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Thread: rear end swap????

  1. #1
    Registered Member reborn55's Avatar
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    rear end swap????

    After 21 years of M-20 and 3:70 rear end and hipo 283 it may be time for a change--I have complete 3:08 sitting in the corner of garage--thinking about changing out the rear ends. Can't really go to overdrive just yet with early model 283 still in car. any opinions. Just a little tired of running 3500 rpm's and more on long trips. getting ready for Route 66 tour in a year or so. May just opt out for crate motor and 200r. thanks. Still liking shifting but running 3500 and above on the interstate for 3-400 miles at a time gets old.

  2. #2
    Registered Member chevynut's Avatar
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    Why can't you go to an overdrive transmission?
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


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    Registered Member WagonCrazy's Avatar
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    I'm running a nearly stock 350 crate motor with a 600 cfm carb, and a 200-4r trans with a 2000 rpm stall speed torque converter, and 3.55 rear gears in my 9 passenger wagon.
    70 mph at 2400 rpms.

    if I had a 3.08 in there, the rpms would make this thing waaaaaaaay tooooo sluggish.
    1957 Nomad- LS1/T56 on C4 chassis
    1959 Fleetside Apache 1/2 ton, shortbed, big window, 327ci.

  4. #4
    Registered Member reborn55's Avatar
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    First--I still like the 4speed and second early 283 where the starter still bolts to bell housing--

  5. #5
    Registered Member chevynut's Avatar
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    Quote Originally Posted by reborn55 View Post
    First--I still like the 4speed and second early 283 where the starter still bolts to bell housing--
    Seems like you still have some options. What about a Tremec 5-speed? They bolt right to the stock muncie bolt pattern so you can keep your bellhousing. I think another option is a T5 but I understand they're not very strong.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
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    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  6. #6
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    3500 rpm sounds very high for a 3.70 rear gear unless you cruise pretty fast.

    But let's use your numbers. If you go with a 3.08 you still are going to be turning 2900+ rpm at the same speed. Still pretty high by modern standards.

    A typical overdrive transmission has a 0.7 overdrive ratio. This would take you to 2450 rpm if you didn't change the axle gear ratio.

    The other half of the rear gear swap is that you reduce your torque at the rear wheels in any gear by 18%. This is going to cause you to slip the clutch when starting from a stop, or to downshift to 3rd much more often. In fact 3rd is going to feel like what you have now in 4th. With the overdrive you wouldn't have this performance reduction.

  7. #7
    Registered Member reborn55's Avatar
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    I ran the numbers like you did--with my setup and tires I would only decrease the rpm's by about 500 so it is not much of a trade off. Still researching 5 speed as I took it out for a drive today and was a joy to drive. Do like the idea of automatic overdrive and will look into it also. Whenever we take a long trip--usually 200 miles or more a lot of it is interstate where we run 70-75 MPH most of the time if not more. thanks for info

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    I run a TKO-600 in my 55 with a .060 over 396 with two Holley 600s and cruise 2000rpm at 70mph with a 56 inch wide Dana 60 with 35 spline axles and 3.54 gears and a Powerlock. I Run 275/60/15 tires on Torq Thrust Ds that are 8.5 wide. Biggest complaint with Tremec hard to hit 3rd at 6000 rpm, however, I find the 700R4 in my 56 boring to drive by comparison.

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