The windings on the old bass strings loosen over time making a
'thud' sound, or as we in the trade call them, 'dead'.  Any attempt
to rejuvenate old bass strings is temporary at best.  Replace them;
it's about the same amount of work.  New strings from Mapes are about
six dollars each and are far better than the old ones that are dead.

Twisting the strings will only be a short-term answer and the pins
will then be loose.  Repin with oversized pins.

Don Teach
Shreveport, Louisiana