Disc brakes vs Disc/drum brakes

[Ratbag]

^^ Rally, I am not, and never have, suggested that drum brakes are superior to discs. What I have said is that they aren't the villain of the piece either ...

I have also never suggested that disc brakes are in any way inferior.

Please don't generalise specific comments I might make about specific vehicles to apply equally to all vehicles, both past and present.

The XA and its predecessors and descendants in standard form are a perfect example of under-engineered cars at almost every level, not just brakes and suspension.

A late 1960s/early 1970s Falcon/Holden/Valiant with disc/drum brakes would stop from 60 mph in between 170 and 180 feet, under ideal conditions. Under the same conditions, most British and European cars of the times would stop from 60 mph in between 130-140 feet. Now, that is a huge, significant difference.

Interesting to watch the Fords and Holdens at Bathurst being passed at the end of Conrod straight by the BMC Works racing Cooper S cars back then. The Holdens and Fords had to start braking a long way before the corner ... It wasn't just their poor handling, it was also their poor braking.

IMO, Ford cars produced in Australia live up to the dictum of Henry Ford III (IIRC), that "When the public is prepared to pay for safe cars, Ford will make safe cars.". I'm still waiting ... :lol:.

My examination of various Ford produced cars over the years has led to my conscious decision never to travel in a Ford motor car. They scare me with the minimalist approach to serious structural and design features, both of running gear and body structure.

I have never had brake fade in any of my BMC cars - not even in the fully drum-braked Mini. Not even when driven with the "I am immortal and indestructible" attitude of youth and inexperience.

Ditto my LC with it's drums all round.

My original comment was that "I actually prefer front discs and rear drums ...". This could be because I have never owned an under-engineered car in my life, and am not about to start now.

 

[guzzla]

Interesting to watch the Fords and Holdens at Bathurst being passed at the end of Conrod straight by the BMC Works racing Cooper S cars back then. The Holdens and Fords had to start braking a long way before the corner ... It wasn't just their poor handling, it was also their poor braking.

Do you remember watching the first Bathurst race where the first series XU-1 Toranas with the 186 engine were up against the Falcon GT? On the first lap the Falcon went to the front with extra performance up the mountain but at the end of Conrod Straight the Torana whistled past the Falcon under brakes. It stayed ahead for a few laps but couldn't sustain the pressure. I can still remember all the Holden fans screaming like crazy as that Torana headed the Falcons up the main straight at the end of that first lap. Weight was a big factor there.

I really miss the series production racing we had in Australia during the 70's.

I also remember when the Falcon GT's went to rear disc brakes for better braking performance but the XU-1's never did.

 

[guzzla]

As Kevin has said, it crossed my mind last night just to delete the whole lot as OT.

Noooo, don't do that - you're a library of interesting information from another era that some of us (senior oldies) can relate to.

 

[Ratbag]

^ And "this" era?

Want to discuss theories of gravity? Light? Quantum mechanics ("QED" in today speak)?

Genetics?

Aetiology of disease processes?

Computers and computing?

Plate tectonics?

Pre-Cambrian fauna?

How brakes actually work?



Sorry, I'm neither feeling well today, nor am I in a good mood (partly because of it ... ); so a bit touchy - not as in "touchy-feely" ...

 

[Ratbag]

Do you remember watching the first Bathurst race where the first series XU-1 Toranas with the 186 engine were up against the Falcon GT? On the first lap the Falcon went to the front with extra performance up the mountain but at the end of Conrod Straight the Torana whistled past the Falcon under brakes. It stayed ahead for a few laps but couldn't sustain the pressure. I can still remember all the Holden fans screaming like crazy as that Torana headed the Falcons up the main straight at the end of that first lap. Weight was a big factor there.

I really miss the series production racing we had in Australia during the 70's.

It was wrecked by the progressive introduction of cars that never saw a road in their life. My father's Torana was one of the road versions of the XU-1, in effect. I managed to take off at a T intersection without spinning the wheels on one occasion. Turns out I was in third, not first ... Mongrel of a thing to drive.

BTW, the Bathurst 500 started in the mid-1960s:
https://en.wikipedia.org/wiki/Bathurst_1000

Taking my father and two sisters to my mother's funeral, it managed a whole 13.5 mpg at a steady speed on the open road ...

I also remember when the Falcon GT's went to rear disc brakes for better braking performance but the XU-1's never did.

They never actually achieved an acceptable level of braking or handling, IMNSHO. The phrase "cheap and nasty" springs all too readily to mind ...
Primary and secondary safety were so bad that the model range killed itself off, as well as many of its occupants ...

 

[havachat]

Reading this thread reminds me of the arguments that were had in the 1970's with the advent of radial tyres replacing cross ply tyres
People who weren't driving then will probably have no idea what I am on about

I am trying to resist getting involved in this one having owned a fleet of cars from the 1950's and 1960's

 

[Ratbag]

^ Gidday HC

Like seat belts. As soon as they became available, I had them fitted to my car/s - even though this involved drilling a hole right through the centre pillar and putting reinforcing plates there. The BMC cars were pre-fitted with lap belt anchor points ... Just not the upper mounting for lap/sash belts.

I immediately saw the point of being held in position behind the wheel from a primary safety point of view. Hard to steer or brake if you are sitting on the passenger's lap, or them on yours ...

I had Michelin X tyres on my Morris 1100 (and Veith; and Vredestein).
I fitted Avon radials to my Wolseley 24/80 almost immediately after buying it s/h. They were OEM fitment on Rolls Royce at the time. They made a dramatic difference to the whole performance of the car. So did fitting the 3x 1.25" SU carburettors ... . For a dinosaur, it wasn't a bad car.

Since then, the only car (truck ... ) I have ever run cross ply tyres on was my '68 LC.

 

[Rally]

The 60's was an era of cars like the super light Mini's and over powered muscle cars. The Mini's got away with their brakes because they were so light. People tend to only look at Bathurst, which suited the muscle cars like the GT-HO because brakes and handling were less critical there. Go to Warwick Farm or Amaroo and the scenario changes.

Allan Moffat always said the worst thing about the GT-HO were the brakes. Sure, Ford put extra wide finned drums on them, but they really were not good enough. The front discs should have been bigger too. But take a smaller car, like the Torana SLR 5000 and L34. Both had real braking problems and they were much lighter than a GT Falcon. They also had rear drum brakes. That issue was addressed with the A9X when it finally switched to rear disc brakes.

The problem for drums are:
1) They retain a lot more heat than discs do. Heat dissipation is what any good braking system requires. You could say that braking is turning kinetic energy into heat energy.
2) They are more difficult to maintain
3) They are more easily waterlogged and take more time to recover from a water crossing.
4) The choice of linings is more limited than with pads. There is a large range of different pad compounds for different types of driving. It is more difficult to get that choice with linings.
5) By their very design, drum brakes are more likely to lock than discs.
6) Drum brakes are much harder to upgrade. You cam relatively easily get slotted rotors or even bigger rotors and callipers. With drums, you are more limited, often to drilling holes or, if lucky, installing finned drums as well.

Manufacturers went to rear discs, despite greater manufacturing and engineering costs, because they worked better and that is the way the market went. Ford actually made rear discs standard on the GT Falcon in 1973, and across the Falcon range in about 1986 or 1987. Subaru went to rear discs across the Impreza range in 2000. As for Rolls Royce, they stayed stagnant in motor vehicle design until the 90's or something. That is when they finally got rid of the ancient 6.75 litre pushrod V8 and GM TH400 gearbox 30 years after Mercedes had done the same. They held on to 4 wheel drums until he 70's I think. Their anti rust treatment- numerous oil leaks from all over the car- survived almost till the 21st century.

 

[ateday]

I think I must hold the record for Michellin X tyres.
On my 1968 Renault 10, running on, I think 135X380 tyres I managed to wear them out in about 30000 miles........
It went around corners well though, with just a tad of body lean, and had 4 wheel disc brakes.

 

[Ratbag]

The 60's was an era of cars like the super light Mini's and over powered muscle cars. The Mini's got away with their brakes because they were so light.

Minis "got away with" their brakes because they were adequate to the task ...

The problem for drums are:
1) They retain a lot more heat than discs do. Heat dissipation is what any good braking system requires. You could say that braking is turning kinetic energy into heat energy.

It is precisely how brakes do work; then having sufficient disc to pad area and air flow over them to dissipate the heat at least as fast as it can be generated by the friction of the pad on the disc. If it cannot do this, no amount of pressure of pad on disc (or shoe on drum) will do anything, and the brakes will have "faded".

2) They are more difficult to maintain
3) They are more easily waterlogged and take more time to recover from a water crossing.
4) The choice of linings is more limited than with pads. There is a large range of different pad compounds for different types of driving. It is more difficult to get that choice with linings.
5) By their very design, drum brakes are more likely to lock than discs.

Not necessarily. Brakes tend to bind because the surfaces are not smooth. That is why machining or skimming discs is important, as is honing drums, if either are uneven or otherwise not 'flat'

6) Drum brakes are much harder to upgrade. You cam relatively easily get slotted rotors or even bigger rotors and callipers. With drums, you are more limited, often to drilling holes or, if lucky, installing finned drums as well.

Most decently designed cars did not require brake upgrades in order to perform adequately; even when substantially modified the way my Morris 1100 was.

Manufacturers went to rear discs, despite greater manufacturing and engineering costs, because they worked better and that is the way the market went. Ford actually made rear discs standard on the GT Falcon in 1973, and across the Falcon range in about 1986 or 1987. Subaru went to rear discs across the Impreza range in 2000. As for Rolls Royce, they stayed stagnant in motor vehicle design until the 90's or something.

This is simply not correct.

The Silver Cloud and prior had a full chassis. The Silver Shadow and later were all monocoque construction, with sub-frames. The Silver Shadow saw the introduction of 4 wheel disc brakes and independent suspension. The former performing better than the already excellent 4 wheel drums they replaced.

That is when they finally got rid of the ancient 6.75 litre pushrod V8 and GM TH400 gearbox 30 years after Mercedes had done the same. They held on to 4 wheel drums until he 70's I think. Their anti rust treatment- numerous oil leaks from all over the car- survived almost till the 21st century.

For all that, a Silver Shadow Rolls was nearly as fast as an E-Type Jag 0-100 mph, and nearly as fast from 80 mph to stopped. Not bad for a car that weighed what it did.

If you want to look at excellence of design parameters, Rolls Royce have always been more than adequate to the task.

Build quality is better in almost all modern cars because they are largely built by robots, and therefore the human element is all but removed.

You have to remember that it was a commonplace in the post-WWII period until around 1975 for cars to require extensive maintenance and engine gearbox rebuilds by around 50,000 miles. That was not the case with Rolls Royce cars.

And please, no anecdotal stories about the Holden taxi that purportedly did a million miles, depending on the story variant, on the same set of tyres ... .
The documented average for the old fashioned London taxi was around 4,000,000 miles at the time. It is also well known that cars that never get cold will last far better than those that are started and stopped a lot. This is as true today as it was then.

 

[NachaLuva]

Rally, that pic of your WRX brakes is pure brake porn!

I think we all agree that brakes that are matched to the car (& driver demands Rally haha) is what is needed. The trouble with drums is that there arent many cars that are light enough for them to be suited to. As has already been mentioned, there are a number of other issues with drums.

Basically, IMO drum brakes are just old technology. Like halogen driving lights. They're cheap but nowhere near as effective as HIDs. Then there's LED lights which are rapidly becoming the best option.

Drums are just last centuries technology...

 

[El_Freddo]

Awesome - a disc and drum discussion.

Drums are still on a lot of trucks due to cost and simplicity of production.

Drums are more effective at braking - until they get too hot.

Discs are more effective at cooling and therefore have a better braking capacity/potential to be build into them.

More trucks and trailers are being fitted with disc brakes from the factory. Discs are easier to maintain/service in general and the technology has gone a lot further.

That's all for now - continue with the argument/discussion

Cheers

Bennie

 

[Rally]

Yeah, I love by brakes. One thing to keep in mind about truck brakes is that all the big trucks run air brakes. So while there will definitely be heat in the shoes and drums, that is about it. there is no hydraulic fluid to boil. But the big issue for these trucks is that they must be adjusted. Many truck accidents occur because the adjustments have not been done. Still, one should be careful about comparing road cars with trucks. What works in one does not always work in the other. After all, there are trains out there with disc brakes, and trains are heavier than trucks.

 

[Douglas Ferrier]

I am staggered there is even discussion on this.

Having serviced both
Drums = PITA
Disks = ohh so much easier

Heat dispersion and retaining linings at optimum temperature for the friction surfaces is the magic to produce the best brakes both designs can achieve this, the operating performance range on a disk is nominally much higher due to the ability to disperse heat.

The rotational mass on a disk is less than a drum which can perform to an equivalent level , which means less energy goes into rotating mass and thus a more responsive and efficient vehicle - drums will be dead before our lives finish!

For those that like drums enjoy them while you can - scarcity before extinction will be just like peak oil, only a few will win and I doubt we are among them :iconwink:

 

[Rally]

Drums are best left for rock bands I reckon.

 

[Ratbag]

This thread is now locked, as most commenting do not appear to have read what was said.

 

[Ratbag]

After some discussion with another admin, and one response to my PM to all participants, I have decided to open this thread again.

Please keep the smart comments to a minimum, or at least indicate your intentions by using Smilies, as these are often the only way that others can discern the intention of the poster.

Might I suggest that any participants or readers read the pretty complete article on Wikipedia about brakes. It is here:

https://en.wikipedia.org/wiki/Disc_brake

Here is a link to an article discussing drum brakes:

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

Note also the section on the use of slotted rotors on racing/rallying and road cars here:

https://en.wikipedia.org/wiki/Disc_brake#Brake_disc

Particularly:

Discs may also be slotted, where shallow channels are machined into the disc to aid in removing dust and gas. Slotting is the preferred method in most racing environments to remove gas and water and to deglaze brake pads. Some discs are both drilled and slotted. Slotted discs are generally not used on standard vehicles because they quickly wear down brake pads; however, this removal of material is beneficial to race vehicles since it keeps the pads soft and avoids vitrification of their surfaces.

{emphasis added by RB}

IMHO, the single greatest innovation with disc brakes was the separation of the friction surfaces that generate heat converting the kinetic energy of the car into heat energy, from the heat dissipation surface/s that radiates this heat away. This is achieved by the use of ventilated discs.

With solid discs, the friction generating surface and the heat dissipation surface are both the same (approximately true ... ). This is far from ideal.

With ventilated discs, the friction surface is always bright and shiny, but this is not the best for the re-radiation of the heat generated. The internal surface is far larger in area than the friction surface, a fact enhanced greatly by the rough surface of the raw casting. It is also dark coloured, and this enables the disc to shed heat better as it more closely resembles a theoretical 'black body' from a radiation perspective.

This occurs (in reverse) the same way a white shirt is cooler to wear on a sunny day than a black shirt.

To reiterate my own position on this subject:

Even I don't agree with the idea that drums are superior to discs, but they aren't as bad as some make them out to be, either.

What I was trying to get across is that under-engineered brakes are no good, regardless of whether they are discs or drums or both.

Properly engineered brakes work properly, regardless of whether discs or drums or both.

Neither will stop one getting killed if one drives recklessly or badly ...

 

[Kevin]

My 2 cents: For offroading brakes I prefer my Foz to the Trition. The Foz has slotted discs all round whereas the Triton has drums in the rear. The slotted discs clear the crap away very quickly and do not suffer from brake-fade as easily on steep descents. After being in sloppy mud or wet sand, the Triton's drums are next to useless for a while; the build up of crap even stops the handbrake from working - lucky to get it up once notch. I would be very happy if I had slotted rotors all round on the Triton as well.

 

[Ratbag]

Gidday Kevin

I can understand that ... :iconwink: :lol:.

But it does illustrate what I am trying to get across about design/engineering of the components. I drove my '68 LC through all sorts of garbage, often towing a tandem axle double horse float. I never experienced any kind of problem with its drum brakes. Not after water, mud, rocks, sand, bunnies (that's another story ... :iconwink: :rotfl or any combinations thereof, not with the handbrake; nothing. They just worked.

Of course, one should always follow the procedure after water immersion of gently applying one's brakes for a bit to dry them out. This applies to discs as well as drums, but drums do take longer to dry out to an acceptable level, and discs are more vulnerable to scoring from sand, mud and gravel, as a general rule.

When I was in the USA in the late 1960s, I drove a number of cars, including a Camaro 350 SS; a Potvin blown Shelby Mustang 500; 302 'Tunnel port' Mustang (hire car); Pontiac Firebird; Fiat 500 (my flat mate's ... I made it work again ... :iconwink; Fiat 125 Sports (we didn't get this one here); and a couple of others.

Apart from the two Fiats, they were all incredibly bad for brakes, suspension and steering. Woeful, in fact. At suburban speeds they were barely acceptable. At highway speeds they were quite alarming!

Up until the mid-70s here, I have driven quite a few of the "muscle cars" from Holden and Ford including a GTO/GTHO (I can't remember which) as well as my cousin's Pontiac GTO 400. All had appalling brakes, suspension and handling. Lots and lots of performance in a straight line, but that was it.

It all comes down to proper design and engineering - it doesn't really matter what the component. I choose to own Subarus because they are quite well designed and engineered, and suit my needs and wants. That doesn't mean they are "perfect" in any way. Anyone who expects perfection in a consumer car - or any other car, for that matter - is in for a very rude shock at some stage!

 

[Venom]

Drums/discs are very vehicle dependent and not readily comparable. Either succeeding or failing in their own right as much on the engineering in each particular application than whether one or the other design is better in principle and practice. Then there's a whole world of variation in discs just by choosing different pads and discs.

Then there's breaking "feel" and outright breaking power, something I think a lot of people confuse. Then there's repeat breaking performance, which is testing the breaks ability to dissipate heat built up from multiple breaking events.

For me I upgraded my Valiant front brakes from drum to the early solid rotor disc type (better), then to the later VJ vented 2 piston caliper was a great upgrade for overall feel, breaking power and confidence. A bit soft in the pedal but I just need to upgrade to a larger bore MC at some stage. My dads Val with the VJ brakes and matching MC has really great pedal bite with good modulation giving a good overall feel and lots of breaking confidence. There is no choice for drum upgrades, which is actually probably what drives and influence a lot of the drum/disc debate.

Thought about a rear disc conversion for the 9" in the back of it, Street Machine did a pretty comprehensive review on the Hoppers Stoppers 9" disc brake kit. Comparable first/second stop power between drum/disc, huge difference after 2 or 3 repeat stops with the discs dissipating heat more efficiently. Will do this upgrade at some stage at the behest of my fetish for upgrading and modding my cars as much as improved breaking (or not improved to some).

Use what works for you and makes you happy (and hopefully safe)