Drum Vs. Disc

[1972RedNeck]

Originally Posted by mrein3

Weight.
When the government tells you your fleet miles per gallon average has to be X, and you can remove 10 pounds of steel from each vehicle by using thinner metal, you do it.

Besides, with air bags, crumple zones, and a ton of other safety features your 3600 pound 72 Chevelle is less safe than your 2850 Chevy Cruze. Yes your fender gets totally mashed in a small fender bender but what price do you put on safety? Ask an ambulance chasing lawyer that question.

Why does Ford spec 5W-20 oil for their engines? Same reason. Oils are better now and if you can shave .1 mpg off the fleet by specifying thinner oil, you do it. Those tenths of a mile per gallon add up.

Ok, I'm done arguing and being an inquisitive idiot.

[trkfrk]

Drums

* Pro - Less expensive since they're already stock on most of our trucks
* Pro - Drums work better then discs as emergency brakes
* Con - They stop poorly when wet and can get clogged with mud
* Con - Stopping power can fade with repeated hard braking
* Con - Larger tires


Discs

* Pro - More consistant, straight line stopping power
* Pro - Dissipate heat better to stay cooler
* Pro - Less affected by water or mud
* Pro - Easier to maintain and faster to replace pads then shoes
* Con - More expensive to install (but maintenance costs should be less)

[67chevemall]

Drums are better and so are carbs.....old school = less parts and better built.
computers are better on your desk. ABS and FI, no thanks...I like me and my steel parts doing the thinking.


$0.02

[Dano69c10]

For those of us who were around "back in the day",
Remember disc brakes were implemented when the compression ratios of engines were decreased for emissions reasons.

I figure that unless you're running an old skool high compression engine, where your truck almost stops when you take your foot off the accelerator, discs would be the way to go.

Just my $0.02
Dano

[406 Q-ship]

Originally Posted by Dano69c10

For those of us who were around "back in the day",
Remember disc brakes were implemented when the compression ratios of engines were decreased for emissions reasons.

I figure that unless you're running an old skool high compression engine, where your truck almost stops when you take your foot off the accelerator, discs would be the way to go.

Just my $0.02
Dano

Not in cars........GM put disc brakes on the option list when the 375 HP/396 Ci and the 425 HP/ 427 CI was king, the trucks may have not gotten them until 71 but then none of the other manufactures were putting disc brakes on a truck until after 1971. In fact on SS Chevelles after 1969 Disc Brakes were a required option, so GM knew that they were much better than drums.

[Dano69c10]

Originally Posted by 406 Q-ship

Not in cars........GM put disc brakes on the option list when the 375 HP/396 Ci and the 425 HP/ 427 CI was king, the trucks may have not gotten them until 71 but then none of the other manufactures were putting disc brakes on a truck until after 1971. In fact on SS Chevelles after 1969 Disc Brakes were a required option, so GM knew that they were much better than drums.

1970 beginning of new smog regulations for car manufacturers.

[ProStreet68SB]

Originally Posted by 69heavychevy

thats like saying carbs are better than fuel injection...

Each has their own advantages.
Carb will make more peak power. But Fuel Injection will make more AVG power over the given RPM band.

Originally Posted by Dano69c10

1970 beginning of new smog regulations for car manufacturers.

What does smog have to do with brakes?

[Dano69c10]

Originally Posted by ProStreet68SB

...What does smog have to do with brakes?

I guess nothing.

[406 Q-ship]

Originally Posted by Dano69c10

1970 beginning of new smog regulations for car manufacturers.

Not right either, there was emission equipment as early as 1967 (A.I.R and PCV). The compression didn't start to drop until 1971 (minor drop) and plumeted in 1972.

[Dano69c10]

Originally Posted by 406 Q-ship

Not right either, there was emission equipment as early as 1967 (A.I.R and PCV). The compression didn't start to drop until 1971 (minor drop) and plumeted in 1972.

The new regulations that were implemented for 1970, were what led to lower compression engines.
What I've researched is that when GM engineers were testing vehicles with lower compression engines they found that the drum brakes were inadequate, and stopping distances greatly increased. (Implementation of PVC and A.I.R. had no effect on stopping distances, on pre-disc brake vehicles.)
Disc brakes then became mandatory in order to stop the newer vehicles in an acceptable distance with respect to safety.
Obviously if drum brakes were not doing to do the job and disc brakes can do the job, then it logically follows that disc brakes are better.

If my research is wrong, then so be it. I'm man enough to admit when I'm wrong.
But either way, (research right or wrong) my conclusion is disc brakes stop better than drums.

[VWBeamer]

Drums are lighter.

[Tkmadone]

What do the big semis use? Last I checked it was drum, and I'm pretty sure it's not because of cost.

Like has been said, there are advantages and disadvantages to both systems.

[ProStreet68SB]

Originally Posted by Tkmadone

What do the big semis use? Last I checked it was drum, and I'm pretty sure it's not because of cost.

Like has been said, there are advantages and disadvantages to both systems.

Big trucks are slowly switching to front discs.

[MARKDTN]

Originally Posted by ProStreet68SB

Big trucks are slowly switching to front discs.

Correct-this week actually is a major decrease in allowable stopping distance for road tractors. A lot are going to discs. There are some going with bigger drums and/or more aggressive shoe materials. The cost does increase some either way.

[brad_man_72]

Originally Posted by Tkmadone

What do the big semis use? Last I checked it was drum, and I'm pretty sure it's not because of cost.

Like has been said, there are advantages and disadvantages to both systems.

I've never seen a big truk do a panic stop without locking up multiple tires. In my personal experiene with the disc brake swap is that disc are easier to modulate near the limit of traction. My disc also stop straighter, really notice this when I'm pulling the boat.
I'll keep my disc brakes and my computerized efi engine with double the power and mpg than the larger carbed engine that was in it.

[Longhorn Man]

i'm not sure that discs were ever mandated... and if they were, it was much later than most think. The ford escore EXP in the early 80's still had drums up front.

[69sixpackbee]

Originally Posted by Longhorn Man

.The ford escore EXP in the early 80's still had drums up front.

That's because it was a roller-blade with two extra wheels

[stich626]

efi is better for costly more, not much else..
it was cold start emmissions and idle'n..
untill senquental(sp?) injection came along did the mpg really pick up..
batch fire injection puts fuel at the back of 3 intake valves that are closed and one thats open,,
but back to drums, if they could get the fade issue fixed, with todays abs and mpg goals, a 4 wheel drum system would be king, with 52mpg cafe regs coming don't be shocked if drums system makes a come back with the tires rim bing the drum ..
with todays offsets and the area aval. with 17" plus wheels,
remember everything old becomes new again.. abs/air bags, efi are not new..
just the tech and materials needed came along to make it work..
remember the caddy 4/6/8 , that same idea is the only reason the v8 is still on America's roads inforce..

[VWBeamer]

THe MPG's really didn't improve until the OD trans started coming, but EFI let them meet emissions at the low lugging RPMs od transmissions allow. They go hand in hand.

Originally Posted by stich626

efi is better for costly more, not much else..
it was cold start emmissions and idle'n..
untill senquental(sp?) injection came along did the mpg really pick up..
batch fire injection puts fuel at the back of 3 intake valves that are closed and one thats open,,
but back to drums, if they could get the fade issue fixed, with todays abs and mpg goals, a 4 wheel drum system would be king, with 52mpg cafe regs coming don't be shocked if drums system makes a come back with the tires rim bing the drum ..
with todays offsets and the area aval. with 17" plus wheels,
remember everything old becomes new again.. abs/air bags, efi are not new..
just the tech and materials needed came along to make it work..
remember the caddy 4/6/8 , that same idea is the only reason the v8 is still on America's roads inforce..

[ProStreet68SB]

Originally Posted by stich626

efi is better for costly more, not much else..
it was cold start emmissions and idle'n..
untill senquental(sp?) injection came along did the mpg really pick up..
batch fire injection puts fuel at the back of 3 intake valves that are closed and one thats open,,
but back to drums, if they could get the fade issue fixed, with todays abs and mpg goals, a 4 wheel drum system would be king, with 52mpg cafe regs coming don't be shocked if drums system makes a come back with the tires rim bing the drum ..
with todays offsets and the area aval. with 17" plus wheels,
remember everything old becomes new again.. abs/air bags, efi are not new..
just the tech and materials needed came along to make it work..
remember the caddy 4/6/8 , that same idea is the only reason the v8 is still on America's roads inforce..

Thats funny because because I look at cars that get great MPG. (Geo Metro, VW Polo, Honda Insight, etc etc etc) All have disc brakes on the drive wheels if not all the way around.

Lets also not forget that the piston seal in a caliper, brings the pistonback in when pressure is realeased, there for you should have zero to unnoticeable amounts of drag.

Lets also think about this from a manufacturing stand point. Cheaper is better, thats plain and clear. Ease of maintenance for factory techs. Drums yes are "cheaper", but at the factory that's more stuff they have to assemble on the vehicle there for making it more expensive in the eyes of the manufacturer. Drums take longer to service than disc brake setups. Why choose to take the more time consuming route when you can, take the easy way out and still charge the same amount of money.

[Daves70]

I recently converted my 67 to disks.This was after building a healthy motor and a OD swap.On my next project the FIRST thing I will do is the disk brake swap.When these trucks were built there were alot less cars on the road and even less idiots.I am guilty of it but I think it is stupid to do performance modifications without adressing the brakes first. JMO

[aussiejohn]

G'day,

In answer to Redneck's original question, I offer the following. Vehicles slow down due to four main facors, wind resistance, rolling resistance, off-accelerator engine drag and the friction generated by applying the brakes.

Automotive companies look at all four when designing a car, even a truck these days. No vehicle manufacturer releases a car for sale that has not been tested in a wind tunnel. Low drag bearings and low viscosity oils are used to minimise rolling resistance. Compression ratios have come back up from the seventies due to more efficient fuel and spark delivery.

But the biggest advance in stopping a car is in the braking department. Stopping a car (or truck) relies on the amount of friction generated by applying a stationary friction pad to a rotating piece of cast iron. The bigger the size of the pad, the more friction there is, but this is all dependent on the amount of force applied to the pad.

On the same size and weight car, a drum brake will generally have more square inches of friction material than that on a disc braked car. Therefore less force is needed to be applied to the pad in order to generate the same amount of friction, and therefore stopping distance. That is why virtually all cars up until the sixties and early seventies had non-power drum brakes.

That was all that was needed for the traffic conditions of the day. However, as the post war affluence filtered through to the car manufacturers and they made more cars and the cars they made got heavier, stopping distances increased. To overcome that, the driver had to apply more pressure to the pedal, and this was felt more by the so-called weaker sex, whose leg muscles were in many cases, less than those of a male.

This is why vacuum power boosters were offered, first as an option and then as standard. This worked well for a while but, as the wages went up and the relative price of the cars came down, the amount of road traffic went up. More cars on the same amount of roadway meant that the gap between cars on the road became less and less. Motorists were starting to use their brakes more often and this is where the drum brake's major disadvantage began to show itself.

Brake fade! This condition is caused by a lack of heat dissipation. Science tells us that as a metal heats up, it expands. Brake drums do exactly that when they get hot and they expand AWAY from the friction material. As well as that, the friction co-efficient of a hot cast iron brake drum is LESS than that of a cold one.

So, when a drum brake gets hot, its ability to slow the car becomes less and less. A drum brake also takes longer to cool down, as there is no natural way for it to dissipate its heat, other than by radiation of that heat, and that takes time.

However the disc brake, particularly the ventilated variety, solves all of that. As well as having two friction surfaces instead of one, the disc takes longer to heat up. Then, due to the hollow nature of the vents in the disc and the naturally occurring centrifugal force of the spinning rotor, cold air is "sucked" from the centre of the disc up through the vents, cooling the cast iron and expelled as hot air.

This is the main advantage of discs over drums. Heat dissipation.

The only real downside is that the driver needs to exert a lot more force on the pads for them to slow the car, and that means a booster is required. And this adds cost and complexity to the car. However, most people agree that this is a small price to pay for a far superior overall braking system.

There is only one area where a drum is far superior to a disc and that is as a parking brake. Much less effort is required to apply a drum parking brake than for a disc parking brake (of a similar amount of friction material) for the same amount of cold static friction.

That is why the 1965 Corvettes had the most advanced braking system in the world when introduced. They had huge ventilated discs on all four wheels, but still had small drums incorporated into the rotor for the parking brake in the rear hub assembly.

As an aside, I drive buses for a living, and all of the new buses we get have disc brakes at each end. And they are all power boosted, but by air pressure rather than vacuum or hydraulic assistance.

I am not a certified mechanic, and all of the above is based on my many years of working on cars and the knowledge I have picked up from people I've met who knew more than I did. And I'm still learning.

Regards from Down Under.

aussiejohn

[1968CHEVYC10]

In 2007 GM switched all of their 1/2 ton trucks back to rear drums, wonder if emission requirements had anything to do with it.

[Longhorn Man]

Originally Posted by 1968CHEVYC10

In 2007 GM switched all of their 1/2 ton trucks back to rear drums, wonder if emission requirements had anything to do with it.

It was before 07... we have an 05 at work with drums.
Regardless, brakes have nothing to do with smog requirements.

There are a few reasons to do this;
1 Better parking brake
2 last longer with far fewer service intervals (100k out of rear drums with zero maintenance is common)
3 less drag which equals better MPG.
4 cheaper
5 less weight (even better MPG, but fractions of a MPG)

The MPG thing is a huge one, being that GM (and all other auto makers) need to meet CAFE requirements. So even a .25 MPG increase is a huge thing for them to meet the requirements put on them by the feds.

[Pont406]

EFI is mostlly to keep three way cat alive!