A Status Report

You may be wondering, “When is Ate Up With Motor going to stop messing around and provide some actual new content?” This is a fine question and you’ll find an answer of sorts below.

For the past X number of months, I have been laboring away at a revamp of the second part of my 2010 Hydra-Matic article, covering other early GM automatics (Dynaflow, Powerglide, Turboglide/Triple Turbine, and the second- and third-generation Hydra-Matic). This has been easier said than done because of the sheer scope of the article, which I must admit was not one of the smarter editorial decisions I’ve ever made.

To be clear, I’m not simply going through an older article and tidying up the grammar and punctuation. I’m actually trying to delve into the detailed workings of each of these transmissions in an effort to understand and then explain how they operate, which has involved digging through service manuals, technical literature, and an alarmingly long list of patents (the deciphering of which, I must say, requires patience, dedication, and a unique species of masochism). This is something that, to be perfectly frank, I had skimmed over in the original version of the article, to its occasional detriment.

Being a professional writer, but not an engineer, I am conscious of (and sometimes guilty of) a certain authorial tendency I call “black-boxing.” This occurs when you have a broad idea of what something is supposed to do, but really don’t grasp the mechanics of how and lack the time and/or the technical background to puzzle it out. So, you treat that system as a black box: You describe where it’s located, what it does, mention salient details that differentiate the black box from other or previous black boxes, and carefully tiptoe around the parts you don’t understand well enough to explain. You might say, for example, that a new torque converter now provides 20% more stall torque while having only the most approximate idea of how a torque converter operates or what “stall” means in this context.

(Writers also sometimes do this if they’re missing certain non-technical facts and have no way to get the missing information, at least in time for their deadline. Some readers and a few editors get irate about this — just as some editors despise the passive voice, which is an important black-boxing tool — but it happens and sometimes there’s no way around it.)

As you might expect, this can lead to various factual errors and misconceptions, some of them inherited from other writers who didn’t understand the thing either. The big problem with black-boxing is that you don’t necessarily recognize when you make a mistake. It can also compound other types of factual screw-ups. I’ve seen at least two historians (who shall remain nameless) present narrative descriptions of some of these transmissions that are reasonably accurate except for the troublesome fact that they’re describing a different transmission than the one they’ve named.

I’m trying very hard to avoid that kind of thing this time around, although there are still going to be compromises in the interests of readability and space. Service manuals for these transmissions often spend 30 or 40 pages just describing the functional basics, and even that often presumes a lot of prior knowledge on the part of the reader. Take a look at a complete hydraulic system schematic for even the most rudimentary two-speed automatic and you’ll see why at some points I had to say, “Yeah, that’s going to have to do.”


Figuring this out for even one early automatic transmission is a lot of work, as I found with Hydra-Matic. The problem this time around — and the reason it’s taking so long — is that this article tries to deal with (depending on how you do the count) at least 11 distinctly different transmissions of several distinct varieties, viz:

  • Dynaflow
    • Early dual-impeller/dual-stator/single-turbine (1948–1952)
    • Dual-turbine/single-impeller series:
      1. Twin-Turbine Dynaflow (1953–1954)
      2. Variable Pitch Dynaflow, single-stator (1955)
      3. Variable Pitch Dynaflow, dual-stator/Twin Turbine/Turbine Drive (1956–1963)
    • Flight Pitch Dynaflow/Triple Turbine (1958–1959)
    • Dual-Path Turbine Drive (1961–1963)
  • Powerglide
    • Early dual-impeller/dual-stator (1950–1952)
    • Single-impeller/single-stator self-shifting series:
      1. Iron-case (1953–1962)
      2. Corvair Powerglide transaxle (1960–1969)
      3. TempesTorque (1961–1963)
      4. Aluminum-case (1962–1974)
    • Torque Drive (1968–1970)
  • Turboglide (1957–1961)
  • Hydra-Matic
    • First-generation single-coupling/four-speed series (described in Part One)
    • Second-generation dual-coupling (Controlled Coupling Hydra-Matic) (1956–1964)
    • Third-generation single-coupling/three-speed (Roto Hydra-Matic) (1961–1964)

Some of these were closely related to each other (for instance, the earliest Powerglide and the early dual-impeller Dynaflow were more alike than not), but you can see the scope of the problem, or, perhaps more to the point, the problem of scope.

Now, I could split each of these transmissions into a separate article and run them one at a time between now and Labor Day. There would be several irritating practical and logistical problems involved in doing that, however, and I’m not sure anyone would really be that thrilled to read the text that way. Also, because some of these transmissions are closely related to one another, it does make sense to discuss them together. (Flight Pitch/Triple Turbine/Turboglide makes a lot more sense considered as an extension of the Twin-Turbine Dynaflow, for instance.) If I had it to do over again, I would probably have separated the second- and third-generation Hydra-Matics into their own article, but it’s a little late for that now.


The lengthy and involved work involved is currently entering its final stretch, so I will hopefully have the revised article done Sometime Real Soon Now. I had hoped to have it ready this week, which is the eighth anniversary of the creation of this website, but that will depend on my comprehension levels of the remaining material and the intrusion of other work.

So, I appreciate your patience and hope to have something more substantive for you in the very near future!


Add a Comment
  1. Thank you for keeping us up to date with your progress Aaron.
    Also I think your articles are at once accurate, impartial, and entertaining.
    Good job you didn’t choose politics as a career!.

  2. We appreciate the incredible amount of work and dedication you invest in this site. It will surely be worth the wait for the revamped article. Thanks so much for your time and effort.

  3. Thanks so much for your hard work and dedication to accuracy. I enjoy tremendously each of your articles that I read. waiting patiently for the revamp.

  4. Soon enough if correct.

  5. I’m guilty of black boxing when I have to summarise a technical point within my non-technical pieces. Your commitment to parsing out the real story is not only invaluable, but inspiring as well. Looking forward to further AUWM stories.

  6. The articles are always worth the wait! A longer wait often means a longer read, too. Keep up the excellent work.

  7. I’m consistently in awe of the level of detail your articles go into (and how they remain riveting despite the minutiae, something very few writers can achieve on a regular basis).

    It must take a colossal amount of work to produce each article so I for one am more than happy to wait :)

    1. This transmission thing feels like writing a dissertation, if that tells you anything. I’ve been trying to decipher vector sum diagrams. Vector sums! I haven’t dealt with vector sums since college, which was, er, time ago.

  8. Yours is one of the best websites I’ve discovered. Thankyou for all your work.

  9. Your site is the best automotive site I have stumbled across. Keep up the good work!

  10. Thanks for keeping us in the loop, Aaron. The content on AUWM site is so thoroughly researched and coherently presented that it would be churlish for any of us to be impatient. :-)

    As a recovering technical writer myself, I know there comes a time when, to keep your sanity, you just have to say the moral equivalent of, “Look, pal, the framis gets disaggregated, OK? Look it up!” To your point, however, sometimes the “look it up” part involves material that wasn’t always well constructed, or doesn’t hold up over time. Your dedication to completeness and accuracy is greatly appreciated.

    1. Thanks, George. An issue I’ve repeatedly confronted in dealing this this article is that while it’s often tempting to say, “Just look it up,” with some of this stuff, doing so leads you into a frustrating array of basically circular definitions. What is a framis? “It’s the thing that disaggregates.” What’s disaggregation? “A natural function of the framis, q.v.!”

      To give you all a further update, the initial draft of the revised text is about done. It needs lots of copy-editing, having been written in a fairly scattershot way over the course of months, and there are a number of technical decisions I need to make. Its length has more than doubled compared to the pre-revision version and at this point is about 21,000 words, not including the bibliography!

  11. I really do not care how long you take as every one of your articles is a unique gem. Thank you for your dedication.

  12. I didn’t read all that crap, I’m out this is BS.

  13. Aaron if you can make all of these automatic transmissions easily understandable for the layperson you deserve a Nobel prize or a Pulitzer, or something!

    1. I am hoping that people will come away from it feeling like they better grasp of the mechanics. I feel like I’m still giving somewhat short shrift to the hydraulic function — I went back into the Hydra-Matic text to try to explain the idea a bit better — but while the principle is really fairly straightforward, the hydraulic control valve layout of even a simple two-speed automatic becomes like a street map. Or a computer program, since the basic principle is essentially mathematical.

      (The principle: A centrifugal governor driven by the output shaft delivers hydraulic pressure P proportional to road speed while a throttle-controlled valve delivers hydraulic pressure TV proportional to throttle/accelerator position. Each shift action requires opening or closing a shift valve normally held closed by throttle valve pressure and spring loading S, so the transmission will automatically upshift when P > S + TV and downshift if P falls below S + TV. Add some manually selectable choices — such as Neutral, Reverse, and Low — and you get a shift program that becomes more and more complicated the more speeds and manual choices you add. With a pre-computer transmission, this is all-analog, so you end up with a complicated network of different hydraulic lines and control valves to handle it all!)

  14. Keep the faith good sir! You are not attacking an easy subject. Automatic transmissions always seemed like black magic to me. The advancements in a given period and variations must be mind boggling. I hope your future article will shed light on feeble mind. Torque converters? What?

    1. Edward,

      You may be sorry you asked!

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