The Stovebolt Site Forums The Shop Area General Truck Talk Steering Box Fill Plug Size

I lost my fill plug today by not paying attention and forgetting to put it back in before moving the truck. Anybody know what size it is? I had a 1/4 NPT plug but it was to small. This is on a 52 3100.

EDIT: Does 3/8 NPT sound right? Looked up in my assy manual and found 3 parts numbers that I looked up in GMPartWiki and they're listed as 3/8. So I guess I answered my own question.

3/8 NPT is what my 1949 3100 gear box is so it sounds like you are correct.

Some fill plugs are drilled to provide venting so any garden variety hardware store NPT plug may not work correctly.

Are they supposed to be vented? I know the one I lost wasn't. But if it needs a vent hole I can drill one no problem.

I have never seen a vented one and I have seen a lot of trucks.

There is no seal between the upper bearing and the steering column so the box can vent that way if it was needed

picked up a 3/8 npt plug at the hardware store today but my honeydo list project didn't leave me enough time to make sure it fits. Maybe tomorrow.

Didn't have a vent in it before so unless someone can convince me it's needed I'm leaving it as is.

Chad,

Last night I did an inventory on all of the steering boxes I have. It turns out that only the 1940-41 trucks had a vented fill plug.

[img]http://www.surfacezero.com/g503/data/3176/2013-12-22_14_26_34.jpg[/img]

[img]http://www.surfacezero.com/g503/data/3176/2013-12-22_14_25_59.jpg[/img]

I think you are good to go with your "new" model truck.

Paul

Thanks Paul. I'm about to go out and put the new plug in my "new" truck and go to town for a tank of gas.

Update: 3/8 NPT is the correct size.