Warped rotors again

[UncleBob]

Originally Posted by curtis73

The proper solution is to properly bed in new pads.

If this was the case, then you would see new cars and bikes with pulsating brakes with under 5000 miles. I've never seen one

Can't speak for cars, but I know for a fact that bikes do not have the pads heat cycled or anything else when they come out of the crate

[curtis73]

Not bedding in pads doesn't mean they WILL pulsate. Correlation does not prove causation. I'm not saying that all new car will have pulsating brakes, I'm saying that bedding in pads prevents it.

But... you also bring up a good point. Bikes have thin, lightweight, non-vented rotors. Ever test runout on a hot one? They are out by a good bit since they don't have the heft and mass to hold heat like a big cast iron car rotor. Every time you hit the brakes on a bike, they heat up and get way out of round, but they don't pulsate because of it.

[UncleBob]

Originally Posted by curtis73

Not bedding in pads doesn't mean they WILL pulsate. Correlation does not prove causation. I'm not saying that all new car will have pulsating brakes, I'm saying that bedding in pads prevents it.

quite the contrary, using your model for brake pulsation cause, it would be just as likely on a brand new car as a car with miles. assuming that in all situations being investigated, there is no caliper or rotor issues in addition to the pad bedding issue. How could it be otherwise in your model?

Bikes may have thin rotors, but they have far less kenetic energy and have massive brakes for what they are. They don't even get luke warm until you use them in an extreme manner.

[curtis73]

Not sure about all bikes, but after a casual ride to work, raindrops on my rotors sizzle with a passion.

I've known some factory cars with brake pulsation after very short mileage. Mine went back three times under warranty. The other thing not being addressed in this part of the discussion is brake pad material. Factories use less expensive usually organic brake pad material which has less likelyhood of causing inclusions, but its rare that owners use organic pads when they change brakes. Either they pony up the extra $3 for ceramic or metallic pads, or the shop doing the work upsells the "better" pads with a longer warranty.

[UncleBob]

Originally Posted by curtis73

Not sure about all bikes, but after a casual ride to work, raindrops on my rotors sizzle with a passion.

I've known some factory cars with brake pulsation after very short mileage. Mine went back three times under warranty. The other thing not being addressed in this part of the discussion is brake pad material. Factories use less expensive usually organic brake pad material which has less likelyhood of causing inclusions, but its rare that owners use organic pads when they change brakes. Either they pony up the extra $3 for ceramic or metallic pads, or the shop doing the work upsells the "better" pads with a longer warranty.

My problem is, you're basing all of this off of one central assumption, and everything you have theorized has no evidence outside of that

You found a physical condition that causes brake pulsation, and from there you lept to the assumption that its due to poor break in. I've yet to see any evidence that justifies that assumption, and it definitely doesn't jive with what I have seen during my years as a mechanic.

I have had many pulsation issues that came back repeatedly, even with different pad compounds, even with rotor replacement, rotor machining, and personally breaking in the pads before giving the vehicle back to the customer.....and then we would do nothing but replace a single component, such as the calipers, or the master cylinder, and suddenly the problem doesn't come back

Your explanation makes no sense in these examples, and I have dozens of them.

[curtis73]

I think you assume too much from my singular example. I've had brakes that were fine for thousands of miles (nearly to the end of the pads) that started exhibiting pulsation; often times from visible inclusions with no runout. My stating that proper break in PREVENTS pulsation does not mean that its a cure-all and that not doing it is always the cause.

I'm merely stating that from my research, runout may not cause it, and improper bedding can lead to pulsation from inclusions.

[UncleBob]

Originally Posted by curtis73

I think you assume too much from my singular example. I've had brakes that were fine for thousands of miles (nearly to the end of the pads) that started exhibiting pulsation; often times from visible inclusions with no runout. My stating that proper break in PREVENTS pulsation does not mean that its a cure-all and that not doing it is always the cause.

I'm merely stating that from my research, runout may not cause it, and improper bedding can lead to pulsation from inclusions.

at what point the pulsation happens in the pads life, still seems like a leap to me on the cause. The cases I'm referring to, often were late in the life of the brake pads.

Again, you are making assumptions that do not necessarily corrilate with your findings. Inclusions being present does not automatically mean improper break-in. How can you verify this?

[curtis73]

Inclusions being present does not automatically mean improper break-in. How can you verify this?

That's not what I'm saying. I'm not being argumentative, but I gotta say this again: proper bed in PREVENTS inclusions, not eliminates them. I never said that improper bedding will always cause it, nor did i say that proper bedding won't allow it to happen.

Inclusions can happen for one of many reasons; grease or other foreign material on the rotor, an abnormally hot rotor that is stopped with pad pressure applied, improper rotor finish, many things which could happen later in pad life. I'm simply saying that I believe rotor inclusions are more to blame than warping.

[UncleBob]

Originally Posted by curtis73

proper bed in PREVENTS inclusions

based.....on......what?

Thats all I want. Is it a leap, or do you have some evidence other than the existence of inclusions?

[curtis73]

Like I said before...

Originally Posted by curtis73

I did lots of research on this, including looking at about 45 rotors under a scanning electron microscope

I had tons of rotors from the shop, documented symptoms, driver reports, and runout. Then each of them I fractured into four pieces and used a scanning electron microscope to analyze surface composition on the molecular level at four positions around the rotor. In almost all of the cases, rotors that exhibited runout without significant inclusion variation demonstrated no brake pulsation. Those that exhibited no runout but had significant inclusion variation were the ones that DID have brake pulsation.

As I said before, there is a ton of evidence that says warped rotors cause pulsation, but its all superficial. A driver takes a car to the shop and complains of brake pulsation. The shop takes the rotor off, measures runout and machines the rotor. Bingo, problem solved. The problem is, almost all used rotors will show some runout. It is therefore assumed that runout is the cause. The further assumption is that by machining the rotors true, the lack of runout is what cured the problem. What I believe firmly based on my research is that the convenient side-effect of machining rotors removes the inclusions, and THAT is what cures the pulsation, not the lack of runout.

All I can say is that of the 45 or so rotors I tested, it played out like this. Forgive me for not having my numbers handy... this was in 1993.

-On rotors that had significant runout AND significant inclusion variation, they came from cars where the driver ALWAYS complained of pulsation.
-On rotors that had insignificant runout AND had significant inclusion variation, they came from cars where nearly all the drivers complained of pulsation.
-On rotors that had significant runout BUT showed even inclusion over the rotor's surface, they came from cars where almost no drivers complained of pulsation.

What I'm saying is this... for decades, shops have been taking on brake jobs for pulsating brakes. They measure significant runout and machine the rotors to fix the problem. By default, it is assumed that runout is the cause. It has become so accepted that shops don't even typically measure runout anymore, they just go straight to the lathe. However, since most shops that I know of don't have scanning electron microscopes, they can't see inclusions in the rotor surface. I have seen them and documented it.

Now... to further emphasize another point that has been misinterpreted: Bedding in pads PREVENTS uneven inclusions on the rotor's surface. It does not mean that bedding pads will forever make it perfect, nor does it mean that if you DON'T bed pads your rotors are doomed. Its a break-in procedure just like piston rings in a new engine. Proper break-in gives you the best chance at optimum ring seal and long life, but doesn't guarantee it. Inversely, not properly breaking in a new engine does not mean its doomed to die quickly.

So, I guess what I'm saying is; I want to see your proof that runout CAUSES pulsation and inclusion variation doesn't. You can cite how a rotor with runout had pulsation, but that doesn't prove it was the CAUSE of it. I've done the research, I'm just wondering if you're basing your argument on decades of how shops have assumed it was, or actual first-hand research on the molecular level.

I also have to add that I fully respect your knowledge and experience on this matter and I enjoy the debate. I don't want you to think I'm being disrespectful or argumentative. I'm enjoying the discussing greatly

[KiwiBacon]

Another view on the initiation of inclusions indicates they can be caused by simply stopping when your rotors are still hot. The lack of airflow can lead to the rotors cooking brake material from the pads.
Even without the brakes being applied there is still enough pad/rotor contact for this to happen.

Interestingly enough a car of mine has begun to suffer pulsation only 10,000km from a new set of rotors (same pads).
I have been aware of the inclusion argument for a while and IMO the way this car is driven shouldn't cause such things to happen. In fact the brakes are used sparingly and much of it is open road with plenty of opportunity for cooling both during and after the occasional hard use (it crosses a 1000m mountain pass regularly).

[UncleBob]

Originally Posted by curtis73

Bedding in pads PREVENTS uneven inclusions on the rotor's surface.

BASED.....ON....WHAT?!

If you have no basis for the assumption, then just say so.

As for rotor runnout can cause pulsation: simple. While mounting a tire on my bike, I accidently slightly bent one of the rotors. It had no pulsation before the tire install, it pulsated after.

Take a hammer to your bike rotor, let me know what conclusions you draw from it.

[KiwiBacon]

Originally Posted by UncleBob

BASED.....ON....WHAT?!

If you have no basis for the assumption, then just say so.

As for rotor runnout can cause pulsation: simple. While mounting a tire on my bike, I accidently slightly bent one of the rotors. It had no pulsation before the tire install, it pulsated after.

Take a hammer to your bike rotor, let me know what conclusions you draw from it.

I don't think there's any argument that severe runout causes pulsation, there's only a certain speed that fluid can transfer from one side to the other without being felt. Sliding calipers probably have a higher tolerance.

[curtis73]

Originally Posted by UncleBob

BASED.....ON....WHAT?!

If you have no basis for the assumption, then just say so.

.

Based on the fact that bedding in pads prevents pulsation. Pads that have been properly bedded exhibit more even deposition on the rotors. That is based partly on customer reports during that test, but also from the fact that 6 of the rotors in my tests were mine, so I know their histories.

I also recall saying this:

Originally Posted by curtis73

My research has shown me that a "warped" rotor with consistent thickness almost never causes pulsating brakes. If it does its at very low braking efforts where the brake torque being applied is only a small percentage of the pressure required to overcome the movement of the floating caliper, but if you consider the huge brake torque compared to the resistance to caliper movement, its no contest.

I think you may have taken my arguments too literally.