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ZF5 to ZF6 in a 1989 f250?

Discussion in '6.9L IH & 7.3L IDI Diesels' started by firehonomichl, Sep 22, 2019.

  1. firehonomichl

    firehonomichl Registered User

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    Hey fellas just wondering what it take and modifying to take my ZF5 out and put in a ZF6? It is 4x4 and a 7.3L of course lol
     
  2. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

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    Do a search, there’s no advantage to the zf6 other than it will leave your wallet lighter than a zf5.
     
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  3. firehonomichl

    firehonomichl Registered User

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    I was just thinking it would get my RPMs down having that one more gear ya know
     
  4. IDIoit

    IDIoit MachinistFabricator Supporting Member

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    the 6 is essentially the same trans as a ZF5. final OD ratio is a .01 difference.
    biggest difference is a granny 1st.
    if you don't tow heavy, there is no need to do it.
     
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  5. firehonomichl

    firehonomichl Registered User

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    Ok well that’s good to know thank you guys!
     
  6. Randy Bush

    Randy Bush Full Access Member

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    And if you do tow heavy a wide ratio ZF5 will give you all the granny you need .
     
  7. Macrobb

    Macrobb Full Access Member

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    If you want an extra gear, basically you need to go with 3.55s(higher top gear but harder to start off the line towing), or keep your 4.10s and install an overdrive box like a Gear Vendor box.
    I have a GV Overdrive on one of my trucks, and it's perfect, but expensive! Low gears for towing, A split 3rd to help if you need, plus double OD for highway cruising.
     
  8. firehonomichl

    firehonomichl Registered User

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    Ya I don’t tow much at all I mite look into 3.55s
     
  9. Randy Bush

    Randy Bush Full Access Member

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    With mine I did lose topend speed when I rebuilt it to a wide ratio, but I can still do 70 at around 2200 rpms. Towing 18k -20k I can easily let out on he clutch then throttle up.
     
  10. firehonomichl

    firehonomichl Registered User

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    That’s good to know! Right now I’m at like 2200 at 65
     
  11. Macrobb

    Macrobb Full Access Member

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    I don't know why? http://www.dieselhub.com/trans/zf-5-speed.html Wide ratio is .01 /taller/ ratio than short ratio. So you should see a very slight increase in MPH at the same RPM.
     
  12. Randy Bush

    Randy Bush Full Access Member

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    I don't know why neither, just know lost 5-10 mph on topend. But I don't care because now it will pull heavy. Before I had to be careful on a grade , slip the clutch a little to get going or kill the engine. I don't remember anymore just what the parts donor trans came out of other then a 4x4 so had to pull gears out of it to put in mine.
     

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