What are the causes of brake failure in a hydraulic braking system?
3 Answers
The causes of brake failure in a hydraulic braking system are: loose connection between the brake pedal and the master cylinder, no or severely insufficient fluid in the brake fluid reservoir, broken brake lines causing oil leakage, or ruptured master cylinder piston cup. If there is no sense of connection between the brake pedal and the master cylinder, it indicates a loose connection between the brake pedal and the master cylinder, which should be inspected and repaired. When pressing the brake pedal, if it feels very light with slight resistance, check whether the brake fluid in the master cylinder reservoir is sufficient. If there is no fluid or severely insufficient fluid in the master cylinder reservoir, add brake fluid to the specified level. If there is still no sense of resistance when pressing the brake pedal again, check whether the brake hoses or metal pipes from the master cylinder to the wheel cylinders are broken or leaking oil. When pressing the brake pedal, if there is some resistance but the pedal position cannot be maintained and it sinks noticeably, check whether there is brake fluid leakage at the push rod dust cover of the master cylinder.
I've encountered hydraulic brake failure several times, with the most common causes being insufficient brake fluid or oil leaks. Last time I inspected an old car, I found oil stains all around the wheel cylinder piston, clearly caused by seal ring aging leading to fluid leakage. Air in the brake lines is also a major issue, especially when the brake fluid was just replaced but not properly bled - the pedal feels spongy, severely affecting braking force. If the master cylinder is severely worn and the piston cup seals aren't tight, pressure can't build up properly. Also worth noting is deteriorated brake fluid - excessive water content lowers the boiling point, making vapor lock likely during continuous hard braking. Finally, don't forget to check pedal travel - excessive free play leads to insufficient effective stroke. When facing these situations, don't hesitate - get it repaired immediately! Safety is no trivial matter.
Over the years of running my repair shop, I've summarized five key factors for hydraulic brake failure: First is brake fluid leakage, which may seep from pipe connections or wheel cylinders; second is air entering the hydraulic system, usually occurring when pipelines aren't thoroughly bled after disassembly; third is internal failure of the master cylinder, where aging rubber seals cause internal leaks; fourth is brake fluid deterioration, especially in vehicles driven for three to four years, where reduced boiling points lead to severe heat fade; finally, mechanical brake failures, such as seized caliper pistons or poor return. The most dangerous scenario is sudden brake hose rupture causing immediate brake failure. I recommend changing brake fluid every two years and checking fluid levels and pipeline conditions during every maintenance service.
