I will say that drum brakes didn't have anywhere near the trouble with warping that disc brakes do.
They had their own problems which I think are much much worse.
. Driving through water…Brakes are GONE until the water is gone…which could take a while.
. Adjusting… Some vehicles you drove in reverse a pressed the brakes, others the rear brakes were adjusted every time you used parking brake. The problem was that many people didn’t do enough reverse driving or use their parking brake enough to keep their brakes adjusted. It became a dangerous situation for many drivers.
I prefer disc brakes over drums on the vehicles I drive.
A comment about regenerative braking in hybrids and electrics. That only works when the batteries are not fully charged! A fully charged battery can’t absorb all the regen being sent its way.
First thing in the morning, a fully charged Leaf will require much greater pedal effort to stop unless there is some sort of variable power assist mechanism. Imagine rolling right through the first morning’s Stop sign because you aren’t pushing the brake hard enough!
Plug-in hybrids have the same problem. Fully charged to maximize range means no capacity for re-gen. Non-PHEV hybrids don’t have as big a problem with this unless you are driving down a looong grade using re-gen.
The first GM electric, the Impact EV-1 had a fully brake by wire system with mechanical backup to address this problem. It also had a “brake pedal emulator” - a device used to fake the feel of a normal brake system.
^I’m surprised there isn’t some means of dumping regen electricity to ground when the battery is full, much like a M/C alternator dumps off excess charge when not needed. I don’t doubt what you’re saying; just wondering “why?”
Mustang, about that hybrid comment, it applies if you happen to live at the top of the hill. When you use energy to get going on flat ground, you use more energy than you can recapture. The battery is not going to be as full after you come to a stop.
The problem with regenerative braking surfaces after you climb a hill. That’s where you need more energy than the battery had stored and the thermal engine provided the extra energy. When you go downhill, the battery may get topped off before you reach the bottom and the driver should be using old fashion engine braking. In the hands of the ignorant driver who relies entirely on the slow pedal, I don’t think drum brakes are sufficient
I prefer disc brakes over drums on the vehicles I drive.
Me too. In the cars we drive today, even though drums have a few subtle advantages, discs seem most adaptable to the engineering and requirements we have today. Copious amounts of Power assist is not the issue. Discs appear to rule.
I would say 20% of the people around here drive like maniacs, they floor it from a red light and stay on the gas until they brake hard for another red light, not a light that just changed to red either.
@meanjoe75fan: The only way to dump energy would be to use it to power or heat something. It has to go somewhere. Probably it’s a lot easier to directly turn it into heat with the brakes than try to use the regen braking system when there’s nothing to regenerate.
@chunkyazian, You may or may not use more energy to get the car going than stopping depending on how fast you accelerate and how hard you brake. Plus there are losses coming out of the battery to the wheels and going back in during regen. And the amount going back in doesn’t include the 30% braking from the rear since there is no rear regen mechanism on most hybrids.
That said, the closer to “topped up” the battery is, the less energy it can accept. In other words, there is more regen when the battery is at 60% state of charge than at 97% state of charge. That plays games with the driver who expects consistency from his inputs. That’s my main point. It is much harder to achieve consistency than it would appear on the surface.
Diesel trains have huge arrays of resistors and fans to dissipate braking energy. Not cheap.
And hybrids need mechanical brakes because of the RATE of energy dissipation, not just the amount. Emergency braking requires big brakes. But it’s also right that the brakes have to work with a full battery.
“But it’s also right that the brakes have to work with a full battery.” @texases are you saying brakes may fail in a dead alternator and draining battery situation?
Brakes operate by converting the kinetic energy (motion) of an automobile into heat energy. That’s their only job, convert energy into heat, disc brake shed hear better than drum brake which is why I have seldom heard of a case where the disc brakes overheat, while with drum it was and is a major concern.
“If power brakes were not an option would you want 4 wheel disc brakes?”
Sure, given that in 1949 Chrysler used that Ausco Lambert disc brake system that required less force than the drum brake system, had better cooling and less fade, it was costly which is why it was dropped. In tests by Chrysler conventional drum brakes required 120 pounds of pedal pressure to lock all four tires, the disc brakes took only 75 pounds to achieve lockup. After five back-to-back panic stops, the drum brakes required 200 pounds of effort and overheated to the point of being useless. Discs were good for 15 panic stops with pedal pressure rising to just 90 pounds by the end of the test session. Also the brakes were self energizing but tended to be grabby.
But, that is a huge flaw in his argument, peddle pressure really doesn’t have much to do with the pressure at the calipers, let’s say you want a max force of 300 psi at the master cylinder but you need 1,200 psi at the calipers. To keep it simple we’ll say the master cylinder’s cylinder is 1 sq. inch. That would mean you’d need a cylinder 4 times greater, but you’d have to press then master cylinder four inches to move the caliper cylinder 1 inch.
In the end disc brake are better, they are more efficient, they can be made self energizing, they are self adjusting, they are less likely to overheat, they shed water better. Why do you want to go back to drum brakes so badly?
But, that is a huge flaw in his argument, peddle pressure really doesn’t have much to do with the pressure at the calipers, let’s say you want a max force of 300 psi at the master cylinder but you need 1,200 psi at the calipers. To keep it simple we’ll say the master cylinder’s cylinder is 1 sq. inch. That would mean you’d need a cylinder 4 times greater, but you’d have to press then master cylinder four inches to move the caliper cylinder 1 inch. So the pressure at the master cylinder or brake pedal.
THANK YOU!
About time somebody threw the concept of mechanical advantage out there! Un-assisted disc brakes could be quite low effort with an unpowered hydraulic system–you’d just have to have a LOONG pedal stroke!
Also, just because there’s no need to servo-assist disc brakes (when power brakes are available)…doesn’t mean no means of doing so exists! It wouldn’t surprise me at all to learn there’s a patent or three for servo-assisted disc brakes out there.
I edited out “So the pressure at the master cylinder or brake pedal.” because I didn’t finish the thought which is why it doesn’t show up in my post. meanjoe75fan got to it before I edited it, sorry.
You can’t use the Ausco Lambert disc brakes as an example here because they are really a variation of a drum brake. The difference is that the friction surface is on two spinning discs mounted inside a two piece drum instead of on shoes in a one piece drum. It increases the surface area of the friction material.
These brakes resemble the brakes used on modern aircraft more than disc brakes used today on cars.
It does seem to be a variation of drum brakes, with the pads pressing on the vertical surfaces of the drums rather than the horizontal surface. But on the other hand, the pads are on discs rather than on shoes. I guess I’d respect the inventor’s description and go with calling them disc brakes. I’ll bet there were a lot of other weird designs in the early years.
“After five back-to-back panic stops, the drum brakes required 200 pounds of effort and overheated to the point of being useless”
That sounds exactly like Rick’s experiment with his older truck with drum brakes all around . . . the one where he himself said after the brakes were hot, he wasn’t able to stop before sailing into the intersection
It pretty much makes the point as to why drum brakes all around aren’t being used on automobiles and light trucks
In my opinion, for what it’s worth
I’m not talking about class 8 air brake equipped trucks