I recently bought a '66 Valiant convertible with 9" brakes. The brakes were adequate in light traffic. But the car just could NOT stop as well as any current car. The car is now in the shop having 10" brakes installed and I'll probably put on disc brakes when I find all ofthe parts for small bolt pattern wheels.

Locking the brakes up = longer stopping distance, not shorter.

The self energizing drum brake, by its very design, transitions between slight breaking force and total lock up very quickly, it cannot be modulated to a fine degree, no matter who's foot is on the pedal. Letting off the pedal to unlock = no braking for that amount of time and distance. Then starting the whole process over again. There is allot of movement involving both shoes, and it takes time.

9" and 10" drums actually see fade DURING the first panic stop.

The disc's advantage is not only heat rejection, but the ability to apply great braking force WITHOUT locking .

Plenty of real testing has been done by all the auto makers, race teams etc. There is plenty of data about this out there, from many sources. The only thing that makes some of it hard to find is that much of it is 30 some years old by now.

Besides, anyone who has driven more than one car should know something about which does this or that better, is this really a mystery?

There is an aspect to braking that I will call "pedal range". Basically it is the amount of distance the pedal moves between light braking and full lock-up. (I don't know if there is another term for this)

I find that small drum brakes seem to have the least amount of pedal range, disc brakes seem to have the most.
Having a good amount of pedal range helps the driver find that place were maximum braking / stopping power occurs, hard braking... right before the wheels lock and skid.

I have found that 9" drums seem to go from light, to heavy, to lock-up with a small amount of pedal movement... something the driver needs to be aware of.
Combine that with the fact that most 9" drum brakes, even in good working condition tend to "pull" to one side or another, even different sides at different speeds, make these small brakes a challenge to drive.
DD

Good point, Doc. Pedal travel, feel, effort, etc are all related to the driver's ability to modulate the braking, and the feedback the driver gets.
Back in the early 60's, IIRC, there was some experimentation with "treadles" - very short-throw pedals effectively built into the carpet. The testers found they could, with practice, effectively operate the controls. However, switching between those and normal pedals was not easy. Simply changing the driver's shoes threw the feel off enough to cause problems.

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"When you find a big kettle of crazy, it's best not to stir it." - Pointy-haired Boss

1964 Valiant V200, 225/Pushbutton 904
BBD, CAI, HEI, LBP, AC, AM/FM/USB, EIEIO

After reading the above post, I have a car in the shop with the 73 and up Factory A- Body disc set up and weighed the parts for one wheel. 55 lbs for the Rotor ,Caliper ,Spindle ,Brackets and Upper control arm. Next will be a 10" set up when I dig it out of storage some time this week. I don't have a 9" set up to weigh, maybe some one out there ?

The amount of pedal travel is directly related to the relative sizes of the master cylinder and wheel cylinder (or caliper ) pistons. Disk brakes have relatively large diameter caliper pistons which translates to relatively more pedal travel. That is offset to some extent by the fact that disk brake pads are typically in light contact with the rotor and therefore have only a short distance to move before applying braking force. A master cylinder with a larger piston will have less pedal travel. A hydraulic brake system is very much like a lever where the relative distance between the pivot ( fulcrum ) and load on one end and the pivot and applied force on the other follow a mathematical relationship. In the case of a hydraulic system, the line pressure is equal to the force applied to the piston divided by the face area of the picton. a 1" piston will have a face area of about .785 sq inches. A 100 lb force applied to the piston will produce a line pressure of 78.5 lb per sq in. The pressure is then applied to the caliper piston and the formulas are reversed. With a line pressure of 31.4 lb/sq in applied to a 2" diameter piston, having a face area of 3.14 sq in. will create a force against that piston of about 246.5 lb. For every inch the MC piston moves, the caliper piston will move about 1/4 inch. In the case of multiple piston calipers you would need to use the total face area of all the pistond to compute clamping force and piston travel. I've kind of written a book here but I hope the examples are helpful. Bottom line is that a larger master cylinder bore will create a system in which the pedal travel is less but pedal force is higher for a given braking force.

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David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

It is suprising that we have found so much to say about this. There is no doubt that disks weigh more than comparable drum set ups. I remember someone doing this and publishing it in the old SLant Six News. I think maybe it was Doug. Disks also create very slightly more drag on the system which properly adjusted drums do not. And as we have seen in other posts, they can be a little noisier than drum brakes. If you are discussing things other than drivability, there are other factors both good and bad that differentiate them. Disk brakes are much easier to change the pads on than changing the shoes on drums. You can check the wear on disk brakes more easily. Disk brakes get your wheels dirtier than drums.

The bottom line there is superior modulation, stopping power, and directional stability produce a much more relaxed driving experience with disks brakes. Except for the poor soul behind you with drum brakes.
Don't be afraid of the conversion if that is what holding you back. It is basically just blacksmith work that is pretty straight forward. I am surprised at the fine hobby mechanics who shy away from brake and front end work. Diving into it will take away the mystery. When I do the brakes on my kids cars, I always test drive it though. I never send them off without doing so. (They are now 30 years of age or older).

ARe there any cars made with front drum brakes anymore?

Sam

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Hmmm, I can't think of anything with front drums anymore.

Sam is right... digging into a suspension takes away the mystery.
I took my A-body down to completely empty wheelwells when I installed the suspension kit (no upper arm, no lower arm). Once you do that (one side at a time!) you get over the fear of the process!

-Mac

I cant beleive that this question generated so much interest.I have converted several Mopars to disc including my 60 Valiant and my daily driven 63 Dart but I knew that I was going to drive them much harder than they were originally intended,my daughters Valiant ,on the other hand is to be driven as originally intended but I didnt take into account that she will be dodging soccer moms on cell phones that are doing everything but concentrating on driving and also the amount of traffic on the road around here has nearly doubled in the last 15 years and that she may want to drive somewhere besides this small town.
I never had a question of whether drum brakes were as good as discs but whether they would be safe in modern traffic if used responsibly.I know now that I should put disks on and have my daughter in car that can perform in a modern traffic enviroment.
I would like to thank everyone for there suggestions and helpful advice.

Thanks again
HyperValiant

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1960 Hyper-Pac Valiant(rolling test-bed)
1963 Valiant V2OO(Son's summer project,- he just turned 15 )
1972 Valiant 4dr(Daughter Kelly's repair in progress)
1974 Valiant (v8) daughter Kelly's work in progress

my first and only car is a 66 barracuda with 9in drums. I've gone through the whole brake system on the car and i'm gonna have to agree with everyone else. In traffic when someone panic stops i'm looking for a way out. I'll be the first to admit that i'm no expert but i'm a whole lot safer to be in a car with because of it. Not having anything power and weak brakes makes ya a very defensive driver. I hadn't noticed how bad it was until i drove my father's honda for a a few days while my car was in the shop. It's getting disc brakes as soon as possible.

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'66 Barracuda super six turbo??