Replacing rear bearing races in drum

[FB71]

correct! and cooling is much more difficult to control vs. heating. But heating only to a max of 250-275 diminishes the impact of colling to a moot point.

[Pu241]

250 - 275°F will cause loss of temper?
I would think that your brakes can reach this on a prolonged hill trying to keep your speed down!
Or after a few long hard stops.
Was thinking 250 to 275°C, but I'm not a metalurgist!

[FB71]

no, stopping at 250-275 prevents temper change caused by uncontrolled cooling. Any hotter and the cooling process becomes critical.

[Pu241]

no, stopping at 250-275 prevents temper change caused by uncontrolled cooling. Any hotter and the cooling process becomes critical.

Once again cruising down say interstate 68 and you know the "law" is laying in wait for you! So you apply brakes to keep your speed in check.
After about 2+ miles on a 5-6% grade I would think your drums as well as rotors would be well over 250, if not 300°F. And air cooling would be rather uncontrolled. But once again, I've never used a thermal gun on these so I'm just guessing!

[FB71]

heat generation will be in excess of 350-400 during braking events, but consider the rotors and drums are constantly shedding heat, so their average temp stays well below 300

[jglutz]

^^Jim, to supliment what your saying...If brake heat wasn't soaked out...alot of wheel bearing grease would fail....cheap Lithium based ±325°....Molyed based ±425°

[FB71]

correct! avoid soap-based lubes in high heat environments.

[scitzz]

Could you take it to 400, drop in the race, and then cool it quick in water and oil? Seems that would only strengthen the metal......

[kzbill]

if I remember those are cast iron, throw it in water and you may crack it badly. A blacksmith friend of mine used to weld cast iron manifolds for tractors. he would preheat, weld, then put them in a large bucket or garbage can full of wood ash. The ash acts as an insulator and holds the heat in. It would slowly cool in the wood ash for about 8 hr.
My brother uses fibreglass heat blankets to control the cooling of cast iron.

[Pu241]

kzbill,
Don't think these are cast iron in composition.
Cast iron is characterized by a high carbon content and is generally brittle.
It is also not readily machinable.
The drums are cast into shape via a rough mold then machined into shape, I would think they are more of a mild steel, which is much easier to machine.
Might be a grade or two higher than mild steel, just depends upon carbon content and other alloying ingredients; molybdenum, chromium, nickle, boron, etc.
Also as discussed above cast iron does not take a temper and is not amenable to case hardening which some drums and rotors are subjected to.
Actually drums due to their mass are probably made of a lower grade material than are rotors.
Once again I do not hold a degree in metallurgy, I just have to know a lot about materials subjected to high neutron flux!

[jglutz]

KZ &PU:
Welding is a different issue...the weld filler and base metals, if not properly selected will cool at different rates thus inducing stress fractures. Most iron...arc welds very well...like you describe...with a nickle based rod.
The primary difference between iron and steel is the carbon...and how it's introduced...in steel...carbon is burned out and the reintroduced.
Cast iron is very machinable....poorly made cast iron is not... the high carbon content turns to carbidie structures...carbide can make the iron seem like glass (brittle and hard).
Iron can be cast better than steel...also...with in reason...iron can be tempered.
The most common and maybe the best alloy to added to iron is magnessium...the result...is ductile iron.
A great many every day products (c-clamps) and highly stressed car parts (engine mounts) are made from ductile iron.

What are drums and rotors made of....I don't know.....but i would guess steel...why....It can be forged.

[Pu241]

What are drums and rotors made of....I don't know.....but i would guess steel...why....It can be forged.

I don't think either rotors or drums are forged though!

[FB71]

drums and rotors are typicall cast ductile iron, high performance rotors are cast steel.