Author Topic: 91.5 1st Gen D61/71  (Read 354 times)

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Offline 180proof

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91.5 1st Gen D61/71
« on: May 7, 2020, 08:55:37 pm »
Looking at swapping in some 1 tons, found a set of Dana 61 & 71 out of 91.5 Cummins w250. Fa tory 4.10's, Kingpin.
Want to put them in 78 RC. What if any issues with this?

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    Offline u2slow

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    Re: 91.5 1st Gen D61/71
    « Reply #1 on: May 7, 2020, 08:59:45 pm »
    With 4.10 gears stock... they're a regular D60 & D70.

    Driveshafts will need shortening, unless you lift enough to compensate.
    DD: 90 D250 6BT|5spd|D60/3.54/Lockright
    Tow/haul: 93 W250 Club 6BTA|5spd|D60/80/3.54/Lockright|4" lift|35's|HX35|5x.012s|4" pipe
    Projects: '84 D250 Ramcharger (cummins); '90 W250 Ramcharger (360TBI)
    Hers: 2005 Jeep Liberty V6|6spd|3.73/Trac-lok |3" lift, 245/75R16E Nokians

    Offline 180proof

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    Re: 91.5 1st Gen D61/71
    « Reply #2 on: May 7, 2020, 09:40:55 pm »
    With 4.10 gears stock... they're a regular D60 & D70.

    Driveshafts will need shortening, unless you lift enough to compensate.

    Well shit the bed, even better! He has them advertised as 61/71, not that it matters.
    Thanks for the reply.

    Offline Elwenil

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    Re: 91.5 1st Gen D61/71
    « Reply #3 on: May 8, 2020, 06:22:17 am »
    I would double check that they are indeed 4.10s.  D61 normally has 3.08 gears, though can be found with 3.54s as well, but not 4.10s.  They can be difficult to swap to deeper gears due to the pinion offset.
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    Offline Mad Max

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    Re: 91.5 1st Gen D61/71
    « Reply #4 on: May 8, 2020, 08:22:43 am »
    definitely pop both covers and count the revolutions with your own eyes to be 100% certain those are not D61/71

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    Offline u2slow

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    Re: 91.5 1st Gen D61/71
    « Reply #5 on: May 8, 2020, 06:39:15 pm »
    A Dana '71' casting is easy to identify externally. There is extra machined surface (i.e. 'corners') on the top right and bottom right on the center section that the diff cover leaves exposed. My two 3.07 D71 diffs have that, and any other D70 I have does not.

    I'd post a pic, but can't scrounge one up.

    DD: 90 D250 6BT|5spd|D60/3.54/Lockright
    Tow/haul: 93 W250 Club 6BTA|5spd|D60/80/3.54/Lockright|4" lift|35's|HX35|5x.012s|4" pipe
    Projects: '84 D250 Ramcharger (cummins); '90 W250 Ramcharger (360TBI)
    Hers: 2005 Jeep Liberty V6|6spd|3.73/Trac-lok |3" lift, 245/75R16E Nokians

    Offline 712edf

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    Re: 91.5 1st Gen D61/71
    « Reply #6 on: May 8, 2020, 06:59:02 pm »
    Weren't the D61/71 only in the automatics?

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    Offline u2slow

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    Re: 91.5 1st Gen D61/71
    « Reply #7 on: May 8, 2020, 08:29:45 pm »
    Weren't the D61/71 only in the automatics?

    AFAIK, yes - the Cummins/727 trucks (no overdrive).

    I believe some members here have encountered the odd exception.
    DD: 90 D250 6BT|5spd|D60/3.54/Lockright
    Tow/haul: 93 W250 Club 6BTA|5spd|D60/80/3.54/Lockright|4" lift|35's|HX35|5x.012s|4" pipe
    Projects: '84 D250 Ramcharger (cummins); '90 W250 Ramcharger (360TBI)
    Hers: 2005 Jeep Liberty V6|6spd|3.73/Trac-lok |3" lift, 245/75R16E Nokians

    Offline RXT

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    Re: 91.5 1st Gen D61/71
    « Reply #8 on: May 10, 2020, 09:03:43 am »
    My recommendation will be similar. Pop off the cover and count teeth to be certain of the gear ratios. You'll also get to see the condition of everything inside and wether there are any goodies in there, or not.

    The Dana 61 usually came with the 3.07 gears when installed under a Cummins w/ 727 automatic. However, at some point back a few years ago, some attempted to install different gears into the 61 using 60 gears and a custom spacer to make up for the 61's pinion offset. So, it could be possible that someone might have made a successful gear swap using 4:10 D60 gears. Theres also that possibility that a factory 4:10 was available for the 61, (though my quick research suggests otherwise) but none were used in the Dodge truck application. (Ford also used 61s as rear axles on some vehicles) So such a gear set, if it existed, could have also been swapped into a Dodge Dana 61 at some point.

    To be sure you're looking at a 61 or a 60, Dana makes it real easy to identify which axle you're looking at by casting either a "61" or "60" into the web or gusset between the tube and the housing. If you do not readily see it, it maybe under years of crud accumulation but it will be there, somewhere.

    As far as the rear "71" goes. Technically there is no such thing as a Dana 71. In actuality, this axle is known as the Dana 70U (and will be marked as such) it is a variant of the 70 model, featuring a unique cast housing thats more tear drop shaped and the only 70 variant with 32 spline shafts. Unlike the Dana model 60, Dana 70's were made with three different pinion offsets and with different pinion and carrier bearing sizes. These differences can make gear changes more of a problem if you don't know which version of the 70 you're working with. But at least there are numerous gearing options available for the 70U, including a 4:10 ratio.

    If you are fortunate and the axles, regardless of wether the front is a 60 or 61, are equipped with 4:10s, you'll be golden for this swap. However, if the gears are the typical 3.07 ratio 61/70U as used the Cummins automatics, your gearing will be way too tall. The rear can be re-geared but the 61 will be next to impossible to re-gear to something more useful, and all the 61 re-gearing options were discontinued years ago. Which means you're on your own if you attempt to install 60 gears into a 61.

    Ed
    « Last Edit: May 10, 2020, 09:11:35 am by RXT »
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    Offline u2slow

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    Re: 91.5 1st Gen D61/71
    « Reply #9 on: May 11, 2020, 07:15:02 pm »
    The Dana '71' is actually a 70-2UA. What makes this casting unique is the 31/32" pinion offset to allow for the massive 3.07 pinion gear. The external indicator is the machined corners/eyebrows on the right side that the diff cover doesn't cover.

    The regular Dana 70U is a 5/8" pinion offset. These are 3.54+ diffs.
    DD: 90 D250 6BT|5spd|D60/3.54/Lockright
    Tow/haul: 93 W250 Club 6BTA|5spd|D60/80/3.54/Lockright|4" lift|35's|HX35|5x.012s|4" pipe
    Projects: '84 D250 Ramcharger (cummins); '90 W250 Ramcharger (360TBI)
    Hers: 2005 Jeep Liberty V6|6spd|3.73/Trac-lok |3" lift, 245/75R16E Nokians

    Offline RXT

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    Re: 91.5 1st Gen D61/71
    « Reply #10 on: May 13, 2020, 05:17:29 am »
    The Dana '71' is actually a 70-2UA. What makes this casting unique is the 31/32" pinion offset to allow for the massive 3.07 pinion gear.

    Correct! And unlike the Dana 61, the 70-2UA can be re-geared... I have a 4.56 in mine

    Ed
    If we lose freedom here, there is no place to escape to. This is the last stand on Earth.

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