The main reasons for unequal length cables are incorrect adjustment of rear brake shoes and/or one of the cables seizing in the cable sheath/guides due to rust/dirt etc.
There are two cables, one end to each drum and the other ends to equaliser plate under the handbrake lever. These hook on and the adjustment is taken up by a central nut and threaded rod which tightens or slackens the equaliser plate.
Handbrakes should always be adjusted at the drums first. This is where most problems are found.
Assuming the rear shoes, retainers, springs and adjusters are clean and not gummed up (which is often missed on a service) the correct way of adjusting them is (according to my Haynes manual);
Centralise the brake shoes by gently tapping them.
Wind in threaded adjusters just enough to let the drum slide over the shoes.
Once drum is secured, pump brake pedal several times to enable adjusters to take up shoe to drum clearance. If you have someone to assist, you should be able to hear a clicking sound from the drums as the adjusters do their thing.
Now at the handbrake end, apply hand brake several times.
Now pull up handbrake to fully applied position but count the number of clicks from the ratchet. Should be between 4 and 7. If not, adjust as follows;
Apply handbrake to FIRST NOTCH. Rotate adjusting nut at handbrake end until only a slight drag is felt on rear drums. Release handbrake and make sure rear wheels rotate freely. Now fully apply handbrake while counting number of clicks from ratchet. If not between 4 and 7 adjust again.
If you still have one cable longer than the other, it may mean either one of the cables is the incorrect one for the car or it's incorrectly routed where it passes under the rear exhaust heat shield. Cables can stretch over time but an inch means something else is wrong.
Hope this helps,
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