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1HDFT auto diff gearing

Discussion in '80-Series Tech' started by NielsC, Jan 12, 2018.

  1. NielsC

    NielsC

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    Hi all,
    I have a HDJ80 1HDFT, with an a442f swap, so still running stock 3.73 gears (Europe spec), and running 35" tires.
    As you know the auto is supposed to have 4.1 diffs, AND im running 35s, my gearing is way out.
    Now I'm thinking either regearing to 4.56 , as this will bring it to "stock" ratio on 35s, or either swap in a set of 4.1 diffs and sell my old 3.73 diffs, wich might be the cheaper option of the 2.
    I'd like to know from people who have this combo what would be the allround best setup?
    Like for example, how much RPM you make in OD on 35s at say 100kph/60mph ?

    I already have mild tweaked pump, 3" exhaust, big intercooler, it goes like stink, but I steel feel its a bit sluggish as it's an auto, especially taking of and the shift points overall...

    thanks
     
  2. IanB

    IanB SILVER Star

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    Have you tried adjusting the auto trans shift cable? It can stretch over time, and having it properly adjusted makes a big difference. You didn't say if you had the fully mechanical ('90-'92), or the electronically controlled ('93+) version of the A442F that came on the HDJ's.
     
  3. NielsC

    NielsC

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    The cable is adjusted, the shifts are quick and firm.
    It is the a442f electronic.
    It has the marks4wd speedo correction unit to adjust the speedo according to the tires.
     
  4. mudgudgeon

    mudgudgeon

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    Swap in standard gearing - better on road, the 1HD-FT should have the torque to cope with it, especially with a decent tune, and possibly cheapest option

    Use the savings to put in low range reduction gearing in the t case - gives you better off road gearing, and keeps good highway gearing
     
  5. NielsC

    NielsC

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    The engine has plenty of torque indeed, even with the 3.73 it pulls like a train, but I feel that for normal daily driving ( I don’t do much highway) the gears are way too long. For example I make 1200 RPM at 70km/h in overdrive.
     
  6. Lumpskie

    Lumpskie

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    I have a hydraulic A442F behind a 1HDT on 35s with 4.10 gears. I really like it. I can crawl offroad, have decent acceleration and cruise at 80mph (130kph) on the highway to keep up with traffic.

    If you never go faster than 70kph, or want to go bigger in tires, I can see 4.56 gears being handy. But, for me, 4.10s are perfect for 35s.
     
  7. NielsC

    NielsC

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    I took it for a spin today on the stock tires and it drives pretty good, more power, smoother, the overdrive is more usable. According to my calcs, more or less the same as 35s with 4.1 gears.
     
    Lumpskie likes this.