2001 Jeep Cherokee Front Brake Rotors

Nice try, guy. I'm going to claim invalid status (my cardiologist will love me) and stay out of this fight.

Reminds me of the time we went up against a plaintiff in Quebec. The steering sector shaft in a hot B body was broken (monotonic torsional impact from hitting something) and I'd cut a section and polished it for micro examination, drawn my conclusions, and returned the bits to the plaintiff's lawyers. Their expert testifies in court that the smiley faced marks on the polished face were "microfissures" rather that the marks made from rattling around in the bag. I was able to approach the judge on the bench with the bits, bang them together to make another mark and say "Comme ca".

Hubs are usually nodular (malleable in the early days). As "jim" says, drums are grey cast iron (notice the provincial spelling) but I wouldn't want to hang my hat on rotors being nodular.

There was, believe it or not, a nodular foundry a while back in Sudbury, ON. doing rotors but they were taken over by a Chinese operation which numbers among its subsidiaries things like WIX. It's been too long for some of this stuff. I'll be attending a Chrysler Materials Engineering Corn Roast on the 18th and will get the answers then, if not before. I think it may have something to do with the flat style rotor with a separate hub and the integral hub design.

My feeling has always been that a freshly machined GCI part will "probably" blush rush quicker that a nodular part but that's a pretty subtle difference. This reminds me of the brake shudder debate. Thousands of vehicles in storage yard mud and weeds, and we wondered why the pad outlines were "printed" on the rotors so that the pedal pulsated after a while as that rust either got wiped off or converted to a hard, adherent oxide and a high spot, or was it a low spot?

I don't know for sure what a "semi metallic pad" really is. Of course, I never really bothered to find out what a "trimetal" bearing shell really was, either. It was a matter of "WGAF?" for me....they were all made out of soft stuff, as far as I was concerned. Tin, antimony, lead, copper, bismuth, even aluminum.....as far as I was concerned those were not very interesting things.

No matter how you spell grey somebody complains. I'm going by my experience with what I see being sold nowadays. So few are made in USA any more. It has been a long time since I've seen a grey iron rotor. It is not like the rotor composition has any direct bearing on the question of rotors becoming stuck to the hub. The discussion was about the friction material which is different for drum and disc brakes. And that could be in part due to the different metals generally used. The claim that is being discussed was that The problem of rotors becoming bonded tight to the hub is "more or less non-existent if ceramic pads are used".

That may be. The integral hub type may be less likely to be nodular iron.

Main difference is Nodular iron is stronger for the same weight of material.

A long time ago I was told that semi-metallic brakes contains a lot of Bronze powder, but I don't know. I'm willing to accept they have some iron content. Of course the brake dust is going to have some iron content anyway. I think there wasn't much difference in any brake friction material 30 years ago when asbestos was being used. Since that was removed there have been all kinds of things used.

-jim

My post was originally intended to be a PM to aarcuda but there's many a slip.....

Anyway, yours for continuing moderate discussion.

Hmmm.. interesting theory, but to me it looks as if its a circuit to nowhere with no dissimilar metals involved. The circuit would be Rotor->hub->bearing->steering knuckle->bracket->caliper->pad->back to rotor, with nothing but ferrous metals anywhere. If there were some copper or brass or zinc, then maybe a current would flow, but not with all ferrous metals.

I said it was a ground loop (that is a circuit to nowhere). And there are apparently several metals other than iron also used in brake pads.

But , I also said that it was not my theory but my guess as to what someone else had theorized as to be the cause of a non existent effect.

You don't need a ground loop to suppose some current might flow across the rotor to hub interface due to static buildup on the wheels. But that would have nothing to due with the pad composition

-jim

jim wrote in news:hsqdnX1AbcHKHuTXnZ2dnUVZ snipped-for-privacy@bright.net:

The sledge won't help with rust anyway. The sledge will do nothing but cause damage. What /does/ do a lot of /good/ is the exact opposite: A tiny 8-ounce ball-peen hammer judiciously applied to the sides of the top-hat.

The ball end of the hammer is used to firmly and repeatedly rap the sides of the top-hat to break the rust bond between hub and rotor. After that, you need to keep going in order to fracture and flake off as much of the rust from the sides of the top-hat as possible so the rotor can move.

Of course, the drier the climate, the less rust there is and correspondingly the easier the rotor is to remove. I envy you residents of Phoenix AZ, even with your 110-degree summers.

Last time I did rotors I meant to take a video of the job, but my camera's battery went dead.

I suspect it's just metal from the rotor. (I have, however, discovered that aftermarket pads often result in a LOT more rust in general around wheels and disc brake assemblies, which is one reason why I no longer use them. OEM all the way, baby.)

The inside of the top-hat gets wet with environmental moisture (rain, snow, etc.). The moisture stays in there for a long time, since it's pretty well protected from air flow. The rust then builds up until it "hooks" the hub onto and behind it, somewhat like the rust ridge on a brake drum. Yes, that rust is much less dense than steel, but it's still awfully hard to pull a rotor over it. It's anything but crumbly and must be removed by chipping it off with a hammer and an old screwdriver.

After you break the initial rust bond on the hub perimeter, the rotor may wiggle, but if the rust on the rest of the top-hat is severe enough it will be impossible to remove until you drag it off the hub over the rotor's own rust.

The Toyota rotor example in the photos was relatively easy to remove on account of the interrupted hub perimeter design. A fully-circular hub can be a real pig.

Having never used ceramics, I can't say either way.

True. But it's also true that rust is extremely brittle and fractures very easily. And fracturing it is all you need to do to get that rotor off, hence the tapping with a half-pound hammer.

"." wrote in news:q30dm.49406$ snipped-for-privacy@newsfe11.iad:

I'm no chemist, but I do have some experience with rust.

You're assuming that all iron oxides are the orange or red substance commonly known as "rust" (Fe2O3). There are in fact many combinations of iron and oxygen (all known as iron oxides), just as there are many combinations of hydrogen and carbon (all known as hydrocarbons), but having vastly different properties.

There have existed for decades corrosion treatments that convert Fe2O3 to other, much more stable compounds that are also iron oxides. For instance, phosphoric acid, the active ingredient in such potions as Naval Jelly, convert highly reactive orange Fe2O3 to the relatively unreactive black iron oxide Fe3O4. Fe3O4 will itself resist further corrosion, but any surrounding or underlying raw steel is still susceptible to conversion to Fe2O3 if the Fe3O4 coating is less than perfect.

I can attest personally that Fe2O3 converted to Fe3O4 and afterwards sealed from further oxygen intrusion is about as stable as one could want, for as long as one could want, in a motor vehicle environment.

Tegger wrote in news:Xns9C5ECB9198EDEtegger@208.90.168.18:

Clarification: "oxides of iron". Might that be more correct?

Where did the phospherous go?

Bret wrote in news:pmq9vqu2n66d.1flplradvvrjx$. snipped-for-privacy@40tude.net:

Not being a chemist, I have no idea.

I notice though, that phosphoric acid has four O's, one P and three H's.

The four O's went into the Fe, I guess. But where did the P and the three little H's go? Anybody?

Yes I'm aware of that. You should have written your explanation for the OP.

It sounds like once he broke free he was able to handle the rest without difficulty.

I'd like to see a movie from the guy who said to cut the rotor off with a sawzall.

That doesn't happen on all cars. Some rotors that inner wall of the hat is as-cast, which means it has draft and more clearance than on rotors where that surface is machined.

That rust you get to after breaking free is crumbly . And the OP made it clear that wasn't the problem he asked about.

Yeah if it is a snug fit to begin with. But getting it to break free was what the OP said was the problem. And that is due to the rust that expanded inside where the hub and rotor fit together. It is often the inner bore that really gets compacted.

I've used ceramic pads and I haven't notice that it makes any less rust for cars driven in a lot of salt.

It isn't just that the rust is brittle, the small hammer matches the high resonant frequency of the rotors so that the maximum amplitude impulse carries thru the metal. You need to be able to hit it to make it ring.

-jim

I'm thinking the black stuff is iron phosphate?

rust on the outside is not what holds the bolt from breaking free.

"Any fool" is SO appropriate...

The "fool" (that's you) isn't going to wire brush the threads because they can't be gotten to until the rotor is removed, the rotor can not be removed because the brake caliper bracket impinges on removal of the rotor, it is the bolts in question that attach the brake caliper bracket to the steering knuckle.

As I suspected, you don't have a clue about any of this.

(BTW, I never said he'd have trouble breaking the bolt free. Yet another example of you substituting words to support your ill informed book learnt opinion)

You can just keep advertising your incompetence. I don't care.

If your running into problems because you are dragging that external rust on the end of the bolt into the threaded hole, then don't expect sympathy for problems of your own making. They do make narrow wire brushes ya know. and there is plenty of room to reach the ends of those bolts. And if the brakes pads are worn, there will be that much more room. Even a screw driver and some penetrating fluid will work to keep from dragging rust into the hole. The old AMC brakes were the worst for this. they had a couple turns of threads sticking out the hole and if you didn't clean them up, you were really screwed.

But you are correct I shouldn't be speculating on what foolish nonsense might have led you to make that statement. I've known people who regularly break things changing air filters.

-jim

There most certainly IS NOT. You would know that if you had actually ever been near this particular vehicle.

WTF does pad wear have to do with anything?

The caliper and pads CAN be removed, that however does not provide for any better access to the bolts in question. You would know that if you had actually ever been near this particular vehicle.

Blah-blah-blah...

Not talking about old AMC brakes, but thanks for proving my point anyway.

So, your addled brain thinks that breaking a T-60 Torx bit is the same thing as breaking a bolt loose. To borrow a phrase from Art Linkletter; "kids say the darnedest things."

No, you shouldn't. Especially about things which you have no knowledge or experience with.

Conversations with other mechanics (not residents of cubicles). Conversations with tool vendors and their comments about the unusually high breakage rate of T-60 Torx bits.

You've gone from primer paint to your family members, quite a versatile guy you are.

In the absence of anything clear and coherent what is someone supposed to think? Do you suppose someone reading your babble will be thinking that you break a T-60 Torx bit by dropping it on the floor?

Again i'm speculating as to what your unclear incoherent statements mean, but that statement sounds like you have no personal experience with working on these brakes. Are you only going by what others have told you?

-jim

You have been from the beginning.

Remember your first words in this thread? ("I thought")

You mean when you wrote:

HA HA HA . So now you finally reveal your secret -> *No thought*

Notice that I used the word "will" not 'did.'

I guess there's no point in waiting any longer for you to cite a SAE spec that supports your "thought."

You asked "don't you suppose" not whether I "thought."

Were I to "suppose," it would mean that I was speculating without any basis in fact. I don't need to "suppose" that a brake rotor and wheel hub can rust together, apparently it may take some years of college for others to "suppose" such an action.

Now we'll move to the second sentence (you DID see that there were TWO separate sentences there didn't you?) in the above quoted exchange: "The problem" I described is applicable IF (not because) high iron content brake pads are used and thusly "is more or less non-existent if ceramic pads are used" is completely valid whether you like it or not.

Just so you understand this completely; "the problem" I was referring to is not related to something YOU had brought up, it bears direct relation to a statement I had made about pad content because it mentioned a different pad content.

Sorry that you can't read and don't know what a period is used for Jim but it really isn't my fault. Blame whatever school system you went to.