Bally mushroom rubbers must be the least replaced rubber ring on all
pinball machines. They are a bit of a bother to change, but are well worth
These rubber rings are 7/16", which size is rarely used elsewhere.
To change them, raise the playfield and undo the large nut that
holds the assembly on the playfield. When the nut is fully unscrewed,
remove the assembly from the top of the playfield while holding the nut in
place. When the assembly is fully extracted, then the nut will slide out
from under the switch easily.
Examine the assembly and note that at the bottom is a tiny E-clip. Remove
that clip (needle-nose pliers do this well), and remove the brass ring and
spring inside the end. Lift out the mushroom lifter plastic from the top
end. Now you can easily remove the old rubber ring and replace it.
When reassembling be certain to first slide the large nut behind the switch,
and then lower the completed assembly back into the playfield. Be sure to
only tighten the nut finger tight. It does not need to be any
tighter, and will ensure that the next time the rubber is replaced it will