Brake pedal goes to the floor intermittently

[CARLOS DE LA CRUZ]

Hi guys I have a 2016 KIA Sorento 2WD EX and suddenly (only 3 times until now) brake pedal went to the floor and then recovery as normal. Do you think is with removing all the brake fluid and purge would work? Or maybe my master cylinder is damaged? Do you think I need to be worried about the ABS?
Thanks

 

[atikovi]

I would start by looking at the brake lines for a leak.

 

[Nukeman7]

Hi guys I have a 2016 KIA Sorento 2WD EX and suddenly (only 3 times until now) brake pedal went to the floor and then recovery as normal. Do you think is with removing all the brake fluid and purge would work? Or maybe my master cylinder is damaged? Do you think I need to be worried about the ABS?
Thanks

99% certain that it is a bad seal in the master cylinder. I experienced the exact same intermittent brake anomalies over a 3 month period in a Hyundai Elantra (w/only 40K miles) and suspected air intrusion in the system. After flushing/bleeding it twice over a month, the symptoms would reappear once or twice every few weeks.

Finally, I replaced the Master Cylinder in April '24 and the symptoms have disappeared. Be sure to bench bleed the new MC and transfer the o-ring from the old MC to the new unit (if it doesn't come with a new o-ring). Otherwise, it will cause a vacuum leak at the brake booster (don't ask how I know that).

 

[Highlander 1459]

indicative of a defective master cylinder more than anything else

 

[CARLOS DE LA CRUZ]

I would start by looking at the brake lines for a leak.

I already check it, none, no fluid on tires or floor. Also no missing fluid in the container. Thanks

 

[CARLOS DE LA CRUZ]

99% certain that it is a bad seal in the master cylinder. I experienced the exact same intermittent brake anomalies over a 3 month period in a Hyundai Elantra (w/only 40K miles) and suspected air intrusion in the system. After flushing/bleeding it twice over a month, the symptoms would reappear once or twice every few weeks.

Finally, I replaced the Master Cylinder in April '24 and the symptoms have not disappeared. Be sure to bench bleed the new MC and transfer the o-ring from the old MC to the new unit (if it doesn't come with a new o-ring). Otherwise, it will cause a vacuum leak at the brake booster (don't ask how I know that).

So, even I change new fluid it will be the same, because this looks old now and a little bit discoloration. Thanks

 

[WylieCoyote]

Your master cylinder is bypassing. This happened to me when I was in college with my first car. Everything was fine, then it wasn't. If I applied firm quick pressure, it would stop fine, but if I use normal pressure that you would use in stop & go traffic, the pedal would go to the floor. So basically I had to drive like an idiot until I got it to a mechanic. Master cylinder swap, no problem since.

 

[CARLOS DE LA CRUZ]

indicative of a defective master cylinder more than anything else

So, no a problem with the ABS valves or something, right? Somebody told me maybe a relief valve could be damaged. Thanks

 

[CARLOS DE LA CRUZ]

Your master cylinder is bypassing. This happened to me when I was in college with my first car. Everything was fine, then it wasn't. If I applied firm quick pressure, it would stop fine, but if I use normal pressure that you would use in stop & go traffic, the pedal would go to the floor. So basically I had to drive like an idiot until I got it to a mechanic. Master cylinder swap, no problem since.

ok Thanks, any recommendation for a brand for this master cylinder. I am looking in Autozone, do you think duralast is fine or not? Thanks again

 

[WylieCoyote]

I can only say that I haven't had any problems with Duralast parts, but I've never used one of their master cylinders.

 

[CARLOS DE LA CRUZ]

I can only say that I haven't had any problems with Duralast parts, but I've never used one of their master cylinders.

I used one time long time ago, 2002 maybe, lol, in a Chevrolet Caprice 1979 2 doors, but not sure that was duralast. Thanks

 

[Nukeman7]

ok Thanks, any recommendation for a brand for this master cylinder. I am looking in Autozone, do you think duralast is fine or not? Thanks again

I'd recommend the Beck-Arnley master cylinder from Rockauto if you can wait for shipping. It is $79 + shipping and likely to be from the OEM manufacturer. That is what I used on the Hyundai and it was an OEM (Mando) part.

 

[CARLOS DE LA CRUZ]

I'd recommend the Beck-Arnley master cylinder from Rockauto if you can wait for shipping. It is $79 + shipping and likely to be from the OEM manufacturer. That is what I used on the Hyundai and it was an OEM (Mando) part.

Excellent, Thanks a lot

 

[Highlander 1459]

So, no a problem with the ABS valves or something, right? Somebody told me maybe a relief valve could be damaged. Thanks

basically the master cylinder is a pump in what is a closed hydraulic system... the ABS acts as a distribution point for the oil in the hydraulic system and doesn't actually bleed pressure so much as cycle the pressure electrically thru some solenoid valves.. so if the pump( master cylinder) is leaking internally the pedal will be spongy or continue to move all the way to the floor...

it is the most likely culprit..

now if you have leaks, it is whereeever the leak is but that will have different sysmptoms than you stated

 

[Nukeman7]

Excellent, Thanks a lot

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[CARLOS DE LA CRUZ]

basically the master cylinder is a pump in what is a closed hydraulic system... the ABS acts as a distribution point for the oil in the hydraulic system and doesn't actually bleed pressure so much as cycle the pressure electrically thru some solenoid valves.. so if the pump( master cylinder) is leaking internally the pedal will be spongy or continue to move all the way to the floor...

it is the most likely culprit..

now if you have leaks, it is whereeever the leak is but that will have different sysmptoms than you stated

Excellent explanation, thanks, I appreciate it.

 

[CARLOS DE LA CRUZ]

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Wow, thanks

 

[mrbreezeet1]

indicative of a defective master cylinder more than anything else

Yeah, lf no fluid loss is noted, probably the master cylinder.

 

[VersatileGuy]

I can only say that I haven't had any problems with Duralast parts, but I've never used one of their master cylinders.

It depends. The stuff might be made in China but compared to what KIA sources, it might actually be better for their materials(they certainly are not Toyota). Autozone also backs it with their limited lifetime warranty. At least for brake pads, I just used it yesterday no questions asked.

 

[CARLOS DE LA CRUZ]

Well, finally guys I just changed all the brake fluid, removing all from the master cylinder with a pump, the refill with new and bleeding each wheel starting on the far one from the master cylinder and now is much better, I just check some information and I guess this is what happened to my vehicle.
Check this link: