Why drum brakes? 3

[floattuber]

Why do manufacturers use drum brakes on passenger cars/trucks rather than disk brakes? Because of their simplicity, it seems like disks would be cheaper to build plus they stop better. What advantage do they have over disks?

 

[GregLocock]

lighter, cheaper, don't need a servo, don't squeal, don't get black dust on your wheels. Park brake actuation s non problematic.



Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[WGJ]

Top answer, take a Star.

Add better progression as well.
Drums can fade a lot when hot but that can be helped with modern lining materials and higher pressures.

Bill

 

[floattuber]

Thanks. This one has been bothering me for a long time now. I had a suspicion disks were in fact cheaper.

 

[GregLocock]

Without banging on about it - your park brake system in a disk brake is almost the equivalent in complexity of an entire drum brake, in some cases it IS an entire drum brake!



Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[dgallup]

I think the parking brake advantage is the only reason drum brakes are still around. Nobody is using them on front wheels. That & ancient tooling still being used in 3rd world countries like Michigan.

 

[Bribyk]

The rear discs and calipers on our 3/4- & 1-ton field trucks seem to take a beating from rocks thrown up by the front wheels. Surely this could be easily remedied, if not already done, but score another point for drum brakes.

 

[evelrod]

Current engineering (at least at the OEM level) dictates disc brakes in common usage. However, don't let the "modern theory" override common sense...There have been many very good drum brake systems in the past, some substantially better than the disc. In some of the racing applications in my past was a 948cc Austin Healy Sprite raced in the SCCA class of HP. I converted to the "modern" disc setup of later model BMC cars to "improve" my brakes...At that time, 1960's, it turned out to be a big mistake...the little drums were FAR superior to the disc setup of the time. Of course I did not convert back (I was not that smart) but continued to try to "fix" the disc brake...right up until I sold the car!!!

I suspect that the drum brake is pretty much history these days, not because they do not work, but because of advertising's influence on the market---drum/bad---disc/good!

Rod

 

[ivymike]

dunno... both of my vehicles (2005 and 2006 m/y) have drum brakes in the rear.

 

[thundair]

I like drums on the rear because of the easy progression
of braking. You can really notice it when I road raced my old Norton the feel on the drum was a lot better especially trail braking.
Anyways why put disk on the rear and use a brake bias valve to turn them down by at least 40%.

Cheers

I don't know anything but the people that do.

 

[rmw]

There is a saying in the heavy duty over the road truck/trailer size vehicle market (where you can fade out a set of drum brakes real fast on a long mountain downhill) that disc brakes will destroy themselves but save the rig (from a runaway) while drum brakes will destroy the rig but save themselves. When the drum brakes on a crashed runaway vehicle at the bottom of the gorge cool off they will work just fine. Too bad the rig they are on won't.

rmw

 

[swall]

Thundair--have you considered that the excellent rear brake feel on the Norton is due to mechanical rather than hydraulic actuation? So, maybe it is not a disc vs drum issue.

 

[thruthefence]

I had begun accumulating parts to convert my '70 Europa to rear disc brakes, but after looking at it from other then a war-story perspective, I realized the drums were lighter then my disc set up ( merkur )and offered no real advantage for my non-racing use of the car.

 

[evelrod]

I race a couple cars from time to time, both with rear drums. The Lotus Cortina's drums have never given problems in over 40 years of racing (we recently re acquired this car and it still has the OEM rear drums). The same drums that are on a Europa?

As to a Norton...I have one of the ES2/International race bikes, converted to street, from 1948 and it has very large mechanical drum brakes that work well...for a 1948 bike. Now for the BEST brakes I have used on a bike, I'll take my old '77 KZ 650's duel front and single rear hydraulic disc brakes....Anytime. I'm sure if they were that good in '77 the advancement in braking on bikes must be better today.

Rod

 

[izzmus]

"I think the parking brake advantage is the only reason drum brakes are still around. Nobody is using them on front wheels."

They are still being used on heavy trucks, yes on the front too...

 

[thruthefence]

I think the Europa's rear brakes, at least on the S2 are from the Triumph Herald/Spitfire parts bin.

 

[gt6racer2]

Actually, for all the reasons Greg mentions I think you'll notice a re-adoption of rear drums as small, cheaper cars proliferate. ( Yes, Japan, Korea - and EU too ). One early reason for the change to disc was (expected) difficulty implementing ABS, but that has proven manageable. Discs of course will stay on any vehicles desiring a sporty image, although, like evelrod, experience on my EP GT6 showed that drums worked* fine. ( * with the front grip /weight transfer of my nose heavy car on 9.5" slicks - I don't think they did much stopping )

 

[Rob45]

Izzmus, you're living in the past!
Drum brakes are on the way out in heavy trucks as well; disc brakes have the great advantage that they can dissipate prodigious amounts of heat to the air.
The big disadvantage of drum brake is that the friction surface is shielded from the air, except in rather specialized racing applications where the backing plates were cut away and air is ducted into them.

The big advantage of drums of course is that they can be designed to be self-energizing and self-adjusting.

There is one more advantage I have not seen mentioned here:
unlike disc brakes, drum brakes have no drag when released, and so contribute to better fuel economy.

 

[RossABQ]

Anyways why put disk on the rear and use a brake bias valve to turn them down by at least 40%.

Exactly! I had a Saturn with 172k miles and the original rear brake shoes (drum), they were less than half worn. (2150 lb car helps)

 

[patprimmer]

The disk brakes I have used are self adjusting.

If deigned correctly they retract enough to have no more drag than a well adjusted drum.

I would have thought for a front brake, a single spot floating calliper disk is less complicated and less costly than a twin leading shoe self adjusting drum of lesser braking power and similar space requirement. Rear brakes is a whole new ballgame or the reasons Greg mentions.

A rear disk with separate drum for the handbrake does add an extra but probably unnecessary safety factor.

Regards
Pat
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