Non-conductive zinc

[lionelsoni]

I could get no conductivity with an ohmmeter by probing between pairs of points on the sideframe nor between the sideframe and the bolster nor between the sideframe and the axles.  Only by cutting into the sideframe could I find conductive metal.  It appeared that there was some remarkably robust film all over the zinc casting, including at the bar-end crimp to the bolster.  I probably could have reamed out the axle pockets; but I was afraid to remove much metal there.  In any case, that would not have helped with the connection to the bolster.  That crimped connection, by the way, was completely tight, not at all loose.

The problem existed on all four sideframes of the caboose's two trucks.  There was a lot of rust on the wheels and all the steel parts.  The light clip had rusted in two.  The coupler assemblies were so badly rusted that I simply replaced them.

[hielsie]

I know you have much more knowledge of electronics that I, however, did you run an Ohm meter on one of the sideframes itself to check "connectivity" at several points? i.e. that the "metal" in the sideframe was in effect a circuit unto itself. Your Exacto sentence seems to indicate that the surface of the sideframe had some type of insulator either as a complete coating or a coating at the point of contact of the axel pocket and also where the sideframe contacted the bolster.

[lionelsoni]

I had already removed the wheels and axles and cleaned them of rust.  I also cleaned the sideframe sockets.  But there still was no connection between axles and sideframes nor between sideframes and bolster.  The only way I could make any connection to the zinc at all was by digging aggressively into it with an Exacto knife.

I wound up soldering in wires to create jumpers between the coupler assemblies and the bolsters, bypassing the zinc parts.

[phillyreading]

Not 100% sure about zinc and what is poured in when making a zinc mold. I can ask my dad who was a metalergist with at a major steel company what they use for zinc.

Have you cleaned up everything including the side sockets where the axles go into? Also possible that  the truck assembly has been replaced or the rivot replaced with a plastic one?

Lee F.

[Anonymous]

Bob,

           I've never heard of or seen this problem before.  My first course of action would be to remove the axles from the trucks and clean their ends and holes in the sideframes.  There is probably rust on the ends of the axles.

[lionelsoni]

I just encountered a phenomenon new to me, non-conductive postwar zinc sideframes.  They are on both trucks of a caboose from a set I was just given.  The 1952 671, despite some interesting previous repairs and modifications, cleaned up nicely.  But the badly rusted 6417 caboose surprised me when I got it back together--no connection between the wheels and the frame.  The sideframes are making no connection to the axles nor to the bar-end steel bolster.  There is no evidence of zinc pest, just some sort of heavy-duty coating, apparently even under the bar-end crimps, which are tight.  I think I will have to add jumpers from the coupler assemblies to the bolsters.  Has anyone else ever seen this problem?