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Why do these rotors rust after washing and letting sit? I spent 10 solid hours making a 4k , 2 month old giulia look better than delivery day including some paint correction, onto to drive to work today to see the rust all over my nice , recently waxed rims. Frustrating and never happened in any car ive owned ever.
 

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Why do these rotors rust after washing and letting sit? I spent 10 solid hours making a 4k , 2 month old giulia look better than delivery day including some paint correction, onto to drive to work today to see the rust all over my nice , recently waxed rims. Frustrating and never happened in any car ive owned ever.
IMHO totally normal. I have CCBs on my Quad but my last two cars (both Porsches) had steel Brembo brakes pretty much the same as the Alfas. Both of them would rust every time you wash them and I have seen it on other cars too. The oxidation is very shallow and rubs off with a little bit of driving.

If you haven't noticed this before, could it be that your previous cars didn't have such openly visible rotors?
 

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Steel rotors rust, this is nothing exclusive to Alfa cars, it’s normal for any car with steel rotors and open spoke wheels.
 
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2020 Alfa Romeo Giulia Sport Ti AWD
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I've never had a car where it didn't happen. Perhaps your Giulia's rotors are simply more visible than those of your prior rides?
 
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Yes all these things. It just means the rotors are working, clean and were wet. Just tap the breaks a bit and they are rubbed clean. Don't sweat it. Once they are hot and you go somewhere, they will stay more dry and not rust so much til the next soaking.
 

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I've never had a car where it didn't happen. Perhaps your Giulia's rotors are simply more visible than those of your prior rides?
This is exactly it in my case. I don't see the rotors on the F350 and the Mini has fat spokes filling up the whole wheel and hiding the rotor so you don't even see them. However, because of the design of the wheels on the Ti's I was first looking at I noticed it immediately and said what is up with the rust? He said totally normal and I thought yeh right. Well washed the Mini the next time and peaked in at the rotors and sure enough they looked rusted. I have CCMs so I don't have to worry about rust and brake dust just replacing them when they wear out. Alfa probably wants to show the rotors because they are brembo. Can't tell you what the Mini has but I can say they work very well.
 

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Yeah it’s totally normal. Cast iron rusts. It comes off after you pump the brakes so it’s no biggie.
 

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There are processes that keep the surface rust from happening AND extend the usable life of the disc. GM started using a heat treatment program a few years ago on many of their brake rotors, and it works great (the rotors on my 2015 GMC Sierra do not rust).



https://media.gm.com/media/us/en/gm/news.detail.html/content/Pages/news/us/en/2011/Nov/1130_fnc.html



http://www.woodworthheattreating.com/brake_rotors.html


The process, FNC (Ferritic NitroCarburizing), has been around for decades... not sure what GM is doing that makes their process patent-able. I've spec'd FNC as the surface hardening process for some of the parts one of my businesses manufactures, although I never thought about it for brake rotors though until I read about GM doing it in one of the auto industry engineering mags that I get.
 

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In Houston, which was very high humidity, my disks almost always have a thin coat of rust in the morning. Not just after a wash or rain.
 

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worry not friend

Why do these rotors rust after washing and letting sit? I spent 10 solid hours making a 4k , 2 month old giulia look better than delivery day including some paint correction, onto to drive to work today to see the rust all over my nice , recently waxed rims. Frustrating and never happened in any car ive owned ever.

Feel free to use my 180 second, $0 cost method:

1) at end of wash, which I finish by a chamois dry, doorsill/trunk/hood (that’s bonnet for da’ UK folks) wipedown, start Giulia
2) back out of driveway and go around the block. Mild braking 3 times (5-10mph to zero in 20 ft)
3) blow off any rust on rims with your compressor.
4) park car in garage

disks will be bright and shiny when you roll her out for the next session. Rust on rims, considering they’re alloy, must be coming from the brake rotors. Low speed braking sheds rust onto brakepads usually. I’d expect step 3 will be not required.

Never fails.
 

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2018 Q4 with Fiamenghi Ti exhaust, Race Mod, and Tecnico wheels.
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Maybe there is a water quality issue in play here? Although I get a very slight dusting of rust on my rotors after I wash my girl there is never enough to have visible rust transfer to the wheel.

There are always coated rotors which rust less than plain cast iron. I got a set from Ceika but have not had a chance to determine if the rotors will rust when I wash Giulia.
 

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Would surface coatings and treatments really make much difference if the rotor itself is wearing down over time anyway?
 

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Would surface coatings and treatments really make much difference if the rotor itself is wearing down over time anyway?
Steel ships use bolted on blocks of zinc to control corrosion, so I would think that a galvanic coating does not have to cover the whole thing to help.

The OEM Q4 rotors have some kind of very thin gray colored coating on them. On my rotors this coating is absent from the rear of the hat and from the wheel mating surface. I suspect this is a phosphate treatment, but do not know.

My Ceika light weight rotors came with gloss black anodizing on the aluminum hats and a black coating of some kind (zinc based paint?) on the iron (silver coatings are also available). The braking surface is milled (not turned), so even though most of the coating gets knocked off almost immediately there are shallow scratches still holding coating on the braking surface. I suspect that this will wear down after time and only then will I know if the rotors stay nice. There are also 6 slots on each side that hold some of this coating in a wear resistant fashion.

I have not tried such products, but I am suspicious of any cleaning chemicals stronger than a very mild detergent and will not use them on my car.

Softened water and/or well water in some regions can be acidic and enhance the rusting rate of iron.
 

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Would surface coatings and treatments really make much difference if the rotor itself is wearing down over time anyway?
For surface coatings like zinc plating and phophate treatments, no. Any place that the caliper and pad meet, you'll quickly scrub away the coating and get down to bare cast iron, which will then rust.


The ferritic nitrocarburizing (FNC) process GM uses gets absorbed into the surface of the rotor. I have no idea how deep GM's case depth is, but when I've specified FNC as a mild surface hardening treatment for shafts / pins and hydraulic pistons, we've gone 0.010" deep. That doesn't seem like much in terms of depth, but your also greatly improving the surface hardness of an FNC treated part, so that the component is much more resistant to abrasive wear. The case depth is going to be dependent the exact process parameters GM is using, specifically the duration of the process (the longer the run time, the greater the case depth). GM could also be optimizing the alloy content in their rotors when they have them cast to make them more conducive to the FNC process, to either get deeper case depths or reduce the process time for a specific case depth.
 

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The only thing that sux about rust on rotors is if you have dark, black, glossy wheels. Argh....just one trip to shave off the rust from the rotors from braking can make the wheels look a little dirty again. Oh, the problems we have.......
 

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For surface coatings like zinc plating and phophate treatments, no. Any place that the caliper and pad meet, you'll quickly scrub away the coating and get down to bare cast iron, which will then rust.


The ferritic nitrocarburizing (FNC) process GM uses gets absorbed into the surface of the rotor. I have no idea how deep GM's case depth is, but when I've specified FNC as a mild surface hardening treatment for shafts / pins and hydraulic pistons, we've gone 0.010" deep. That doesn't seem like much in terms of depth, but your also greatly improving the surface hardness of an FNC treated part, so that the component is much more resistant to abrasive wear. The case depth is going to be dependent the exact process parameters GM is using, specifically the duration of the process (the longer the run time, the greater the case depth). GM could also be optimizing the alloy content in their rotors when they have them cast to make them more conducive to the FNC process, to either get deeper case depths or reduce the process time for a specific case depth.
But is FNC treated cast iron resistant to rusting?

Off topic, but what is this magic treatment on the operating shafts of the hydraulic operators of my backhoe? It seems impervious with no discoloration, wear/abrasion or any other sign that it is not brand new after sitting in the weather for 20 years and accumulating 4300 operating hours. It looks like chrome plating, but I've never seen chrome be so durable. Everything else on the backhoe is rusting and/or showing its age.
 

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But is FNC treated cast iron resistant to rusting?

Off topic, but what is this magic treatment on the operating shafts of the hydraulic operators of my backhoe? It seems impervious with no discoloration, wear/abrasion or any other sign that it is not brand new after sitting in the weather for 20 years and accumulating 4300 operating hours. It looks like chrome plating, but I've never seen chrome be so durable. Everything else on the backhoe is rusting and/or showing its age.

If you read the docs from GM above, they specifically went with FNC to eliminate surface rusting in addition to lengthening the life of the rotor.



Hard chrome plating isn't the same as conventional cosmetic chrome plating. Hard chrome is the industrial variant, 70+ HRC surface hardness and typically much thicker layer buildup... really durable for decades if applied properly and seals and things are maintained. Useful when you have relatively low surface loadings, but require a very hard surface for long term durability. Hard chrome plating is also useful for shaft and hydraulic piston repair, because the damaged part can be machined or precision ground undersize, and built back up with the hard chrome, and then finish ground to final size to restore the item back into service.



There are certain components that you can interchange hard chrome and FNC... like steel pistons for production brake calipers. Through the 1970s they tended to be hard chrome plated, today if they're produced from mild steel, FNC is the preferred process.
 

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Add me to the list. Never noticed it before with my old car but just washed my qv today and adjacent to my shiny dark 5 hole are rusty rotors :frown2:
 

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The only thing that sux about rust on rotors is if you have dark, black, glossy wheels. Argh....just one trip to shave off the rust from the rotors from braking can make the wheels look a little dirty again. Oh, the problems we have.......

I don’t have that problem...........:grin2:
 
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