1964 Cadillac Series 62 – Last Year Of A Very Unusual GM Hydra-Matic Transmission With TWO Fluid Couplings

The 1964 model year was the last hurrah of the entry-level Cadillac Series 62, and the final year for the ’50s-vintage Controlled Coupling Hydra-Matic, an unusual four-speed automatic transmission with two fluid couplings rather than just one. Let’s take a look at the final Series 62 Cadillac and how its dual-coupling floor speed transmission compared to the three-speed Turbo Hydra-Matic used on senior Cadillacs,

Take a moment to pour one out for the Cadillac Series 62 line (1940–1964), which was struck down at the age of 25 after years of success. When it debuted, the Series 62 was the cheapest Cadillac model (with the club coupe pictured above the cheapest version). From 1941 through 1951, the Series 62 became the second-tier Cadillac model, above the entry-level Series 61, but it again became the base model starting in 1952.

For a long time, the Series 62 accounting for the bulk of Cadillac sales, and the more glamorous De Ville and Eldorado originally began as Series 62 sub-series. By the early ’60s, however, the Series 62 was being overshadowed by the better-trimmed, more expensive De Ville. The De Ville outsold the Series 62 in 1962 and 1963, and the gap was widening. After 1964, Cadillac would retire the venerable Series 62 designation in favor of the similarly positioned Cadillac Calais.

1964 was a transitional year in several other ways as well. This was the first year for the bigger 429 cu. in. (7,008 cc) engine, with 340 gross horsepower, but Cadillac was preparing to abandon the still-controversial self-supporting GM X-frame in favor of the more flexible perimeter frame, and to adopt an all-new automatic transmission, the latest three-speed Turbo Hydra-Matic. This new automatic actually made its Cadillac debut on the 1964 De Ville, Sixty Special, and Fleetwood Eldorado, but the Series 62 and Series 75 retained the older four-speed unit for one more year.

I’ve noticed that the four-speed Hydra-Matic of this period is not well-understood even by Cadillac owners. Originally known as the Controlled Coupling Hydra-Matic, it was the second-generation Hydra-Matic transmission, introduced in 1956. Detroit Transmission Division (renamed “Hydra-Matic Division” around the time the 1964 models went on sale) had extensively redesigned the earlier Dual Range Hydra-Matic, aiming for smoother shifts and greater torque capacity. This second-generation transmission was used by Cadillac from 1956 to 1964, most Oldsmobiles and Pontiacs from 1956 to 1960, and the Pontiac Star Chief and Bonneville through 1964. It also showed up on some 1957 AMC models.

The Controlled Coupling Hydra-Matic was an extraordinarily complicated transmission, so I’m not going to try to explain its operation in detail, and understanding its nuances is much easier if you’re already familiar with the earlier 1940–1955 Hydra-Matic transmissions it replaced. However, its most unusual feature was that it had two fluid couplings rather than one: a main coupling and a second, smaller one in the case behind the torus housing.

Why would a transmission have multiple fluid couplings? A fluid coupling is a type of clutch, using hydraulic fluid to transmit power, and in principle, it can be used in most applications where one would otherwise use a plate clutch or multi-disc clutch. The first-generation Hydra-Matic transmission used a fluid coupling as a main clutch, and it executed its various shifts with two multi-disc clutches, two brake bands, and a reverse pawl (replaced in 1951 by a cone clutch). In the second-generation Hydra-Matic, the bigger coupling remained as the primary clutch — it kept the engine from stalling with the car stopped in gear or at very low speeds — but a new smaller coupling replaced the previous front multi-disc clutch.

If you know a little about how fluid couplings work — two torus discs, each shaped like half a bagel, with blades to circulate hydraulic fluid — you might be wondering how one can be engaged or disengaged. With a plate or multi-disc clutch, the clutch is disengaged by separating the plates. A fluid coupling can be disengaged by draining all the oil out of the torus housing, and then reengaged by filling the housing with pressurized oil, which is what Hydra-Matic did.

In the dual-coupling Hydra-Matic, a hydraulically operated coupling valve and coupling exhaust valves controlled the flow of oil into or out of the coupling. Since the coupling was small, as shown in the photo below, it could dump or fill in a fraction of a second.

The object of doing this rather than using a multi-disc clutch was smoothness. When the second-generation Hydra-Matic debuted, Detroit Transmission offered this graph showing the engagement of the controlled coupling versus a band and multi-disc clutch. As you can see, the coupling transition (which I’ve highlighted in red) is a mostly smooth line, with no jerk or bump:

What did the controlled coupling control? I’ve color-coded the patent illustration below to show how the second coupling fit into the power flow. (This is actually an illustration of a Hydra-Matic variant that was never actually produced, but it’s close enough to the production Hydra-Matic in this section view.) All of the components in red were connected directly to the engine flex plate, so they always rotated at engine speed. The torus cover rotated the drive torus of the second coupling, the front oil pump, and the ring gear of the first planetary gearset (which in a second-generation Hydra-Matic was tucked neatly inside the torus cover, next to the primary coupling). The second coupling’s driven torus, highlighted in green, drove a sleeve shaft connected at the left to the sun gear of the front gearset and at the right to a sprag clutch (not shown).

With this smaller coupling empty, the front gearset was in reduction: The ring gear turned at engine speed, and the sprag clutch held the front sun gear stationary. When the small coupling filled, which it did in 2nd and 4th gears, it drove the sun gear forward, releasing the sprag clutch and putting the front gearset in direct drive. The coupling alternately emptied and filled like this:

• Park: Empty
• Neutral: Empty
• 1st: Empty
• 2nd: Full
• 3rd: Empty
• 4th: Full
• Reverse: Empty

Because the engagement and disengagement of the small coupling and the sprag clutches was almost seamless, most shifts were now very smooth. The rear gearset still had a conventional multi-disc friction unit (along with a second sprag clutch) — Detroit Transmission considered replacing that with a third fluid coupling, but decided that would be too expensive — but the old Hydra-Matic jerkiness was gone, at least in Drive-Left (D4) range. (Shifts were firmer in Drive-Right (D3) and Lo because they used a band and an additional disc clutch to keep the transmission from freewheeling when coasting with the throttle closed.)

You might be wondering if this dual-coupling arrangement was less efficient: Fluid couplings always slip at least a little bit, even at high cruising speeds. In this case, because the front ring gear was mechanically connected to the engine flex plate, the small coupling only ever had to carry about one-third of the engine’s torque (35.6 percent), and it was empty at low speeds (where fluid coupling slip the most), so it didn’t cause very much slippage when it was operating. In 4th gear, where power flowed through both fluid couplings, neither coupling carried more than 40 percent of total engine torque, which kept the actual slippage in each coupling quite small. This arrangement wasn’t as efficient as the earlier single-coupling Hydra-Matic, but it compared well with contemporary torque converter automatics like Chrysler TorqueFlite or Buick Turbine Drive.

From the driver’s perspective, the Controlled Coupling Hydra-Matic worked just like the older Dual Range Hydra-Matic, except that there was now a separate Park position. For most driving, you selected Drive-Left (D4), which used all four gears and provided the smoothest shifts. Selecting Drive-Right (D3) kept the transmission out of 4th until highway speeds and ensured engine braking in hilly terrain, although it made shifts somewhat harsher. For slower hills, Lo mostly kept the transmission in 1st and 2nd. (It would eventually upshift to 4th if there was danger of overrevving the engine.)

Ordinarily, you’d think a three-speed automatic would be a step down from a four-speed unit, but the arrival of the three-speed Turbo Hydra-Matic was a great improvement in both performance and refinement. Why?

The Controlled Coupling Hydra-Matic was not a four-speed overdrive automatic like the automatics of the ’80s and ’90s; its top gear was direct (1 to 1). It had a high numerical 1st gear (3.97 to 1) for off-the-line performance, but it was programmed to upshift early from 1st to 2nd, and that shift brought a big drop in engine speed, trading some performance for less noise. Also, fluid couplings can’t multiply torque the way a torque converter can, so the four-speed Hydra-Matic was dependent on its geared ratios for acceleration and hills. To compensate, it was programmed to downshift automatically at part throttle, but that wasn’t always a good thing, and it was often helpful to hand-shift to Drive-Right or Lo for better performance.

Turbo Hydra-Matic had only three geared ratios rather than four, but they were very similar to 2nd, 3rd, and 4th in the four-speed Hydra-Matic: 2.48, 1.48, and 1.00, compared to 2.55, 1.56, and 1.00 in the older transmission. The extra-low Hydra-Matic 1st gear wasn’t needed because the torque converter could multiply engine torque by up to 2 to 1 (giving a total starting ratio of up to 4.96 to 1 in 1st gear) and then fade smoothly away, with no big drop in engine speed. The converter was also useful in 2nd and 3rd, providing a bit of extra torque multiplication without needing to downshift.

All this provided better real-world acceleration at all legal speeds — good enough that Turbo Hydra-Matic was programmed to only kick down at full throttle, eliminating the older transmission’s sometimes unwanted part-throttle downshifts.

On top of that, Turbo Hydra-Matic was mechanically simpler, weighed about 60 lb less than the old transmission, was just about as smooth, and had greater input torque capacity. It was probably less efficient than the four-speed dual-coupling units (and definitely less efficient than the older single-coupling Hydra-Matic), but overall, Turbo Hydra-Matic was a better, more modern transmission.

Cadillac owners who switched between Controlled Coupling and Turbo Hydra-Matic cars had to be extra-careful when selecting Reverse, which was next to Park with the new transmission and next to Lo with the old one. (Oscar Banker, who insisted the PNDLR pattern was unsafe, was undoubtedly outraged.) Otherwise, Cadillac arranged the controls the same way as on the older Hydra-Matic, with separate Drive-Left and Drive-Right (D2) positions. It was still essential to select Drive-Right in hilly terrain, although that made the shifts harsher.

Series 62 buyers couldn’t order Turbo Hydra-Matic as an option; the Cadillac Series 62 data book warned, “essential parts that are not interchangeable and precise production schedules require that all cars be built with the type of transmission designed for each body style. No substitution can, therefore, be made.” I don’t know of any period road tests of the 1964 Series 62, but a De Ville or Eldorado with Turbo Hydra-Matic felt more spry at all legal speeds, and was probably a few tenths of a second quicker 60 mph and through the quarter mile than a Series 62.

This transmission difference was a one-year-only oddity, probably a result of logistical issues at Hydra-Matic Division (which was still building three distinct transmission families in 1964). Starting in 1965, Turbo Hydra-Matic became standard across the Cadillac line, with a new variable-pitch stator (on all but Series 75 cars) to provide an extra half-step between the gears.

Even with its older transmission, the final Series 62 sacrificed very little compared to the De Ville. It was the same size (223.5 inches on a 129.5-inch wheelbase), and it took a sharp eye to distinguish a Series 62 from the senior models at a glance. It certainly wasn’t cheap: The turquoise Series 62 pictured above, which has Comfort Control air conditioning, an AM radio, and a few other options, originally listed for $6,188.80 including destination charge. That was over twice the average new-car price in 1964.

You paid $118.45 extra for the power windows that were standard on the De Ville and Fleetwood cars, but Series 62 cloth upholstery was nice enough (nicer, to my eyes, than the following year’s Calais interior choices), and if you could live with vinyl rather than leather seat bolsters, you could save up to $419 compared to a 1964 De Ville and be happy with your choice.

Only 35,079 1964 Cadillac buyers made that choice, however, and those that did found that after two years, their Series 62 was worth $150 to $250 less in trade than a De Ville, especially if they insisted on winding their own windows.

I doubt that had anything much to do with the transmission. The four-speed Controlled Coupling Hydra-Matic suffered some teething problems in 1956–1957, but by the early ’60s, it was a solid, reasonably dependable, surprisingly efficient transmission —even if fewer and fewer people today understand how it worked.

Related Reading

Vintage Autocar Road Test: 1964 Cadillac Coupe De Ville – “Somewhat Costly Motoring One-Upmanship” (by me)

Vintage MT Road Test: 1964 Cadillac Sedan DeVille – The Fastest And Best Classic Cadillac (by Paul N)

Carshow Classic: 1964 Cadillac Sedan DeVille Four Door Hardtop – Every Car Has A Story, But Some Are Just Better Than Others (by Spridget)

1964 Cadillac Fleetwood Eldorado – The Brief Return Of The Open-Wheel Eldorado (by me)

1965 Cadillac Comparison: Cadillac Calais Sedan Vs. Coupe De Ville – Was The Budget Caddy A Bargain Or A Bust? (by me)