Confronted with some old metal sharknoses that ran too fast and after a lot of research and head scratching, this method was developed. The power trucks on older diesels and trolley cars had motor shaft mounted worms with a 14/1 gear ratio and ran too fast. Replacing the gears with NWSL Mod 0.3, 230005-6 worm and 231028-6 wheel, at 28/1 would cut speed in half. The major problem is that removing the armature from the the housing, to change the worms, would demagnetize the motor. The solution is to drill holes in the ends of the casting large enough to pass the worms through. This was tried on an old junker first.
First remove cover plate screws or drill out rivets.
Caution: On many earlier versions
with cover plate screws, there were no bearing straps to retain armature.
Rubber bands should be slipped over shafts, to prevent pop out, before
completely removing axle bearing plates.
Remove cover plate, wheels and wheel bearing plate(s). With armature in place drill end holes. Carefully remove any chips.
Note: Adjust brightness and contrast for optimum viewing.
Hole in housing end.
Note: Adjust brightness and contrast for optimum viewing.
Bottom view showing worms removed.
Pull worms through holes. Press new worms, using opposite end of shaft as back stop, not the armature. Change driver gears and possibly wheels. Reassemble using flat or pan head screws from the bottom and nuts at the top to replace rivets.
Check gear mesh. The original MMP axle center distance is .255", while NWSL's .256". Any adjustments for mesh can be made by very LIGHT filing or adding a brass shim between bearing plate and housing. You might consider changing wheels to RP-25 at this time. You may also want to plug holes with turned down scrap sprue to reduce dirt penetration.
