disk brake rotor oxindation

[professor229]

Help. I have never seen this before. I put my kit car into storage for two years, and just took it out, performed the tasks necessary to put it back on the road, and when done, got a surprise. When applying the brakes, there was a pull to the left for a micro second, then a pull to the right for a micro second and then the car stopped straight. The brakes were "fine" before I put it away. When I pulled the front wheels, I saw immediately that the rotors were not shiny but a dull black color with some sort of coating that I would characterize as something between black paint and extremely thin undercoating... since it was not "rust" I know my brakes are not steel.. but probably aluminum. Research told me that if they "oxidized" the rotors should have a dull whitish look. They didn't look this way; and instead had a darker black look as described. I have never seen this before in all my years. I tried to clean them with a scotch brite pad and brake cleaner after removing the calipers. It took some time but they are "better" but far from shiny like I would like them. A road test found them to be much better... Any ideas on what that coating is? and how to remove it? Is it aluminum? or an alloy? My choice might be to resurface the rotors at a car dealership, but I would like to know what the substance is, and would prefer to remove it myself.... with a cleaner? PS. I got some of the substance on my hands and GOOP would not remove it. Brake cleaner would slightly remove it, so I tried carburetor cleaner and rubbed pretty good... that did it... but... is there something better, and not know what the substance is will drive me crazy.... help, suggestions, recommendations, ideas etc. all appreciated.

[Letterman7]

Hi Dennis! Older iron rotors will darken. I've never seen aluminum rotors and never will.. they don't have the strength. Besides, aluminum oxidizes to white powder. Steel rotors will rust before they do anything else.. can't say I've seen any that turn a color. Do you remember where you got them from?

I wouldn't worry about it - as you drive the car the rotors should eventually return to their previous shiny state. As long as it still stops reliably, the discoloration is nothing to worry about.

[Dale M.]

First off the rotors are either cast steel or cast iron.... They are NOT aluminum... I believe your research to be wrong.... The surfaces are bare virgin metal becasue of brake pad always in contact (scraping) surface of rotor and will always start to corrode or rust as vehicle sets still even if just over night... Its just the way things are ... No amount of cleaning or preventive maintenance can stop it becasue anything the will stop the corrosion will hinder brake operation and put your ability to brake in jeopardy....

If brakes are functioning normally after first or second application of brakes you have to learn to sort of live with it.... If problem get worse you may seriously have to consider replacing rotors with better quality ones...

Once had Ford ranger pickup that EVERY MORNING right front caliper/rotor would squeak till second or maybe third application of brakes, then was good for rest of day... Brake unit was inspected several time and always found to be good.... It was something about the metallurgy in that particular rotor...

Only real relief if you can't live with it may be replace rotors...

Dale
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All suggestions and advice are purely my own opinion. You are free to ignore them if you wish ...

[BL3Manx]

Maybe somebody snuck in and replaced the rotors with carbon, but I doubt it. Sounds like you've put some substances on the rotor which have likely now contaminated the pads. You might want to replace the pads with new and if you just want to use some medium-fine sand paper to clean the oxidation off the iron rotors, that won't hurt either.

Or you can just take them out and use them hard and a lot and they'll likely be just as good.

[jsturtlebuggy]

Since you have not said what brand of disc brakes or show pictures of what you have, it going to difficult to understand what is really happening.
Wilwood does sell aluminum rotors of all sizes and shapes.
CNC at one time (maybe still do) sell aluminum rotors for the lightweight sand buggy disc brake kits.
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[professor229]

Actually, here is more information... I bought the car with the aftermarket conversion already completed so I have no idea what was put on the car. I did write to two companies that manufacture aluminum rotors to ask them if they had ever heard of a chemical change that would have turned them black. Since this was done on Friday afternoon, it comes under the category of good luck for an answer this weekend. I might pull off one of the wheels one more time, to use a magnet to find out if they are aluminum or iron. It would be the next logical step.... I am not sure about sandpaper but several of the sites I researched said to avoid steel wool; therefore the use of scotch brite. I also have to get the car up to at least 50 mph and could not do that yesterday, but will Monday and try the brakes. I also contacted a metalurgist (spelling) that has a phd and asked him; waiting for that answer too. The rotors were perfect when put away so this was a chemical change over the two years and of course, un-noticeable while the car is in storage. Someone mentioned iron rotors discoloring. What causes that? The brake pads are essentially brand new and when I cleaned them, there was none of this residue on them at all. Also, the residue that came off with the brake cleaner/scotch brite was undoubtedly why the brakes grabbed initially... they actually had a "sticky" initial feel to them. Thanks to all for the information; as I said, I might pull them once more and hit them after removing the calipers, with carb cleaner on the scotch brite but I want to try them first. The professional performance mechanics initially were guessing that the pistons formed a ridge and released to push the pads at different times... that was not the case... Thanks again

[Wolfgangdieter]

Emory paper is prefered sand paper for steel - if you want them cleaned up.
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[andk5591]

You dont need to pull the wheel - just reach around back of the wheel with a magnet and see.
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There's more, but not keeping them...

[BennHerr]

Maybe somebody sprayed a preservative on the rotors when it was put into storage?

[professor229]

Update.... Actually, the wheel has a metal deflection shield on the inside of the brake assembly that prevents reaching around but I did pull the wheel, and I did use a magnet and they are NOT aluminum so I can only guess they must be iron? Steel would have rusted badly I suspect... could be wrong. So what kind of oxidation or whatever am I facing with iron rotors? And yes, I have used emery cloth before so I will give that a shot too.... the scotch brite prep pad has worked on other metal surfaces but doesn't seem to do much with this problem... Again, thanks for the idea... just one more step in the process....

[professor229]

PS.. I put the car in storage in my own garage for the two years... there were other issues with the car and I decided to take up fishing instead.... now we have moved and fishing is no longer an option and my son and I decided it was time to put the car back on the road..... It was trailered to its new location and sat for this third winter now.... Will try it down the back highway on Monday to see how the brakes react....

[jspbtown]

Turn them, install new pads...and worry about something else.

[slalombuggy]

Just drive the car. I see this all the time in the spring on classic cars that sit all winter in storage. We never do anything to clean the rotors unless the is heavy scale rust build up from sitting for years in a damp environment. If it is just a discoloration of the surface the rotors will clean up after a few brake applications.

brad

[professor229]

Thanks Brad.....one piece of advice I got from the pros was to just drive it a bit and see if that cures it, and I will tomorrow.... but it always bothers me when "something" happens to a car that I just don't understand.... and it is kind of a challenge to learn why it happened. Also, every spring I would pull out one of the street rods and one in particular always needed special attention before starting.... Buick 215 engine and you had to pull the distributor each spring, and put a drill with a special tip down to spin the oil pump to prime it; pulled valve covers and when oil came through, you were good for the rest of the summer... always something. I have to go through the wiring on this again too and make sure the connections are all good.... but otherwise, the 1600 has never run so good... Still working on a problem that has existed for years and might do a post on that... venting the gas tank as that is all after market.... but I need to get to NAPA ..... and ask them.... Again... thanks for all the advice and help and ideas and suggestions from everyone; they are all very much appreciated.

[GoMopar440]

Ever heard of rust bluing? It's how old gun manufacturers and gunsmiths used to blue all the guns way back in the day before they started using the hot salt bluing process. It's basically a process of controlled corrosion to get the steel or iron parts to corrode and turn to a deep dark shade of blue, black or brown. The heavy top scale gets removed with a file card after a while and the the metal gets prepped to go back into the humid rust bluing cabinet. The process keeps repeating until you reach the dark shade you want. Metal that is left untouched for a while (like in storage) can mimic the rust bluing process somewhat, especially in hot and humid environments. That could be the source of the dark color on your rotors.

As far as the sticky gunk you encountered, I don't have a clue about that.
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Link to my rail (re)build thread: http://www.thesamba.com/vw/forum/viewtopic.php?t=629493

[professor229]

Wow... I never thought of that and I thank you... I now have something to research and yes, I had heard of bluing in the past but it never occurred to me..... I almost wonder if the sticky gunk was not brake dust on the back of the metal splash guard on the back of the assembly..... All I know is that the mixture of brake cleaner and the substance, once on your hands, was incredibly hard to remove.... Again... thanks... and yes, I think you are 100% right and I will now do some serious research....