Disk Brakes

Makes sense. Thanks for such eccentric thought good one !!

bean counting is part of the answer, as disc brakes are more expensive.

but you also have to consider that only 25% of braking is applied to the front brakes.

also disc brakes dont work very well at low speeds but drum brakes do, so itas a compromise between high speed effiency and low speed .

and up till reently hand brakes operating on dis brakes were not teribbly good.

so the dru brakes were retained so hand brake could be connected to them

sorry for the coplex answer but it is complex

but you also have to consider that only 25% of braking is applied to the front brakes

well spotted. i could say i did that deliberatly to see if you were reading it

but sadly my old brain has trouble taling to my pingers (fingers)

yes it should be 75% to front brakes and 25 to rear unless the is a load sensor then it all changes according to load and speed

i will consider myself SLAPPED

But then, we don't really hold the brake drum thru hand brake lever, do we? I always have thought we hold some other part of the transmission system. Sorry for my layman ignorance.

auto matics have a pawl that engages when you put it into park but this isnt a brake

yes we do use hand brake on drum brakes

on some larger vehicles there is a transmision brake but on land rovers its a drum brake

http://en.wikipedia.org/wiki/Drum_brake

Drum brakes are still used in some modern cars because of some engineering and cost advantages. Drum brakes allow simple incorporation of a parking brake. They are often applied to the rear wheels since most of the stopping force is generated by the front brakes of the vehicle and therefore the heat generated in the rear is significantly less. Drum brakes are also occasionally fitted as the parking (and emergency) brake even when the rear wheels use disk brakes as the main brakes. In this situation, a small drum is usually fitted within or as part of the brake disk also known as a banksia brake.

Thanks! That was quite an information.

Very good point Pete. You beat me to it- small drum incorporated into the rear disk to serve as emergency brake. This set-up really works better IMHO than those tiny little pads otherwise used as emergency brakes on disks; those silly things will hold the car when stopped, but not much else in my experience. Rayzer

The rear disk brakes may be included as part of an optional sport package on some cars.

I've seen both drum and disk brakes on the rear car wheels.

These packages can add significant cost to the base model.

Disregard this statement, as it is obviously incorrect.

Thats not always the case, I had a V8 Falcon Panel van with 4 wheel disc brakes, had an occasion to cross a flooded road way, she wouldn't pull up afterwards till I'd driven quite a ways. Disc brakes will clear water away but only at speed...

Bye.

Wait another 2 to 3 years and you will understand why your "old" car had drums at the rear and why your new one shouldn't have had discs.

The answer is in one word: Rust

niels

In addition to the "beancounter" mentality discussed below add marketing considerations. Auto companies make relatively little profit on low priced models so they are always looking for ways to encourage buyers to "move up" and purchase the more expensive model. And one way is to put disc brakes on the rear, which explains why you can not buy optional rear disc brakes on low priced models. Rear disc brakes are not needed on a passenger car: drum brakes are more than sufficient. In fact, heavy duty trucks, which do need powerful brakes, invariably use drum brakes. I don't know the cost differential between drum and disc brakes when the manufacturer purchases millions of units but a caliper is certainly more expensive to manufacture than a brake cylinder.

I think it all boils down to the manufacturer trying to save costs or being cheap. I had a 99 dodge 2500 4 wheel drive truck that had conventional drum brakes on the rear wheels without anti lock. This truck had the 24 valve Cummings engine and it was a heavy truck when is came to trying to stop it. It did have the anti lock stuff on the I had to do a brake job on the front every 4 months because it was so hard on the pads. I kept the truck till last year and I never did replace the rear brake shoes.

MARKETING!!!!. Everyone feels 'excitement' about the implied NEED FOR disc brakes because 'they are a high speed driver' and everyone want to feel capable of being that high speed driver. In fact, properly designed and sized DRUM brakes are just as good for almost all passenger car and light truck service. Drum brakes are much less effected by road splash water, which can and will render disc brakes worthless till they dry off.

However, if long duration high effort braking is needed, a large ventilated disc fitted with cooling air scoops WILL dissipate more heat and resist heat fade somewhat better than a similar weight drum brake. That service is very seldom required in passenger and light truck service.

Heavy trucks use drum brakes because they need maximum braking at low speeds and on long grades. Also, it is easy to make the drum brakes 'fail safe' so they apply on loss of air pressure, which is very difficult to do with disc brakes. Also, a large open drum will better handle the heat dissipation at the low speeds heavy truck typically encounter.

Trucks also do not accelerate to high speed very quickly, giving the drum brakes more time to cool down between uses. High performance autos DRIVEN on race tracks MAY need the capability to brake from very high speed every few seconds and ventilated discs simply work better under those extreme conditions, when braking durability is more a function of heat dissipation capability than swept area or rotor /drum mass. A caliper (and the hydraulic fluid) are much easier to cool with blast air than is the 'cylinder' in typical drum brakes.

Disc brake assemblies , in the automotive size range, are more compact and weigh less than equal 'repetitive stop capability' drum brakes. Less Weight = improved fuel economy