Add Fill Plug To Rear End Housing?

[basstrix]

Have any of you added a fill plug to a ford 9 inch rear axle housing? I have a differential I want to install, but it has no fill plug. Wondering if the portion of the housing opposite of where the differential bolts up is thick enough (sufficient thread engagement) for a gasketed plug.

 

[Spike Morelli]

To my knowledge, the fill plug is in the drop-out center section. Now, adding a drain plug might be handy. Some early rear end housings had drain plugs, I worked on a '67 Shelby that had a drain plug in the housing .

 

[basstrix]

To my knowledge, the fill plug is in the drop-out center section. Now, adding a drain plug might be handy. Some early rear end housings had drain plugs, I worked on a '67 Shelby that had a drain plug in the housing .

Not on all castings.

 

[tony-muscle]

Some of the fabricated housings sold by Strange, Moser and the like have a drain plug on the rear cover. Obviously, the fabricated ones have been reinforced but I don't think the rear cover is much of a structural component in the OEM versions. If that's the case, then it would be a good place where to weld a filler plug. I have thought about it. I will definitely make the filling process much easier.

 

[Sheriff41]

To my knowledge, the fill plug is in the drop-out center section. Now, adding a drain plug might be handy. Some early rear end housings had drain plugs, I worked on a '67 Shelby that had a drain plug in the housing .

I welded a bung for a 1/2" threaded plug on my axle housing. I welded a ring cut from a piece of pipe around the bung so placing a jack under the housing lifts on the ring rather than the drain plug. I've seen others simply drill and run a self-tapping oil drain plug, though I thought the metal was too thin to be a reliable solution.

I considered add a fill hole, as well, but mine diff case has the fill on it. For as seldom I change the gear oil, I figured the stock fill port was sufficient.

 

[basstrix]

@Sherriff, I was considering something similar for a drain plug, when I had the housing removed due to the same concern you noted. I never did install a drain plug.

I'd be done with this install if the stock fill point existed on this housing

 

[basstrix]

My plan is to drill a clearance hole in this flat area on the rear panel of the axle housing. I believe this is where Ford punched, then tapped a hole for the earlier models that required a fill plug in the axle. In other words, I don't think it's a coincidence that this flat spot is is positioned to allow a fill level just below the axle tubes. I'll be tacking a high strength 1/2-20 nut to the inside of the axle housing. I did a rough check of the flatness using a washer the same OD as the plug I bought....looks like it will seal.

 

[Don C]

You are correct, that is not coincidence, here is a picture of the stock location for '66 and earlier 9-inch differentials.

The stock fill plug is a pipe thread plug, which does not require a gasket or flat surface. I believe that I would cut a 1/2" black pipe coupling and weld it in and use a pipe plug
https://www.homedepot.com/p/Southla...PT-x-FPT-Coupling-Fitting-521-203HN/100210807
https://www.npdlink.com/product/drain-plug-12-npt-magnetic/167597/203245