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Thread: geering for ford 9 inch rear
          
   
   

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  1. #1
    tyler1967ss is offline CHR Junior sMember Visit my Photo Gallery
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    geering for ford 9 inch rear

     



    hi, new guy tyler here,recently purchased at auction 1967 chevelle with ford 9 inch rear super low geering, original 4 speed standard trans, 396 bb, rear tires are 255/60r15. can someone please tell me what to get for daily driver,ocational hiway gears? i like to order from summit racing, if you could recommend gears and part number that would be so great.thank you.tyler

  2. #2
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    A simple SWAG on my part. 3.25 or 3.50 or 3.73 / but there are many variables - even things like tire O.D. make a difference.
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  3. #3
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    Those rear tires have an OD of just 27" and the stock 4 speed is a 1.0 final drive ratio. If you run 3.25 gears you'll be turning 2831rpm at 70mph. If you jump up to a 30" rear OD tire the cruise revs drops to only 2548rpm. If you drop down to 3.00 gears those numbers drop to 2613 (27's) and 2352 (30's) at 70 down the road. You've got to balance what you want for driveability, economy and performance.
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  4. #4
    tyler1967ss is offline CHR Junior sMember Visit my Photo Gallery
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    thanks, if i want to keep tire size, what should i get for gears to run about 2300 rpm at 70 mpr?

  5. #5
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    Since this thread is not terribly old, just a few months then I thought I would add to it for
    others that read it later.


    A rear gear ratio of 2.7, trans final ratio of 1:1 and tires diameter of 27 inches would yield

    a 2352 rpm at 70 mph.


    If you have an OD trans with a final ratio of 0.7, then you could use a rear ratio of 3.9

    and the engine would turn 2378 rpm.



    TireSize_RPM-Calcs01-1.jpg


    TireSize_RPM-Calcs01-2.jpg
    Last edited by Indy; 08-03-2020 at 05:00 PM.
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  6. #6
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    What I do when I want low gears I put in the low pig I have a separate pig for hi way. Its is easier to pop the pig out than change gears
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    need to keep in mind low gears at high speed create a lot of heat. overdrive/short tires/low gears can lead to a burnt up rear end.

  8. #8
    Indy's Avatar
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    Quote Originally Posted by cffisher View Post
    What I do when I want low gears I put in the low pig I have a separate pig for hi way. Its is easier to pop the pig out than change gears
    OK, I will bite ...... what is a PIG ???
    .
    Last edited by Indy; 08-03-2020 at 05:06 PM.
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  9. #9
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    Quote Originally Posted by shine View Post
    need to keep in mind low gears at high speed create a lot of heat. overdrive/short tires/low gears can lead to a burnt up rear end.
    Good point, just because the engine is loafing along does NOT mean the rear gears are doing the same.
    .
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  10. #10
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    Quote Originally Posted by Indy View Post
    OK, I will bite ...... what is a PIG ???
    .
    rear gear case with gears intact, aka pumpkin, third member.
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  11. #11
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    I have a friend who still tells horror stories about when he got out of the Navy in '72 and drove back to S. Dakota from San Diego in July in a big block Chevelle with 4.11:1 gears, no air conditioning, a pregnant wife, and 2 dogs!!!! The right gearing is very important! PS, they're still married!
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  12. #12
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    rear gear case with gears intact, aka pumpkin, third member.
    Guess I should have figured that one out !
    .
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  13. #13
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    Quote Originally Posted by Indy View Post
    Guess I should have figured that one out !
    .
    Don’t beat yourself up, it’s slang terms. Now you know and can stump someone else.
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  14. #14
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    Quote Originally Posted by Dave Severson View Post
    I have a friend who still tells horror stories about when he got out of the Navy in '72 and drove back to S. Dakota from San Diego in July in a big block Chevelle with 4.11:1 gears, no air conditioning, a pregnant wife, and 2 dogs!!!! The right gearing is very important! PS, they're still married!
    I'm sure he realizes now, but if she survived that she's a keeper.
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