A long time ago I posted questions about causes of brake pulsations.
This is an update on the problem.

History: Under warranty dealer turned rotors twice and replaced the
rotors once, then refused to do any more warranty work. I was
determined to get to the root cause of the problem.

I purchased a runout gauge and started measuring the runout at various
stages of pulsations and wear. It turned out after new rotors and a
couple of rotor turnings that runout was not the problem. There was
not a correlation between pulsations and runout.

I purchased very expensive racing rotors and pads to try but they were
worse than Hyundai parts. I suspected brake pad material was the
cause of the problem. So I started buying differ pads to try since I
read that all manufacturers use different formulas for their pad's
material.

What worked? The cheapest pads sold by AutoZone. They have been on
for 6 months now and are still smooth. With the racing rotors that
have been turned once. It has been an interesting endeavor but the
problem seems to be solved for now.

Feedback is welcome and I hope this may help someone else with this
issue.

 

southluke wrote:
> A long time ago I posted questions about causes of brake pulsations.
> This is an update on the problem.
>
> History: Under warranty dealer turned rotors twice and replaced the
> rotors once, then refused to do any more warranty work. I was
> determined to get to the root cause of the problem.
>
> I purchased a runout gauge and started measuring the runout at various
> stages of pulsations and wear. It turned out after new rotors and a
> couple of rotor turnings that runout was not the problem. There was
> not a correlation between pulsations and runout.
>
> I purchased very expensive racing rotors and pads to try but they were
> worse than Hyundai parts. I suspected brake pad material was the
> cause of the problem. So I started buying differ pads to try since I
> read that all manufacturers use different formulas for their pad's
> material.
>
> What worked? The cheapest pads sold by AutoZone. They have been on
> for 6 months now and are still smooth. With the racing rotors that
> have been turned once. It has been an interesting endeavor but the
> problem seems to be solved for now.
>
> Feedback is welcome and I hope this may help someone else with this
> issue.
>

Ha!!
I love a good experiment.

Thanks for sharing your efforts.

Jim

 

southluke wrote:
> A long time ago I posted questions about causes of brake pulsations.
> This is an update on the problem.
>
> History: Under warranty dealer turned rotors twice and replaced the
> rotors once, then refused to do any more warranty work. I was
> determined to get to the root cause of the problem.
>
> I purchased a runout gauge and started measuring the runout at various
> stages of pulsations and wear. It turned out after new rotors and a
> couple of rotor turnings that runout was not the problem. There was
> not a correlation between pulsations and runout.
>
> I purchased very expensive racing rotors and pads to try but they were
> worse than Hyundai parts. I suspected brake pad material was the
> cause of the problem. So I started buying differ pads to try since I
> read that all manufacturers use different formulas for their pad's
> material.
>
> What worked? The cheapest pads sold by AutoZone. They have been on
> for 6 months now and are still smooth. With the racing rotors that
> have been turned once. It has been an interesting endeavor but the
> problem seems to be solved for now.
>
> Feedback is welcome and I hope this may help someone else with this
> issue.
>

Unfortunately, I can't find the site now, but there is a site that
discusses this and makes a pretty compelling argument that most brake
pulsing is due to an uneven distribution of pad material on the rotor
and NOT due to a physical warping of the rotor. The site discusses how
to properly break in pads to prevent this and also how you MAY be able
to correct it via several successive and hard stops. I've done this and
it worked and I'm not a believer in this theory. Your experience thus
far seems to support this as well.

Matt

 

I'll ditto Matt's post, less the website which I haven't seen, and add
a little.

I believe the root cause to be a variation in coefficient of friction
around the circumference the rotor. Pads leaving material in various
places on the rotor is one way to cause this variation in friction.

Another way for this to occur is simply via corrosion. If you leave
your car sit for a few days outside (or just overnight in some areas),
you'll see some light rust on the rotors (if you can see through the
wheels). Roll the vehicle so that each wheel makes about half a turn,
and you'll see that there's an absence of rust on the portion of the
rotor which was behind the pad. Over time, the rotor accrues varying
levels of corrosion around its circumference.

In most cases, I'm unable to make the problem go away by hard
braking. When resurfaced, rotors display little runout, but after
resurfacing, the problem is gone. This leans me toward the latter
issue rather than the former, since the corrosion does eat away
unevenly at the surface, even if it isn't noticeable with the eye.

 

I think this is the site you are referring to.
http://www.stoptech.com/tech_info/wp...akedisk.shtml#

Voyager wrote:
> southluke wrote:
>> A long time ago I posted questions about causes of brake pulsations.
>> This is an update on the problem.
>> History: Under warranty dealer turned rotors twice and replaced the
>> rotors once, then refused to do any more warranty work. I was
>> determined to get to the root cause of the problem.
>>
>> I purchased a runout gauge and started measuring the runout at various
>> stages of pulsations and wear. It turned out after new rotors and a
>> couple of rotor turnings that runout was not the problem. There was
>> not a correlation between pulsations and runout.
>>
>> I purchased very expensive racing rotors and pads to try but they were
>> worse than Hyundai parts. I suspected brake pad material was the
>> cause of the problem. So I started buying differ pads to try since I
>> read that all manufacturers use different formulas for their pad's
>> material.
>>
>> What worked? The cheapest pads sold by AutoZone. They have been on
>> for 6 months now and are still smooth. With the racing rotors that
>> have been turned once. It has been an interesting endeavor but the
>> problem seems to be solved for now.
>> Feedback is welcome and I hope this may help someone else with this
>> issue.
>>
>
> Unfortunately, I can't find the site now, but there is a site that
> discusses this and makes a pretty compelling argument that most brake
> pulsing is due to an uneven distribution of pad material on the rotor
> and NOT due to a physical warping of the rotor. The site discusses how
> to properly break in pads to prevent this and also how you MAY be able
> to correct it via several successive and hard stops. I've done this and
> it worked and I'm not a believer in this theory. Your experience thus
> far seems to support this as well.
>
> Matt

 

Hank wrote:
> I think this is the site you are referring to.
> http://www.stoptech.com/tech_info/wp...akedisk.shtml#

That isn't the original site I read years ago, but it has much the same
information.

Matt

 

> southluke wrote:
> A long time ago I posted questions about causes of brake
pulsations. This is an update on the problem.
>
> History: Under warranty dealer turned rotors twice and replaced
the rotors once, then refused to do any more warranty work. I was
determined to get to the root cause of the problem.
>
> I purchased a runout gauge and started measuring the runout at
various stages of pulsations and wear. It turned out after new
rotors and a couple of rotor turnings that runout was not the
problem. There was not a correlation between pulsations and runout.
>
> I purchased very expensive racing rotors and pads to try but they
were worse than Hyundai parts. I suspected brake pad material was
the cause of the problem. So I started buying differ pads to try
since I read that all manufacturers use different formulas for their
pad's material.
>
> What worked? The cheapest pads sold by AutoZone. They have been
on for 6 months now and are still smooth. With the racing rotors
that have been turned once. It has been an interesting endeavor but
the problem seems to be solved for now.
>
> Feedback is welcome and I hope this may help someone else with this
issue.

Matt,

Yes, you sent me that link a year or so ago and I tried it 2-3 times.
It seemed to help but not enough to make the brakes tolorable. But
the article was very good info that had even more relavent concepts.

Thanks...Luke

 

I've experienced the same problem. It came on after I had a brake
job done: new pads, all new rotors: 2000 Sonata. All aftermarket
parts. The pulsation came on a while after the work was done. My
mechanic is good.

Let's assume that it's a case of melting pad binder material.
It's hilly around here with a few "San Francisco"-type grades. A
long time ago when disk brakes weren't common, I learned to "jab
brake" from a racing driver; the idea was to prevent brake fade
by slowing with hard jabs, allowing the drums to cool between the
jabs. A hard habit to break ("brake," get it?).

If so, is there a decent DIY solution such as manually sanding
the disks?

Richard

 

> southluke wrote:
> A long time ago I posted questions about causes of brake
pulsations. This is an update on the problem.
>
> History: Under warranty dealer turned rotors twice and replaced
the rotors once, then refused to do any more warranty work. I was
determined to get to the root cause of the problem.
>
> I purchased a runout gauge and started measuring the runout at
various stages of pulsations and wear. It turned out after new
rotors and a couple of rotor turnings that runout was not the
problem. There was not a correlation between pulsations and runout.
>
> I purchased very expensive racing rotors and pads to try but they
were worse than Hyundai parts. I suspected brake pad material was
the cause of the problem. So I started buying differ pads to try
since I read that all manufacturers use different formulas for their
pad's material.
>
> What worked? The cheapest pads sold by AutoZone. They have been
on for 6 months now and are still smooth. With the racing rotors
that have been turned once. It has been an interesting endeavor but
the problem seems to be solved for now.
>
> Feedback is welcome and I hope this may help someone else with this
issue.

I tried sanding the rotors, thinking it would clean them
up. Even with heavy industrial sandpaper and electric sander, it did
not help.

Update: It has now been approximately 25,000 miles and all is still
good. I looked at the pads the other day and they were not hardly
worn at all. Never before did the car go this long without the
pulsating. I recommend turning the rotors and get the cheap pads.

The car has 100,000 miles on it now and I finally changed the spark
plugs. The ones in the rear were burned away worse than any I have
ever seen, but the car still ran fine. Interesting.