'31 Coupe
I ordered the modern style zerks from Snyder's along with the modern installation tool. Unscrewed the threaded ones and replaced with no problem, then pried out the old press-ins with a chisel (worked great) and I can't drive the new press-ins in more than about 1/4 of their shank... the grease gun blew two of them right back out.
I'm using a heavy ball-peen hammer with the installation tool (A-353020-M) and fram the fitting like I mean it... only one of the four ridges on the shank drive into the car part - which ever it may be. WHAT am I doing WRONG?
And the angled drive-in ones are still on my bench... don't have a clue how to drive them in.
The advantage of the old style alemite fitting on the Model A is that the pressure of the gun helps hold them in place.
Think of the Model A grease gun - the one that was part of the tool kit. You push with your hand on the handle and the pump portion of the gun takes on this hand pressure and moves grease into the alemite fitting and bearing cavity. You also push down on the alemite fitting to make and hold the seal.
Thus, you pressurize the bearing cavity BUT for alemite system the pressure in the cavity cannot exceed the pressure of the gun on the top of the alemite fitting. Everything works although the arm and hand of the alemite operator is not QUITE so happy having to do the "opposite & equal" force on each and every fitting.
NOW replace an Alemite fitting with a Zerk fitting. You have possibly 10s of thousands of pounds of hydraulic pressure to move grease and pressurize the cavity and you need only a modest hand pressure to hold it in place because the grease gun "locks" onto the fitting. You pressurize the bearing cavity and the relatively unrestrained pressed in Zerk backs out of its press fit doing what hydraulic forces meant for it to do.
I have tried the Zerk fittings when I was into my "make it better - make it easier" stage of Model A evolution. Unfortunately I had EXACTLY the same problems as you're having now. And I imagine a whole lot of those who "did the conversion" are now wishing they did not.
It is possible to compensate for the tendency of Zerk fittings to back out: this done by HOLDING the Zerk gun in a press fit on its Zerk fitting. But that kind of defeats the purpose of a Zerk fitting? Besides possibly messing up the click-on clutch inside a Zerk nozzle?
I mean how badly do you want to have the advantage of a Zerk fitting? It is possible to tap and use a 1/8" pipe thread on EVERY lubrication point - no doubt there are Zerk fittings made that will accommodate and replicate every funny Model A type fitting - and they all screw into 1/8" pipe. Or some other thread?
Sorry for the bad news. I wish I kept all those Zerk conversion fittings for the Model A - so I could sell them half price to those who want to experience a Model A mistake at lesser total cost.
As it was they went in the trash.
Joe K