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Customs Merc rear end

Discussion in 'The Hokey Ass Message Board' started by 50 Merc Man, Dec 29, 2021.

  1. 50 Merc Man
    Joined: Aug 2, 2020
    Posts: 358

    50 Merc Man
    Member

    Ford or Merc differentials
    Question guys, the rear end in my Merc is low geared, feels like possibly 4:11’s, I have a 3 speed w/overdrive in it which makes it wind out even more, what do you recommend for a taller gear so I can drive it on the freeway without hitting 5000 rpm’s lol, possibly 3:73’s? Help me out guys
    Mike C
     
  2. seb fontana
    Joined: Sep 1, 2005
    Posts: 7,463

    seb fontana
    Member
    from ct

    If you have 4.11 gear in it would be around 2,95..
     
  3. 50 Merc Man
    Joined: Aug 2, 2020
    Posts: 358

    50 Merc Man
    Member

    2.95???? Can you explain that to me please?
     
  4. Mine has a 9". When i got it, it had 4.11, or something close to that. Changed it to 3.16 and it runs on the freeway just fine now. Used to pull 4500rpm, now it's about 2600rpms at 70. I think 3.55's are the best though.
     
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  5. If your overdrive is working, when engaged the .7 OD ratio effectively drops your final drive ratio to a 2.87 (assuming a 4.10 rear axle).
     
    ottoman likes this.
  6. If the rear is the original Dana, the ratio is more like 4.27. Is the over drive unit working? If it is, the overall ratio would be about 2.95
     
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  7. seb fontana
    Joined: Sep 1, 2005
    Posts: 7,463

    seb fontana
    Member
    from ct

    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^!!
     
    X38 likes this.
  8. 50 Merc Man
    Joined: Aug 2, 2020
    Posts: 358

    50 Merc Man
    Member

    Yea it’s workin, when I bought the car, the previous owner didn’t have the overdrive hooked up!! Is it a matter of changing out the gears themselves or replacing the whole punkin center? I like 3.55’s idea
     
  9. seb fontana
    Joined: Sep 1, 2005
    Posts: 7,463

    seb fontana
    Member
    from ct

    The car didn't come with 4.27 for no reason plus more cubes/hp than a Ford. You will loose a lot in first three gears, like 17%.
     
    X38 likes this.
  10. 50 Merc Man
    Joined: Aug 2, 2020
    Posts: 358

    50 Merc Man
    Member

    It winds out too much, too much strain on that little flattie man
     
  11. phat rat
    Joined: Mar 18, 2001
    Posts: 4,680

    phat rat
    Member

    If your OD is working you won't like the higher gears like 3.55. keep the 4.11's and use the OD. Years ago, early 60's, I ran 5.13's with a flattie now that winds a motor up going down the highway. But I still drove it to the drags close to 100 mi away
     
  12. 50 Merc Man
    Joined: Aug 2, 2020
    Posts: 358

    50 Merc Man
    Member

    I am using the OD bro, I’ll figure something out
     
  13. The effective rear end ratio is under 3 with a working O/D and it's 'winding out too much?'
    How fast are you going?
    You say 5000 rpm, but what is it really? Are you using an accurate tachometer?
     
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  14. 19Fordy
    Joined: May 17, 2003
    Posts: 7,534

    19Fordy
    Member

    I recall49-51 Merc station wagons had a 3:31 rear gear but are pretty rare.
     
  15. Beanscoot
    Joined: May 14, 2008
    Posts: 2,375

    Beanscoot
    Member

    Maybe cruising speed is over a hundred and twenty?
     
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  16. miker98038
    Joined: Jan 24, 2011
    Posts: 769

    miker98038
    ALLIANCE MEMBER

    I’m not sure about a 50 Merc. But mid 50’s o/d Ford’s were all around a 4.11 or so. 6 cylinder wagons used the 4:27 Dana’s, and Thunderbird’s the 4:11. Passenger cars either 4:11’s or a 3.9?, maybe a 3.73 in Kansas. They were all about a 27” tire. Those ratios didn’t change much even after the 9” or the 312’s were introduced, as long as the o/d was there. Once the FE came out, I don’t know.

    But even in Brawley, with 3.55’s your going to be pretty hard on clutch’s and spend more time in 2nd over on the highway than you want to. On the other hand, coming home from Banning you can go like hell.
     
  17. Beanscoot
    Joined: May 14, 2008
    Posts: 2,375

    Beanscoot
    Member

    Okay, I just plugged the numbers into one of those online calculators.
    5,000 rpm, 4.11 diffy, .70 OD and 27 inch tall tires works out to be 139-1/2 miles an hour.
    But then some guys like to drive fast!

    Edit: With the 4.27 rear end gears it would only be 134 miles an hour.
     
    Last edited: Dec 30, 2021
  18. twenty8
    Joined: Apr 8, 2021
    Posts: 1,046

    twenty8
    Member

    Here is some excellent info on the transmission.
    https://www.motortrend.com/how-to/1007sr-borg-warner-overdrive/
    Note that the overdrive is 0.7 to 1.

    Here are the gear ratios for the transmission.
    Ford & Mercury Cars
    With the 28-24-18-14 Cluster Gear and the 16 tooth Main Drive Gear (1949-50)
    1st Gear: 2.820 to 1
    2nd Gear: 1.604 to 1
    3rd Gear: 1 to 1
    Taken from the following link.
    http://www.vanpeltsales.com/FH_web/flathead_trans-gearratios.htm

    Here are the rear end ratios.
    Taken from post #2 in the following thread.
    https://www.jalopyjournal.com/forum/threads/1950-mercury-rear-end-ratios.944120/

    All the work done for you.........:)
    Calculation
    Engine RPM: 2233
    Transmission Ratio 1 : 1
    Overdrive Ratio 0.7 : 1
    Ring & Pinion Ratio 4.27 : 1
    Tire Diameter inches: 27"

    Total Gear Ratio 3 : 1
    Speed MPH: 60

    At 5000 rpm you would be doing 134.4 miles per hour !!!!!!!......:eek::eek::eek:
    If you mean that you are hitting 5000 rpm easily through the gears, change earlier.
    Your current setup sounds spot on to me...........
     
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  19. jimmy bruns
    Joined: Jun 21, 2011
    Posts: 81

    jimmy bruns
    Member
    from Chatsworth

    My merc rear has 3.73s in it with a camaro T5 cruises on the freeway 75-80 all day long.
     
  20. phat rat
    Joined: Mar 18, 2001
    Posts: 4,680

    phat rat
    Member

    OD is not going to make the motor wind out more it'll drop the rpm's. As has been stated with the OD engaged you would effectively had a final ratio of high 2's or low 3's. You can take the advice given here by more experienced guys or ignore it and as you say "figure something out"
     
  21. 50 Merc Man
    Joined: Aug 2, 2020
    Posts: 358

    50 Merc Man
    Member

    Lmao , hey the 5000 r’s was an exaggeration, it just sounded like it brother, I was only goin 55 on the freeway
     
  22. From the original post of the OP, I suspect the OD has an issue. The unit engages manually with a pull handle and electrically by a switch beneath the accelerator pedal. The switch is designed to disengage the OD at full throttle. If the switch or the solenoid on the unit is not working, no OD even with the manual handle engaged.
     
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  23. 50 Merc Man
    Joined: Aug 2, 2020
    Posts: 358

    50 Merc Man
    Member

    No offense please, just lookin for some advice that’s all
     
  24. 50 Merc Man
    Joined: Aug 2, 2020
    Posts: 358

    50 Merc Man
    Member

    Thank you
     
  25. My 50 Merc has 3.73 rear end that came Stock with a 3 Speed
    The Auto was a Different item which was 3.23 Rear,
    and the Over/drive was 4.11 rear end.!


    Just my 3.5 cents


    Live Learn & Die a Fool
     
    50 Merc Man likes this.
  26. twenty8
    Joined: Apr 8, 2021
    Posts: 1,046

    twenty8
    Member

    Then, with a 4.27 : 1 rear ratio, and the overdrive engaged in top gear, you would be sauntering along at 2047 rpm.............
    Like I said, I don't see what you are complaining about.:confused::confused::confused:
     
    gimpyshotrods likes this.
  27. You are welcome. There is more involved electrically with this system than that quick overview. If you want more info, I have a shop manual somewhere. PM me.
     
    Boneyard51 likes this.
  28. 38 coupe
    Joined: May 11, 2008
    Posts: 160

    38 coupe
    Member
    from Texas

    I helped friends assemble and install a stock 50 Merc engine with overdrive into their grandfather's old car (the family bought the 50 Merc car "used" in late 1950). Stock 4.27 rear axle ratio in overdrive loves the freeway. One evening we swapped cars, I drove their Merc and they drove my stock 53 Ford with 4.11 and overdrive. Merc was smooth at 80 with a lot of pedal left. I left my 6 cylinder Ford in the dust!

    From the sounds of your concern you aren't dropping into overdrive. If you still have freewheeling at 55 mph (let off the accelerator with the lock-out cable pushed in and the car coasts without engine braking) then your overdrive isn't working.
     
  29. 50 Merc Man
    Joined: Aug 2, 2020
    Posts: 358

    50 Merc Man
    Member

    Thank you very much
     
  30. 50 Merc Man
    Joined: Aug 2, 2020
    Posts: 358

    50 Merc Man
    Member

    So if it’s not working, is it the overdrive solenoid itself or possibly something else?
     

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