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  • Rear Axle: Diff ratio

    I am converting my 61 Hawk 259 manual/od to auto C4 .What diff ratio would be the best. ? It currently runs a stock 3.54

  • #2
    What's most important to you? Gears and tires make the feel of the car.

    Off the line acceleration - if so, keep the 3.54
    Quiet highway cruising - go up to a 3.07

    Tire widths and diameters change the equation as well:

    I once had a Stude with 6.70x14" tires on 4.5" wheels. Those skinny little hoops would spin the right rear at will.

    When I changed to DR70x14" on 6" Ford station wagon steel wheels, it felt like a different car. They were heavier and had so much traction, it almost seemed like the engine had lost power.

    When I tried 6.70x15", that was like changing the rear axle ratio and again, it felt like a different car; cruised down the road with almost no engine noise, but also almost no acceleration.

    jack vines
    PackardV8

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    • #3
      Stock (or close) diameter rear tire, you've got a great all around ratio right now.
      I would not change it. I drove my 259 powered Lark just over 93,000 miles with the same ratio. This means 300 mile trips, 250 mile trips, 75 mile trips and to the grocery store..!

      Again, the 3.54 is a great all around ratio.

      Mike

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      • #4
        The Fords that used the C4 typically had a 3.0/1 ratio rear axle, but, the small Ford makes power differently than the Stude. I agree with Mike, go with the stock 3.54/1, if you don't like it you can swap to the 3.07/1 later or go with a Ford axle 3.0/1 or the less common 3.25/1 ratio. The 3.54/1 works fine with my GM 4L60 overdrive trans, just as it did with the original OD three speed.
        sigpic

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        • #5
          C4 is a good transmission but an FMX is a great transmission. Why would you go to all the trouble to change from FMX to C4??

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          • #6
            I went from four-on-the-floor to automatic on my '62 Gran Touismo and like the automatic much better. Problem is, I'm not sure what my speed is; need to have someone drive at a given speed so I might figure it out. Going from stop to a certain speed is a lot smoother and the car picks up its speed faster.

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            • #7
              Originally posted by bensherb View Post
              The Fords that used the C4 typically had a 3.0/1 ratio rear axle, but, the small Ford makes power differently than the Stude.
              Just wondering if you could expand on what you've found to be the differences.

              I once owned a '66 Falcon 289" which came with the all-synchro 3-speed and a 2.80 rear axle ratio.

              jack vines

              PackardV8

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              • #8
                Jack,
                DR70x14" Really?? I haven't seen an alpha numeric size like that in decades!
                Jeffrey is correct as I have FMX guts in my FOM and it shifts superbly(hard but superb). I changed my ratio to 3:73 as I wanted the stronger acceleration but it does rev high on the highway -Approx 3000 rpm at 60 mph so you need to have your motor built to rev higher than stock. 3:54 is probably the best compromise.
                Bill

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                • #9
                  To directly answer your question, the best Ratio for a Direct Drive Trans. with a 259 is the one the Factory most often engineered for good performance and cruising with good economy.
                  THE Best all-around Ratio for the Torque/RPM range of that engine with a 1 to 1 Output Trans. would be the 3.31 Ratio.

                  I am surprised no one has asked HOW the OP was able to get a C4 Ford to connect to a Studebaker 259!
                  Input shaft, Torque Converter, Converter Housing, Throttle Pressure control all would seem to be a mismatch to a much newer Ford version of the old Borg Warner Ford-O-matic.

                  Any change from Overdrive to a Direct 1 to 1 Ratio Trans. is very definitely a step Backwards in My and most people's book!

                  With the 3.54 Ratio Axle you had plenty of acceleration AND you could cruise comfortably at at 70 MPH.

                  UPDATE: corrected the Typo on the Ratio, thanks Jack!
                  Last edited by StudeRich; 07-31-2020, 12:39 PM.
                  StudeRich
                  Second Generation Stude Driver,
                  Proud '54 Starliner Owner

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                  • #10
                    Originally posted by StudeRich View Post
                    With the 2.54 Ratio Axle you had plenty of acceleration AND you could cruise comfortably at at 70 MPH.
                    Of course, Rich meant the 3.54 ratio.

                    The world and how we perceive the automotive experience changes every day. I grew up driving the 3.54 and 3.31 Studebakers and the passenger compartment noise and the heat were just the way things were. A few years back, I rode from Spokane to the Colorado Springs IM in a restored '55 Stude. It was 90+ for three days each way. We survived it but those who didn't grow up with that would have thought they were dying.

                    Today, we've become accustomed to double-overdrive transmissions which cruise at 1500-1800 RPM, with sound insulation which quiets even that slight whirr, with electric fans which don't make a sound at highway temperatures and AC which enables the windows always closed.

                    Bottom line, if there's regular highway driving in a restored Stude's future, consider spending some money on AC, sound deadening, sealing the firewall and a 3.07 rear gear.

                    My Packard-powered '55 E12 has tall tires and is 2.95 in the T89 overdrive. It turns 2168 RPM at 70 MPH. Even that begins to be busy on the long stretches of interstate here in the west. However, sometime in the future, I'm thinking of building another TwinTraction Dana 60 with 3.73 gears and have a 2.68 top gear.

                    Then, there's that Viper T56 six-speed with overdrive on the top two gears I've adapted to the Packard V8. Sixth gear is .50, so with the 4.10s in the truck, it would give a 2.05 cruising gear.

                    It's all fun, however with only three speeds and a direct top gear, picking the sweet spot where the engine will be happiest is the challenge.

                    jack vines


                    PackardV8

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                    • #11
                      You are the only one who can decide on what level of performance and comfort you want. If you think that you want a taller G/R, like a 3.31 experiment with a set of 16" tires and wheels. They should give you about the same gear change. Reread Jack's post #2.

                      As for the trans change-your choice is a head scratchier. I guess if I didn't care about an OD, which I don't, I would dig up an available Studebaker Power Shift trans. It would be a lot less hassle. Parts are out there and you would keep it all Studebaker. Maybe you can explain why the C4?

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                      • #12
                        Originally posted by Hallabutt View Post
                        If you think that you want a taller G/R, like a 3.31 experiment with a set of 16" tires and wheels.
                        That depends entirely on the actual tire size. I went from 215-70-15 tires to 235-55-17 tires with vertually no change. The 17s are only about 1% larger in diameter.

                        sigpic

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                        • #13


                          That depends entirely on the actual tire size. I went from 215-70-15 tires to 235-55-17 tires with virtually no change. The 17s are only about 1% larger in diameter.

                          I'm not talking about low profile tires, which I think a complete waste on a stock Studebaker chassis.

                          Bill

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                          • #14
                            There are 2 reasons why a C4 trans is being considered
                            1 . I have been trying to source stude trans and associated parts since april but have had no luck
                            2 . My mechanic who specialises in engine transplants etc recommended using a C4

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                            • #15
                              Originally posted by PackardV8 View Post
                              Just wondering if you could expand on what you've found to be the differences.

                              I once owned a '66 Falcon 289" which came with the all-synchro 3-speed and a 2.80 rear axle ratio.

                              jack vines
                              Well, RPM for one. From my experiance the Ford revs both faster and higher comfortably; in stock form anyway. I've had MANY Mustangs, (basically a Falcon in different clothes) and all the V8 auto trans ones had 3.0 axles when I got them, as did my Thunderbird, But I do have 2.69, 3.25, 3.55, 3.70 and 4.11 third members as well. I've put way more mileage on with the 2.69, though for normal around town driving I like the 3.55 best.
                              sigpic

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