Drum Brakes and Disc Brakes, A Historical Question

Any comparison of a non-assisted braking system to an ASSISTED braking system with the booster non-functional or disabled is specious. It is FAR harder to stop a car with a dead power brake booster than it is to stop the same car with MANUAL brakes.

As an example- my daily driver is a 1966 Dodge Polara. It originally had power drum brakes that would throw you through the windshield with a feather touch on the pedal. It was fine once you were used to it, but a real shocker if you'd been used to driving another car. It was also a single-cylinder master cylinder, which I consider unacceptable to drive daily- a single blown hose would take out the whole system.

When I gave the car a makeover last year, part of the upgrade was to put on front disk brakes (bolt-on using a '73 New Yorker as a donor car for the spindles, calipers, rotors, and brake lines). At the same time, I got rid of the whole power assist assembly and replaced it with a manual brake pedal linkage from a '65 Dodge 880, hooked to a modern aluminum master cylinder from an 89 Diplomat, with the proportioning valve, safety valve from the Diplomat. So the car now has a fully split braking system, with safety valve to isolate the halves of the system from each other in the event of a blown hose or wheel cylinder, and warning light that comes on when the safety valve has to do its thing. AND it has manual front disk/rear drum brakes. I *love* the brake feel- its more tactile than power boosted brakes and does have a somewhat higher pedal effort, but much lower pedal effort than just disconnecting a power booster. I can bring that big C-body to a stop faster than the ABS and

4-wheel power disks on my wife's 93 Vision TSi can stop that car. About the only gripe I have is that manual brakes demand that the resting height of the brake pedal be a bit higher than power brakes, because there has to be more total pedal travel. Its back to the feel of my '68 Ford and '49 Plymouth from years gone by- you have to slightly LIFT your foot to move it to the brake pedal, rather than just slide it left. No problem once you're used to it, but I am considering putting power brakes back in (using a modern booster) for just that reason. After all, my wife does like to drive that car, too. She doesn't mind the pedal feel at all, but the height does bug her because she had literally never driven a manual-brake car before in her whole life. I learned on manual brakes, so its second nature to me.

Imperial had a 4-wheel disk system ( with an odd full-disk caliper) briefly in the 50s. I'm not sure exactly when they started, but I know that in 1966 Budd 4-piston disk brakes were optional on all the full-size Chrysler products (Polara, Monaco, Fury, Newport, 300, New Yorker, Imperial). The midsizes (Belvedere/Satellite, Coronet, Charger) had them optionally no later than '67. Both of those systems are now very hard to get parts for- I considered tring to scare up an original Budd system for my Polara but gave up quickly. Most owners of those cars now retrofit the single-piston Kelsey-Hayes calipers that were standard (and darn near universal) in the 70s and 80s. Cheap, available, work 99% as well as 4-piston brakes anyway. The only real advantage of the

4-piston setup is more even inboard vs. outboard pad wear and more tolerance to warped rotors (not necessarily a good thing- I'd rather feel a warped rotor and FIX it, personally).

Not so much the design of the steering mechanism or the difference between SLA and struts - a good recirculating ball steering box is just as good as a good rack and pinion setup, from the driver's perspective; likewise a SLA suspension arguably provides better wheel control than a strut type suspension. Heck, BMW kept using their excellent recirc ball boxes long after everyone else went to R&P and BMW's are renowned for their incredible steering feel and precision. However, back in the day, power steering was always an extra cost option, and cars were designed as such. What this meant was a) the suspension was set up with less caster, to reduce steering effort, and b) the steering

*ratio* - i.e. how many degrees the front wheels turned for a given rotation of the steering wheel - was generally set up to provide the driver with more leverage. The first thing that people notice when driving a 50's vintage car is that the steering tends to be a little "numb" (due to the lack of caster) and "slow" (due to the slow ratio) which is just the nature of the beast. And, yes, the steering wheels tended to be large - 17" or even larger, to also give the driver more leverage in slow speed situations. As automakers realized that more and more people were ordering cars with power steering anyway, caster specs were changed and ratios quickened to provide a better experience for the driver, but that made vehicles without power steering almost undriveable unless you had decent upper body strength, so eventually the manual steering option was pretty much dropped across the board except for small, light cars that didn't really need it to begin with.

Based on looking at the wear patterns on the shoes of drum brakes; I would say that it doesn't appear that the front shoe has appreciably less contact area than the rear as a percentage of total lining area, assuming that the brakes are kept in proper adjustment. That said, from a pure physics standpoint, it really doesn't matter how much lining area there is at all; the greater area is only useful when it comes to resisting fade (as is the ability of the drum or rotor to quickly shed heat buildup.) What is important in terms of brake torque, for either system, is the *diameter* of the drum or disc, as the same frictional force will provide a greater torque on a larger diameter drum or disc.

nate

Steve wrote in news:75mdnao8V6ArGYfYnZ2dnUVZ snipped-for-privacy@texas.net:

Those were the Lambert discs. Not at all like Jaguar's system of 1957. Very odd, and a very interesting concept.

The big problem with the Lamberts was that they used the same hydraulic wheel cylinders used by drum brakes, but operated them at 4 times the usual hydraulic pressure. Apparently fluid ruptures were too common for comfort, so the Lamberts were discontinued.

That's right, I had forgotten about that. I never really did 'grok' how that system worked. As far as I know the earliest post-war use of disc brakes in the U.S. was in the 1949 Crosley -- however those were basically unmodified aircraft brakes. These would lock up solid due to corrosion when used on salted winter roads.

That's also SOP for the early AMC/Rambler disc brake systems. Retrofitting the single-piston Bendix calipers from 1980s-vintage AMC cars is pretty much a bolt-in operation.

To be sure, it is possible to fade discs as well, you just have to work at it and ride 'em a lot more. That's why I use gears as well as brakes to control speed in the mountains. It's easy for that speed to creep up and hauling that 4,000 pound car down takes a lot more braking effort than holding a constant speed. The guys I've seen that get themselves into trouble go fast into a corner, hit the brakes and repeat the process in the next corner. No set of brakes is designed to take that kind of purposeful mistreatment for an extended time.

Roger Blake wrote in news: snipped-for-privacy@moog.netaxs.com:

Didn't pretty much every NA manufacturer move to single-piston floating calipers by 1968?

Well there you go. Far from being behind the curve, it now appears American manufacturers had been working on discs pretty much as long as the Europeans had.

...and wasn't even made by AMC, but by the British Motor Corporation of England on BMC's A30 chassis. It was sold as the Austin Metropolitan in the UK.

So there were some exceptions to the rule.

The Toyota Corolla was available with front drums as late as 1975, but those were not installed in Canada or the US.

Good point. The real problem with the Bendix non-servo drums used in conjuction with the early Rambler disc brakes is lack of parts. At this point most parts catalogs don't even list them properly, unless you can get to the old printed books. Even so the parts have all been discontinued, can't even get replacement shoes any more let alone the bizarre ratcheting adjuster, etc. (At least shoes can be relined.)

It seems to me that at some point I looked into this and found that they were no interchangeable parts. The standard "fix" at this point for those old Rambler disc systems is to retrofit the brakes from a "modern" 1980s-vintage AMC car (like a Concord). Parts for those are still readily available, probably because they were shared with the Jeep line.

Yes, as I recall 1967 was the first year for federally-mandated dual circuit brakes.

Roger Blake wrote in news: snipped-for-privacy@moog.netaxs.com:

I thought it was Jan 1, 1968.

A bunch of new safety regs came in for the 1968 model year. Headrests,

3-point seat belts, side marker lights, door beams, among other things. AFAIK, 1968 models built in 1967 didn't need them, but some makers installed them early anyway.

If it has a ratcheting adjuster, the brakes are NOT the same as a Studebaker. The Studes with front discs used eccentric adjusters behind the shoes. I thought I might be able to help you out, but I guess not.

nate

I think AMC used the 4-piston Bendix jobs through 1970, moving to Kelsey-Hayes single-piston floating calipers in 1971, and Bendix single-piston in 1975. (Though my '75 Hornet was built early in the model year and still has the KH brakes.)

The Metropolitan was designed by Nash in the U.S. (actually an outside designer named Bill Flajole). It was determined early on in the Met's design that it would be built overseas to take advantage of lower labor costs and to get around steel shortages in the U.S., Fiat was initially considered, Austin ultimately chosen. There was a book called "The Metropolitan Story" that came out a few years back that goes into the car's history in great detail, and of course much may be found on "thuh web," such as:

I thought it was 1967, but I could be wrong, it was a long time ago and I'm going by my own memory. As I recall that same year the collapsible steering columns came into play, though Ford went with a big cushion in the center of the steering wheel at first. (AMC and Checker purchased the GM collapsible columns.)

Porsche's brakes are. Other manufacturers are not quite as competent (even the ones who are willing to spend the same kind of money and use the same suppliers (Brembo calipers, I think, although Porsche says that they make the cross-drilled disks (which are not made by drilling) in-house).

And, BTW, "purposeful mistreatment" ?

Roger Blake wrote in news: snipped-for-privacy@moog.netaxs.com:

Safety regulations came in dribs and drabs at first. The first may have been headlight height restrictions, and the requirement of sealed beams in

1940. I'm not sure when safety glass was first required.

Lap belts were first required in 1965.

The 1968 model year saw a whole whack of regulations all at once, sparked by the furor surrounding Ralph Nader's book from a few years earlier.

I don't know what was usual in those days. But I know that my parents'

1973 Opel Kadett (General Motors Europe) had front disk brakes. Since this was not an expensive or sports car, I would expect that front brakes were more the norm than the exception at the time.

I find this appalling !

Somewhate apropos I read an interview in the French Sport-Auto magazine with an old race driver. This guy used to drive for Lotus (50s or 60s). In that interview he said "Chapman was a genius but he always wanted to make things too damn light" (quote from memory). So during a race the brake line on this guy's car burst and since it was a single-circuit he lost all brakes.

He managed to not hurt himself in the subsequent crash, but when he got back to the boxes he stopped at the Ferrari box and asked the team director for a place in the team. The next race he was driving for them.

Speaking of Metros..

A friend of mine in HS had about 5 of those. His last name was "Hudson", and he claimed it was one and the same with the Hudson Automobile company that got absorbed into Chrysler. Says his dad was part of the Hudson RnD team and stayed on in Chrysler up into the 70s.

I always thought they were neat little cars, but I don't remember if any of them ran or drove. They were all in a field behind his house, along with some other stuff I have never seen before or since- most notably a set of fuel injection heads for a 440, and a '56 New Yorker with a 392 Hemi prototype in it, a pushbutton transmission, power everything (windows, seats, steering wheel adj, mirror adj, etc) and (of all things) a phonograph that could play 45s.

Btw, this has been an interesting thread to read, with all the historical bits. Thanks to everyone who has chimed in!

-phaeton

Discontinued due to design problems shortly after its introduction IIRC. :)

Discontinued which? The braking system, the OHC 4-cyl, or the whole car altogether?

:-P

-phaeton

Roger Blake wrote in news: snipped-for-privacy@moog.netaxs.com:

I had a look at that page. And this one:

They say nothing about what Nash ended up using as the basis for the Metropolitan. The Wiki page does say the car was built using "existing mechanical components". The Met was built using the Austin A30 chassis and (originally, apparently) the Austin A-series engine. I suspect Bill Flajole ended up contributing little outside of the body styling.

The identical chassis and engine family was used for the original Austin-Healey Sprite, although the original Sprite never received a B-series engine.