Rusty disc rotors.

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Dooner
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Rusty disc rotors.

Postby Dooner » 6 Mar 2020, 12:29am

Hiya. My avid disc rotors are slowly going rusty in the spines out towards the braking surface. The odd thing is I haven't ridden my bike for a couple of weeks but not a spot of rust on the outer rim. They are deffo one piece. 1. What is going on, is this contamination or are the brake rotors actually rusting? 2. Is this rust normal or a manufac. Issue? Worried they will start pitting and weaken. Please help. They are standard fit with Sram level brake sets. I obviously, just want more opinions before I go to Sram for advice.

reohn2
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Re: Rusty disc rotors.

Postby reohn2 » 6 Mar 2020, 8:28am

Is this just surface rust?
Do you live/ride near the sea?
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NATURAL ANKLING
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Re: Rusty disc rotors.

Postby NATURAL ANKLING » 6 Mar 2020, 10:19am

Hi,
This could simply be dust from the pads if you're using sintered pads (Metallic compounds).
Even cheap pads sometimes have metal parts in them but they tend to be brass so should not rust.
You say standard fitment I'm assuming you're talking about six bolts button head?
What ever the bolts are they will not be stainless steel that's for sure.
Centre lock discs, I would imagine also the mechanism although I don't use centre lock and I would have to go and look, Will not be stainless either / Part of the screw, washer and or disk centre will be steel And electro plated even.
Likewise with the 6 bolt design these will be a steel plated.
I would show you a picture of mine but it will probably scare you, There will be rust there will be a steel hub too :)
Check the retaining bolts or centre lock mechanism is tight, That's all.
Rust staining could be also part of the hub that are rusting, Axle washers cones et cetera, or cartridge bearings.
So belt and braces is to remove the wheel, Inspect hub and bearing for Grease Or lack of, check disk lock/bolts/screw are tight, reassemble wheel into fork.
Pump brake several times and Spinningwheel to make sure it is free.
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reohn2
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Re: Rusty disc rotors.

Postby reohn2 » 6 Mar 2020, 1:39pm

I've never had anything what even resembles rust on rotors and I use sintered pads exclusively.
I ride some pretty mucky muddy trails and never had the OP's problem.
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NATURAL ANKLING
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Re: Rusty disc rotors.

Postby NATURAL ANKLING » 6 Mar 2020, 3:34pm

Hi,
I am only putting forward suggestions.
I used to get what appears to be rust debris using sintered pads (dunlop) in the eighties on motorcycles with stainless steel discs.
It might me the disc material that turns brown / leaves a stain, which some stainless steel will rust in certain conditions?
But as I said it might also be something to do with the axle / bearings?
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reohn2
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Re: Rusty disc rotors.

Postby reohn2 » 6 Mar 2020, 7:13pm

NATURAL ANKLING wrote:Hi,
I am only putting forward suggestions.

I'm merely stating that is shouldn't be the cause going off personal experience with Avid rotors andnit seems going off the lack of response to the OP,no one else seems to have had the problem.

But as I said it might also be something to do with the axle / bearings?

I very much doubt it.
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Brucey
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Re: Rusty disc rotors.

Postby Brucey » 6 Mar 2020, 7:26pm

Dooner wrote:Hiya. My avid disc rotors are slowly going rusty in the spines out towards the braking surface. The odd thing is I haven't ridden my bike for a couple of weeks but not a spot of rust on the outer rim. They are deffo one piece. 1. What is going on, is this contamination or are the brake rotors actually rusting? 2. Is this rust normal or a manufac. Issue? Worried they will start pitting and weaken. Please help. They are standard fit with Sram level brake sets. I obviously, just want more opinions before I go to Sram for advice.


Most brake discs are either laser or plasma cut from sheets of ~12% Cr stainless steel. The cuts are normally not perfectly clean and have a roughened surface which is contaminated with a mix of oxides and nitrides, and may be partially denuded of Chromium near the surface . The combination of a roughened surface and the chemistry of the surface means that the usual conditions which allow a surface to resist corrosion (i.e. the formation of a stable and coherent film of chromium oxide) do not occur.

The usual advice when stainless steel has been thermally cut, welded or even machined is to polish the surface until it is clean and free of contamination. This gives the best conditions for 'passivation' to occur i.e. for the surface oxide layer to reform in a coherent fashion. What they do with brake discs couldn't be further from that; they leave a really crappy surface wherever they have been cut and if you are lucky they put a little bit of paint on the cut edges of the spokes. Avid discs are often machined on the OD and this surface is more resistant to corrosion.

In our lovely climate you tend to get salt spray off the roads at this time of year and if that is left on the bike the vulnerable parts of the disc (e.g. the cut edges of the spokes) will soon start to corrode. Once the corrosion starts the surface becomes ever rougher, ever more acidic and this again makes repassivation more difficult. Before too much longer you have pitting conditions and then the corrosion may continue even in conditions that are reasonably benign (so benign that such corrosion would never have started).

The good news part of this is that you can usually stop the corrosion in its tracks. You can clean up superficial corrosion with scotchbrite (eg on the faces of the spokes), but it is better to use something more aggressive on the cut edges of the spokes, e.g. a Dremel tool with a small grindstone on it, (to get rid of any remaining dross from cutting) then some kind of finer abrasive. You don't need a perfect polish; finishing with ~300 grit abrasive is usually good enough. It takes a while to do it, but if you want your discs to stay shiny with less cleaning, that is one of the few things that works.

Years ago I was annoyed to find my (then pricey) Hope Wavey discs were imperfectly smooth on the outside edge where they had been cut. Having seen lots of other discs start to corrode on cut edges, I dressed my discs on the OD and there have been no problems. I've also had to polish cut edges on disc spokes from several other manufacturers.

FWIW these cutting processes can vary in quality quite a lot with small changes in parameters; it just takes a slightly worn nozzle and a small change in gas flow rate and the cuts can easily be horrible.

If you can post pictures of your corrosion this might be helpful.

cheers
Last edited by Brucey on 6 Mar 2020, 9:52pm, edited 1 time in total.
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RickH
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Re: Rusty disc rotors.

Postby RickH » 6 Mar 2020, 7:45pm

reohn2 wrote:
NATURAL ANKLING wrote:Hi,
I am only putting forward suggestions.

I'm merely stating that is shouldn't be the cause going off personal experience with Avid rotors andnit seems going off the lack of response to the OP,no one else seems to have had the problem.

But as I said it might also be something to do with the axle / bearings?

I very much doubt it.

+1 I'm with you there R2.

I've got 2 sets of wheels with SRAM Centerline discs (which I presume aren't too far removed from Avid ones. One set had been in use for 3 years, the other for over 2.

They never have anything done to them apart from the odd squirt of muc off cleaner & rinse down once every month or 2. Actually I tell a lie - I did once wipe them down with water soluble degrease before washing one time, probably late 2018 or early 2019.The bike is ridden year round on & off road. Whichever is the spare set of wheels will likely get put in the shed as they are when taken off.

I don't think I've ever spotted any rust on them!

Brucey
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Re: Rusty disc rotors.

Postby Brucey » 7 Mar 2020, 5:11pm

discs (of all makes but not so much shimano, I think they use a different material in some models) have been going rusty for years;

https://www.pinkbike.com/forum/listcomments/?threadid=82531

cheers
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Dooner
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Re: Rusty disc rotors.

Postby Dooner » 7 Mar 2020, 10:54pm

Thanks for all the responses. I've never seen rusty rotors before either. I am going to scotchbrite them and leave them for a week. I will report back next week!

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NATURAL ANKLING
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Re: Rusty disc rotors.

Postby NATURAL ANKLING » 7 Mar 2020, 11:44pm

Hi,
I'll post a picture of mine sometime probably make you cringe a bit.
I don't think I've cleaned them in several months.
I do clean them now and again to get rid of the staining, when I can be bothered :P
Normal organic pads, Cheapo halfords discs.
Just fitted some sintered pads, It will be interesting to see how they perform in the wet.
Also how different the disk wear will be, Had to change the front disc as it was getting thin in the middle.
Only ever use organic pads up to now.

P.S.I would imagine if you clean your bike thoroughly often, then you might not see much staining?
R2's Bikes always look very clean.
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reohn2
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Re: Rusty disc rotors.

Postby reohn2 » 8 Mar 2020, 9:05am

NATURAL ANKLING wrote:Hi,
Just fitted some sintered pads, It will be interesting to see how they perform in the wet.

I think you'll find they're not much different to organics,they just last much longer in mucky conditions

Also how different the disk wear will be, Had to change the front disc as it was getting thin in the middle.
Only ever use organic pads up to now

I've yet to wear out an Avid disc either Wavey or CS2's and I've done many thousands of miles on CS2's though not as many on Waveys,a lot of those miles have been offroad on mucky trails 95% on sintered pads.

P.S.I would imagine if you clean your bike thoroughly often, then you might not see much staining?
R2's Bikes always look very clean.

My bikes if muddy after a ride,which is more often than not at this time of year,get a hose down whilst still wet,a good bouncing to shake off any excess water,a quick wipe of the frame with an old towel and the mechs and pedals a good squirt with GT85.The chain gets lubed if it needs it.The rotors get cleaned with soapy water when I decide the bike needs a thorough clean,the braking surface gets a dose of brake cleaner now and again.
I've never experienced the OP's problem,it's a mystery to me :?

The bike is then left outside to dry off.
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NATURAL ANKLING
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Re: Rusty disc rotors.

Postby NATURAL ANKLING » 8 Mar 2020, 9:20am

Hi,
Well my experience says that sintered metal pads Vastly improved wet weather performance?
Are you saying that they don't.
Also in my experience sintered metal Pads also chew up discs.
But I'll be very honest with you I only ever had sintered metal pads On any motorcycle.
So I can't compare them with what organic pads would've done.
The disk on the front of my bike which now has the sintered metal pads Was replaced recently with a nice flat one.
I need to get out on the bike next week and the weather is perfect for a test isn't it.
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reohn2
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Re: Rusty disc rotors.

Postby reohn2 » 8 Mar 2020, 9:44am

NATURAL ANKLING wrote:Hi,
Well my experience says that sintered metal pads Vastly improved wet weather performance?
Are you saying that they don't.
Also in my experience sintered metal Pads also chew up discs.
But I'll be very honest with you I only ever had sintered metal pads On any motorcycle.
So I can't compare them with what organic pads would've done.
The disk on the front of my bike which now has the sintered metal pads Was replaced recently with a nice flat one.
I need to get out on the bike next week and the weather is perfect for a test isn't it.

My experience with disc brakes is,other than a Honda 750 four I had in the '70's,is on cars,which don't count,and bicycles.Other than early on when I was new to discs on bikes and feeling my way a bit,I found organics to wear out PDQ in mucky muddy gritty conditions,I've worn out a pair of organic pads in one ride on a really bad day :shock: .I went over to sintered which last ages and stop well with minimal rotor wear.
Just been out to the w/shop and measured rotor wear with a digital micrometer on my Longitude MTB(four years old with about 4K miles ridden exclusively off road riding in our millstone grit area of the Pennines and some riding in the Berwyns in North Wales)
The 'spokes' measure 1.87mm,the the brake area measure an average of 1.72mm both same on front and rear rotors.
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NATURAL ANKLING
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Re: Rusty disc rotors.

Postby NATURAL ANKLING » 8 Mar 2020, 10:58am

Hi,
So is there any time lag with metal pads in the wet?
I too have almost worn out organic pads in about 30 miles, not unlike a rim brakes also on a very bad day.
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