* Caliper sticking or seizing: The most likely culprit. A seized or sticking caliper piston on the right rear will keep the brake pad pressed against the rotor, causing excessive wear. This could be due to corrosion, a faulty caliper seal, or a build-up of debris preventing the piston from retracting properly.
* Parking brake cable issue (less likely): A problem with the parking brake cable specifically on the right rear could cause constant, slight engagement, leading to uneven wear. However, this would usually show other symptoms, like difficulty releasing the parking brake.
* Wheel cylinder (drum brakes, if applicable): While less likely on a Z34 which usually has disc brakes all around, if there's a rear drum setup on that specific model year, a wheel cylinder problem could cause the same effect as a sticking caliper.
* Faulty brake pad or rotor: While less probable to cause this *specifically* on only one side and so quickly, a manufacturing defect in the pad or rotor could lead to uneven wear. It's far less likely than a caliper issue.
* Something rubbing against the brake rotor: Check for any foreign objects (small stones, debris) or damage to the caliper bracket that could be constantly forcing the rotor and pad together.
What to do:
1. Visual inspection: Carefully inspect the right rear caliper for signs of corrosion, leaks, or anything preventing the piston from moving freely. Also check the brake pad and rotor for unusual wear patterns.
2. Check the parking brake: Make sure the parking brake is releasing completely. Try to manually release the parking brake cable (if accessible) to eliminate cable issues.
3. Test the caliper: Try to manually push the caliper piston back in. It should move smoothly. Resistance or difficulty indicates a problem. If you can push it back, see if it stays.
4. Professional inspection: If you're uncomfortable with any of this, take it to a qualified mechanic. They have the tools and expertise to diagnose the problem accurately.
It's crucial to address this quickly. Driving with a seized caliper is dangerous and can lead to brake failure. Replacing just the pads without addressing the underlying cause will just repeat the problem quickly.
