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Axle & Diff Carrier Spline Count

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    Axle & Diff Carrier Spline Count

    I have a K-Code 8.8 and was wondering what the axle spline count is for the stock axles in these units? 28 or 31?
    Which type of differential carrier is everyone using in their boxes? Aftermarket or Ford Trac-Loc?
    What gear ratio are people liking for their daily drivers? High or low?
    1985 2-Door: CFI, K&N Filter, Edelbrock Performer 289 Intake, E7 Heads, BBK Shorty Headers, Summit H-pipe, Hooker Max Flow Mufflers, E-Fan, 3G Alternator, ASP Underdrive Crank Pulley, Bilstein Rear Shocks, Rear Lowering Springs, KYB Front Shocks, Front Lowering Springs, FTI 2400 Stall Converter, PA Performance Valve Body, Ford Racing 4.10 Gear, Eaton LSD Differential - I own the fastest CFI powered box to the 1/8th mile: 9.658@70.74mph
    1991 4-Door (Dad's Car): Pro-M EFI, 306ci, Forged Pistons, Ford Racing Aluminum Heads, COMP XE264HR cam, Cobra 1.7 Rockers, Edelbrock Performer RPM 2 Intake, 30lb. Injectors, Custom 65mm TB/EGR Spacer, Pro-M 75mm MAF, BBK Ceramic Shorties, Custom Summit H-pipe, Walker Mufflers, Jegs Built AOD, Roadrunner 3000 Stall Converter, Ford Racing 4.10 Gear - Best 1/8th mile time: 9.76@72.03

    #2
    IIRC the panthers switched to 31 spline in 2005. Except for limo applications which had 31 spline many years earlier. My opinion is a clutch based unit like fords works just fine for typical driving. Gear ratio depends on your goal. 3.55 should have some get up and go and still be ok for around town.
    03 Marauder DPB, HS, 6disk, Organizer Mods> LED's in & Out, M&Z rear control arms, Oil deflector, U-Haul Trans Pan, Blue Fuzzy Dice
    02 SL500 Silver Arrow
    08 TC Signature Limited, HID's Mods>235/55-17 Z rated BFG G-Force Comp-2 A/S Plus, Addco 1" rear Sway, Posi Carrier, Compustar Remote Start, floor liners, trunk organizer, Two part Sun Visors, B&M Trans drain Plug, Winter=05 Mustang GT rims, Nokian Hakkapeliitta R-2 235/55-17
    12 Escape Limited V6 AWD, 225/65R17 Vredestein Quatrac Pro, Winter 235/70-16 Conti Viking Contact7 Mods>Beamtech LED headlight bulbs, Husky floor liners

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      #3
      If you do a lot of city driving and never any highway... 3.55 or higher.
      If you do mixed driving... 3.27-3.73 (3.55 preferred).
      If you do mainly highway driving... 2.73-3.27

      3.55 will require the 21 tooth driven speedometer gear for speedometer correction. 3.73 is 23 tooth and any more than that, it's not made and will require speedo correction gears or transmission modifications (change output shaft).

      Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
      rides: 93 Crown Vic LX (The Red Velvet Cake), 2000 Crown Vic base model (Sandy), 2003 Expedition (the vacation beast)
      Originally posted by gadget73
      ... and it should all work like magic and unicorns and stuff.
      Originally posted by dmccaig
      Overhead, some poor bastards are flying in airplanes.

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        #4
        Are the 31 spline axles from a 2005 up panther the same length as the 28 spline axles in the stock Box k-code rear?

        Could I use 31 spline 2005 up Panther axles if I got a 31 spline Ford Trac-Loc differential carrier?

        Would I run into issues with the driveshaft bolting up to a 31 spline diff carrier as opposed to the 28 spline diff carrier in the stock K-code rear?
        1985 2-Door: CFI, K&N Filter, Edelbrock Performer 289 Intake, E7 Heads, BBK Shorty Headers, Summit H-pipe, Hooker Max Flow Mufflers, E-Fan, 3G Alternator, ASP Underdrive Crank Pulley, Bilstein Rear Shocks, Rear Lowering Springs, KYB Front Shocks, Front Lowering Springs, FTI 2400 Stall Converter, PA Performance Valve Body, Ford Racing 4.10 Gear, Eaton LSD Differential - I own the fastest CFI powered box to the 1/8th mile: 9.658@70.74mph
        1991 4-Door (Dad's Car): Pro-M EFI, 306ci, Forged Pistons, Ford Racing Aluminum Heads, COMP XE264HR cam, Cobra 1.7 Rockers, Edelbrock Performer RPM 2 Intake, 30lb. Injectors, Custom 65mm TB/EGR Spacer, Pro-M 75mm MAF, BBK Ceramic Shorties, Custom Summit H-pipe, Walker Mufflers, Jegs Built AOD, Roadrunner 3000 Stall Converter, Ford Racing 4.10 Gear - Best 1/8th mile time: 9.76@72.03

        Comment


          #5
          79-89 boxes are the same. 90-91 boxes an inch wider. So no, newer axles wont fit your 85. WagonMan
          89 Colony Park
          90 Colony Park
          70 HEMI Daytona Convertible

          Comment


            #6
            The carrier has nothing to do with how the driveshaft bolts up. You would need custom axles to use the available 31 spline carrier.
            If you are going for big power, it would possibly be worthwhile, if not...find a stock 28 spline diff and axles.

            Sent from my SM-G975U using Tapatalk
            1989 Country Squire - Twilight Blue, 347 stroker


            2005 Crown Victoria Sport - Black - Stainless Works full exhaust with Borla Pro XS mufflers, BBK 75mm TB, Accufab plenum, CVPI airbox, Heinous control arms, etc...

            Comment


              #7
              A 3.55 posi rear which is what you have is often the aim of many on this site for a daily driver.

              I know this was not what you asked but what often kills the rears is bad axles seals. this can be caused by the seals going bad and or worn axles which cause the seals to leak. When the seals go the oil drains out and poof , bad rear end.

              It is fairly easy to check for worn axle bearings/worn axles. Put the rear of the car up on stands placed on the frame not the axle housing. Visually check the pinion seal for leaks. Then in turn move each wheel up and down by hand. If there is vertical play in the housing you need that axle and bearing. If one axle is bad replace that axle and do bearings and seals on both sides.

              While the car is up place it in neutral, E-brake off, provided it is safe. Rotate a wheel by hand. The wheels should rotate in the same direction. If they do it means you have a posi carrier in there and there is at least some clutch material still working in there. Still the clutches might be well worn so if you are doing axle bearings that is the time to replace the clutch linings. Some use upgraded material of squash in an extra clutch but for a typical daily driver stock works just fine, unless as Black Vic says you are going for Big power. The posi carrier that is in there generally does a good job.

              If you are up to a more complex job you can also do carrier bearings and even the pinion seal and bearing. This requires a dial gauge setup, and shop press. I suggest the factory service manual if you are going to do carrier and or pinion bearings.

              Spider bearings are expensive but they should be inspected when a carrier is out for service.

              Good OEM axles can often be had mostly be sweat equity in a junk yard. The axles are the same and interchange left and right. Usually the left axle wears first so it is easier to find a good right axle. I am not a Dorman fan so I prefer a good used axle to one of their new ones but they are used by many as they are a popular replacement brand.

              if the vehicle can not be laid up what some do is get a used rear 1990-?? (What is the newest year for a straight swap? I can't remember) and control arms. This is about an inch wider which is a small improvement. Rebuild it including new control arm bushings then do a complete swap when it is ready. You can also upgrade to disk brakes from 1992-03 at the same time. If you decide to do that there is much info on here about the different options and what is necessary.

              The cost depends on how many new parts you use vs used parts and how much you are capable of doing yourself due to experience, tools and workspace availability. For example some have waited to find a junker with all new brakes and saved good money there. Pads, rotors, calipers and E-Brake parts, you also need backing plates and mounting brackets.
              Last edited by jaywish; 02-08-2020, 07:38 AM.
              03 Marauder DPB, HS, 6disk, Organizer Mods> LED's in & Out, M&Z rear control arms, Oil deflector, U-Haul Trans Pan, Blue Fuzzy Dice
              02 SL500 Silver Arrow
              08 TC Signature Limited, HID's Mods>235/55-17 Z rated BFG G-Force Comp-2 A/S Plus, Addco 1" rear Sway, Posi Carrier, Compustar Remote Start, floor liners, trunk organizer, Two part Sun Visors, B&M Trans drain Plug, Winter=05 Mustang GT rims, Nokian Hakkapeliitta R-2 235/55-17
              12 Escape Limited V6 AWD, 225/65R17 Vredestein Quatrac Pro, Winter 235/70-16 Conti Viking Contact7 Mods>Beamtech LED headlight bulbs, Husky floor liners

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