parts diagrams available on caseih.com. I haven't looked in my I&T yet. At this point, I'm more perplexed and obsessed about the plug's mere existence considering even the web and the machinery's handbooks don't have anything about a 7/16" countersunk square. I can totally see this becoming all-consuming, even when I should be way over it. Bugs me all the more because my old man would only be 59 right now, and would be able to tell me if he ever replaced it, but he up and died on me so I can't ask him anything. I'm left to wonder. I hate not knowing things.

DJ54 · Aug 8, 2017

Most of the IH plugs of that era were countersunk. The one's underneath, were probably that way to keep from snagging on something, possibly causing damage to it, or the differential. I say that, because it seems every time I change diffy oil, I need to dig dirt, or mud out of the plug.