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4 speed automatic transmissions

Home Page Forums Discussion Topics – Ask the Experts 4 speed automatic transmissions

This topic contains 6 replies, has 1 voice, and was last updated by 7 years ago.

Viewing 7 posts - 1 through 7 (of 7 total)
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    Nov 15 2009, 4:55 PM
    4 speed automatic transmissions

    I’ve been told that all Jetfire automatic transmissions are 4 speed hydromatics. i only feel 2 shifts and it appears to wrap up a lot and shift down a lot whether accelerating rapidly or normally. Are the F85 (non-jetfire) autos different, i.e. 3 speed?

    Nov 20 2009, 10:21 PM
    Re: 4 speed automatic transmissions

    That’s the first I’ve heard of that. I would be surprised. I thought it was either a 3 speed hydramatic or a 4 speed manual. I had the 3 speed hydramatic in my car (still have it in my basement) the first few years I owned the car. It did wind up and then drop down into gear (losing some power along the way, which was my chief complaint with it). Mine particularly did that between 2nd and 3rd. You can adjust the bands to make it a tighter shift, but I never got that far to do it. I decided to install a ’62 Borg Warner 4 speed (came out of a Skylark with a 215)and I’d never go back to the auto.

    Nov 21 2009, 1:53 PM
    Re: 4 speed automatic transmissions

    Thanks for your comments. i know that at least some of the automatics were 4-speed hydramatics. just dont know if all of them were, especially in different years.

    Nov 29 2009, 5:48 AM
    4 Speed Automatics

    I’m still on vacation and away from my reference material, but I’m sure that the 1963 and 1964 F-85 used the Roto-Hydramatic three speed transmission. (Commonly referred to as the Slimjim) I don’t know about the ’61, but Wikipedia states that the Slimjim was used by GM from 1961 through the 1964 model years. Wikipedia also says that the shift from first to second was “long and drawn out”. Perhaps that is what you perceive as wrapping up? Or maybe it does need an adjustment. It is 46 years old after all. The factory service manual has a whole chapter on adjusting and or rebuilding the Slimjim. And if you want to rebuild it yourself, it looks like Kanter sells rebuild kits for it . I’d imagine that your local NAPA store or other sites on-line could provide a rebuild kit as well.

    Dec 8 2009, 3:59 AM
    4 Speed Automatics

    If you have any questions about the transmissions on the F-85’s, just get a 63 Service Manual and check out section 3 and go to page 3-101 and that will tell you all about the transmissions. They are 4 speeds and the gear ratios are as follows, First 3.64:1, Second 3.03:1, Third 1.57:1, and Fourth 1:1. Reverse is 3.57:1. I also read somewhere that the ratios were different in 62 and 63 but I haven’t been able to locate that information. I did check the 62 Service Manual and that had the ratios the same as 63. When I find that information I’ll post it.

    Jan 8 2010, 9:29 PM
    Re: 4 speed automatic transmissions

    I’m new today on the forum. Hello. I’ve had my 62 Cutlass convert for a little over two years now. And I appreciate the confirmation about the 4th speed. I have been certain that I could feel that shift at about 60-65 in mine but as others have said here I was told no they only had 3 speeds. I do agree about 1st to 2nd being long and drawn out 😉 Last fall, just before winter shutdown, I had been noting a serious surging unless I started up in the ‘S’ position and then shifting into D at about 25 mph. Seems to run OK after that. Does this imply a problem with the trans or something else??? Thanks!

    Mar 9 2010, 6:11 PM
    Re: 4 speed automatic transmissions

    Re this entry: “Last fall, just before winter shutdown, I had been noting a serious surging unless I started up in the ‘S’ position and then shifting into D at about 25 mph. Seems to run OK after that. Does this imply a problem with the trans or something else??? Thanks!”

    3/9/10 after the weather got OK to remove the covers, I checked and found the fluid was down about 1/2 pint. That aint much but it was enuf. Bringing the level up has solved the surging problem. Trans shifts as smooth as can be expected from that design. LOL



    The 61 F-85’s were 3 speed Automatics, which have 3 forward speeds and 1 reverse. The 62 and 63 F-85’s were 4 speed Automatics, which have 4 forward speeds and 1 reverse. The shifts from 1st to 2nd were basically not felt when it shifted and you could feel the 2nd to 3rd shift and the 3rd to 4th shift.
    The F-85 came standard with a 3 speed syncromesh transmission and the Automatic and 4 speed were options.


    I’m going out on a limb and say, of over a dozen 62/63 automatics I saw, all were the 3 speed slim jim. A lousy trans it was, for such a small displacement engine. Yes big cars had a 4 speed, but not the F85. Bruce Roe



    The 1962 Service Manual calls it a “four speed automatic” and even shows the four different hydraulic flow paths in the color diagrams, but in reality this trans is pretty much the same internally as the three speed auto. The “fourth” speed comes from the way the “accelerotor” is used to change the torque multiplication in the converter. This is similar to how the switch pitch transmissions from 1964-67 operated.


    OK the manual does describe 4 gear ratios. So there is no specific “shift” from “third” to “fourth”; a variable ratio follows throttle. Guess that is technically OK, but I’m having trouble counting that as a fourth “gear”. The later 60s switch pitch converters were independent of gear shifting. Bruce Roe



    OK – See what you ’63 Jetfire gurus can tell me about This:
    I’m in the middle of a total restore of said vehicle and am now trying to get the transmission squared away. I’ve been involved with 3 different cars and they all have the so-called SlimJim auto tranny which is a 3-speed with the terrible 1st to 2nd shift ratio.
    I have 2 of these ubits in unknown condition and have just taken them to an acknowledged reman source for exam and reman as necessary. I thought I would be helpful to the reman guy and so I copied the entire transmission section (Section 3, F-85) out of the manual and sent it to him. I also read this section and realized it did NOT cover the SlimJim and instead covered a more conventional 4-speed Hydramatic! I would love to have the 4-speed unit in my car but I can’t find one anywhere – was this just a goof in the manual or are there 4-speed Hydramatics that fit the 215 actually out there?


    That trans has 3 distinct gear ratio, and a variable ratio fluid coupling that
    sometimes is referred to as a 4th speed (not by me). I don’t believe there
    is another automatic that just bolts up. The Special 215 used a torque
    converter and 2 speed. I collected that flex plate & flywheel in hopes of
    bolting on a newer torque converter trans, like a TH350 with an adapter
    plate. But never finished the idea.

    That trans doesn’t like abuse, and are hard to get fixed. In a Jetfire that
    trans is totally unable to handle the torque, I could never shift under
    power. In addition, the shift control mechanism is badly suited to a hot,
    small displacement engine. My opinion is, all Jetfires should have 4 speed
    manuals, or a modified TH350/TH400 trans. At one time I had 13 slim
    jims around in various states of broken. good luck, Bruce Roe

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