* Parking brake cable/mechanism: This is the most likely culprit. A sticking or partially engaged parking brake cable can cause the rear brakes to drag, especially noticeable when reversing. The cable itself might be frayed, corroded, or seized. The parking brake lever mechanism might also be malfunctioning.
* Rear brake caliper(s): A seized or sticking rear brake caliper piston will keep the brake pads pressed against the rotor even when the brake pedal isn't depressed. This is more likely to be a problem on one side, causing the car to pull to one side when reversing. This is a serious mechanical issue.
* Brake lines/hoses: A restricted brake line or hose, especially in the rear, can cause pressure buildup that leads to dragging brakes. This is less common than the caliper or parking brake issue.
* Master cylinder: Although less likely to cause a problem only in reverse, a faulty master cylinder could contribute to uneven brake pressure distribution, potentially causing issues when the weight distribution shifts in reverse.
* Proportioning valve: This valve regulates brake pressure between the front and rear wheels. A malfunctioning proportioning valve could send too much pressure to the rear brakes when reversing.
* ABS system: While less probable to cause complete lock-up, a malfunctioning anti-lock braking system (ABS) component could contribute to the problem, though this is usually accompanied by ABS warning light illumination.
Why it's more noticeable in reverse:
The weight distribution changes when reversing. A slight drag that's barely noticeable when driving forward becomes much more significant when reversing, potentially leading to the brakes locking up.
What to do:
* Do not drive the vehicle until the issue is resolved. Locked brakes are extremely dangerous.
* Have a qualified mechanic inspect the braking system thoroughly. They'll be able to diagnose the specific problem and carry out the necessary repairs. Don't try to fix this yourself unless you have significant automotive repair experience.
Ignoring this problem could lead to accidents, so immediate professional attention is crucial.
