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Thread: 4:10 to 3:55 interchangeability

  1. #1
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    Default 4:10 to 3:55 interchangeability

    will the guts from a known good 3.55 rear swap directly into the casing that had 4:10's?
    Is it a direct part for part just gut the tubes and hog head and put the guts from a good rear in it?

    We already determined that both the front and rear drive train are bad due to a visual inspection.

    we have a known good front and rear drive train standing by but would like to know if the guts interchange. the truck is pretty heavy and sits up so high that im afraid i dont have a jack or jack stands to get it up on.

    i just figured if the guts will interchange,, it would make more sense to do it this way rather than all that heavy and possibly dangerous work.
    help anyone?

  2. #2
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    Default Re: 4:10 to 3:55 interchangeability

    as long as the housings and carriers are the same, then yes
    It's Gumby's fault.

  3. #3
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    Default Re: 4:10 to 3:55 interchangeability

    as shawn said, if the housings and casings are the same then its no prob

    been putting the bronco trough some abuse

    Demon- 87 LX 302, E7's, ARP bolts, Mallory Unilite Distributor, MSD 6A, Edelbrock Performer Intake, Edelbrock 600 Carb, Flowtech Lts, 5Speed, 8.8w/3.55's, Granatelli Tube K-Member & LCA's, Coil Overs, KYB 4ways, CHE arms, 3" rear drop springs, BBK C/C Plates, Fuel Cell, Bat. Relocation, Mac Mufflers, Stinger Tails, Sunpro gauges, Custom Lip Spoiler
    88 LX-Mostly stock, headers, h-pipe, flowmaster 40's and that's about it

  4. #4
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    Default Re: 4:10 to 3:55 interchangeability

    may be more of a dog with less gear to move those big tires and heavy truck just remember that. part about it
    trick flow street heat intake , 24lbs injetors, ported GT-40's (Chip) long tube headers. and a Performance Automatic C4, with a hurst shifter!

  5. #5
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    Default Re: 4:10 to 3:55 interchangeability

    I would not try it... Getting the pinion depth correct is critical, each housing and gear set is a little different. I'm bettin it'll howl, or the gear won't last because of incorrect tooth pattern or backlash.

    Get out your service manuals and check out what is needed(tools and parts) when chainging a gear set.






    My other rides (that actually do run & drive)

    1969 Fairlane Cobra 428CJ 4-Speed

    1972 Comet GT - 306 C4

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    Default Re: 4:10 to 3:55 interchangeability

    I've done this. A mechanic friend of mine informed me that Ford has very strict tolerances on their rear axles. I researched this and found more info to back his claim up on the net. What this means is that (with care and proper checking after) you can swap different gears from same style (i.e. 7.5 to 7.5 or 8.8 to 8.8) housings without a lot of fuss. Generally if you obtain the used pinion with the bearing still pressed on - leave it and the shims on. install it this way using a new pinion nut/crush collar. Install the ring gear onto the carrier and reinstall the carrier using the old shims from the car you are fixing. Do not mix them up side to side. Check the wear pattern with white grease or similar. I've done this twice with excellent results. Maybe I got lucky, but maybe I've found a way to save $150 for myself. If it didn't work I'd have had to pay out anyways and all I'd have wasted was my time.

  7. #7
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    Default Re: 4:10 to 3:55 interchangeability

    you guys all are on the same path im thinking. I knew that if this were done, id need to carry all the parts from the new differential to the old ***********including shims. Im not comfortable nor have the smarts to poperly tune a rear so i figured if the casings were the same,, id make darn sure each part from the new went into the old housing.

    see,, im just trying to figure out a way were we dont have to pull the entire front end and the rear end.

    this is not for my wifes bronco,, this is for a friend who asked if i would lend a hand doing this. I just thought if we gut both the front and the rear, it would work if the casings were the same.

    maybe i did not explain that properly the first time.
    does it still seem possible and ok for a work truck considered to be a throwaway?

  8. #8
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    Default Re: 4:10 to 3:55 interchangeability

    if its just a temp fix on a work truck I think it should still work. But only as a temp fix. It sounds like it would not line up all rightand just slowly shard away metal. It shoud still be okay for a good couple hunderad miles. Maybe more.
    Quote Originally Posted by jcassity
    I honestly dont think you could exceed the cost of a new car buy installing new *stock* parts everywhere in your coug our tbird. Its just plain impossible. You could revamp the entire drivetrain/engine/suspenstion and still come out ahead.
    Hooligans!
    1988 Crown Vic wagon. 120K California car. Wifes grocery getter. (junked)
    1987 Ford Thunderbird LX. 5.0. s.o., sn-95 t-5 and an f-150 clutch. Driven daily and going strong.
    1986 cougar.
    lilsammywasapunkrocker@yahoo.com

  9. #9
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    Default Re: 4:10 to 3:55 interchangeability

    if it wont last that long,, its a no go.

    tom,, ive heard the same about each differential being different. My brother in law works for Dana and he says the same. Tuning a rear is pretty tricky stuff from the warnings ive had handed to me. Ive never worked on one or had the fortune of being around someone who would consider it to be easy.
    Last edited by jcassity; 06-18-2005 at 03:55 PM.

  10. #10
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    Default Re: 4:10 to 3:55 interchangeability

    not a temp fix on my 7.5 -- 30 000kms and going strong!! These are hard drivin' miles BTW. Also J, not all shims are carried over from the donor to the recipient, just the pinion shim. The carrier shims are reused from the recipient as stated in my previous post. best of luck!

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