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Hot Rods rear gear opinions

Discussion in 'The Hokey Ass Message Board' started by blackanblue, Aug 31, 2019.

  1. blackanblue
    Joined: Feb 20, 2009
    Posts: 408


    52 GMC half ton 350 high output crate motor with claimed 340 horse backed by a built 700r4 with a one wheel peel open drive rear maybe 3.10. I want to put a posi in so while its open, change gears, we do lots of long hauls and quite often pull our old camper maybe 3500*. Right now running 60mph around 2000 2200 rpm what gears would be ideal for snappy around town and hyway hauling. Snappy, never thought I'd ever say that, must be getting old. Thanks.......Snappy,, kinda growing on me.
    Unique Rustorations likes this.
  2. My first choice would be 3.73. Second would be 3.42. 3.42 would be better on the freeway, 3.73 better around town and towing.

    Sent from my iPhone using The H.A.M.B. mobile app
    pitman, juan motime, loudbang and 4 others like this.
  3. Boneyard51
    Joined: Dec 10, 2017
    Posts: 5,024


    They don t make gears that are great in town and great on the highway, you must make a choice in between and that compromises both town and highway. For me it would be around 3:50, that’s what I’m putting in my Galaxie! But I don’t have the overdrive transmission like you, so I would recommend around 3:70 or so, maybe a tad lower.

    Last edited: Aug 31, 2019
    Special Ed likes this.
  4. oldiron 440
    Joined: Dec 12, 2018
    Posts: 2,214

    oldiron 440

    3.42 can be snappy with the application of enough throttle and won't kill you on the hyway.

  5. Mr48chev
    Joined: Dec 28, 2007
    Posts: 29,515


    I just bought a 3.5 limited slip 9 inch Ford for my 48. 292 straight six, mild cam lump ports 4 barrel intake with runners that are too big for common sense and cast headers backed up by an AX-15 5 speed.
    I may end up pulling a light weight camp trailer.
    This chart lets you put in a few knows and get the rpm at certain speeds

    This one is for don't laugh electric car folks but it is so freaking simple to use. Plug in any 3 known variables and get the 4th. The only thing is that you end up multiplying the result rpm by the overdrive ratio to get your rpm with overdrive
    That doesn't take much though as mine at 70 with a 26.5 tall tire 3.5 gears came out to 3106 rpm X .79 od ratio = 2795 rpm at 70 in 5th gear.
  6. mgtstumpy
    Joined: Jul 20, 2006
    Posts: 8,837


    I have 3.54:1 with a 5lt and 700R in my 35 Chebby. Cruises @ 2k rpm at 60mph with 28mpg and 235.75.15 tyres.
    pitman and firstinsteele like this.
  7. wicarnut
    Joined: Oct 29, 2009
    Posts: 7,402


    3:73 with your 700R4 OD trans is what you want. Plenty of Snappy and will pull your trailer. no problem.
  8. raven
    Joined: Aug 19, 2002
    Posts: 4,614


    Where your cam comes in is going to have a lot to say about what the right gear should be.

    Sent from my iPhone using H.A.M.B.
    X-cpe likes this.
  9. Mike VV
    Joined: Sep 28, 2010
    Posts: 2,387

    Mike VV
    from SoCal

    Talk to the experts..!
    The folks that actually build the T-200-4R's and the T-700-R4's. They will tell you, the best overall rear gear is the 3.73. Even the Ford ADO's, same thing.
    Been their..!

    mgtstumpy and Truckdoctor Andy like this.
  10. DDDenny
    Joined: Feb 6, 2015
    Posts: 15,037

    from oregon

    It's not always the perfect outcome but tire diameter juggling can play a big roll in gear ratio selection, some cars allow more flexibility than others though.
    A non fendered car may not look quite right with a shorter tire but it may accomplish a "happy medium" when the ideal gear ratio is not available or the timing is not right for an expensive ring and pinion change.
    On the other hand, full bodied cars have limited clearance to accomodate large diameter tires without major modifications.
  11. bill gruendeman
    Joined: Jun 18, 2019
    Posts: 526

    bill gruendeman

    700r4 od = .68 ? In o/d so 1 3.73 becomes 2.53 . 373 for take off and 253 for highway looks like win win to me
    pitman and Truckdoctor Andy like this.
  12. miker98038
    Joined: Jan 24, 2011
    Posts: 604


    IIRC, the 700 has a pretty deep first gear to get you rolling. You might also want to talk to the rebuilder and see if it’s set up for a locking torque converter. What’s the cam like in the motor?

    My buddy has a 330hp GM crate (several years ago) with 3.5’s or so in a 56 Nomad. It locks up a little early in town. Lots of variables, but there’s a sweet spot somewhere.
  13. Mike VV
    Joined: Sep 28, 2010
    Posts: 2,387

    Mike VV
    from SoCal

    This is exactly why the T-200-4R is a better all around trans.
    Lighter than the T-700
    Smaller than the T-700
    Much...better gear ratios than the T-700
    Properly built, equal to a "little" stronger in the first three gears than the T-700-R4.
    Much closer rpm drop at all gear shifts than with the T-700-R4 so you don't need two redlines marked on your tach.

  14. mgtstumpy
    Joined: Jul 20, 2006
    Posts: 8,837


    Forgot to mention my DD (SUV) has 3.73:1 rear axle with OD auto and 235.75.15 tyres. My 35 Chevy is a lot lighter and can easily get away with 3.54:1. 3.73:1 would be better in a heavier PU. If you use a 200R or 700R and need to drive 1:1, e.g. Tow a heavy load, leave it in 3rd gear and don't use OD.
  15. gimpyshotrods
    Joined: May 20, 2009
    Posts: 18,315


  16. F-ONE
    Joined: Mar 27, 2008
    Posts: 2,828

    from Alabama

    My OT truck, 5.0 AOD with 3.08 rear is made for the Hwy only. It’s a miserable towing vehicle.
    Getting moving is hard on the engine.
    Stopping even at low speed is hard on the brakes.
    You really really need that engine / gear braking capability. Just that little extra helps with grades.
    It’s not fun to be pushed through the yellow/red at 3 mph with a heavy trailer.
  17. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 3,372

    from illinois

    There's trailer brakes , ya' know ..........
  18. blackanblue
    Joined: Feb 20, 2009
    Posts: 408


    OK so I decided on 373's thanks for the input,,,you guys are great.

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