Howdy,
Only other thing I'd check is hub play. If its big enough, going around a
corner or something can cause the wheel to rock, pushing the caliper back
in the bore. When you hit the brakes, they travel longer getting the pad
back to the rotor, so one pump, then the brakes feel fine.
Check it like you would wheel bearings, jack the car up and try and move
the wheel pushing at the top of the tire and pulling at the bottom, then
vice versa.
Or take it to a big parking lot and turn violently one way then the other,
then try the brakes.
Mark
On Mon, 30 Aug 2010, Arvid Jedlicka wrote:
> Ok, here is the story ...
>
> I was out of town and my nephew called. He was driving his girlfriend's 2000
> Kia Sephia Spectra. When he stepped on the brake pedal it went to the floor.
> On the second pump the brakes worked well enough that he was able to stop the
> car. He then drove carefully to a safe parking lot using the "two pump"
> method and then called me. I asked him to look at the wheels to see if there
> was any sigh of fluid loss and to check the master cylinder reservoir.
> Everything looked to be in good shape. I then suggested that he either call
> AAA or if he felt comfortable he could take back roads and drive the car over
> to my house. He took the latter option.
>
> He called me when he got to my house and said "on the way over it was fine,
> the brakes worked on the first try". Given that it was now in my driveway and
> thinking that the large hammer principal might discover what might be amiss I
> asked him to go out and step on the brake pedal as hard as he could. The
> assumption being that if he blows a seal or a rubber line at least it was in
> the driveway and easy to fix. He went out to the car and said the pedal again
> went easily to the floor but would pump up like it had earlier.
>
> I told him where the keys were for my car so he and his girlfriend could at
> least be on their way and told them I would look at the Kia when I got home.
>
> Upon getting home I took the car for a drive and the brakes seemed fine.
> Reasonable pedal feel, reasonable stopping power ... after all it is a 10
> year old Kia Sephia so the bar was not real high to begin with ... all seemed
> to be fine.
>
> I am reluctant to give it back to them with a clean bill of health. The only
> thing I can think of is to replace the master cylinder, but that seems like
> throwing parts at the problem. But the master cylinder is the only thing I
> can think of that might cause a soft pedal without leaking fluid on the
> ground and "recovering". The thought of a small piece of rust or what ever
> causing an intermittent seal failure between the front and back portions of
> the master cylinder is the scenario I was thinking of.
>
> So if anyone has any other suggestions on how to diagnosis this I would
> appreciate it. And even if you don't have a firm diagnosis, a well reasoned
> "throw this at it" would be appreciated ... assuming it is short of replacing
> the car or the entire brake system.
>
> Thanks,
> Arvid _______________________________________________
>
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