What You Pay
We don't have a flat number to quote you here, because cable repair pricing depends on whether you're on an extension-spring system or a retrofit torsion conversion, whether one cable went or both, and whether the drum or pulley took damage with it. What we can tell you is that a straightforward two-cable swap on an extension system, which is what we expect to find on most doors from Clayton's building era, costs less than letting one cable failure turn into a bent track or a cracked bottom panel from the door dropping unevenly. We price the job after we've looked at the drums, the pulleys, and the track alignment, not before - a phone quote on cable work is a guess, and we'd rather not guess.
How We Fix It
First we check whether the door is still square on its tracks after the cable let go - a door that drops on one side can rack the track out of alignment, and that has to get straightened before new cable goes on, or the new cable wears the same way in half the time. We release spring tension safely, pull the old cables and inspect the drums and pulleys for the groove wear that's common on doors this age, then run new galvanized cable sized to the drum and re-tension both sides evenly. On a double door we replace both cables together even if only one failed, because the surviving one is on the same clock. Last step is cycling the door a dozen times by hand before we call it done, checking for drift, listening for a cable riding rough on a pulley that should've been swapped too.
Can You Do This Yourself
Don't. A garage door cable under tension from an extension spring can take a finger off or whip hard enough to put someone in the hospital, and that's true whether the door is new or from 1972. If a cable has already snapped and the door is down, the honest DIY move is to leave it alone, keep the car inside if you can, and call someone - don't try to winch it back up by hand or cut the other cable to make the door sit level, which people do and which makes the next repair worse. The one thing you can safely check yourself is whether the track bolts are loose or the door is visibly racked sideways; if it looks crooked, that's useful to mention when you call, because it changes what we bring.
