Surface rust on disks

the entire

regulary. Does this

should be. Any

where I bought the

All steel discs do that. Doesn't indicate any fault at all. The slightest bit of humidity will rust a perfectly grease free piece of steel, almost while you watch it. Mike.

If the car has been standing a long time, then rust on the disks will happen, this should scrub off in time.

I am a bit paranoid when it comes to brakes, I always change the disks, pads, drums, shoes etc.. when I buy a second-hand motor.

Andy

disks will

the disks,

A bit OTT, and possibly unecessarily expensive, when a good inspection is all that's needed to assess their condition. Now if you'd said you always change the brake fluid, that would make a much more sensible policy IMO. Still. Better to be paranoid then ignore them altogether. :-) Mike.

I realise it can be unnecessarily expensive, but most cars I have purchased before I started to do this have had a fault in the braking system.

Usually it is people not assembling the rear drums properly, or leaking slave cylinders, or warped disks (Vaux-cavalier)..

Andy

Agree. There's no need to change the disks unless worn to/near min thickness, warped or cracked.

Agree again - very much neglected.

It's quite normal - the higher ferrous content of modern discs means that they can rust up very quickly.

For example;

(although I'd recommend you go to then to The Ka Diary along the top, then to the DiaryNav bit on the left, then to the relevant entry of 26 May 2002).

In here, there's a picture of Kermit's front brake discs after twenty four hours. Since then, I've seen them go like this in _under ten minutes_ when conditions are just right for it.

have purchased

system.

How unlucky can you get? :-) Most of the s/h cars I've baught, haven't needed more than a set of pads. Although I did buy an SD1 once from a garage that assured me the brakes had been sorted, with new pads and rear linings fitted. They had, but whoever did it, had not fitted the automatic brake adjusters correctly onto the rear brake shoes, which caused them to drag all the time. Unless you know how they fit, it's easy to get them wrong. Annoying but only took about an hour to put right.

or leaking

Never owned a Cav. Did think about it once before commonsense prevailed. :-) Mike.

the entire

regulary. Does

should be.

where I bought

Sorry to be pedantic, but all discs are basically made from iron. Iron is ferrous. Period. It's not something that can be added to, or made higher, to increase it's ferrousness, to coin a word. Maybe you meant they don't contain corrosion inhibiting additives like nickel or chromium, etc. Mike.

Ferrocity? :-)

Don't get me started on the Cavalier, it nearly killed me.... Give me a good SAD anyway.

I took the rear nearside drum off, only to find what I can only describe as a chocolate cake inside. It was the slave cylinder leaking badly, this was effecting the front braking as well, the front disks had both warped badly due to overheating...

FYI:- I also did change the fluid.

Andy

An iron alloy, perhaps?

Indeed.

Quite possibly. After the explanation given to me back in May, I took it that modern discs were softer than pads of ye olde days, primarily because the current brake pads don't contain asbestos, and I therefore made the assumption that the discs contained more iron.

Reading the above, big bad-ass assumption I made there, heh! :)

Stainless steel discs would solve the rust problem, but they don't seem to be readily available. SS is used on motorcycles - I suppose a highly visible rusty disc wouldn't look very nice on a bike. Does anyone know of any possible metallurgical disadvantages of SS, eg friction characteristics.

During my searches, I came across stainless steel 'rotor simulators' which are available in the US, These fit between the rear wheels and the brake drums to simulate rear disc brakes :-)

Terry D.

That's an interesting idea.

characteristics.

I'd suppose that there are disadvantages with using stainless steel on a car - perhaps they are not so efficient at absorbing heat, and given that a car is heavier, the brakes produce a lot more heat . . . ?

Yes, I've seen these, they look appalling!

We have a few Kas with a rear disc conversion, and for certain alloy and disc combinations, nothing beats a used-looking disc brake - in my opinion. These fake bits of tat look appalling! I've even seen some painted orange!

After further searching, I've discovered that stainless steel has a much lower thermal conductivity than carbon steel; for instance, 316L SS has only about half the conductivity of carbon steel at 400 degC. Perhaps it may be better to live with the rust.

Terry D.

Some grades of cast iron rust quicker than others. Stainless steel is used on motorbikes and stays bright even if left unused for 10 years. But even the custom car crew have yet to catch on to SS for good looking disks - some bike ones are laser/plasma cut until there is more daylight though the disk than disk. They still work well, just have a high pad wear rate.

Fit wider wheels and/or ones with less holes. This will shelter the disk from rain and spots that bounce. Even behind steel wheels and plastic wheel trims they will still go rusty from moisture in the air if not used for a few weeks.

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has a much

316L SS has

Perhaps it

I agree. Apart from the disadvantage of it's lower thermal conductivity. Replacement car SS discs would be horrendously expensive. Unlike the discs on a bike, which are basically just round flat plates, the 'top hat' design of most car discs, means they would probably have to be machined from solid, or from welded fabrications. Neither process could compete with the cheapness of manufacture from iron castings. TBH though, the surface rust that I occasionally notice on my discs, has never bothered me in the slightest. I'd never really thaught about it until this thread. As long as the brakes function as they should, that's all I'm interested in. Mike.

Indeedy! Otherwise, we'd get brake fade slowing down from 30 mph. . .

May, I took it

primarily because

made the

:)

Maybe not as 'bad-ass' as you think. I'm no expert in metallurgy BTW, just a simple engineer, but according to how it is cast, cast iron brake discs can be made with different characteristics. Close grained, open grained, plus adding other elements can affect how it behaves in specific conditions. In effect making it soft, hard, or increasing it's wear resistance etc. Mike.

No. A good brake has an alloy or thin steel or even thinner titanium 'bell' (the top hat hub) with disc bolted on to it. Better ones have floating discs. This is true even for car brakes except they still tend to use cast iron for the rotor.

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