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Old 10-10-2010, 01:49 PM
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compare disc to drum brakes

My car:
One drum rear wheel cylinder total piston area is 1.04 sq inches.
One disc front caliper total piston area is 8.45 sq inches.

I would like to find some info to compare the stopping efficiency of drum vs disc brakes. Has to be function of piston area, etc.

I've seen numbers thrown around...like it takes 1000psi to actuate discs and 400 psi to actuate drums. I don't know how much actuation pressures vary with piston area, etc???

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Old 10-10-2010, 02:04 PM
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You are looking up the wrong tree..what the difference is is the better ability of the disk brake to dissipate heat. Brakes work by converting motion energy to heat and the disk is far superior in that regard..as long as the pressure in the brake system is able to lock the brakes up you have plenty of pressure..Brake heat is why the builders have gone to the larger tire and wheel size to allow for larger disks. heat is also why you will find carbon fiber and ceramics used in high performance brakes in cars such as the super cars..

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Old 10-10-2010, 02:16 PM
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Quote:
Originally Posted by OneMoreTime
You are looking up the wrong tree..what the difference is is the better ability of the disk brake to dissipate heat. Brakes work by converting motion energy to heat and the disk is far superior in that regard..as long as the pressure in the brake system is able to lock the brakes up you have plenty of pressure..Brake heat is why the builders have gone to the larger tire and wheel size to allow for larger disks. heat is also why you will find carbon fiber and ceramics used in high performance brakes in cars such as the super cars..

Sam
That is some good info....
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Old 10-10-2010, 02:19 PM
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My 13 year old has asked me over and over how the disc brake can be better when the pads area is so much smaller than the drum brakes shoe, thanks for the good explanation that I can now pass on to him.

Brian
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Old 10-10-2010, 02:29 PM
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It is also real easy to do a drum brake job wrong. If the drums are turned, you cant use standard shoes. You will loose a good portion of the contact area as the radius of the drums will not match the shoes. They will eventually wear in but that will take quite some time.

Back when I was in school, and it was mostly drum brakes, the rule of thumb was 1 square inch of shoe for every 100lbs of vehicle weight.

Disk brakes are not greatly affected by heat or water. Drum brakes were terrible when wet.
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Old 10-10-2010, 02:33 PM
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Funny you should mention this just as I am getting dressed to go out and install my rear drum brakes on my Rambler. I remember my brother had a shoe "recurve" cutter of some sort to match shoes to drums. I also remember seeing guys give the shoe a firm whack with a large hammer to take a little of the curve out of them so they fit the drum better.

Brian
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Old 10-10-2010, 03:20 PM
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Piston area alone cannot be compared. For disk brakes, the piston area acts directly on the pads. For drum brakes, the pistons push on one end of the shoes and there is a lever affect. Drum brakes are also self-energizing in most cases. Finally, pad or shoe area is irrelevant for ultimate braking area. Friction force is simply normal force times the coefficient of friction. Larger pads won't give you any more stopping power. Larger pad area only lowers the PSI force on the pad material, which is a lining materials properties issue. As the pads get larger, the surface pressure is lower and the pads last longer. Also, larger pads do dissipate heat over more area. The friction properties of the pad material may change as it gets hotter.
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Old 10-10-2010, 05:07 PM
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no reason to compare disc vs drum

I know there is absolutely no merit for comparing drum vs. disc performance data.

My car has both drum and disc...I am easily amused ...I thought any data would be neat.
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Old 10-10-2010, 08:50 PM
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When I switched the 8 lug drum brakes to discs on my 64 Bonneville, I noticed two things;
-The discs kept the car straight during panic stops.

-The 11" drums stopped the car faster...

Sometimes I wish I would of did more work to the old 8 lug system.. It did look the best..
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Old 10-10-2010, 09:09 PM
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8 lug...huh?
I don't copy.
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Old 10-10-2010, 09:20 PM
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Pontiac "8 Lugs" were a brake drum wheel set up that was one of the coolest wheels EVER!





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Old 10-10-2010, 09:26 PM
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Quote:
Originally Posted by pitts64
When I switched the 8 lug drum brakes to discs on my 64 Bonneville, I noticed two things;
-The discs kept the car straight during panic stops.

-The 11" drums stopped the car faster...

Sometimes I wish I would of did more work to the old 8 lug system.. It did look the best..
They may possibly stop the car faster, but if you had to stop the car fast more than once the disc would kick the drums butt.

I remember a road test from 65 when Corvette went to four wheel disc. The panic stop the year before with the 64 all drum vette yielded one stop from 100 and the next stop was about twice as far and after that it wouldn't even stop. In 65 with the four wheel discs they made about 10 panic stops with no difference and just gave up.

Disc makes a BIG difference.

Brian
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Old 10-10-2010, 10:22 PM
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Quote:
Originally Posted by MARTINSR
Pontiac "8 Lugs" were a brake drum wheel set up that was one of the coolest wheels EVER!





WOW!
I like it.
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Old 10-10-2010, 10:28 PM
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Quote:
Originally Posted by MARTINSR
They may possibly stop the car faster, but if you had to stop the car fast more than once the disc would kick the drums butt.

I remember a road test from 65 when Corvette went to four wheel disc. The panic stop the year before with the 64 all drum vette yielded one stop from 100 and the next stop was about twice as far and after that it wouldn't even stop. In 65 with the four wheel discs they made about 10 panic stops with no difference and just gave up.

Disc makes a BIG difference.

Brian
The memories.
Racing around town in my 67 drum/drum in 1979.
That's when I learned the limits of drum brakes.
O my surprise when the hot drum brakes wouldn't slow the beast.
Stopped by a nose. Learned my lesson for the day.
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Old 10-10-2010, 11:40 PM
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Quote:
Originally Posted by 001mustang
WOW!
I like it.

Oh Heck yeah they were awesome. And you know what, I had an experimental set from a 58 Ford T-Bird at one time! Yep, Kelsey Hayes made with the same basic design, I looked all over for documentation on them, close as I came was a late 50's Continental concept car Ford had made that never got anywhere. I sold them on Ebay (this was about 10 years ago). Don't remember what I got but I wish I had them today and continue researching them.

Brian
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