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Thread: Ford 9 inch rear swap

  1. #1

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    Ford 9 inch rear swap

    Does anyone have any info on what all is needed to do a Ford 9 inch rear end swap on a 91 mm?

  2. #2


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    Grab a 9 inch, narrow it, install it

  3. #3

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    ...that's about it. Gotta ask - why a 9" rear on the MM? They add a lot of weight and can only really be justified if the factory diff has reached it's limitations. What engine upgrade are you planning?

  4. #4


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    I'll actually add real quick....

    The 8.8 is less than 1/4 inch smaller than the 9 inch, and much easier to scout/narrow/install, and it can be upgraded almost exactly the same as the 9. It's pretty tough to beat.

    I also made 4 or 5 write-ups regarding identifying, selecting, narrowing, and installing an 8.8 into a MM. They're located in the tech section..... can't miss them. You can also read my build thread which has lots of pics and such showing the install.

  5. #5

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    i'm doing an LS1 swap and i want a stronger rear end.

  6. #6

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    can you send a link. i can't find it

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    8.8" out of a Ranger/Explorer, Toyota 8" out of a 4x4 both are good for around 600hp and if you do the 5 lug conversion in the front you will run the same bolt pattern.

  8. #8


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    I can't link on my phone.

    "The Tech Section" is in the main forum page. Click on it, there are 4 titles that start with "How To: Narrow a Ford 8.8"

    Start with the prelude and Q&A, and follow the order. Each Hot To contains a link to the next one at the bottom of the write up. It will take you to the next one in order. If you can't figure that out, you're on your own

    If you scroll through the 2nd Gen forum, find "Merrill's 4G64 DOHC" thread. That will show you what it looks like in a MM (specifically a '91). All the details are there if you read them. The pics are pretty self explanatory, and there is no shortage of them.

  9. #9



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    Would the rear end really need to be as strong as you folks are talking about if the tires are not oversized to a point that they rip a rear end out? I can see strength being a benefit, don't get me wrong, but if your not lining up at the x-mas tree all the time, why can't a stock rear end be strengthened some to give it that bit of help. I'm just curious for the day that I start doing what you all have or are doing.

  10. #10

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    i found it. will an 8.8 out of a 97 lincoln mark 8 work?

  11. #11



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    it will work but will need to be narrowed. another alternative is a 9" rear out of a montero 92-99 - they are stronger than a ford 9", need no narrowing, have disc brakes, and can be found with air locker diffs. Only disadvantage is most of them are 4.63 ratios, but 9" ford diff gears may fit.
    Pennyman1
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  12. #12

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    I had a narrowed passenger car 9 in. ford under my D50 and broke one of the caps that holds the spool in. If you are making a lot of power I would put a nodular iron center section or a after market one in it. I am thinking about buying one of the Strange aluminum center sections.
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  13. #13

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    +1 for the 8.8 rear. I have been running one in my 4G63T powered 81 Challenger since 2003. 31 spline axles, and an Eaton Diff, I probably have over 500 drag launches off a trans brake, plus tons of street driving, and have never had an issue with it. Cheaper, lighter, and just as strong as a 9" Ford.

  14. #14

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    We ran 12.30's on a stock rear axle in a 1986 Ram50 with a 360.
    An Abody 8 3/4 is the perfect width..you just move the perches. We had one but never broke the stock rear end so never swapped it in..

  15. #15



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    and if you get a later A body mopar 8 3/4 rear it will be a 5 x 4.5 bolt pattern, same as a Toyota or 8.8 / 9" ford
    Pennyman1
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  16. #16

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    Or buy aftermarket axles and tell them the pattern you want..

  17. #17

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    Quote Originally Posted by pennyman1 View Post
    it will work but will need to be narrowed. another alternative is a 9" rear out of a montero 92-99 - they are stronger than a ford 9", need no narrowing, have disc brakes, and can be found with air locker diffs. Only disadvantage is most of them are 4.63 ratios, but 9" ford diff gears may fit.
    X2 on this, this would be the strongest cheapest axle and most likely come with an air locker as a bonus. Matching lug pattern and disc brakes should be worth it on it's own but if you want to sweeten the deal find one out of a 3rd gen Pickup/Montero Sport ('97-'99) it has the same leaf perch spacing so even one less thing to do. Trucks with 3.0 V6 have 9" diff with 30.5mm 28 spline shafts and trucks with 3.5 V6 have 9.5" diff with 33.5mm 31 spline shafts. Commonly found ratios are 4.27, 4.63 and 4.90 with the higher ratio (lower numerically) being the cheaper ones.

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