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Ford 8 inch rear gearing question?

Discussion in 'The Hokey Ass Message Board' started by billj, Sep 29, 2010.

  1. billj
    Joined: Nov 1, 2003
    Posts: 184

    billj
    Member

    Hi,
    I just took my 51 Shoebox Ford for it's first ride. It has a 289 with 75 Ford truck 3 speed tranny and thew Ford 8 inch rear end with unknown gearing.
    It was a fun ride with alot of get up and go, tpp much. I don't have the speedo hooked up yet but I am pretty sure I was doing about 50 and the car was revving pretty much.

    The question I have is would changing the gears on the rear do me what I need or do I need to put a 4 speed in it. A friend said the 3 speed truck trans with the 1:1 final drive would be good but not knowing the gears in the rear, who could tell.

    Would the taller gears allow good cruising speeds?

    Thank you, Bill
     
  2. Burny
    Joined: Dec 20, 2004
    Posts: 1,600

    Burny
    Member

    Bill, probably, but you need to get the gear ratios for the transmission you have and your rear tire diameter and plug the numbers into a gearing calculator. The good thing is that the 8" ring and pinion come out as a unit, so I am told they are fairly easy to change out.

    Go here to put your numbers in once you get them: http://www.grimmjeeper.com/gears.html

    Also, check and see if your rear has the aluminum manufacturing tag on it (should be on the droveshaft side of the punkin'). The set of numbers on the lower left will tell you waht your rear gearing is. Here's a site that might help: http://www.woodyg.com/fairlane/finfo/fordrears.html

    Good luck.
     
  3. Both the 3 speed and the 4 speed will have 1:1 top gear, so that won't do anything for you. If the tag is missing from the rear end, then jack up the rear, hold one tire while spinning the other and count the driveshaft revolutions for 1 complete tire revolution to figure out the gear ratio.
     
  4. billj
    Joined: Nov 1, 2003
    Posts: 184

    billj
    Member

    The tag is missing. I will try your method and see what I get. Are 8 inch rear end gears expensive? Is it wise to get used ones"

    Thank you again, Bill
     

  5. billj
    Joined: Nov 1, 2003
    Posts: 184

    billj
    Member

    Wait, it is a posi, what can I do with that?
     
  6. toms37gmc
    Joined: Aug 10, 2006
    Posts: 147

    toms37gmc
    Member

    8" rear gear sets (pumpkins) are pretty easy to find. The most common is 2.73 , 3.00 are fairly common too. I'm surprised the engine was running at high revs. Maybe it being a posi it has some sort of performance gears in it. I have a 2.73 in my truck and at 55mph its turning about 2000rpm.
    8" gears are pretty durable esp behind a mild engine under 350 cubes. My nephew runs them behind a 200HP race car on dirt and has yet to break one in 3 years of trying.
     
  7. Well do like hotroddon says jack it up and if its a posi than don't hold the one wheel and. Count the revolutions on the driveshaft to one wheel rotation that should tell you the ratio for the rear
     
  8. With a posi you do the same thing, only don't hold the opposite wheel. Turn the wheels, count the driveshaft revolutions

    Here's another way if you have a tach and Speedo. Take a drive in your car

    In top gear (unless you have overdrive) note your RPM and MPH. Then

    Gear Ratio = (rpm x tire diameter) / (mph x 336)


    8" posi are pretty rare. i would never buy used gears personally unless they came from a rear end shop that would stand behind them. New gear sets for an 8" run about $199
     
  9. I also have an 8" in my roadster with a spool with 462's and have done figure 8's in asphalt parking lots and will be racing in the jalopy drags this weekend I hope the limit is they only make 462's 411's 355's. And highway gears for 8"
     
  10. billj
    Joined: Nov 1, 2003
    Posts: 184

    billj
    Member

    I guess I knew you just don't hold one wheel after I posted. The 2.73 sounds good. Thank you for all the ideas, I will do some more resarch and see what I come up with. This site is great.
     
  11. Hnstray
    Joined: Aug 23, 2009
    Posts: 11,850

    Hnstray
    ALLIANCE MEMBER
    from Quincy, IL

    8" fords are typically 2.79, not 2.73...........not that it matters much.......

    Ray
     
  12. toms37gmc
    Joined: Aug 10, 2006
    Posts: 147

    toms37gmc
    Member

    Sorry, my typo, or brain fade.
     
  13. Jalopy Joker
    Joined: Sep 3, 2006
    Posts: 26,004

    Jalopy Joker
    Member

    another source for figuring things out is at: project33.com once there click on calculations, I have tried the turning a wheel and checking the drive shaft with limited correct results. best to pull third member out and count the gears teeth. the posi is not something to sell cheap. 8" non posi are pretty cheap and fairly easy to find. plus, by pulling 3rd out you will know the spline count on axles.
     

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