If you ask the seasoned Mopar fan when Chrysler first offered disc brakes, there’s a good chance they’ll tell you 1966, which was when caliper discs became optional for many Chrysler, Plymouth, and Dodge cars. However, 16 years before that, back in 1949, Chrysler introduced a very different type of disc brake for the Crown Imperial limousine and a handful of other models, with an unusual ball ramp self-energizing mechanism. Often called “Ausco-Lambert” brakes (which isn’t exactly correct), these disc brakes were very rare even at the time, and they’re poorly understood today. Let’s take a look at how they worked.
Chrysler Disc Brakes
When someone says “early disc brakes,” most people envision something like the photo below, which shows the front brake of an MGB.
These are caliper disc brakes, which used to be called spot discs because the brake pads are quite small relative to the size of the actual disc.
The disc brakes Chrysler used from 1949 to 1955 were NOT caliper discs. Early ones looked like this:
These brakes used friction pads bonded to two aluminum discs inside a drum-like finned brake housing. (In the image above, you can only really see one of the discs, but there were two of them, back to back.)
The Chrysler disc brakes are often described as Ausco-Lambert discs, which isn’t entirely accurate: They were developed under Homer T. Lambert’s patents, which Chrysler used under license, but the Chrysler brakes weren’t made by the Auto Specialties Manufacturing Company (Ausco). Ausco had developed an automobile version of the Lambert brake, which they had been testing and demonstrating since the late 1930s, but Chrysler engineers regarded the Ausco-Lambert automobile brakes as still experimental, and the Chrysler discs differed from them in some respects. Therefore, it would probably be more correct to call the Chrysler brakes “Lambert-type” discs.
The new discs were first announced in August 1949 and became available that October. They were standard equipment on the 1949 to 1955 Chrysler Crown Imperial — the company’s big long-wheelbase formal sedan and limousine, equivalent to the Cadillac Fleetwood 75. Disc brakes were also standard on the limited-production 1950 Chrysler Town & Country Newport hardtop.
Because the 1949 Crown Imperial didn’t arrive until late in the year, the new disc brakes were not available until about five months after Crosley introduced its short-lived Hydradisc caliper disc brakes, so Crosley, not Chrysler, was the first American automaker to offer discs.
Some sources erroneously describe the Chrysler disc brakes as “power front discs,” apparently in the mistaken assumption that they were similar to the caliper disc brakes Chrysler used in the ’60s and ’70s. This is incorrect: The early discs were always installed at all four wheels, and they were NOT power-assisted. Chrysler did offer power brakes in those days — the optional “Vacu-Ease” booster, whose name makes it sound distressingly like a home enema kit — but the disc brakes didn’t use, or need, a booster.
Self-Energizing Discs
Caliper discs of the kind used on virtually all modern cars work by using small hydraulic pistons to force the brake pads against both sides of the disc, which rotates with the wheel. There are many variations in configuration and design, but the basic idea is the same: The pads clamp inward on the rotating disc and convert its momentum into friction heat.
In a Lambert-type brake, the discs themselves (also called pressure plates) are instead forced outward until the friction pads press against the inner faces of the brake housing.
With the Chrysler disc brakes, each brake housing was cast iron, 12 inches in diameter, with a swept area of 99 square inches. The discs themselves were aluminum, 9 inches in diameter, with six friction pads per disc and a total braking lining area of 66 square inches per wheel. This gave the Chrysler disc brakes 31 percent more swept area and about 30 percent more effective lining area than 12 inch by 2 inch drum brakes, providing greater stopping power and more resistance to fade.
What made Lambert’s brake design really novel was the way the discs were actuated. Instead of applying brake force to push the discs towards the sides of the housing, the Lambert-type brakes worked by twisting one disc relative to the other, like trying to unscrew the lid off a jar.
The inner sides of each set of pressure plates (the sides without friction pads) had a set of metal ball bearings, each sitting in its own small ramp. (Chrysler used six 0.875-inch steel ball bearings; some Ausco-Lambert brakes used different numbers and sizes, and some used rollers instead of balls.)
As illustrated in the above diagrams, when one disc started to rotate relative to the other, it would force the steel balls to climb their ramps. The movement of the balls up the ramps pushed the discs laterally outward, forcing the friction pads against the sides of the brake housing. (This also compressed the return springs, which aren’t shown in these illustrations.)
The ramps also acted like a lever, using the relative rotation of the discs to increase the force on the brake pads. This kind of effect is called self-energization, and it gives more braking force for a given pedal effort.
Duo-servo drum brakes are also self-energizing, but caliper discs normally are not. (It IS possible to give caliper discs a small amount of self-energizing effect by angling the anchor surface, but it’s not usually desirable because it reduces brake stability.) On heavier vehicles with non-self-energizing brakes and no power assistance, it can take a lot of pedal effort to get good deceleration rates. If the vehicle is REALLY heavy, even a vacuum servo might not be enough to keep pedal effort within reason, requiring a hydraulic booster or pneumatic brakes instead.
The Chrysler Crown Imperials that used the Lambert-type disc brakes were very heavy cars, with shipping weights of more than 5,200 lb. Chrysler therefore chose a ramp angle of 32.5 degrees, which gave a total braking force of up to 2.44 times the force applied by the wheel cylinders. (I say “up to” because the way the pressure plates were anchored meant that only the rear brakes could self-energize if the car was moving backwards. Since drivers were unlikely to go very fast in reverse, Chrysler didn’t consider this a problem.)
As the “Effectiveness” graph shows, even without power assistance, pedal effort with the disc brakes was about 35 percent less than with drum brakes. (One drawback was that the discs could be a bit snatchy in really hard stops because the relationship between pedal effort and deceleration wasn’t linear, but duo-servo drums had the same problem.) As the “Fade” graph illustrates, the disc brakes WOULD fade with repeated hard use, even in a car a half-ton lighter than a Crown Imperial, but the margin of safety was much greater than with drum brakes.
Although the disc brakes had better fade resistance than drums, it would have been even better still if Chrysler had used aluminum rather than cast iron brake housings.
The Ausco-Lambert automobile brakes used aluminum housings, with cast-in iron wear surfaces in the areas the pads contacted. However, while aluminum housings provided better heat transfer, Chrysler had trouble finding a satisfactory way to securely attach the iron surfaces to the aluminum housings in series production. Using aluminum would also have added to the cost of an already-expensive system. With cast iron housings, Chrysler estimated that the early discs cost them about $125 more per car than drums.
In 1951, Chrysler took a different approach to reducing brake temperatures and brake fade on the Crown Imperial: forced-air cooling. This added a set of vanes in each wheel that acted as a cooling fan to draw air past the brakes and then out through a half-inch gap between the wheel rim and the wheel cover. Chrysler claimed that this reduced brake temperatures by up to 35 percent, reducing fade and giving about 50 percent greater lining life.
The fact that the forced-air system was necessary at all illustrated a basic limitation of the Lambert-style brake: As with a drum brake, the discs and their friction pads were enclosed and not directly exposed to the air stream. The forced-air wheels helped, but these brakes just didn’t have the cooling ability of a caliper disc brake.
The Chrysler discs were self-adjusting, using a spring-loaded adjuster to maintain a constant distance between the pads and the housing surface as the pads wore.
Early vs. Late Discs
From 1949 to 1952, Chrysler disc brakes used four-arm support spiders to connect the pressure plates to the wheel hubs.
Chrysler had a lot of trouble with these spiders: They tended to rattle on bumpy roads and caused an annoying “clocking” sound as they changed direction, but the mechanisms added to prevent that could cause binding or even warpage. Chrysler revised the design of the spiders, but it evidently didn’t help enough, so the brakes were redesigned for 1953 to eliminate the spiders entirely.
The above illustrations from the 1953 shop manual don’t clearly show the other big change for ’53: The brake wheel cylinders, which were previously mounted in the brake housings on either side of the spider, were relocated to the steering knuckles (in front) and the axle flanges (in back).
Each cylinder actuated a pushrod (highlighted in red above) that acted against a bus cast into each outer pressure plate. This was somewhat less expensive than the earlier design, and seems to have solved several problems. One interesting benefit of the new arrangement was that the brakes could now be completely removed for service without needing to disconnect the hydraulic lines.
Unfortunately, the disc brakes were still very expensive to manufacture. With cast iron housings, they were also significantly heavier than drums, which added to unsprung weight — not a pressing issue with the gigantic Crown Imperial formal sedan and limousine, but hardly ideal for smaller, lighter models.
For those reasons, use of the Chrysler disc brakes was quite limited. They were not offered on the “standard” Imperial, only the Crown Imperial, and I found no indication that they were available on any DeSoto, Dodge, or Plymouth.
The disc brakes DID become optional on the Chrysler New Yorker starting in 1951, but installing the discs involved substituting a lot of Imperial suspension and axle components, so the option was very expensive (over $400) and thus very rare. I think the few that were sold probably went mostly to racers, like the Chryslers that competed in the Carrera Panamerica Mexican road race. The discs were also fitted to some early ’50s Chrysler concept cars.
Dropped for Cost Reasons
Chrysler continued to use the self-energizing discs on the Crown Imperial through 1955. They were discontinued after that on cost grounds, although I’ve seen some anecdotal claims of discs being fitted to 1956 cars. (The parts book doesn’t indicate their being optional in 1956, although I supposed it’s conceivable that a few might have been installed using ’55 parts.)
Crown Imperial production was always very low (these were big formal sedans and limousines, not owner-driven luxury cars), and so the total number of cars built with the Chrysler discs was fairly small. Standard Catalog of Chrysler puts combined 1949–1955 Crown Imperial production at 1,628 cars, to which we can add the 700 Town & Country Newport hardtops built in 1950 and a handful of other disc-equipped Chryslers. In all, I’d guess something fewer than 2,500 Chrysler cars were originally fitted with these disc brakes between fall 1949 and the end of the 1955 model year.
Not all of the survivors still have their original discs. Once parts were no longer readily available, some cars were retrofitted with drums, which didn’t work as well, but were easier to service.
I think the Chrysler brakes were the only production automotive application of Lambert-type brakes. However, Ausco-Lambert discs were still widely used in other applications. Homer Lambert developed many variations of his self-energizing brake concept (he received more than three dozen U.S. patents between the mid-1930s and the early 1950s). By 1954, Auto Specialties advertising claimed that they were used in 60 models of 18 tractor makes, and Lambert-type brakes had shown up on armored fighting vehicles, aircraft, and heavy equipment. Ausco is still in business today, and still makes brakes for off-highway vehicles, including modern variations of the Lambert ball ramp self-energizing disc.
Given their cost and complexity, it’s not surprising that Chrysler eventually gave up on its Lambert-type disc brakes. The problem was that Chrysler didn’t have a better solution. Chrysler engineers had recognized even in the late ’40s that drum brakes were falling short: Cars were getting heavier, speeds were getting higher, and the trend towards smaller-diameter wheels limited brake size and cooling airflow. Ultimately, the Lambert-type disc brakes weren’t the solution to that problem, but they were an interesting if costly step in the right direction.
Related Reading
1950 Chrysler Crown Imperial: Four Wheel Disc Brakes Standard – But Not Like Modern Discs (by Paul N)
1954 Chrysler Crown Imperial: The Widest Production Car Ever (by Paul N)
1949–1950 Crosley Hydradisc Brakes: The First Disc Brakes On An American Car (by me)
Wow, I would hate to work on these. It’s a novel design that seems needlessly complex, but one thing I’m not quite understanding is why their fade resistance is any better than a standard drum. As you mentioned, the air flow through the system wasn’t any better; was it because the friction surfaces were “segmented,” unlike a drum brake shoe?
Both the lining area and their swept area was greater, so they could absorb and dissipate more heat than a drum of the same diameter, and the pads did not shift away from the housing surface the way a hot drum lining did.
The spacing of the pads was also a factor. Chrysler initially assumed that it would be best to have an uninterrupted ring of lining material so there would be maximum lining contact area. However, they found experimentally that leaving space between the pads was much more effective because it left room for ablated lining material to escape. With an unbroken ring, hot ablated material would be deposited on other parts of the friction pad, which was obviously counterproductive.
As always, a better explanation than I’ve ever seen before. TLDR: it was a clutch repurposed as a brake. The sliding balls were freewheeling repurposed as part of a brake.
Almost any friction brake can be used as either a brake or a clutch depending on how it’s connected, but yes, Lambert stated explicitly in most of his patents that the mechanism could be used either way.
Excellent article. Thank you Aaron.
You cleared up misinformation on my part; I thought Chrysler used Ausco brakes. I didn’t realize their first disc brakes were a Chrysler take on the Lampert design. I find the design interesting in that it seems more of an evolutionary step to discs from drums.
The use of a ball/ramp for self energizing was clever. I admire the simplicity.
While the enclosed design prevented maximum cooling it must have helped prevent road debris from fouling up the works.
Credit to Chrysler for recognizing limitations with drum brakes and the need for better brakes. Too bad they gave up on this effort.
It’s mind blowing to think Detroit was OK a decade after the discontinuation of the Chrysler-Lampert brakes with using outdated drum brakes on the heavy and powerful cars to come.
I love the ’55 limo you included.
Great article! I thought you would have also touched up a bit on the tiger and panther tanks with them.
Never really knew these brakes existed. Great article. Thanks!
My parents had a 1953 Custom Imperial, and dad had either gotten a shop manual with the car or gotten one later. As a young boy, I was somewhat infatuated with the car. It had the drum brakes, the 331 ci Hemi V8, the last of the M6 semi-automatic transmissions. It had the optional Kelsey-Hayes wire wheels, standard power steering, but no AC. I used to spend hours going through the shop manual.
The Crown Imperials, in addition to the Lambert disc brakes also received the new for 1953 Powerflite full automatic 2 speed transmission, which was an option for the custom Imperial. We had that car from 1955 – 1962 when dad bought a Plymouth Belvidere wagon to replace it.
Thanks for exposing yet another reason why I can be thankful for how things have worked out in the world. Given that for me brake jobs are something that I do pretty much as needed on any given day, a task that can be accomplished in about 45 min and $200 per axle, I simply cannot imagine what it would be like to have to work on these things. Probably not something any diy-er would undertake.
Granted, back then, no one – particularly not the lucky few with Imperial Crown limos or T&C Woody Sedans – did their own work. But still, what a nightmare.
I do have to ask though, for the surely small number of people who still have these setups and haven’t converted to standard caliper disc brakes, where do they get parts? Is someone custom-fabricating those friction discs?
This thread on the AACA forums talks about them, Jeff. It sounds like you’re either making your own parts, having them made, or doing a conversion.
https://forums.aaca.org/topic/446678-ausco-lambert-brakes/
Thank Aaron for that link.
And call me crazy, but the more I look at the physical examples and back again at Aaron’s illustrations in this article, I say “bring it on”. I’d imagine that if this somehow had managed to become a common and dominant technology, it would eventually have been possible to buy just that inner set of pressure plates as a unit. The friction surfaces, ball bearings, and little bits holding the plates together would have been pre-assembled. The front units would maybe also evolved into a pre-assembled unit that included the bearings. Easy peasy. And maybe even easier to deal with than the last time I had to do regular drum brakes (the Honda Fit has those…) which for me at least are a pita after getting too used to caliper disc brakes.
One thing though…I wonder how these things handled rust. Back then, there was probably less salting of roads than is the case now. I suspect that self-energizing mechanism could get pretty rusty driving in a New England winter.
Wonderful essay! Very much appreciated. In the 1907’s when I worked at Chrysler’s New York Zone Office, one of the service representatives was old enough to have dealt with these brakes. He praised them. He also said that because of the cost of renewing the system, owners were given a $300.00 chit to help pay for this.