disc to drum

[70orangeboy]

hey all, just finally getting the stuff to convert the front end to discs.
i was hoping you guys could give me some reasons why i want to do this.
i know there are some defiinite benefits but from what i understand, drums have more actual braking power, but the discs don't lock up as easy so does that make you able to stop faster, or what? a list of benefits is what i am after. please help

[cableguy0]

actually disk brakes are far better will stop sooner and have more clamping force plus the cool off ten times better. the drums trap the heat inside and cause pedal fade like crazy meaning you cant stop if you have to make a long hard stop. plus you dont have to constantly adjust disk brakes like ya do with drums. dont have to touch em until the pads wear out. i reccomend using ceramic disk pads they made a huge difference on my truck and i have installed them on a lot of vehicles in the shop the braking improved a lot

[70orangeboy]

i guess that disc don't lock up as easy so you can stop better , but drums have more actual braking force ,cause they are self energizing, which is why they lock up easier

[raggedjim]

Self energizing? I've heard of self adjusting, but I don't think I've heard of self energizing...

I've had both and I'd replace front drums with disc everytime. They are easier to work on, stop better and calipers are less prone to leak as cylinders. Just mt opinion.

Rg

[sneakysnake]

A few years ago 5 lug had a lot more rim options over 6 lug.

[70orangeboy]

self energizing means that when the brakes engage, they engage themselves more. as friction increases, the centrifugal force makes the brakes apply more and more

[1972]

I put rear disc brakes on my '79 K20 with 38.5" tires and it stops a lot better now. The rear disc upgrade on big 4x4's is popular because of the increased braking power and decreased stopping distance, I don't see how front disc could be worse than front drums.

[raggedjim]

Thanks, I learn something on here everyday!

Rg

[67ChevyRedneck]

Drum brakes DO NOT have more braking CAPABILITY thank disks....that a better word??? You can't compare the "force" because they operate completely different. Drums may have more force, but less stopping power due to pushing out and heat. Disks clamp and dissipate heat better. Why do you think ALL automobile manufacturers use disks up front, and a lot are now using them in the rear. I had drums on my 67 for 6 years, they sucked! I put disks on last year....holy crap....my truck STOPS when i want it to!!!!!! Plus, brakes are easier to change on disks. 2 bolts, 2 clips, repeat for other side, bleed, done.

[toddtheodd]

Originally Posted by 67ChevyRedneck

Drum brakes DO NOT have more braking CAPABILITY thank disks

Yes they do. How many vehicles have you seen with non-power disc brakes? It takes too much pressure to stop disc brakes without some sort of power assist. Oh sure, it can be done, but it takes a WHOLE lot more pressure than drum brakes. The problem with drum brakes is that they build up heat and gasses are trapped inside causing the brakes to not work. Disk brakes don't do this because there is nowhere for the gas to be trapped. Also, water was a big problem for drum brakes. Finally, you don't have to adjust disc brakes. So that means that your brakes will work the same way everytime you hit the pedal. Drums have to be adjusted. The more out of adjustment they are the more the pedal moves before they start to contact the drum. THAT is why automobile manufacturers switched to disc brakes.

And 70orangeboy, it's not centrifugal force that causes drums to stop better. It's because they "screw into" the drum when pressure is applied to them.

Finally. They still use drum brakes on 18 wheelers. Why? Because disc brakes wouldn't be able to lock up under 80,000lbs unless their was a HUGE power booster. Funny thing about big truck drum brakes is that they use air pressure instead of brake fluid. And they use the air pressure to hold the shoes AWAY from the drum. The only thing applying pressure to the brakes on that truck are the springs inside the drum. No matter how hard a trucker slams on the brakes, it's still the spring doing the stopping.
Todd

[Tx Firefighter]

Originally Posted by toddtheodd

The only thing applying pressure to the brakes on that truck are the springs inside the drum.
Todd

Actually, the springs are in the brake cannisters, which are mounted to the axle, not inside the brake drum anywhere. The cannister works a linkage that applies the brake shoes.

[vfrdude]

I have disc brakes without power assist, and I have no problems with the force it takes to stop the truck. It's at least as hard as drum brakes, maybe easier....Huge 18 wheel trucks are a lot different than 3500-4000 lb trucks.

[1972]

Finally. They still use drum brakes on 18 wheelers. Why? Because disc brakes wouldn't be able to lock up under 80,000lbs unless their was a HUGE power booster. Funny thing about big truck drum brakes is that they use air pressure instead of brake fluid. And they use the air pressure to hold the shoes AWAY from the drum. The only thing applying pressure to the brakes on that truck are the springs inside the drum. No matter how hard a trucker slams on the brakes, it's still the spring doing the stopping.

Drum brakes don't lock up either under 80,000 lbs. The springs inside the drum just keep the shoes off of the drum. The spring in the brake chambers (air canisters) is what is used for the parking brake. The brakes do work by air pressure, hence the "application pressure" gauge mounted in the dash. The steer axle and often 1 of the drive axles don't have parking brakes, therefore these brake chambers don't contain any springs, just a rubber diapham that moves when air pressure from the brake pedal is applied. None of this really applies here, just letting you know it works.

[67ChevyRedneck]

You can't compare pick-up truck brakes to 18 wheeler brakes, the design is different and have you ever seen the shoe size???? HUGE! By the way, it takes less pressure to stop disk brakes. Vehicles with disk front, drum rear have a proportioning valve, whether they are power assist or not. Usually somewhere around 40% to the front and 60% to the rear whereas in drum/drum its a 50/50 split. All power asssist does is reduce pedal pressure. Non-power disk/drum requires same pedal pressure as non-power drum/drum.

[67ChevyRedneck]

Crap, I said that backwards. It does take less pressure to stop disk brakes BUT it's usually 60% up front 40% rear to keep the rear brakes from locking. If you applied the same pressure to the back brakes as you did the front the back brakes would lock up first and the front would still have more stopping ability before lock-up, IE stronger brakes. The disks have more stopping power before lock-up than the rear do. Therefore less fluid is required to stop the rear brakes at the same pedal pressure. I've gone from drum to disk, you'll never convince me that drums have more stopping ability, excluding big rigs which operate completely different.

[toddtheodd]

Drum brakes don't lock up either under 80,000 lbs.

I've got a few truck drivers that could argue with you on that one.

Many drum brakes are self-actuating. Figure 5 shows that as the brake shoes contact the drum, there is a kind of wedging action, which has the effect of pressing the shoes into the drum with more force.

The extra braking force provided by the wedging action allows drum brakes to use a smaller piston than disc brakes.

This is a quote from How Stuff Works .com.

[1972]

Originally Posted by toddtheodd

I've got a few truck drivers that could argue with you on that one.

I am a truck driver, and in my 8 years driving I have been in many different trucks, and none of them will lock up the brakes with 80,000 (assuming it is distibuted legally - 12,000 lb steer axle, 34,000 lb drives, and 34,000 lb trailer axles). With 65,000 lbs and under, maybe; but not 80,000lbs.

[1972]

Originally Posted by toddtheodd

This is a quote from How Stuff Works .com.

Nice link, I never heard of "self-actuation" before, very informative.

[toddtheodd]

Originally Posted by 1972

I am a truck driver, and in my 8 years driving I have been in many different trucks, and none of them will lock up the brakes with 80,000 (assuming it is distibuted legally - 12,000 lb steer axle, 34,000 lb drives, and 34,000 lb trailer axles). With 65,000 lbs and under, maybe; but not 80,000lbs.

Almost 2 months ago. In Lewisville. Unfortunately he also laid it over on it's side.
There was 100 foot of rubber and flat spots on the trailer tires. He was fully loaded and headed to his first stop.
There was also a big brown stain in the driver's seat, but that is expected.

[70orangeboy]

thanx alot, i learned a lot. there is more force on drums, but they lockup quicker, with discs you can put down more pressure and not lock up so your threshhold braking is improved, so you can stop faster with discs, am i in the right ballpark?

[Kas68c10]

and a lot less maintenance, imo, I had em both as well, found the discs much better and easier,

[67ChevyRedneck]

Yup, Disk's have more stopping power per square inch, look at how much smaller the disk pads are then drums, but because of their design and size a proportioning valve is needed to keep the backs from locking up. Drums have more force on them because of thier size. More friction per square inch. On a proper set up disk brakes stop about 60-65% of a vehicles weight and the drums stop 35-40% Simple physics lesson for ya!!! That is why I have been saying disks have more "stopping ability", but drums have more force on them. It has to do with the area, square inches, of the pads themselves. If a set of disk brake pads had the same area, square inches, as drums do they would have TOO MUCH stopping power!!! Hope I've helped and not confused. To put it simply, go with the disks. My truck stops WAY better! I promise.

[3 on the tree]

Drum brakes lose their braking ability as they heat up. On a long downhill run, drum brakes can fail completely. This is not some rumor, I have had it happen to me. Also, water has a very adverse affect on drum brakes. I have driven through water and had to pump the drum brakes to get them to dry out and work again. If you drive through a puddle with just one side of the vehicle, the dry side drum brakes will pull you HARD to that side until the wet side dries out. All in all, for anything but a restoratiion, disc brakes are the way to go. You will have to use a disc brake master cylinder cause discs use displaces about twice as much brake fluid as a drum setup.

[whitesswj]

ok, i've read this post and I'm understanding the part where discs are better.

about the part w/ water, w/ mine i havn't had that problem and i've even tired to get some water in there.

then i have to ask myself this (keep in mind that i understand that you can't compare apples w/ cucumbers), Why haven't they made it standard for semi's to have disc brakes if they're "so much better". Mind you I've grown up in the Trucking industry i know a little about it.

and if you've got to stop in a fully drum car, you'll push hard enough to get the thing stopped, trust me, i have.

also, it is just this fact that makes me want to go to discs: Down hill stoppage. it's true that they can and will fail due to heat. but on the other hand if you drive proplery going down hill then you shouldn't be on your breaks enough for them to get that hot. use the next lower gear; let the engine do the work, take the curves a mile or two faster, slow down before you top the hill to go down it. but i can't seem to get the people in front of me to get off of their brakes so i can't so discs are the way to go just due to that person(s)

my .02, sswj

[Zeke]

I might be wrong but I think the auto companies went with disk because they cost less to make, fewer parts, doesn't mean they charge less, more profit. Disk can us smaller pads because dissapate heat better, again less cost more profit. Machining a flat surface vs basically the inside of a pipe perfectly round is cheaper. Disk are easier to work on. For those as old as me kinda like when the telephone companies switched from rotary mech switches to electronic switches, cheaper, more efficient, less maintenance, less room needed but they still charged extra on the bill when they upgraded.
Point disk are better overall.