This is a little off topic. Is the manufacturing cost of drums really lower than discs? I guess I don't understand the use of drums still.

 

drums last longer than discs but discs are more efficient for stopping

 

For info see
http://www.edmunds.com/ownership/tec...7/article.html

Today's modern designed brake systems especially with ABS are completely adequate for stopping standard cars, SUVs or trucks.

Drum brakes are cheaper and simple and will work for the rear brakes just fine since they are not required to do the bulk of the braking duties assigned to the front disc brakes. Even if a little money can be saved by having discs in the front only this saves for every car made. This would be completely different if the cost were essentially the same but they are not.

An easy way to find the difference in cost would be to find a modern Honda like the CIVIC and part out the cost of a set of rear drum brakes (standard on the LX) vs a set of rear disc brakes (standard on the EX). Just include all of the needed parts and see how it would be in a relative sense. Find out if the disc option is roughly 40% more expensive or whatever.

Since the FIT is light weight it doesn't need huge brakes and four wheels discs. It would if you load it up completely or you are towing something heavy.

Discs handle heat build up and performance driving much better than drums. Most times for street use this is not an issue except going down long steep hills.

 

I understand the performance aspects. But I guess it had always seemed to me that the design of disc brakes was beautifully simpler and didn't look like it would be significantly more expensive if at all. Why are drums cheaper?

 

From-
http://auto.howstuffworks.com/drum-brake.htm
Quote:
Drum brakes have more parts than disc brakes and are harder to service, but they are less expensive to manufacture, and they easily incorporate an emergency brake mechanism.

Compare with-
http://auto.howstuffworks.com/disc-brake.htm
Maybe the cost of the rotor (with solid disc vs vents, finishing and close tolerances), caliper with larger (floating- self centering/self adjusting) piston (than with the drum brake), or separate emergency brake linkage mechanism for rear disc brake, adds up for higher manufactoring costs.

Here is an old study from Feb 1983
http://www.nhtsa.dot.gov/cars/rules/...te/806359.html
Change the cost to today's $$$ but the difference is fairly small.
Cost of lifetime front disc vs drum brakes in 1982 dollars $21 per vehicle.
Only $2.90 initial cost increase.

The annual costs of the improvements in the United States [in 1982](based on 10 million cars sold) are $170 million for dual master cylinders and $210 million for front disc brakes.

 

I had converted my Corolla's rear drums to discs a while ago (made a huge difference on course). It was very easy to do. I didn't really notice anything "extra" for the e-brake cable. It's not like my EVO which has a separate set of drums just for the e-brake, which isn't necessary for most cars.

 

Aren't drums slightly lighter weight, in equivalent size, than disc brakes?

 

More imprtantly, when will conversion kits be available for the US?

 

I just saw a post a few days ago about an available conversion.

https://www.fitfreak.net/forums/showthread.php?t=8519

JonasM

 

i like the way drum brakes work more, but i like the looks of disks in the back

 

huh? why?

 

Very true.

I have been around a couple older Citroen cars that had the emergency brake on the front (inborard) discs. This was done with an addional mechanical caliper (top left in the photo, normal hydraulic one at bottom right):



But, as I said, this was an inboard application, so this would be difficult with outboard due to cables and steering.

Now, there is another problem with this arrangement. When metal cools, it contracts. So if you set the brakes when hot, as the disc cools, it shrinks. These calipers (when in good condition) had springs that compensated for this, but if something stuck, you had the potential for the car to move as the pads were not gripping metal but air.

You also have two sets (in several cases, there was one Citroen where the main pads/caliper had a built in option for manual application) of pads to replace.

So many of the typical rear disc brake is actually a disc/drum with a small mechanical drum on the inside. Here are a set of Mercedes rear rotors to show both surfaces:



So here is an additonal cost in manufacture and maintenance. It also added unsprung weight. A friend that raced Alfa Romeo sedans always removed the e brakes for this reason.

The disc only e brakes would be similar to the situations listed above, with the mechanisim for the emergency brake on the main caliper. I *assume* the conversion kit link in this thread for the Asian/European Jazz uses this method as his kit included the cable but no other brake hardware. Ditto to the Corolla conversion mentioned I assume?

Now, back to rear drums, all you need to do is incoporate the spring/ratchet mechanisim into the existing shoes to activate these. You can also use the contraction of cooling to your advantage as the drum shrinks, the shoes continue to hold.

Hope this explains the original question.

 

it lasts longer and it doesn't create much brake dust

 

Spule, so your point is that discs aren't as effective as a parking brake because the discs contract as they cool? I agree with that, and that's why I park in gear and, on steep hills, use wheel chocks. I'm not sure if I'd consider this an "advantage" of drums.

Any manufacturing guys out there?

 

I'm not sure that's an advantage from the manufacturer's perspective. I guess that's good for the end user because drums are crap to work on compared to discs.

Most of the brake dust is inside the drum. With drums, I regularly take off the drum to pour out the dust.

 

No, not an advantage, you missed my point, but I did not make it clear.

With rear drums, there is less cost, you can accomplish everything with the drums and without added emergency drums or compensation on the brake caliper.

The parking brakes on a rotor have the disadvantage I had above. Yes, parking in gear will help.

 

In the UK all Jazzes have disc brakes front and rear. Only very cheapest cars are now sold in Europe with drum brakes.

Will ABS work with drum brakes?

 

Rear drums were still good enough for the Spoon endurance race car.

 

The only reason drums still hang on is manufacturers who already have the equipment basically do them for cost.
Discs on the other hand are pretty specific and have some efforts needed to handle parking, aka emergency, brakes.
Disc brakes otherwise are cheaper to manufacture and are a great deal more efficient at slowing wheel rotation than are drum brakes. Drum brakes are far more complicated and have many more components.
There is a reason no respectable performance vehicle has drum brakes up front where 80% or more of the braking happens between front tires and the road.
Front wheel drive vehicles only have rear wheels to keep the rear bumper from dragging. OK, its a joke but it truly describes the braking, driving, and steering end of the Fit.

 

On our cars with the central gas tank, unless you have the back full of bricks or are towaing a trailer. the rear brakes are more than adequate since they are only stopping approximately 10% of the vehicles weight