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Unusual brake rotor wear/metal falling off in chunks

Unusual brake rotor wear/metal falling off in chunks

(OP)
OK you metalurgists, I have come across and unusual patter on front disc brake rotors. The metal on the inside of the front rotors is very rusty and falling off in chunks. The outside of the rotors looks normal. The cars will make a faint scraping sound but the brake performance seems normal although the rotor surface looks terrible.One vehicle had 54k miles original nissan rotors and the other was aftermarket premium rotors, lasted 4 years then all of a sudden started to show this same pattern. I have checked the slides and everything is free, pistons are free,calipers bleed multiplt times, both pads show same type of wear but the inners are wore much more. Look at the pictures and see if you can explain what is happening. I have a guess that the rotors may have been multiple layers of different metals and when the surface metal is gone the underlaying is soft and not up to the stress.

RE: Unusual brake rotor wear/metal falling off in chunks

(OP)
rotor update, sorry only one picture of normal side, this post will have correct picture of wore rotors.
I have tried resurfacing pads and rough sanding rotors but the problem returns in a few weeks again, even mixed pads side to side with same results. Both rotors, inside look the same.

RE: Unusual brake rotor wear/metal falling off in chunks

What is the continuous shiny ring? It seems to be worn through the rusty crust. Is the rotor still at acceptable thickness if it is machined back to good clean metal like seen on that ring.

Can you test for hardness of good clean metal at various points on both inside and outside of the rotor and maybe the hat.

Regards
Pat
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RE: Unusual brake rotor wear/metal falling off in chunks

Are both pictures the same rotor?
The heavy rust scabs look pretty typical of how iron and steel rust up here in the Massachusetts under car environment after a few years.  The only surprising thing is how one side of the rotor could look "normal" and the other could have wide bands that have not been participating in braking activities.

I sure think you will find a matching stepped profile in the pads that ran on "odd" side.

Are the calipers fixed (pistons on both sides of the rotor) or floating (piston on one side)

RE: Unusual brake rotor wear/metal falling off in chunks

(OP)
tmoose: the brake system is single piston inside, look at the next posts to see closeup of each rotor, left and right looked almost identical on the inside, metal rusted and perfect on outside. Car had 54,000 original miles driven every day brakes felt normal but noisy. Also had my own saturn do the same exact thing only on the inside, and I go down a mile long hill every day. I can't explain how the rotors could look like this and still be rusty looking and the pad look almost normal. Again slides were free and moving, pistons free and moving, caliper bleed multiple times, brakes feel normal.

RE: Unusual brake rotor wear/metal falling off in chunks

That looks depressingly normal for certain types of brake pad in certain climates.  The pad material transfers to the rotors, and the rotor will rust beneath this layer of pad material, at which point it starts to flake off and the brakes judder horribly.

 

RE: Unusual brake rotor wear/metal falling off in chunks

Obviously for some reason the clamping on the inboard side is restricted to the shiny ring. You say there is no abnormality in the pad which seems hard to believe. Something in the pad caliper system has to be bearing against the rotor only at the shiny ring so as to pull the outboard pad on. Is it a wear indicator or the like.

Regards
Pat
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RE: Unusual brake rotor wear/metal falling off in chunks

What brand and model of pads?  Were they of the "Lifetime" warrantee type?

In picture ...011.jpg I think I know which pads were on the "bad" side of the rotor. If I had never seen the mating rotor surface I would not describe their wear as "almost normal."

i'd start over with new rotors and Warner or good NAPA pads.

RE: Unusual brake rotor wear/metal falling off in chunks

(OP)
OK one of the cars is my own, driven daily, autozone 2 year guarantee rotors, do not know manf.,Pads were premium ceramic made by Bosch.My braked had about50k miles before they started to do this, pads looked ok ezcept for more wear on inside pad, no cracks or signs of overheating that I could see.
Pictures posted are from 2006 Nissan sentra, original brakes from factory 54,000 miles, daily driven also, never stored or been in deep water.
I replaced rotors and pads, lubed slides and tested movement, bleed brakes tested piston movement and burnished them in. Customer supplied new parts, O-reilly's Bosch rotors, pads I did not recognize name.

RE: Unusual brake rotor wear/metal falling off in chunks

Don't have an answer for you but I can match the experience.

2 cars, Southern UK.  
2001 Focus, front pads less than 1/2 worn, outside looks absolutely fine, but a sudden heavy juddering on braking forced a more detailed inspection revealing rather similar to your photos on the inner side.  A big flake had broken away leading to the juddering.  The caliper pistons and slides were moving freely.  These were replaced in March and so far seem fine.

1996 Audi A6, New Pagid branded discs and pads fitted last October.  Caliper pistons and slides both working properly and the brakes were an absolute revelation after fitting.  15k later, the outsides look perfect and the pads barely worn but the inside surfaces are beginning to show the "rings of death" and a there is now a hint of judder under heavy braking.

Both cars are daily drivers.  The Audi does far higher miles and gets driven harder.

I've not come across this before in this form.  What I have seen quite frequently is a similar effect on the OUTSIDE of rear discs which is invariably a sign that the caliper slides have siezed.

We did have an exceptionally hard winter 2010/2011 with lots of salt so maybe that is a factor?  The proximity of the sheet-metal inner shield may also be a factor.  Would like to know as I hate replacing parts that are only a small part worn!

Regards

Nick

RE: Unusual brake rotor wear/metal falling off in chunks

[The pad material transfers to the rotors, and the rotor will rust beneath this layer of pad material, at which point it starts to flake off and the brakes judder horribly.]

This is what is happening here.

RE: Unusual brake rotor wear/metal falling off in chunks

inner grannular corrosion or lamination of the steel , autozone rotors are made in china , so I wouldn't expect much other than this as the material is probably barely in spec for the designed use , mexican cast roators are the same way , as are alot of the oem Gm ones , best rotors made now are raybestos or uniteds , for performance rotors , powerstop as they are raybestoes .   

making people scratch there heads for 40 years ..  

RE: Unusual brake rotor wear/metal falling off in chunks

(OP)
Thanks much Stimpy1966, I have run into this again, it seems that this does not happen for a few years, my rotors were 3 years old before they started this. Good to know which rotors are higher quality. Remember the Saturn rotors some years back??? Trying to save a buck and causing more trouble that it's worth.
Curious that Bosch did not know what the problem was since it was their brake pads?????

Gary M&G Engineering

RE: Unusual brake rotor wear/metal falling off in chunks

"lamination of the steel".

I think all passenger car rotors will be some flavor of cast iron

RE: Unusual brake rotor wear/metal falling off in chunks

moose , your right its supposed to be iron, but when they use recycled materials the carbon content can drop to a steel alloy range  ( uneven mix in the alloy from not stiring the molten metal with gas, fluxing  or improper alloying of the metal ( burn off too much carbon or not enough added to make the alloy when making from mostly steel scrap its , BAD QA , and corner cutting on costs by shorting materials ( coke costs money )to them metal is metal, unlike the american mfgs) ,
 the mind set of the chinese when it comes to making products is horiable , as they can copy the looks of the product ,but not make the material of the product right . most of there philosphy is make as many as you can as cheaply as you can ,( kind of like the japanese in the early 70's)  

one thing about driving ,is when I deliver containers to these places dist centers ( AX, AA, PB) I get to see the docks on the inside , and one company I will not name names , has gaylords of failed rotors and drums that they load outbound back to china , and most of them are new and never made it out of the dc or was returned from the store , they are cracked or have peices broken out of them from while in use, in transit  or are like his ,spalled , and I have looked at some of them , you can see the grain layering in them from uneven cooling , on a average for the 5-6 containers  of brake castings I return one full one, that says it all.  But today people over look price vs safety ( Darwinism at its finest )
 
when I mean laminate its a layer, not a folding/hammerweld  operation they use to make damascus steel   

making people scratch there heads for 40 years and ask me why??? ..  

RE: Unusual brake rotor wear/metal falling off in chunks

Stimpy1996--No, in the melting of cast iron, the composition CAN NOT drop into the alloy steel range. Absolutely not. The worst that could happen is that the carbon equivalent could drop enough to give you chill, i.e. spots of white iron. If that happened, the rotors would never make it through the machining line. Don't ask me how I know. The biggest failing I have seen with cast iron rotors from China is that no attention is played to graphite flake size/morphology. That of course, can lead to heat checking and subsequent thermal fatigue cracking, but not accelerated corrosion.

RE: Unusual brake rotor wear/metal falling off in chunks

It also depends on where in China the rotors are made and what company made them. Many of your name brand rotors are cast in China, even the high cost trendy brand ones. Last I saw, Raybestos rotors are being made for their parent company Affinia in China.  By the way,Powerstop gets rotors from various sources, not just Raybestos.  I've found their products to be very good because they do a lot of testing and have a lot of control in the plants where the product is made.

Most rotors are made of J431 G3000 cast iron.  This is pretty common stuff.  Bad cooling can cause a lot of problems, and is usually caused by trying to cool things too fast to get more production.

I've had rotors such as seen in the pictures in this post analyzed by a metallurgical laboratory.  There was no anomaly found in the metal and no laminating.  I would have to say that the cause could very likely be corrosion due to the friction material.

 

 

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