Draining the brake system v. bleeding the lines?

Dear Car Talk

Dear Car Talk | Jan 01, 1990

Dear Tom and Ray:

I have read that all brake fluid should be bled out from time to time because it absorbs water. Are they talking about draining the entire system or just bleeding the lines? Also, how often should this be done?

TOM: Good question, Joseph. The draining of brake systems can be traced back to the ancient Egyptians. They used to cut open the veins of sick people to let the bad blood drain out. It worked so well that physicians started recommending it to their mechanics, and brake draining was introduced.

RAY: Actually, your entire brake system should be drained every couple of years. And yes, the reason is that brake fluid does absorb water. Over time, water in the fluid can cause the metal parts of the brake system--the calipers, wheel cylinders, and brake lines--to rust and eventually fail.

TOM: The procedure is done with a device called a power bleeder which flushes out the old brake fluid under pressure and replaces it with new fluid. Any repair manual that suggests the use of leeches is out of date.

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