New Front Brakes and Rotors...

True, but some of us just want to see how far we can go on a set of pads, and I would rather put my old toyota pads back on than some cheap aftermarket pads that may squeak.

thanks for the recommendations John but I got lazy when I noticed my sandpaper had sticky backing, I found the flattest board I could find and sanded them by hand, about five minutes per pad on the 80 grit followed by one minute on the 180 grit sandpaper.

They were smooth to the touch when I reinstalled them and now I'm off to break in my new rotors and mate them to the pads, I foresee a lot of "neutral braking" for the next week or two to bypass the regenerative system, any other recommendations? In my Corolla I often parked it in neutral and used the hand brake so the new pads wouldn't make constant contact with new hot rotors.

 

Well done you will soon know how flat across the pads you managed to get by how much of the rotor shines up.

I like you do not believe in throwing perfectly good pads away when they could have 100,000miles left on them.

Glad to have been of help.

John.

 

thanks John, no shakes or shudders during neutral braking, just nice strong smooth stops, I'm very happy with the job I did and money I saved, I also lubed my caliper slides and used brake cleaner on the rear drums, I also anti-seized the areas that needed it so the next repair goes quicker.

You say you have access to an engineering shop, do you know a lot about metals? I ask because I noticed how nice the caliper and steering knuckle (or whatever it is called) looked after 8 years and am wondering about alternatives to iron for rotors. What is wrong with an aluminum rotor? Even if its softer and wears faster aluminum is so light that you could make it much, much thicker at the same weight to compensate for quicker wear, than rusting wouldn't become an issue.

Stainless steel also does not rust and is very strong. This would be handy not just for the Prius but any hybrid or EV vehicle with regenerative braking.

 

I have a small knowledge of metals and I too came the conclusion that stainless steel should make good discs. It has very good wear resistance but that makes it notoriously difficult to machine.

I looked into making my own out of solid round cut blanks, but this would have meant machining away over 80% of the material. Making the then machine discs vented would prove to be another big problem.

Next was the price of the SS blanks don't ask. So at this point I gave up.

Aluminium although it comes in many grades I think would be to soft (getting out of my depth here) it also has a high expansion rate not good for discs.

John.

 

2 things would drastically reduce the price of stainless steel brake discs:
mass production &
demand (they would almost certainly be standard equipment on hybrids and ev's and who with a nice sports car wouldn't want rotors w/o any rust on them?)

as for difficulty in manufacturing, industrial factories have presses that can exert hundreds of tons of pressure, combine that with heat and it wouldn't be much (if any) more difficult to produce than iron rotors.

here is what google pulled up for SS rotors:
SSBC:: 33264AA3L
funny, they list these benefits:
*Gas and dust are vented away from the brakes. This prevents the dangerous problem of “cake-over†that can form a film on pad and rotor surfaces, making them slippery and reducing their effectiveness
*Heat is dispelled much quicker than with traditional rotors. This feature guards against burning and warping
*Brake pads make much better contact with the rotor surface, allowing you to stop quicker than with the competition’s components

but it doesn't mention anything about being rust resistant.

 

Heavy duty presses won't get you your ventilated rotors though. Conventional rotors are turned from grey iron castings that probably cost about $.75/lb or less in volume. Pretty hard to compete with that.
Steel is much more difficult to cast, owing to the way it solidifies (slushy). As nice as rust-free brakes might seem, not too many people will pay ($50? $150?) extra for them on a new car.

 

Aluminum doesn't rust, but it does corrode, and corrode very quickly. Aluminum is a highly reactive metal that spontaneously reacts when exposed to oxygen. On the other hand, aluminum oxide is very tough and fairly inert. It's what makes aluminum useful as an engineering material.

It works like this: Expose a fresh piece of aluminum to air and it immediately oxidizes on the surface. A very thin film of aluminum oxide forms, protecting the underlying aluminum. This prevents further oxidation as long as the oxide layer remains intact. Unfortunately, each application of the brakes would remove this layer.

Furthermore, aluminum has little tolerance for heat. It softens at fairly low temperatures, which is not a good quality for brakes.

On the contrary, stainless steel does rust. Yours is a commonly held misconception about stainless steel.

The steel in stainless steel rusts just like any steel. Stainless steel works much like aluminum, but it takes extra work to form the protective surface layer. Stainless steel is a steel/chromium alloy which may also contain nickel. A fresh block of stainless steel will rust when exposed to oxygen. To prevent this, freshly machined stainless steel is passivated with a pickling solution. The passivation process removes the steel from the surface of the stainless, leaving only a layer of chromium, or chromium and nickel.

Chromium is a highly reactive metal, just like aluminum. Chromium oxidizes immediately when exposed to air, but just like aluminum, the oxide layer is strong and mostly inert.

So what we have with stainless steel is a rust prone material protected by a microscopically thin layer of chromium oxide. All is good if the passivation is properly done and the oxide remains intact.

Applying brakes would immediately destroy the protective chromium oxide layer. The microscopic scratches caused by braking would promote a failure mode known as crevice corrosion. Microscopic crevices prevent the formation of a protective surface layer, but still allow oxygen to get to the underlying steel. Your brakes would rust from the inside out.

Stainless steel is not the wonder material most people assume. For stainless to work, it must be properly passivated and the surface must be protected. In addition, the surface of stainless steel must be exposed to sufficient quantities of oxygen to maintain the protective oxide layer. It seems counter-intuitive, but sealing stainless steel will promote crevice corrosion. Here is how it works:

Suppose you have a nice stainless kitchen sink. You wash it up before you go on vacation, but accidentally leave the wet wash rag in the bottom of the sink. When you come home, you are horrified to find rust under the wash rag. How could this happen? Isn't the sink stainless?

Well, yes, it is stainless steel, but now we know that stainless steel needs a protective layer of chromium oxide. The wet rag prevents atmospheric oxygen from getting to the surface of the stainless, so the oxide layer slowly brakes down. It isn't able to replace the surface layer, so little fissures open to the underlying steel. Once these fissure open they stay open. The protective chromium is gone. Random oxygen molecules drift into the crevices and form rust with the underlying steel. Paradoxically, it takes less oxygen to make rust than to maintain the protective surface. The surface must be maintained everywhere, whereas one breech starts rust.

So you come home to find rust under the wash rag. You clean the sink again and remove the rust. A few days later the rust is back, even without the wet wash rag. This is because of the crevices. Now that the protective oxide layer is gone, the underlying steel will continue to rust.

The only way to fix this is to passivate the surface again, removing all of the exposed steel. Kitchen cleaners with oxalic acid work well for this. Try Bar Keeper's Friend. Make a wet paste and grind it into the rusty area. Allow it to work for a half hour or so, then wash it out.

The wet wash rag process applies to any buried stainless steel. This is why we don't use buried stainless fasteners when we build our boats. We use bronze. When you bury a stainless fastener, it can't get enough oxygen to maintain the protective chromium oxide surface. Crevice corrosion begins and the fastener rusts away.

Tom

 

thanks for the chemistry lesson Tom, but you missed the point I was trying to make, everything on the automobile has been improved during the century+ that the car has been around except the rotors(okay, there is venting & cross-drilling), they're still made out of iron, can't there be something better that is tough and resistant to rust?

This may sound silly, but what about kevlar?