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Dual master cylinders

Does anyone remember when dual master cylinders became common? I was just looking at an “all original” '62 Caddy on Hemmings and it has a dual master. I was wondering if it could be original, but.i doubt it.

From a Feb 1983 NHTSA report
"Although Standard 105 did not take effect until January 1, 1968,
all domestic passenger cars had dual master cylinders by the 1967 model
some as early as 1962. Table 1-1 shows the percentage of domestic
passenger cars with dual master cylinders, by model year. It is based
on Chilton’s auto repair manuals. The percentage for 1966 could not be
readily determined. Essentially, relatively few cars had them up to
1965 and all had them starting in 1967.’

9% of domestic cars had dual master cylinders in 1962 so it’s possible.

Thank you! So it might be “all original” after all. My 1963 Motor’s auto repair manual doesn’t mention it

The internet is your friend, Rock Auto shows a single M/C for the 61 Caddy and a dual M/C for the 62.

I didn’t know rockauto carried parts for vintage cars! Thanks.

That’s where I was going to look. I would think though it would be pretty hard to retrofit a car to a dual system though. It would require new brake lines be split diagonally and rerouted.

Actually that is relatively common on resto-rods. Upgrading both suspension and brake systems. Converting from drum brakes to a disc/drum or four wheel discs.

I remember an AMC advertisement from around 1964. Two cars, one with single master cylinder, the other with duel. They cut one line at the MC, then drove the cars off a pier, of cours the single MC went into the water and the duel was able to stop.

Piece of cake to do this. I added one to my '64 Pontiac in 1979 or so. The single master feeds one line into a combination valve that feeds one line to the rear and 2 to the front brakes and includes a pressure limiter for the rear brakes.

I took a power brake master and booster off a 67 or 68 drum brake car off a GM of the same size complete with the combination valve. That gave me 3 ports to connect the lines and a duel input combo valve for the duel master and power brakes as well. Much nicer to drive but the 4 wheel drums still were awful.

It is done all the time for safety reasons by people who want to actually drive their vintage cars. Judges at car shows won’t deduct points because of it, also for safety reasons. AACA won’t let you enter a show without a fire extinguisher and they certainly were not original.

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The quality of linings matters a great deal with drum brakes. I bought a 61 Dodge Dart Phoenix with a 318 in 64 with only 22000 miles on it and when I took it up to 70 or over and stepped hard on the brake, the car would shudder and smoke and not slow very fast.

I used to deliver to a brake relining company and I got a set of Grey Rock shoes all around and even over 100 the would hall you down like you ran into a capture net on an aircraft carrier. To me the biggest advantage of discs is in the rain.

I just checked online, they still make Grey Rock linings, I had no idea.

I remember seeing what looked like widespread adoption in 1967.

Probably not the same material as you remember. Current Grey Rock is listed as non-asbestos. I’d guess back in the day, it was asbestos.

The inherent problem with drum brakes is the friction diameter of the drum gets bigger when hot and the shoes no longer match the inner radius so they lose their effectiveness. And drums don’t cool back down very well.

Even with power boosted brakes my '64 Tempest, the car wouldn’t lock the wheels below 30 mpg from a 70 mph stop no matter how hard you pressed on the brake. They faded to almost nothing. Turned me off drum brakes from that point on.

Rick . . . or whatever you call yourself nowadays . . . ?!

this is right up your alley

What’s your opinion?


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Ah yes, our poor old friend, the drum brake. I loved that thread.

I liked the part where Rick said he bought a Caprice with drum brakes all around, just to prove that we were wrong about drum brakes

I also seem to remember he said the brakes faded and he wound up in the intersection, instead of stopping at the red light or stop sign :smiley:


Db, while you’re around, do you remember the model number of the Benz 4 speed automatic of the 60’s?

Sorry, I don’t remember . . . because that’s a little bit before my time

I would guess 722.1 or 722.2 . . . and that guess is based on the fact that the automatic transmissions from the late 1970s and 1980s were 722.3

Thank you very much.

With those Grey Rock linings I could lock the wheels at any speed if I pressed hard enough. That was the brand used on Nascar Stock cars back then and they were already running 200 mph.

Note: I didn’t lock the wheels except very briefly once at high speed because it isn’t the fastest way to stop and if you locked the wheels at 100 for more than a split second, you would have to replace the tires.

Once… then there is too much heat to do it again. That’s why the industry moved to disk brakes. Places like Pikes Peak and the like with long downhill sections that not even engine braking helps very much. Or stop and go driving in Los Angeles. Both were Delco brake testing locations.

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