Drum Vs. Disc

[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.

[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!

[Eddie H.]

I was pulling a trailer with my 69 GMC when the drum brakes faded out on me. I went through a busy intersection with both feet standing on the pedal as hard as I could. after that, I bought a front disc conversion kit. Disc brakes are far superior to drums. I used to be a pilot back in my younger days, and I've never once seen an aircraft equipped with drum brakes. You don't see Boeing trying to stop a 500,000 pound airliner with drums.

[magwakeenercew2jh]

I know for sure that disk brakes were installed in '71 on the front of our trucks because the grandfather of the engineer that started putting them on BMW's thought they looked cool through Mags.

Really.

I read it on the internet.

[trkfrk]

Hands down caliper/rotor combo looks better than drums on big wheels....