Disc brakes vs Disc/drum brakes

[guzzla]

I actually prefer front discs and rear drums ...

Why?!!

 

[Ratbag]

Why?!!

Effectiveness, cost, maintenance, reliability, losing additional unsprung weight, etc.

One still has to have a drum brake in the rear for the handbrake - it's in the centre of the disc rotor. Brilliant bit of design and thinking, but why ...

There's not even a problem with having front drum brakes, as long as they are large enough, and have two leading shoes each. My '68 LC had drums all round, with 8 leading shoes. Stopped excellently (for a relatively primitive truck ... ), even with a tonne in the back. So did the last Silver Cloud Rolls Royce, and it was one of the fastest braked cars in the world (for its type) - 80 mph to 0 in under 5 seconds, in a dead straight line. The 4 wheel disc Mercedes 600 was slightly faster at 4.7 seconds, but weaved all over the test track doing it ...

 

[kiwifoz]

I do agree the drum inside the disk seems a bit odd, but I find the maintenance of disk brakes so easy. Changing pads/rotors on a disk setup is easier compared with pulling a drum setup apart and then trying to get all the fiddly little parts aligned - although I've never done drums, only disks so I can't really comment. I prefer the look of discs though and I didn't want to get a car with drums as the Subaru drums just aren't as good as their disc setups, especially for towing a boat or a car trailer where you want more rear braking.

 

[Ratbag]

^ Nah.

I have towed all sorts of stuff behind cars with 4 wheel drums and disc/drum combinations. No problems with braking at all.

My Impreza had discs/drums, and the drums never needed machining or re-lining in nearly 18 years and 236,000 Kms. Needed the occasional manual adjustment at services, as I always forgot to do the self-adjustment trick of backing about 20 metres with the foot brake lightly applied.

The disc pads on the Foresters always need to be replaced as a complete F/R set, and they ain't cheap! The rear disc pads on our SH are a little bigger than postage stamps, and cost much the same as the set of front pads ...

 

[NachaLuva]

haha RB you cant seriously compare drums to discs. Drums need regular adjustment (don't rely on "auto" adjustment, it works intermittently at best), are awkward to replace linings, & simply dont have the stopping power. Discs OTOH are reliable, so easy to replace pads & stop! :biggrin:

They haven't used drums in racing for many decades, a pretty good indicator

My front pads are still the originals, although they will need replacing soon. So are the discs. That's 200,000kms & I won't be doing the rears for a while, just the fronts :biggrin:

 

[guzzla]

Effectiveness, cost, maintenance, reliability, losing additional unsprung weight, etc. ...

Must disagree about some from my experience.
effectiveness - never, there is a good reason that performance cars and nearly everything else switched to disc brakes years ago. They simply stop faster with less fade and more consistent modulation. Remember your wide bodied Camry? Was it one of the early 4 cylinder ones with drum brakes on the back like my father's had? My V6 had discs and anyone who drove both could tell.
cost - of course, that's why the only drums you see now are on the cheaper versions of the very small cars like the Swift, Mazda2 Yaris etc where they have to use every sneaky way they can to cut the price out of them.
maintenance, reliability - no, a couple of my rear drum cars needed the rear cylinders replaced (as well as the linings) but the 4 rear disc cars I've owned all did more kms with only 1 pad change.
unsprung weight - yes, but at what cost (cheap, nasty & less effective)
etc - alright if I want to bring back memories of my father's cars that I drove in early years - 186 HR Holden wagon, 245 2-barrel VG Valiant sedan (wow that had some power!) and rear axel tramp under brakes and total fade after a couple of seconds of heavy brake application are frightening memories that no drive should have to experience. Gee I used to scare myself ****less in those cars lol. They both had drums at the front too. Arghhhhhh....

 

[Rally]

I think Ratbag is comparing drums not with discs but with opening the door and dragging his feet on the ground. Ask Kevin Bartlett about drum brakes! The reason the rear drums on the Impreza probably did not need attention was probably because they weren't doing much. I remember the last car I drove with rear drums was an XD Falcon- oh what horrible things they were. As above, auto adjust does not reliably adjust. By their very nature they are more prone to locking, and of course after a water crossing take longer to recover. They are an absolute mongrel to work with- I remember changing my WRX over to R180 and cursed at how stupid the handbrake drums were- and they are better than service brakes!

 

[Ratbag]

They haven't used drums in racing for many decades, a pretty good indicator

And what do really big trucks use ... ?

Must disagree about some from my experience.

. . .

186 HR Holden wagon, 245 2-barrel VG Valiant sedan (wow that had some power!) and rear axel tramp under brakes and total fade after a couple of seconds of heavy brake application are frightening memories that no drive should have to experience. Gee I used to scare myself ****less in those cars lol. They both had drums at the front too. Arghhhhhh....

The 186 HR had completely useless discs at the front. Tiny little things that would fade at the merest hint of serious braking. The one's on my father's faded coming down from the Lamington Plateau under moderate braking, and the 2 speed slush box didn't help at all. As you say, scared ****less hitting the corner at the bottom at over 80 mph, with no brakes and lousy handling for good measure!

Harold Dvoretsky asked the rhetorical question, with answer: "Why did they call it the Valiant? Perhaps because that's what you had to be to drive one."

My cousin's Pontiac GTO 400 made the Valiant's slant six look sick for sheer power and (straight line) performance. It had 200 sq. in. of power assisted drum brakes shrug: ). In a single stop from around 80 mph, the brakes had completely faded by the time the car was doing around 50 mph. Crappy design, and appallingly inadequate implementation for a heavy powerful car. An E-Type Jag had 361 (or 461?) sq. in. swept area of power assisted discs. Inboard at the rear to keep the unsprung weight down. It stopped OK! As did the all drums Silver Cloud RR!

It is all but impossible to have brake fade on rear brakes, precisely because they contribute almost nothing to braking; but heaps to stability during braking ...

With towing heavy objects, yes. That's why the LC had 8 leading shoes instead of a single pair of leading/trailing shoes at the back. Even with a braked tandem axle trailer weighing a couple of tonnes, the rear brakes suddenly become important for braking effort of the whole system, and for the prime mover in particular. With many (most?) modern cars having extremely small disc brakes at the rear, it is no wonder that many people towing (relatively) light trailers need brakes on those trailers.

Many American based cars also had leading/trailing shoes on the front. These are easily distinguished. Leading shoes have a slave cylinder for each shoe in each drum, so that precise adjustment is not so critical to performance. Leading/trailing shoes have one slave cylinder for the pair of shoes, so precise adjustment becomes extremely critical.

Early modern consumer cars with 4 wheel discs (mid-1990s) often had the problem that one (or more) of the pistons would seize on one or both of the rear wheels. This did nothing whatsoever for vehicle stability under braking - quite the contrary ... . Swinging caliper design has all but abolished this problem. However, the tiny size of the rear pads should instantly inform one of how much braking effect the rear brakes have ...

As for maintenance. Hands up how often people have had to have their discs skimmed or outright machined? Right ... It's a commonplace occurrence.

I have had to have drums machined twice. Once on the fronts only (Mini); once all round (LC) when I did a complete brake overhaul at around 240,000 miles (~386,000 Kms).

I had to replace the rotors on the Camry at about 90,000 Kms ...
They were worn such that they could not be machined. Apparently the OEM pads were harder than the OEM rotors ...

I am not saying that drum brakes are superior to discs, specially not for modern consumer level cars; specially not for front brakes.
Just that they aren't the rubbish they are made out to be, either.

I certainly wish that my Forester did not have ABS brakes ... Great safety item at a population statistic level - high potential to be rubbish and dangerous if you can actually drive competently. I learned impulse braking before I even got my licence. The technique is still useful for "disabling" the ABS in emergent situations ...

The rear discs and pads on both the SG and SH have about 1/3 the contact area of the front brakes. Both cars brake well. However, neither they, nor any other modern cars, brake from 60 mph in significantly less distance than did my Morris 1100, with discs at the front, and drums at the rear ...

I would also suggest that the Renault 16 (mid 1960s) would probably out-brake them all. It did have 4 wheel discs, and it was the one thing it was really, really good at ... apart from falling to bits ... :biggrin: :lol:.

 

[NachaLuva]

I think Ratbag is comparing drums not with discs but with opening the door and dragging his feet on the ground

:rotfl::rotfl::rotfl:

RB, you've opened a can of worms! :rotfl:

This is KiwiFoz's thread. Might be an idea to move these posts to a Drum V Disc thread

 

[kiwifoz]

:rotfl::rotfl::rotfl:

RB, you've opened a can of worms! :rotfl:

This is KiwiFoz's thread. Might be an idea to move these posts to a Drum V Disc thread

Haha cheers.:rotfl:

 

[Ratbag]

I think Ratbag is comparing drums not with discs but with opening the door and dragging his feet on the ground.

haha, Rally - just call me Fred Flintstone ... :ebiggrin: :biggrin: :lol:.

Actually, I learned to drive on a WWII Jeep that didn't have any brakes at all - the brake lines weren't even connected! It did have a propeller shaft handbrake, but that took a second to apply, and some hours work to disengage :rotfl:.

Given this start to my motoring career, I consider brakes of any description to be somewhat of a luxury item. I am therefore exceedingly grateful that they work reasonably well in many vehicles (OK, leave out Holdens, Fords and Valiants ... :iconwink.

This early history could account for why I have never come close to running up the rear of any other vehicle, even though I drive somewhat 'enthusiastically' at times.

 

[kiwifoz]

It is all but impossible to have brake fade on rear brakes, precisely because they contribute almost nothing to braking; but heaps to stability during braking ...

With towing heavy objects, yes. That's why the LC had 8 leading shoes instead of a single pair of leading/trailing shoes at the back. Even with a braked tandem axle trailer weighing a couple of tonnes, the rear brakes suddenly become important for braking effort of the whole system, and for the prime mover in particular. With many (most?) modern cars having extremely small disc brakes at the rear, it is no wonder that many people towing (relatively) light trailers need brakes on those trailers.

The rear brakes on the Forester really aren't that bad - they're about the same as the front discs on an L-series, with a similar pad area, and larger diameter, with both being of a single-piston design. The rear discs/calipers for an L-series are almost pitiable, they're so small, but the fact that Subaru bothered developing them and fitted them only to turbo models says something about their thoughts on the matter.

As for maintenance. Hands up how often people have had to have their discs skimmed or outright machined? Right ... It's a commonplace occurrence.

I have had to have drums machined twice. Once on the fronts only (Mini); once all round (LC) when I did a complete brake overhaul at around 240,000 miles (~386,000 Kms).

The brakes on my Foz were done less than a year before I bought it, which is great. However, NONE of the cars in our family have ever had to have discs machined - I think this is probably due to the fact that we all use engine braking on downhills to save brake wear, something that is sadly becoming less common as more and more people drive autos.

Last ski season, I was stuck behind a rental Nissan Sunny down Coronet Peak skifield road - brake lights on the WHOLE way down. By the end,I could smell their brakes and see a bit of smoke... I couldn't see the front discs past the steel wheels/plastic trim, but I bet they were glowing. Me, I was in 2nd/3rd the whole way down, only using brakes before corners to scrub additional speed.

I am not saying that drum brakes are superior to discs, specially not for modern consumer level cars; specially not for front brakes.
Just that they aren't the rubbish they are made out to be, either.

I agree. My mum's Sirion has rear discs and they work - but when you stand on the brakes, there's a definite pitch toward the front, more so than my Foz.

I certainly wish that my Forester did not have ABS brakes ... Great safety item at a population statistic level - high potential to be rubbish and dangerous if you can actually drive competently. I learned impulse braking before I even got my licence. The technique is still useful for "disabling" the ABS in emergent situations ...

To a point. They're good on tarmac, but I've almost had a few crashes on gravel/mud due to them, where they have the opposite effect to that desired, of prolonging understeer and preventing the development of an easily controlled skid. I've done a driving course in which we were taught impulse braking on gravel, and I prefer this method for gravel - but on tarmac I like the ABS, it does a better job than I can.

The rear discs and pads on both the SG and SH have about 1/3 the contact area of the front brakes. Both cars brake well. However, neither they, nor any other modern cars, brake from 60 mph in significantly less distance than did my Morris 1100, with discs at the front, and drums at the rear ...

Interesting - but then again, the area of the brakes on the Foz will be significantly greater than that of the brakes on the Morris, so that the overall front:rear braking ratio and weight:clamp force ratios are similar between the two vehicles.

 

[guzzla]

As for maintenance. Hands up how often people have had to have their discs skimmed or outright machined? Right ... It's a commonplace occurrence.

You know that is one of the really great things about the brakes on my SG Foz. At 259,000km the rear discs and pads are original. The original front pads were replaced at the 237,500km service when the rotors were machined, not because there was any warp or shudder but they said that with new pads that they always machine them. I just wish my Foz's brakes had the stopping power and the feel of my Golf's brakes. I bet they don't last as long as the Foz's though.

 

[Ratbag]

Interesting - but then again, the area of the brakes on the Foz will be significantly greater than that of the brakes on the Morris, so that the overall front:rear braking ratio and weight:clamp force ratios are similar between the two vehicles.

I cannot tell you what the ratio of swept area per tonne is for each vehicle. But the brakes on the Morris were discs/drums. Front discs were a relative rarity at that time, specially on 'white goods cars'. Even given better pad material, ventilated discs and better master cylinders; calipers; pistons and piston seals. The Morris did have crude split system braking and pressure limiting valves for the rear - a significant innovation at the time.

Considering that the Morris weighed about 16 cwt, and the Forester weighs about 1.5 tonnes, the ability to convert the kinetic energy of the car into heat, then to dissipate that heat (this is how brakes work - not by "clamping force") has not changed significantly in over 40 years ... :iconwink:.

That's my point.

 

[Ratbag]

You know that is one of the really great things about the brakes on my SG Foz. At 259,000km the rear discs and pads are original. The original front pads were replaced at the 237,500km service when the rotors were machined, not because there was any warp or shudder but they said that with new pads that they always machine them. I just wish my Foz's brakes had the stopping power and the feel of my Golf's brakes. I bet they don't last as long as the Foz's though.

We have been there before. I really don't consider that a couple of feet difference in braking distance between that of a small, sports hatch and a general purpose SUV is significant. I also don't place much store by personal assessments of the "feel" of brakes. According to Wheels, the Audi Quattro bi-turbo brakes "felt" better than those of the twin turbo Liberty they tested it against, but it didn't stop any better, or in less distance ...

If I get 100,000 Kms out of a set of pads, but you get 250,000+ Kms out of yours, then either your pads are made out of some miraculous material that's different from mine, or I drive much more vigorously than you purport to. AND I don't drive on the brakes. Never have.

 

[guzzla]

We have been there before. I really don't consider that a couple of feet difference in braking distance between that of a small, sports hatch and a general purpose SUV is significant. I also don't place much store by personal assessments of the "feel" of brakes. According to Wheels, the Audi Quattro bi-turbo brakes "felt" better than those of the twin turbo Liberty they tested it against, but it didn't stop any better, or in less distance ...

If I get 100,000 Kms out of a set of pads, but you get 250,000+ Kms out of yours, then either your pads are made out of some miraculous material that's different from mine, or I drive much more vigorously than you purport to. AND I don't drive on the brakes. Never have.

It's the driving conditions that have played a large part I think, even though I live in hilly country. And I don't use the brakes unless I have to. The pads are (and were) genuine Subaru factory stuff. I guess all the long distance highway driving I have done counts for a lot.

As far as personal assessment goes and "feel" I really take notice of it. I know I'm comparing two cars with 230kg difference in weight but I have driven the Golf a few times with 4 adults a the boot absolutely loaded (it would have been heavier than my Forester with just me in it, as I often get around) and it doesn't make a difference in comparison - it still out-brakes my Forester by miles. And "feels" infinitely better doing it. They have a reassuring instant bite and suck me to the ground with eye balls popping out of my head feel. I think it must be part of the set up for fast autobahn running where really rapid stopping from 200km/h is needed. It's all comparative though and in isolation my Forester's brakes seemed adequate. However I have to live daily with the contrast. To me better brakes and better road noise and rear body insulation were the 2 most important changes Subaru needed to make to the Forester.

And Subaru certainly have the engineering ability to do it. Just look what they could do with the Gen 4 Liberty / Outback. Much better brake feel than the similar weight Forester and far better body insulation. When I was looking for my Forester back in 2007 the base Outback and the Forester XS had a $3000 difference in price, were almost identically equipped and running the same engine / gearbox. Driving them back to back as I did you could easily tell where the development money had been spent.

 

[ateday]

MY03 5 speed manual. Have now done 307000kms and still original front pads and discs. Will certainly need replacing soon with genuine new pads.
Mechanic suggested that rear pads be changed and discs machined at about 160000kms but think I was conned as I looked at rears about 2000 kms ago and plenty meat left, in fact barely worn.
Beware of over servicing/value adding is the lesson to be learnt.
Pads will last depending upon driving techniques.
Most of my driving is long distances and I look at brakes as emergency stopping devices and try, not always successfully, to anticipate the need to slow down by taking foot off "go" pedal.
This is borne out by average fuel consumption over the entire distance of 8.9 l/100kms which I consider ok for a heavier than normal MY03 carrying SubaXtreme front and rear bars , sump guard, second battery and sparetyre/rim and usually car fridge.

 

[Ratbag]

:rotfl::rotfl::rotfl:

RB, you've opened a can of worms! :rotfl:

This is KiwiFoz's thread. Might be an idea to move these posts to a Drum V Disc thread

Quite right.
Done.
I was too tired last night.

As Kevin has said, it crossed my mind last night just to delete the whole lot as OT. Simple comments in passing should not drag a whole thread OT and become its focus, specially not a personal build thread.

Note to self and others - please try to stay on topic, Folks.

 

[Rally]

My response is in italics below

And what do really big trucks use ... ?



The 186 HR had completely useless discs at the front. Tiny little things that would fade at the merest hint of serious braking. The one's on my father's faded coming down from the Lamington Plateau under moderate braking, and the 2 speed slush box didn't help at all. As you say, scared ****less hitting the corner at the bottom at over 80 mph, with no brakes and lousy handling for good measure!


So you use an example of under engineered disc brakes as an example that disc brakes are no good. I have these discs on the front of my WRX, what sort of drums would bolt on that would be as effective as these?




Harold Dvoretsky asked the rhetorical question, with answer: "Why did they call it the Valiant? Perhaps because that's what you had to be to drive one." A

My cousin's Pontiac GTO 400 made the Valiant's slant six look sick for sheer power and (straight line) performance. It had 200 sq. in. of power assisted drum brakes shrug: ). In a single stop from around 80 mph, the brakes had completely faded by the time the car was doing around 50 mph. Crappy design, and appallingly inadequate implementation for a heavy powerful car. An E-Type Jag had 361 (or 461?) sq. in. swept area of power assisted discs. Inboard at the rear to keep the unsprung weight down. It stopped OK! As did the all drums Silver Cloud RR!

It is all but impossible to have brake fade on rear brakes, precisely because they contribute almost nothing to braking; but heaps to stability during braking ...

I had rear drums on my XA GT Falcon when I first bought it. A spirited drive along with another car saw my rear brakes completely fade out, with smoke billowing from them. A switch to rear discs and I NEVER had that problem again.

With towing heavy objects, yes. That's why the LC had 8 leading shoes instead of a single pair of leading/trailing shoes at the back. Even with a braked tandem axle trailer weighing a couple of tonnes, the rear brakes suddenly become important for braking effort of the whole system, and for the prime mover in particular. With many (most?) modern cars having extremely small disc brakes at the rear, it is no wonder that many people towing (relatively) light trailers need brakes on those trailers.

Many American based cars also had leading/trailing shoes on the front. These are easily distinguished. Leading shoes have a slave cylinder for each shoe in each drum, so that precise adjustment is not so critical to performance. Leading/trailing shoes have one slave cylinder for the pair of shoes, so precise adjustment becomes extremely critical.

Early modern consumer cars with 4 wheel discs (mid-1990s) often had the problem that one (or more) of the pistons would seize on one or both of the rear wheels. This did nothing whatsoever for vehicle stability under braking - quite the contrary ... . Swinging caliper design has all but abolished this problem. However, the tiny size of the rear pads should instantly inform one of how much braking effect the rear brakes have ...

As for maintenance. Hands up how often people have had to have their discs skimmed or outright machined? Right ... It's a commonplace occurrence.


You should never need to machine discs. It is almost always a waste of money. There is no issue with the disc other than there being a build up of material on it, generally due to pad to disc incompatibility and with the way the car is being driven.


I have had to have drums machined twice. Once on the fronts only (Mini); once all round (LC) when I did a complete brake overhaul at around 240,000 miles (~386,000 Kms).

I had to replace the rotors on the Camry at about 90,000 Kms ...
They were worn such that they could not be machined. Apparently the OEM pads were harder than the OEM rotors ...



My Forester has done 232,000kms on the original pads and discs, with almost no lip, no cracks and no so called warping.

I am not saying that drum brakes are superior to discs, specially not for modern consumer level cars; specially not for front brakes.
Just that they aren't the rubbish they are made out to be, either.


But they still are more maintenance, and more difficult to work on, and they fade. They have, quite rightly, been consigned in all but the very small cars to history, where they belong.

I certainly wish that my Forester did not have ABS brakes ... Great safety item at a population statistic level - high potential to be rubbish and dangerous if you can actually drive competently. I learned impulse braking before I even got my licence. The technique is still useful for "disabling" the ABS in emergent situations ...


I am a big fan of ABS and while I learnt to drive on a non ABS car, I am pleased to have it. While my XA Falcon stopped admirably well when confronted with an oncoming road train, especially considering the drivers side wheels were in the dirt



The rear discs and pads on both the SG and SH have about 1/3 the contact area of the front brakes. Both cars brake well. However, neither they, nor any other modern cars, brake from 60 mph in significantly less distance than did my Morris 1100, with discs at the front, and drums at the rear ...

My WRX brakes pretty well! Not forgetting that in most one off applications, it is overall tyre grip and weight that have a bigger determination of braking distance

I would also suggest that the Renault 16 (mid 1960s) would probably out-brake them all. It did have 4 wheel discs, and it was the one thing it was really, really good at ... apart from falling to bits ... :biggrin: :lol:.

 

[Rally]

[ame="https://www.youtube.com/watch?v=o6ClqnvMqac"]Bathurst 1980 - Kevin Bartlett Camaro Pit Stop. - YouTube[/ame]