Automotive History: Factory Four Speed Transmission Behind a Slant Six? Yup, For a Couple of Years Anyway

(first posted 9/21/2017)           I’ve long had a fixation on the lack of four speed transmissions being available on American compacts in the 1960s. The standard three speed manual transmission was a relic from the pre-war era when cars had slow-revving engines, very high (numeric) geared rear axles, and highway speeds were very modest. Driving conditions were different, but most of all, driver expectations were different.

In the 1950s, when the great import and sports car boom were under way, things changed quickly. Highway speeds increased, which meant that rear axle ratios were lowered numerically, effectively increasing the gaps between gears, especially between second and third. With a big lazy V8, or for buyers looking for minimal motoring function, the three speed was adequate enough. But the compacts’ brief was to compete against the imports, which almost invariably had four speed transmissions.

Of course the true import-fighter Corvair had an optional four speed, as of the spring of 1960. And I knew that the Falcon was available with the UK-sourced four speed behind their six from mid-year 1962 through 1964. But a four speed behind the Chrysler slant six on their Dart and Valiant? I was never aware of that, until yesterday.

1964 Valiant brochure

I had to dig up the various brochures online to determine the start and end dates of the four-speed slant-six combo, which really surprised me as to its existence. It started in 1964, which of course is because Chrysler’s excellent new A-833 four speed transmission first saw the light of day that year. It was of course primarily developed for the big V8s, especially since the B/W T-10 was felt not to be strong enough for the wicked 413 Max wedge engine. But there were two versions from the get-go, one for the sixes and the 273/318 V8s, and the other for the big engines.

The version we’re discussing had different gear ratios; 3.09, 1.92, 1.4, 1.0, for first through fourth, to accommodate the lower torque of the smaller engines. This compares to the A-903 three-speed’s ratios of 2.95, 1.83, 1.0.  Note how close first and second gear ratios are in these two boxes. Which explains the very frustrating “hole” between second and direct third, especially with a six.

Here’s the excerpt from the ’64 Dart brochure. Note that it says “Optional on all Dart models”. The reason I point theta out is because I can’t quite tell if the four speed was available behind the 170 cubic inch slant six. Probably not.

This power train chart for the ’65 Dart clearly shows it not being available for the 170 six. Too bad, as it needed it even more. My dad’s ’68 Dart had the 170, and the hole between second and third was really objectionable, especially the way I was trying to drive it.

Here’s a bit more from the ’65 Dart brochure.

Of course the ’64-’65 Barracuda, which was virtually identical to the Valiant except for its glassy fastback, also offered the four speed with the six in those two years.

It all ended in 1966, when the four speed became available only with the V8s.

And then it came back again, in 1975, after the A-833 had been re-engineered into a three-speed and OD transmission, by turning “third gear” into a 0.73 OD ratio, and changing the linkage so that third and fourth were now flipped on the shifter pattern.

Of course this was done in response to the energy crisis. A five speed is what was needed, but necessity is the mother of improvisation. And the gap between second and third was tightened up a bit, with the new ratios of 3.09, 1.67, 1.1 and 0.73.

Other than the Falcon’s brief fling with the UK-sourced four speed behind the six (and the Corvair, of course), that was it for proper gear ratios in the compacts in this era. The Chevy II never offered the four speed with its four or sixes, although the Camaro did. The Rambler American and Studebaker Lark did offer overdrive three-speed transmissions, but they way they were set up to work semi-automatically, it didn’t really give as many intermediate ratios as a four speed (it requires a conversion to manual operation to do that, like in my F-100).

Obviously, the take rate on these six cylinder four speeds was minute. Most American buyers of compacts just didn’t appreciate the benefits, and once V8s were available on them, performance-oriented buyers went that route anyway. But it makes for engaging speculation to imagine a 1960 Valiant offering a four speed behind its little high-revving 170 slant six. Now that would have really vaulted it to the head of the class, even further.