Q: What causes brake to grab? It it a serious problem? Should I have the dealership to investigate the problem.

If the brakes on a car are not functioning properly, they absolutely should be inspected and repaired. Among the many causes of grabbing brakes are contaminated brake pads (dust, grease, fluid), misaligned calipers, loose brake mounting bolts, seized caliper pistons and/or sliding pins and damaged brake lines or rubber hoses. All of these issues are serious safety hazards. Although a dealership can likely inspect and repair the underlying fault(s), you will save considerably if you use a certified Mechanic from a mobile service such as YourMechanic. If you do want to get a second opinion, simple request a brake safety inspection and a certified mechanic will be dispatched by YourMechanic to your location to diagnosis the issue and let you know of the cost to repair.