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4R70W "Mechanical diode" - how much better is it

Discussion in 'Transmissions & Transfer Cases' started by masospaghetti, August 2, 2013.


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    1. masospaghetti

      masospaghetti Well-Known Member

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      I keep hearing about the change in 98 to the mechanical diode instead of a roller clutch inside the 4R70W transmission.

      How much does it matter? For towing, or general use?

      Wondering if I should be avoiding pre-98 vehicles completely. Thanks!
       
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    3. masospaghetti

      masospaghetti Well-Known Member

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      Bump, nobody knows?
       
    4. Turdle

      Turdle Will cook for gas Staff Member Moderator Elite Explorer

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      I moved this thread to the transmission sub forum, hopefully for an answer.
       
    5. FIND

      FIND Well-Known Member

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      The mechanical diode is a heavier duty part. Apparently it is a weak point on the earlier transmissions, but still... the 4r70w is a REALLY reliable transmission, especially by Ford standards. I guess, if you do a lot of towing or are making extra power, it is really worth it to have the 98+ tranny. For general use? I'm not sure if you'd really notice the difference unless you are looking at a fair chunk more than 200k miles.
       
    6. JK080

      JK080 Transmission Moderator Staff Member Moderator Elite Explorer

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      I don't see many failures with the sprag or the mechanical diode in this transmission, the snap ring that holds them both down comes off all the time and chews up the plastic pump washer and creates debris. There is a spiral ring that holds better so I would recommend replacing it if you are in there.
       
    7. masospaghetti

      masospaghetti Well-Known Member

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      Thanks all for the information.

      Sounds like both designs are good...that being said, a lot of the vehicles I see for sale are hovering near 200k miles at this point.
       
    8. 1996BLKBauer

      1996BLKBauer Well-Known Member

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      I have 170,000 on my '96 4R70W, and I only have a hard shift into Second, so for what it is worth, and mine being a fleet vehicle before I owned it, so I know it got abused, it is holding up pretty good. I will most likely be doing a rebuild when I get to 200,000 for the Experience, and for piece of mind. To be honest though, I have seen no difference in amount of miles a 1996 can do over say a 2000, so either way, as long as the vehicle was taken care of, you should be in good hands.
       

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