Slight brake pedal pulse - on a '15 KIA

[Confuzed1]

Hey all. 2015 Kia Sportage, about 60K miles. Brakes were changed (all pads/rotors) about a year or so ago. Up until now, they've worked just fine. But now when slowing to a stop, or even at highway speeds if the brake is lightly applied, I get a slight pulsation in the brake pedal.

So I naturally assume it was a slightly warped brake rotor. I bought the rotors and pads off R*ock Auto. I got the medium priced ones, not the cheapest nor most expensive. Anyways, I took each tire off and spun each rotor to see if it looked warped. Found nothing as they all seemed to run true visually. Then I mounted a dial indicator to measure the runout on each rotor on the outside face of each rotor. The most variance I measured was only .002 to .003..... which is little to nothing. I expected the issue to be easy to find, but of course is isn't turning out that way...

-Anything else I should look for? Otherwise I'll take the thing to a shop and let them deal with it.......

 

[1971demon]

Hey all. 2015 Kia Sportage, about 60K miles. Brakes were changed (all pads/rotors) about a year or so ago. Up until now, they've worked just fine. But now when slowing to a stop, or even at highway speeds if the brake is lightly applied, I get a slight pulsation in the brake pedal.

So I naturally assume it was a slightly warped brake rotor. I bought the rotors and pads off R*ock Auto. I got the medium priced ones, not the cheapest nor most expensive. Anyways, I took each tire off and spun each rotor to see if it looked warped. Found nothing as they all seemed to run true visually. Then I mounted a dial indicator to measure the runout on each rotor on the outside face of each rotor. The most variance I measured was only .002 to .003..... which is little to nothing. I expected the issue to be easy to find, but of course is isn't turning out that way...

-Anything else I should look for? Otherwise I'll take the thing to a shop and let them deal with it.......

A new vehicle maybe??...sorry couldn't resist.....( if it were me..I would go buy the best rotors and try that...even though they run out fine..somethings wrong there..my.02

 

[Slowpoke387]

Normally that's rotors and considering how new they are I'd guess improper lugnut torqueing when the wheels were put back on. From my experience it's usually excessive heat or the torque when it happens fairly quickly after installing. Unless you did torque them. Have the wheels been off since then?

 

[BULL]

Hey all. 2015 Kia Sportage, about 60K miles. Brakes were changed (all pads/rotors) about a year or so ago. Up until now, they've worked just fine. But now when slowing to a stop, or even at highway speeds if the brake is lightly applied, I get a slight pulsation in the brake pedal.

So I naturally assume it was a slightly warped brake rotor. I bought the rotors and pads off R*ock Auto. I got the medium priced ones, not the cheapest nor most expensive. Anyways, I took each tire off and spun each rotor to see if it looked warped. Found nothing as they all seemed to run true visually. Then I mounted a dial indicator to measure the runout on each rotor on the outside face of each rotor. The most variance I measured was only .002 to .003..... which is little to nothing. I expected the issue to be easy to find, but of course is isn't turning out that way...

-Anything else I should look for? Otherwise I'll take the thing to a shop and let them deal with it.......

A number of things to look for, mounting of the rotor (rust/debris on hub face/rotor mounting face), runout (TIR .001" is a common "new" spec depending on vehicle, .010" is considered "bad", subjective "badness" everywhere in between, your .002-.003" is "ok" but marginal).

DTV is a likely source (Disk Thickness Variation). Depending on access to the rotor faces, measure using either a micrometer or calipers at several clock positions around the rotors. A premium rotor (new) will have a DTV of .0002" or less. Economy rotor .0005" or less. Starting at .0005" and greater, this can start to be felt as "pulsing" in the brakes.

DTV is caused by a couple of things. Coming to a "instant stop" (not necessarily "hard") where when you come to a stop, there is zero modulation at the end of the stop, this "imprints" a bit of friction material onto the rotor and creates a "step" for the pad to pass over. Subsequent stops amplify this condition and cause the rotor to wear differently because of different transfer layer thicknesses on the rotor. This can be prevented or reduced by not coming to a instant stop at lights/stop signs etc and by slightly trailing off on braking.

This same condition is made worse by stopping instantly but from a "hard" stop. Same thing, but with much hotter pads and a much larger "step" in the transfer layer created on the rotor.

ALL of this is made worse by not (or at all) properly bedding a rotor from the start. If there isn't a gradual build up of a transfer layer and the first time the brakes do start to lay down a transfer layer, this "step" is in the worst possible scenario. Then it's just a matter of time in usage for the rotors to build up a DTV condition that becomes apparent.


.02

 

[Confuzed1]

Normally that's rotors and considering how new they are I'd guess improper lugnut torqueing when the wheels were put back on. From my experience it's usually excessive heat or the torque when it happens fairly quickly after installing. Unless you did torque them. Have the wheels been off since then?

I was thinking along the same lines @Slowpoke387 .....For about a year after I installed the new pads and rotors, the brakes were fine. No brake pedal pulsing or anything. And I did torque all the lug nuts down to 100 ft lbs (in a "star" pattern).

Then there was an issue a few months ago in which a seal in the rear end was leaking gear oil. I took it to the dealer and it turned out there was a TSB on just that problem....so I got lucky and the rear was replaced at no charge. But there was another note on the paperwork that stated a pulsation in the brake pedal. Both my wife and I drive the car and never noticed it.....but we did after we got the rear end replaced. Just guessing that the dealer never torqued the lug nuts after the rear was replaced and they reinstalled the tires....they rarely ever do that. Just jam them on with the impact gun...

A number of things to look for, mounting of the rotor (rust/debris on hub face/rotor mounting face), runout (TIR .001" is a common "new" spec depending on vehicle, .010" is considered "bad", subjective "badness" everywhere in between, your .002-.003" is "ok" but marginal).

DTV is a likely source (Disk Thickness Variation). Depending on access to the rotor faces, measure using either a micrometer or calipers at several clock positions around the rotors. A premium rotor (new) will have a DTV of .0002" or less. Economy rotor .0005" or less. Starting at .0005" and greater, this can start to be felt as "pulsing" in the brakes.

DTV is caused by a couple of things. Coming to a "instant stop" (not necessarily "hard") where when you come to a stop, there is zero modulation at the end of the stop, this "imprints" a bit of friction material onto the rotor and creates a "step" for the pad to pass over. Subsequent stops amplify this condition and cause the rotor to wear differently because of different transfer layer thicknesses on the rotor. This can be prevented or reduced by not coming to a instant stop at lights/stop signs etc and by slightly trailing off on braking.

This same condition is made worse by stopping instantly but from a "hard" stop. Same thing, but with much hotter pads and a much larger "step" in the transfer layer created on the rotor.

ALL of this is made worse by not (or at all) properly bedding a rotor from the start. If there isn't a gradual build up of a transfer layer and the first time the brakes do start to lay down a transfer layer, this "step" is in the worst possible scenario. Then it's just a matter of time in usage for the rotors to build up a DTV condition that becomes apparent.


.02

Thanks for the reply Bull....I never considered DTV as being a possible issue since the brakes seemed fine for almost a year after the brakes were installed. I'd have to remove all the rotors to verify if any DTV exists. But I think I understand what you're saying about friction material imprinting itself on the rotor face. Visually I didn't see anything.....

- After I didn't find anything obvious and put the tires back on and re-torqued the lug nuts, I took it out for a drive. Again, its a very slight pulsation in the brake pedal that I can only feel just before the car comes to a full stop. Seems a little "jerky" if you know what I mean. This might be a situation where the problem needs to get a little worse to find it. The car isn't anywhere near unsafe or anything...just annoying at this point.