Disc Brakes - Are they very expensive

for_cars1 · 12th March 2009, 15:07

Looks like the decision to have rear drum brakes is a purely cost based. (Drums cheaper compared to Disk brakes)

Source: [COLOR=#0000ff]http://www.edmunds.com/ownership/techcenter/articles/43857/article.html[/COLOR]

nitrous · 12th March 2009, 17:21

Quote:

Originally Posted by SB

But yesterday a colleague had a different take on this. He said parking brake applies to the front wheels. Reasoning being that when illegally parked vehicles are towed away, almost always it is the front which is lifted with only rear wheels making contact with the ground. If parking brake applied to rear wheels, they won't rotate and tyres would end up getting damaged due to car being dragged along.

You didn't know that the handbrake engages the brakes at the rear,Biju?

Edit: Your understanding is right and it is the gospel truth. You should have rubbished his hypothesis,then and there.

supremeBaleno · 12th March 2009, 17:34

nitrous, how come you missed the 1st line of that post of mine - given below ?

Quote:

Originally Posted by supremeBaleno

This is my understanding too.

EDIT: I knew I was right, but I was looking at the context he mentioned - towed-away cars being lifted usually in the front and rolling on rear wheels.

equinox22 · 12th March 2009, 19:07

Quote:

Originally Posted by goandude

Very valid point there. BTW how does a parking break work with rear discs.

There are two designs for a parking brake with the rear disk that I know of.
One is using the standard brake caliper alongwith an extra lever attached to a mechanical device inside the caliper piston. The parking brake cable pulls on this lever. The device then pushes the piston against the pads and applies the brake bypassing the hydraulic system.
The other system consists of a mechanical drum brake unit inside the rear rotor. The brake shoes are connected to a lever that is pulled by the parking brake cable.
Anyone know of any other systems?

goandude · 13th March 2009, 14:18

Quote:

Originally Posted by equinox22

Anyone know of any other systems?

I Think in the Gypsy there is a band which tightens around the propeller shaft. But this obviouslyworks for RWD only

sj_koova · 13th March 2009, 15:22

I guess, those who say, drum in the rear is as good as disk, own a car with drum in the rear. And most of the cars in India need only disk/drum setup as they are not fast enough to utilize all-four-disk setup.

We all know that the disk at the front is very much beneficial, as 70% if the weight is shifted towards front, but it does not mean that the rear can be weak. Disk at rear would definitely add up to the over all braking performance.
All four disks are much superior than disk/drum setup any day. There are ample information available on internet already

Now how many of you would have said "NO", if your car model came with a choice of drum vs disk in the rear at the same cost. I am sure all of you would have fallen for disk.

If it was not for the cost, I am sure most manufactures would have added disk in the rear too.

sgiitk · 13th March 2009, 15:27

The main disadvantage with drums is in the wet. While a disc spins itself dry, a drum does not. So if you happen to run through a water puddle then the drums are u/s for quite a bit. I remember being taught to drive some distance with the brakes lightly applied to dry them out after getting them wet. Otherwise in the dry most cars should be quite happy with rear drums.

nitrous · 13th March 2009, 15:38

^^Sir,drums also fade too soon.

inmate · 13th March 2009, 16:14

This may not be the entire reason for not having discs at the back...Just a thought

Disc brakes very basically are calipers clamping on to the discs when braking is required. This heats up the disc causing it to expand. Now assuming we had discs at the rear , the braking process would be the clamps holding the (expanded) disc tight. When this disc cools off ,it contracts to the origianal size, hence loosening the caliper's grip on the disc. We really wouldnt want the car rolling off.
This expansion and contraction works in our advantage when we use a drum , given that the expanding and then contracting unit is the drum( metal) envelops the calipers.When it contracts the grip becomes stronger.
Im sure there is a by pass solution to this problem now given that there are cars with discs in the rear.

Limpid · 13th March 2009, 17:35

If the disk breaks better than drum breaks, then there should be aftermarket options to install them. Has anyone replaced their car's rear drums to disks? Does this need lot of modifications? I've read in some other thread that ABS works better with all four disk breaks.

How much would it cost to replace Swift's rear drums breaks?

I've also seen there is size difference in front and rear disk breaks in some vehicles what decides the break size?

equinox22 · 13th March 2009, 19:21

@inmate: If that is the logic then the same should apply to the front disk brakes too right? And why would the clamps hold the expanded brakes in the first place? The brakes are not heated until they are applied. They would expand only when they are clamped onto, which would improve the braking performance.

@Limpid: The size difference for the disks is due to the fact that the braking requirement is greater for the front wheels. The same reason why some cars have disks at the front and drums behind.

Atlblkz06 · 14th March 2009, 17:03

I have never seen the parking/emergency brake work on the fronts - ever.

Found this in Wiki:
"Typically the rear wheels are the ones that are stopped with parking brakes. The Saab 99s, Pre-Facelift 900's, the Citroen Xantia and most early Subarus applied the handbrake force to the front wheels, which makes them notable exceptions."

Another design is to use an extra caliper on the rear discs for parking brakes.

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dinar · 15th March 2009, 10:50

Quote:

Originally Posted by Atlblkz06

I have never seen the parking/emergency brake work on the fronts - ever.

Found this in Wiki:
"Typically the rear wheels are the ones that are stopped with parking brakes. The Saab 99s, Pre-Facelift 900's, the Citroen Xantia and most early Subarus applied the handbrake force to the front wheels, which makes them notable exceptions."

Another design is to use an extra caliper on the rear discs for parking brakes.

Which car uses this type of brakes? with two calipers.

does anyone know how is the parking brake on the city with disc brakes? the previous version of VTEC.

SirAlec · 16th March 2009, 00:16

i think drum also have the habit of locking the wheel. which is very dangerous while driving on hills.

^^
hydraulic handbrakes are also there! i am not sure if city uses that

dinar · 18th March 2009, 10:51

Quote:

Originally Posted by SirAlec

^^
hydraulic handbrakes are also there! i am not sure if city uses that

I mean, is it caliper based system or is there a small drum for the parking brake.
Honda used a mechanical [cable operated] brake system on the caliper itself, for operation of parking brake. I want to know what it uses on the city in India? and does anyone [owners] know the price for these?

12th March 2009, 15:07	#31
for_cars1 Senior - BHPian Join Date: Mar 2007 Location: Bangalore Posts: 1,320 Thanked: 3,221 Times	Looks like the decision to have rear drum brakes is a purely cost based. (Drums cheaper compared to Disk brakes) Source: [COLOR=#0000ff]http://www.edmunds.com/ownership/techcenter/articles/43857/article.html[/COLOR]
	() Thanks

13th March 2009, 15:22	#36
sj_koova BHPian Join Date: Jan 2008 Location: Bangalore Posts: 677 Thanked: 623 Times View My Garage	I guess, those who say, drum in the rear is as good as disk, own a car with drum in the rear. And most of the cars in India need only disk/drum setup as they are not fast enough to utilize all-four-disk setup. We all know that the disk at the front is very much beneficial, as 70% if the weight is shifted towards front, but it does not mean that the rear can be weak. Disk at rear would definitely add up to the over all braking performance. All four disks are much superior than disk/drum setup any day. There are ample information available on internet already Now how many of you would have said "NO", if your car model came with a choice of drum vs disk in the rear at the same cost. I am sure all of you would have fallen for disk. If it was not for the cost, I am sure most manufactures would have added disk in the rear too.
	() Thanks

13th March 2009, 15:27	#37
sgiitk Senior - BHPian Join Date: Dec 2007 Location: Gurugram Posts: 7,971 Thanked: 4,799 Times	The main disadvantage with drums is in the wet. While a disc spins itself dry, a drum does not. So if you happen to run through a water puddle then the drums are u/s for quite a bit. I remember being taught to drive some distance with the brakes lightly applied to dry them out after getting them wet. Otherwise in the dry most cars should be quite happy with rear drums.
	() Thanks

13th March 2009, 15:38	#38
nitrous Senior - BHPian Join Date: May 2004 Location: UAE/Lon/Madras Posts: 6,965 Thanked: 329 Times View My Garage	^^Sir,drums also fade too soon.
	() Thanks

13th March 2009, 16:14	#39
inmate BHPian Join Date: Oct 2005 Location: bangalore Posts: 27 Thanked: 0 Times	This may not be the entire reason for not having discs at the back...Just a thought Disc brakes very basically are calipers clamping on to the discs when braking is required. This heats up the disc causing it to expand. Now assuming we had discs at the rear , the braking process would be the clamps holding the (expanded) disc tight. When this disc cools off ,it contracts to the origianal size, hence loosening the caliper's grip on the disc. We really wouldnt want the car rolling off. This expansion and contraction works in our advantage when we use a drum , given that the expanding and then contracting unit is the drum( metal) envelops the calipers.When it contracts the grip becomes stronger. Im sure there is a by pass solution to this problem now given that there are cars with discs in the rear.
	() Thanks

13th March 2009, 17:35	#40
Limpid BHPian Join Date: Aug 2007 Location: Bangalore Posts: 84 Thanked: 9 Times	If the disk breaks better than drum breaks, then there should be aftermarket options to install them. Has anyone replaced their car's rear drums to disks? Does this need lot of modifications? I've read in some other thread that ABS works better with all four disk breaks. How much would it cost to replace Swift's rear drums breaks? I've also seen there is size difference in front and rear disk breaks in some vehicles what decides the break size?
	() Thanks

13th March 2009, 19:21	#41
equinox22 BHPian Join Date: Mar 2009 Location: Chicago/Pune Posts: 165 Thanked: 6 Times View My Garage	@inmate: If that is the logic then the same should apply to the front disk brakes too right? And why would the clamps hold the expanded brakes in the first place? The brakes are not heated until they are applied. They would expand only when they are clamped onto, which would improve the braking performance. @Limpid: The size difference for the disks is due to the fact that the braking requirement is greater for the front wheels. The same reason why some cars have disks at the front and drums behind.
	() Thanks

14th March 2009, 17:03	#42
Atlblkz06 BHPian Join Date: Jan 2009 Location: Atlanta Posts: 164 Thanked: 25 Times	I have never seen the parking/emergency brake work on the fronts - ever. Found this in Wiki: "Typically the rear wheels are the ones that are stopped with parking brakes. The Saab 99s, Pre-Facelift 900's, the Citroen Xantia and most early Subarus applied the handbrake force to the front wheels, which makes them notable exceptions." Another design is to use an extra caliper on the rear discs for parking brakes. Note from Team-BHP Support : Please note that it is now imperative for you to upload pictures directly to the Team-BHP Server. Click here (Uploading photographs directly to Team-BHP) to view our simple help article on uploading pictures. Last edited by Rehaan : 16th March 2009 at 02:13. Reason: Please see note in post. I think you have been reminded of this before as well.
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16th March 2009, 00:16	#44
SirAlec Senior - BHPian Join Date: Sep 2006 Location: zxc Posts: 3,395 Thanked: 727 Times	i think drum also have the habit of locking the wheel. which is very dangerous while driving on hills. ^^ hydraulic handbrakes are also there! i am not sure if city uses that
	() Thanks