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Hissing noise when not breaking

Dear Car Talk Community,



I have recently noticed a hissing noise coming from the driver side floor/leg area of my 2003 Ford Escape. The hissing stops when I apply any pressure to the breaks, but resumes when I release the breaks. This seems to have begun after a spell of particularly hot weather.



Any advice on what may be causing this is much appreciated!



--Molly

The problem might be with the vacuum brake booster. Since this hissing occurs all the time when the brakes aren’t applied, open the hood, start the engine and while it’s idling, take a pair of pliers and pinch off the large vacuum hose going to the brake booster. If the hissing stops, the brake booster diaphram has a leak, and the brake booster requires replacing.

Tester

Thanks so much. I’ll give this a try tonight.

Much appreciated.
–Molly