Old brake discs

Just recently I dug out an ancient brake disc from my junk pile to make a base for a project. I had expected it to be made of steel but was surprised to find it was a very nice quality cast iron and machined beautifully.

I thought cast iron was a strange choice of material for a brake disc due to the high carbon content making it more difficult for the brake pads to grip. I assume modern discs are made of more exotic materials but old discs, as I have discovered, can make a good source of free cast iron.

Doug

I did post a comment but I don't know where it went? Just mentioned that old brake drums were cast iron I believe,

Stand to be corrected

Mick

Old, worn out cast iron disc brakes are prone to micro cracking due to high braking temperatures and and the shock rain water quenching. New, replacement disc brakes are surprisingly cheap to buy online. I would always chose new rather than old : but it does depend on what you are making.

Many old brake drums were made of CI but, for example, Austin Seven ones from about 1935 were a steel pressing. A quick rub over with a newish file should reveal what a brake drum is made from.

When it came to making piston rings for a Stuart Turner S9, I used a section out of a ventilated disc brake, I think it was from a reasonably modern Holden (Australian GM), nice bit of cast iron, used it for a few other bits on the engine too.

Ian S C

As Ian remarked I have heard that the cast iron discs are very good for making piston rings although I have to admit I have not tried it yet - I am still stuck in the stone age and use a graphited yarn for rings, glands and stuffing boxes.

Rik

This paper will help explain the use of cast iron - and not just any old iron - for brake discs.

Keith

That paper is very interesting Keith, I had no idea how widespread the use of cast iron for discs was. Garages must throw out tons of old worn discs every year and would probably give them away to anybody who asked.

Doug

One of our club members did all his own castings for his 6" Garrett T E mainly out of brake disks, I use one for the lid of my foundry furnace, it saves making one & you have a hole in the centre for the exhaust & for pre-warming up the pot fodder.

Doug,

I too use old cast iron disc brakes when I need a piece of cast iron for some project. I get it for free from a local car repair shop. I also use them when I need a sacrficial piece, easy and free to get a new one.

Thor

I tend to keep the odd brake disc under the bench. They are great for making slave plates/jigs etc. With a quick skim over and a few tapped holes.

Hi Doug,

Cast iron was probably chosen for brake disks because it is cheap and easy to cast and still used in lots of cars. I used one recently to mount the steam chest of my engine in a lathe.

Paul.

I find the used rotors excellent as bases for various jobs. I have a drum practice pad mounted to a piece of tube that in turn is fastened to a rotor. I have also used them as bases for my shooting wind flags. For those I drill and tap 3 holes for adjustment legs; weld a bushing for the flag mast across the top; and glue a cheap bullseye level twit to ensure the base is level and the flag staff is plumb. I love the free stuff from the mechanic's scrap bin.