Replacing 904 with 500 Trans

Transmissions and Rear Ends

  1. 81ImpNC

    81ImpNC Member

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    At some point when it is necessary, I may replace the 904 in my 81 Imperial with a 500 OD from like an early 90s Dakota. The thinking being they can be acquired fairly easily and cheaply and offer the option of installed a better ratio ring and pinion in the rear instead of the economy 2.21 that is in there now. The cats have been removed from the car and the smog is freewheeling which has made a noticeable if not gigantic difference. Maybe put in a 2.94 or 3.23. The OD would basically negate the loss of MPG. This is not a daily but when I drive it we will travel to shows so it sees mostly steady highway driving.

    Thanks,

    Craig
     
  2. Aspen500

    Aspen500 Well-Known Member

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    As a reference, my '96 Dakota (with an A500) has 3.55 rear gears and 225/75R15 tires and it turns around 1,900 rpm at 65 in overdrive with the converter clutch locked.
     
  3. 89.Fifth

    89.Fifth Well-Known Member

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    Dakota usually has taller tires too though.
     
  4. 89.Fifth

    89.Fifth Well-Known Member

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    I haven't been able to find anyone that just sells me a built A500. Either it's junkyards and take to a rebuilder or squat. Am I looking in the wrong places?
     
  5. 81ImpNC

    81ImpNC Member

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    If you are replacing a 3 speed with a 4 speed it might be easier to make a deal on a 500 from a yard and just do a bench rebuild. Some places will give you a good deal on a bench rebuild they are quite easy for a good trans guy (RWD are usually much easier) parts are not a whole lot. Also it gets around the core issue.

    I won't go as high as 3.55. No more than 3.23 probably. The Imperial runs 205/75/15 wide whitewalls. I drive it leisurely I just do a lot of steady 45-55-65 roads going to shows. Currently I get about 15MPG in town and 23MPG highway.
     
  6. Aspen500

    Aspen500 Well-Known Member

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    Oops, I lied. My Dakota takes 215/75R15's so only slightly taller than Imp's 205's.

    You can get remanufactured A500's but they go for around $1800-$2000 though. A rebuilt may be a bit cheaper than remanufactured but it'll still be over $1,000 anyways.
     
  7. Duke5A

    Duke5A Well-Known Member

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    Can you fabricate? You'll need to remove a portion of the cross-member to make room for the OD section of the transmission. This will also entail replacing it with something else and making your own transmission mount. I've done this swap on two cars now, but if you can't cut/weld, or at least know someone who can I wouldn't attempt it.