It sounds less like a spring issue and more like a sticky brake.
The easiest things to check are the hard line and the brake cylinder. If it's pinched one wheel will get more pressure than the other, and since the lines are unequal it's easy for it to affect one side. Even a misaligned exhaust can begin to flatten a hard line. A weeping cylinder will cause the same symptoms and just a few drops of fluid can cause problems, it doesn't have to be noticeable with the drums on.
It could also be a partially collapsed soft line from the body to the axle, again the uneven lines and a bit of wear could make one wheel more sensitive to the effects of the collapsed line. They can act as check valves preventing fluid from flowing back as quickly as it enters.
Next I'd suspect a ridge or dirt in the wheel cylinder. Wheel cylinders are very cheap, and if there's dirt in it you may as well replace rather than clean them for the peace of mind.
Brakes are important enough that I wouldn't hesitate to replace original soft lines and cylinders just due to age.
Topic: Hopping rear tire (Read 3740 times)