Brake Pedal Nearly goes to floor, intermittent - Kia Forum

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post #1 of 35 (permalink) Old 03-23-2019, 02:19 AM Thread Starter
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Brake Pedal Nearly goes to floor, intermittent

Recently aquired a 2003 Sorento, and the brake pedal seems to be intermittently going enarly to the floor. Usually it will have good brake pressure with the pedal 1/3 depressed, but then occasionally it will just go way further and need to be pressed nearly to the floor to get good brake pressure.

If I press hard on the brake pedal while stationary the pedal goes slowely all the way to the floor.

From what I've read it sounds like it is most probably the master brake cylinder. Is there any way I can easily confirm this to be the case before buying a new part?

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post #2 of 35 (permalink) Old 03-23-2019, 04:54 PM
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Sometimes the master cylinder leaks out the back but most times it leaks past the seals internally so there is no visual signs.
If it was mine I’d try the cheap easy way first and bleed the brakes first......but it does sound like a bad master cylinder.
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post #3 of 35 (permalink) Old 03-23-2019, 09:52 PM
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Good advice from Old n Slow.
Also I would stop driving it until you get it solved.
I say that because you did not state that you have parked the vehicle.

if you have.

Also to the forum
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post #4 of 35 (permalink) Old 04-03-2019, 04:08 AM Thread Starter
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Thanks for the replies guys.

I know I shouldn't be driving it with this issue.. But.

I've noticed that when taking off, after braking, I will sometimes hear / feel a bit of a clunk, and afterwards the soft pedal braking issue occurs for a short period of time.

It feels like maybe the rear brakes are sticking a bit, and then getting 'jolted open'? Which I'm thinking could mean the gap between pad and disc is much wider than usual when this happens, resulting in the pedal going much lower for a bit? The pedal seems to pretty much come back up after pumping the pedal one or two more times.

Any suggestions on that extra info?

I am going to bleed the brakes this weekend and see if that helps, but I have a feeling somethine else is going on, possible not the master cylinder either.
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post #5 of 35 (permalink) Old 04-03-2019, 10:31 AM
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You might be right......What you describe has happened to me with drum brakes, if they wear down too far and are not adjusted out, the brake pedal will go soft for the first couple of pumps, until the piston finally extends out far enough to have the shoe make contact with the drum.

Let us know what you find this weekend.
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post #6 of 35 (permalink) Old 04-09-2019, 10:46 PM Thread Starter
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Ok so on the weekend I lubricated and bled all 4 brakes. Gave each one a good long bleed to flush the brake system out good.

Since then the issue seems to have stopped all but entirely. I have still noticed the pedal depressing more than it feels like it should on a couple of occasions though =/

I'm thinking, the master cylinder probably is bad, but the fresh brake fluid has made it behave itself a little more normally, for now at least. I will set about replacing the master cylinder soon.

I have picked up a master cylinder from a wreckers, but I'm thinking it wouldn't make much sense to just replace it as it is, since it is likely old and on the way out anyway. So I'm thinking to buy a master cylinder seal kit and recondition this one.

Anyone have any thoughts on doing that? Am I being stupid, should I just buy a brand new master cylinder?
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post #7 of 35 (permalink) Old 04-09-2019, 11:59 PM
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Unles you have experience with rebuilding a MC you might consider buying a rebuilt or if your budget allows, new.

I have begun to understand the saying"Buy once, cry once"

The pedal can still travel more if the pads are worn.
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post #8 of 35 (permalink) Old 04-10-2019, 01:34 AM Thread Starter
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The rear pads were on the low side but still OK. About 6-7mm left in them.

I wouldn't have thought that would be causing extra pedal travel though since the caliper should be adjusting down on them, yeah?
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post #9 of 35 (permalink) Old 04-10-2019, 10:12 PM
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Silly me. I was thinking of the fluid level when I wrote my post.
As the pad wears fluid level will drop. Pedal travel should remain the same.
Unless you are getting leak by on the MC or disk pistons, in which you will get fluid at the brakes,
in the form of a leak or fluid in the passenger compartment, sometimes.
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post #10 of 35 (permalink) Old 04-11-2019, 05:15 PM
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Quote:
Originally Posted by ZacMonkeys View Post
...........

I have picked up a master cylinder from a wreckers, but I'm thinking it wouldn't make much sense to just replace it as it is, since it is likely old and on the way out anyway. So I'm thinking to buy a master cylinder seal kit and recondition this one.

Anyone have any thoughts on doing that? Am I being stupid, should I just buy a brand new master cylinder?
I had no idea you could still buy rebuild kits anymore.....we used to rebuild all the time, the main thing is to have a good cylinder bore with no pitting, but even then we would hone them out with a brake cylinder hone.

It is just a matter of getting quality rubber replacement parts, a good master cylinder core and carefully noting how it came apart and putting it back the same way.

But like the toolman advised, theres nothing like buying new.
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