Brakes fading, then failed

My grandmother had a bit of a scare yesterday. She doesn't drive her Fiat Punto (8 years old, 12k km or so, bought new) very much (it is, in effect, the Real Thing of the 'always driven by an elderly lady' car -- maintained at a local garage on a yearly basis), but yesterday she went to take it around a block or two, mainly to keep the battery from running down (again), and as she described it, the brakes started working less than stellar, and eventually failed completely -- no resistance to the pedal.

She got it home, carefully and with the handbrake. When I looked at it this afternoon, all the fluid levels including the brakes appeared to be in good shape, and starting it up revealed no immediate warning lights[1]. With the handbrake released, I could move the car back and forth by hand easily, but with the brake pedal depressed (which does not now appear to go down to the stops) it had at least enough braking to stop me from doing that (this is not necessarily inconsistent with there not being enough braking action to matter when acting on a ton of metal moving at speeds, of course).

So, what the hell happened? My pet theory: She left the handbrake on a notch or two and the drag caused the brakes to heat up enough to boil the brake liquid. If the garage doesn't find anything wrong with the brakes in the area of things that are actually broken, this'd be my best theory. Are there any other options that cause the brakes to fade out to nothing gradually (that tends to argue against, say, a piece of the caliper breaking off), and possibly return after cooldown?

Jasper

[1] I don't have a license, plus I don't like brakeless cars, so I didn't drive it.
Reply to
Jasper Janssen
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The obvious thing to look at would be when the fluid was last changed and if necessary replace it. Brake fluid absorbs water over time and boils very easily when it gets old.

-- Dave Baker - Puma Race Engines

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Reply to
Dave Baker

Sure sounds like brake fluid vapor lock. I don't why that would happen with just a "drive around the block". Might have been a combination of "wet" brake fluid (i.e. high moisture content) along with something creating a lot of heat.

Many automakers don't have any recommended period to flush the brake fluid - at least for US service. General Motors and Toyota come to mind.

Reply to
y_p_w

Well, longish block. About half an hour or so. But all small roads, max speed 80 km/h (50 mph), not highway driving.

I'll see if I can look at the service book next time I'm there. It's (supposed to have) had all scheduled maintenance, but obviously on the 'time' schedule rather than the kilometer schedule, because at about 2000 km/1300 miles a year average the kilometer schedule would have it in for its first service at 7.5 years old.

Jasper

Reply to
Jasper Janssen

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