A ball coming through the subway stops right where the plastic section meets the lower metal trough, although it should simply drop onto the metal. The next ball pushes it through and does not hang itself. Pitch, level, magnetised balls and burrs were all ruled out.

Ball stops at the end of the subway until another ball pushes it: shim the warped subway

Cause: The subway ramp had warped enough to pinch the ball at that corner.

Checks

• Take the subway out and look along it for warping or a twist.
• Watch where the ball stops: if it is held at the joint rather than rolling slowly, it is being pinched.

Fix

• Put two small washers between the subway and the playfield at its single fastening point to lift that end slightly.

Systems

• WPC-Security (WPC-S)

Games

• Theatre of Magic

Related tips

• Trap door only bumps and won't lift: fit a flipper coil

Source: Pinball Repair help group!! (Facebook group)