Why is this such a big deal to you? Were you bullied by a hydraulically-actuated brake disc as a schoolkid?
Why is this such a big deal to you? Were you bullied by a hydraulically-actuated brake disc as a schoolkid?
Lol… Thats so funny! I have my reasons, I know we beat that old horse till it was dead but here it is again,
From Wikipedia.
Due to the fact that a drum brake's friction contact area is at the circumference of the brake, a drum brake can provide more braking force than an equal diameter disc brake. The increased friction contact area of drum brake shoes on the drum allows drum brake shoes to last longer than disc brake pads used in a brake system of similar dimensions and braking force. Drum brakes retain heat and are more complex than disc brakes but are often the more economical and powerful brake type to use in rear brake applications due to the low heat generation of rear brakes, a drum brake's self-applying nature, larger friction surface contact area, and long life wear characteristics (%life used/kW of braking power).To list advantages of drum brakes:
1- more economical to maintain. The only replacement part was usually the shoes at around $15/wheel instead of pads, rotors and calipers at $150/wheel
2- lower frequency of maintenance. Drums didn’t corrode unlike disks
3- more environmentally friendly due to 1 and 2 and used shoes earned a return credit unlike pads and rotors so nothing was scrapped.
4- safer since no surprises from wet brakes. Disk brakes are exposed to water
5- self energizing resulting from a subtle design feature at no extra cost.
6- Wheel cylinders were simple to recondition by the owner unlike calipers.
7- Drums were lighter than disks, wheel cylinders much lighter than calipers
8- less expensive to produce
I like drum brakes, they worked just fine and I like them just fine. In todays world where everyone is in a hurry and drives crazy, discs are probably the better choice.
You never had the problems with pulsation and warping with drums that you do disc brakes.
Disc brakes are great, however they have many shortcomings as well, I drive a big bucket truck everyday and it has 4 wheel drum air brakes, it stops much better than many front disc setups we have on other trucks.
I’ve examined a lot of rail cars and it looks to me like there is a compressor and storage tank on every unit,if thats the case they must be driven by the wheels on the car and maybe the primary purpose of the locomotives compressor is for signal air to the brake system? -Kevin
On your wikipedia article, I disagree with point #4 and #7. Disc brakes spin themselves dry. Never had a problem there, and the brake drums on my Odyssey are HEAVY!
Also, the drum brakes on air brake-equipped CMVs don’t compare to the drum brakes they put on cars. The brake drums on the school busses where I work take two men to lift! I can lift one of the brake drums on my minivan with two fingers.
Someone added that list of advantages (1-8) to the Wikipedia artical on June 9, 2014.
This sort of misinformation discredits Wiki as a reliable source of information.
rick, have you been wiki- bombing again. it sounds suspiciously like your wording… 
in the last month I have changed my front and rear brakes.
I had to change the shoes, and the wheel cylinders since one was leaking, and the hardware since some had broken. not to mention the adjusters since one was frozen up. oh yeah, I neede a can of brake cleaner too. after I cleaned and wire brushed, I had to look at my manual so I would get all the 25 different pcs back together right. then I took 25 pcs apart and had to clean again. one of my brake lines twisted up when I changed the wheel cylinder, so I had to go back to the parts store. then I had to put it all back together.
it was over 50 dollars. it took all day and the next morning to do it all
on the other hand my front pads cost less than 10 dollars the new caliper bolts I decided to use cost 4.99 for all 4. it took me about an hour and a half. and I did not even need my manual
rick, drums suck compared to calipers IMHO
Rick
Have you so soon forgotten the experiment with your old truck equipped with drum brakes all around?
The experiment where the brakes faded after a few applications, and you weren’t able to stop the truck before winding up in the middle of the intersection?
As for your theories that drums don’t warp . . . that’s funny, but I disagree
I turn plenty of drums on the brake lathe at work
And there’s a lot of adjustments needed, unlike the “lowly” disc brake
@kmccune No, there is not a compressor on each railcar. There is a reservoir (of ptessurized air), but the only compressor is on the locomotive. It’s a clever system. The main brake hose that runs the length of the train is the train line. When pressure is at full pressure, the brakes are released and the pressure is used to recharge the reservoirs. As long as the train line is kept under high pressure by the compressor, the brakes stay released.
To apply brakes, the locomotive releases some of the air from the train line. Not all, just some. That triggers the brakes be applied. Another drop, and they are applied more. To release the brakes the compressor has to get the pressure in the train line back up. It takes a lot of care by the engineer to manage the pressure in the brake system. If they use the brakes too many times without enough time in between applications to build up pressure, the train can run out of brakes and run away.
If the train line pressure is getting low and the engineer is worried, he can signal an emergency stop by dropping the train line pressure to zero. The brakes sense this rapid loss of pressure and apply all the pressure in the reservoir, plus additional pressure stored in an emergency reservoir. After an emergency braking, the locomotive has to pump up the pressure to the maximum to recharge the reservoirs and emergency reservoirs, for the brakes to release. That can take quite a long time and messes up schedules.
Good engineers manage the brakes so they never have that happen. One thing that can be done is for brakes to ve applied manually on some cars before a grade. The brakeman goes from car to car and applies the brakes with a wheel or a ratcheting lever. After the grade the brakeman has to release the brakes car by car. This all has to be done with the train stopped since brakeman don’t walk along the tops of trains doing their job.
@WheresRick4:07PM edited 4:12PM
High speed elevators actually slow down the elevator car using dynamic braking but the electric friction brake holds the car. Usually it’s a great big heavy solenoid that pulls the brake shoes away from the drum.
Very interesting! Who would of though that our under appreciated friend the drum brake is used by so many people every day even if they are not fortunate enough to have drum brakes on their car. When your life depends on it such as making sure an elevator stays in place when your getting off, trust your old misunderstood friend the drum brake.
It’s not an automobile style drum brake, it’s sort of inside out. The shoes close down around the outside of a big drum, like the bands in automatic transmissions. Also, it never rains inside the machine room where the elevator hoists are.
Also understand that a lot of elevator hoists still in use are 40-50 years old, they don’t throw this stuff away just because the new smell wore off.
Most hoist electric brakes use disks, but not like the ones on cars. The disk has the friction pads on it, like a car’s manual clutch disk. The solenoid pulls the pressure plate away from the disk when activated, springs provide the pressure. There are also multi disk designs that have stationary floating plates in between.
Anyway, these brakes are either on or off with on being the no power default mode, that is they are designed to fail locked if power is lost.
rick, have you been wiki- bombing again. it sounds suspiciously like your wording.... :)
I wish I could take credit for that Wikipedia article, I really do, but it honestly wasn’t me. I am going to try to find out who it was and get them to join me here. There are at least two fans of the good 'ol drum brake in this world!
I see “advantage #5” as a disadvantage, not an advantage. Self actuation makes for non-linear brake control. If something like water or high temperature reduces the brake lining’s coefficient of friction, the loss of self actuation that results compounds the loss of braking. That’s why drum brakes almost completely go away when fading or after driving through deep standing water while non-self actuating disk brakes still brake, just needing a little more pedal force when wet or overheated.
If there’s too much self actuation, the brakes will even grab and lock by themselves with even the mildest application of the brake.
My first disk brake front wheel motorcycle was a revelation on just how good brakes could be. I could brake on the edge of wheel skid under control. With drums, the difference between so-so braking and wheel lock was much more narrow and the control hysteresis inherent in a cable activated cam operated mechanical system compounded the control difficulty. When the wheel locked, it wasn’t enough to just reduce brake lever pressure, you had to really let off the pressure to get the brake to release and then reapply pressure, hopefully before you crashed.
Also, I find it a lot simpler to replace disk brake pads than drum brake shoes, both on cars and bikes.
@MarkM,thanks,must be a fierce compressor in the locomotive(thats a lot of hardware to pressurize)How often do they have to replace the shoes on the rolling stock?-Kevin
Yes, the compressors are beefy. But remember this system goes back to the 1850s, so it can’t be too difficult. Trains were much shorter and lighter back then, but the principle is the safe. It does take a while to get the pressure built up before a train first moves. A long train now might have six or eight locomotives throughout the train. The compressors on them can also be controlled by the engineer. I don’t know how long brake shoes work. I never worked for a railroad, though many of my relatives did. One fairly common problem is known as a ‘hot box’ caused by bearings failing on an axle. Along railroads at certain places are hot box detectors that detect the heat from the failed bearings and tell the engineer where the problem is. Rail cars now use highly reliable roller bearings, so hot boxes are less common. In olden days (50 years ago) they used friction bearings packed with grease regularly. Those failed a lot.
Thanks Mark M-Kevin
I see it happening. Electric braking will get accepted at some point. There is no reason we still can’t have a high leverage mechanical backup emergency brake to make old trimers feel better. Engine braking will take over all braking when electric drive motors on all four wheels becomes the norm. Engine braking is elusively used in a lot of industrial vehicles with mechanical braking as a backup and parking break. It’s not ready for high speed because they are hydraulic in nature but electrically operated with the aid of a computer makes the electric motor the ultimate brake. They apply a stronger braking force with no wear then any braking surface possible, are ultimately reliable, powerful and regenerative. Heck, as mentioned…most all brakes are computer controlled any way and using electric motors or servos is just a step away.
Having thought about this question some more, and 115 posts later, I recognize that while electric braking has IMHO no benefits as a braking system it might be that stability control systems will cause electric braking systems to be the system of choice. Dag made a good comment at the end of his post about computers. Tomorrow’s stability control system mandates just may force the issue.
If they do, I predict there’ll be years, maybe decades, of serious problems before manufacturers come up with a robust workable system. I won’t live to see the day.
I knew some people would come around 
From my post on page 9 of 12-
“The implementation may actually cost less in materials too. For example, the ABS feature will not require any additional hardware to accomplish. The master brake controller would simply pulse the wheel brake modules electrically without the need for any special hardware interface like they have now.”
Don’t get me wrong, TT, I still see no benefit to it as a braking system and still believe hydraulic brakes are as good as any system could be and better than most, however the stability control system mandates could take a turn that will require computer controls. I hadn’t thought of that originally, and don’t like the thought of a government mandate forcing yet another major change that’s bound to cause problems, but I recognize the possibility.