Rear Inboard Brake Issues (V12 cars)
Symptoms
Rear brakes binding, poor rear brake performance, difficulty bleeding rear brakes, brake fluid leak near the differential.
Cause
The V12 XJ-S uses inboard rear disc brakes mounted on either side of the differential. This design reduces unsprung weight but makes the brakes difficult to access, inspect, and service. The calipers are exposed to heat from the exhaust and differential, accelerating seal deterioration. Bleeding is notoriously difficult because air tends to trap in the high points of the long brake lines running to the inboard location.
Fix
Rear brake service requires raising the car and working underneath.
Caliper rebuild is similar to the fronts but access is much worse.
Use a pressure bleeder rather than a pedal bleeder for the rear brakes, it's far more effective at purging air from the long lines.
Some owners fit a ventilated rear disc rotor conversion kit for improved cooling.
Budget $500-1,000 per side for a caliper rebuild including new hoses.
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