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Thread: Is there a 5 speed speedometer gear available to use with a 3.90 Torsen ?

  1. #1
    5,000 rpm - there be torque here! MiataQuest's Avatar
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    Is there a 5 speed speedometer gear available to use with a 3.90 Torsen ?

    Right now this is the specification of my 1992 Miata LS:
    * 1.6 engine
    * 5 speed transmission with mechanical speedometer cable.
    * 4.30 viscous LSD rear end

    The drivetrain will be swapped to this in two months:
    * 2.4 GM Ecotec
    * Retain the same 5 speed transmission with mechanical speedometer cable.
    * 3.90 Torsen rear end

    Question:
    Is there a transmission speedometer gear available for the 3.90 gearing?
    I searched a few websites and could not find the answer.

    My gut would say that one is not available as the newer cars have a speed sensor rather than a mechanical cable.
    Maybe a 4.10 speedo gear might get me pretty close.
    Last edited by MiataQuest; 04-23-2017 at 07:39 PM.

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  3. #2
    6,000 rpm - mere mortals would shift NCGreasemonkey's Avatar
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    Rene, I want my speedo. I will try to do some research for you.That is one of my questions with any swap. I want my speedo and tach with Rev love.
    ... Rick

    Quote Originally Posted by Hammerhead View Post
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    MiataQuest (04-23-2017)

  5. #3
    Ninja Messiah kung fu jesus's Avatar
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    Custom gauge face(s). Talk to Adam (rev limiter)

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    MiataQuest (04-23-2017)

  7. #4
    5,000 rpm - there be torque here! MiataQuest's Avatar
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    I never thought about a gauge face change.
    Thanks guys!

    I guess I can GPS it later when it is running and figure out how far I am off.
    Maybe use 70 mph as the accuracy benchmark since the freeway seems to be the source of my speeding tickets!
    I will probably do that after I get new tires and wheels.

    Now I have justification to make some custom "Manticore" gauge faces.

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    NCGreasemonkey (04-24-2017)

  9. #5
    Super Moderator RotorNutFD3S's Avatar
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    You'll need the following parts to build a mechanical 3.9 speed sensor:

    • 1011-17-442A - This is the sleeve/housing that will position the below gear in the proper location to engage the gear within the transmission. If the sleeve that comes in a Miata transmission is used, the smaller diameter gear will be free-floating and will not engage. Thus, no readings at the gauge cluster.
    • M503-17-441 - 20 tooth gear bonded to shaft, 20.5mm diameter (vs. the NA's 24.5mm gear). This gear may be just slightly off on your speedometer with a 3.9 diff. There is a 21T gear that is supposedly more suited to a 3.9 diff, but is apparently unobtainium through any domestic sources. I have heard that people have gone through Maruha Motors in Japan to obtain it. I don't know if it's 20.5mm or 24.5mm in diameter. If it's 24.5mm you'll need the 1669-17-442B sleeve/housing (or reuse your existing housing by knocking the spring pin out and removing your old gear). Maruha link: http://www.maruhamotors.co.jp/miata/...rivengear.html
    • 9922-20-214 - Spring Pin for holding the gear in the sleeve.
    • 9958-60-8166 - Oil Seal for inside the sleeve.
    • 1011-17-443 - O-Ring for the outside of the sleeve.


    Or, you can get a custom gauge setup from Adam.
    I've got a lot less horsepower - luckily they are Japanese horses - usually in better shape and more motivated.

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  11. #6
    5,000 rpm - there be torque here! MiataQuest's Avatar
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    Thanks for the great information.
    BTW - I bought the 3.90 rear and axle half shafts from ShadowMX5 off CR. It will probably take a few weeks to have it boxed and shipped to me.

    So I was thinking.... Perhaps I should not install the 3.90 Torsen at the time of the engine swap and start out with the original 4.30 Viscous LSD rear end that is already in the car.

    That way I would not add additional variables into evaluating the Ecotec swap. I am concerned if I have any excess NVH that I it would be more difficult to solve with adding the rear end, axle shafts, and axle bearings into the equation.
    If everything works great, then I can make the 3.90 rear installation a winter project (now that I have a garage heater!) along with rebuilding the rear suspension.

    On paper, the 3.90 rear end swap makes sense for matching engine power/torque to my driving goals and it is stronger.
    It will just be delayed.
    Initially I can drive my NEW GM Ecotec engine conservatively while breaking it in. I wonder how strong the original 4.30 Viscous LSD at 114,000 miles would after engine break-in if I do a MATG run or Hockings Hill run? I don't drop the clutch from a standing stop, but I would shift aggressively and apply full power after clutch engagement.

    Agree or disagree? Comments?

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    NCGreasemonkey (04-24-2017)

  13. #7
    3,000 rpm - starting to feel the power Rogue's Avatar
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    I would be gentle with the VLSD, they can be fragile.
    I'm going to try a 3.90/5 in my wifes new build, behind a massaged BP4W.
    1992 BnT, 93LE #737, 94M, 95M, 96M, 97PEP, and a few 90s

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  15. #8
    6,000 rpm - mere mortals would shift NCGreasemonkey's Avatar
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    Quote Originally Posted by MiataQuest View Post
    Thanks for the great information.
    BTW - I bought the 3.90 rear and axle half shafts from ShadowMX5 off CR. It will probably take a few weeks to have it boxed and shipped to me.

    So I was thinking.... Perhaps I should not install the 3.90 Torsen at the time of the engine swap and start out with the original 4.30 Viscous LSD rear end that is already in the car.

    That way I would not add additional variables into evaluating the Ecotec swap. I am concerned if I have any excess NVH that I it would be more difficult to solve with adding the rear end, axle shafts, and axle bearings into the equation.
    If everything works great, then I can make the 3.90 rear installation a winter project (now that I have a garage heater!) along with rebuilding the rear suspension.

    On paper, the 3.90 rear end swap makes sense for matching engine power/torque to my driving goals and it is stronger.
    It will just be delayed.
    Initially I can drive my NEW GM Ecotec engine conservatively while breaking it in. I wonder how strong the original 4.30 Viscous LSD at 114,000 miles would after engine break-in if I do a MATG run or Hockings Hill run? I don't drop the clutch from a standing stop, but I would shift aggressively and apply full power after clutch engagement.

    Agree or disagree? Comments?
    If you have the spare setup. And are not far from home... Uh, you met me. Push it till it screams mercy. You can then enlighten the rest of the fold on just when they say Boom!

    With you in the trenches even when you are off working! Peace Rene!

    Fellow Nut!
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    Quote Originally Posted by Hammerhead View Post
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    Ninja Messiah kung fu jesus's Avatar
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    I would yank that 1.6 diff ASAP. I ran turbos for a while. I showed a lot of empathy, but it finally shat the bed when I tried a stock JRSC. It split the pinion and took out the ring. I should mention this happened on my one year wedding anniversary, when we were driving home from dinner. I never confirmed this, but it makes some sense, the driveshaft being unbalanced and the u-joint unserviceable sends a lot of NVH and funky stuff through the pinion. Especially if the ujoints are getting old and stiff.

    If not just for the reliability, do it to get acclimated with the Torsen. It tends to feel a lot different than the VLSD when cornering, it is like understeer when it locks up.

  17. #10
    5,000 rpm - there be torque here! MiataQuest's Avatar
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    I now see two responses concerned about the strength.
    Maybe I should install the 3.90 Torsen at the same time.

    Here is what I think I need:
    * Full Torsen rear end assembly, comes with poly bushings. *check*
    * Two complete half shaft assemblies. *check*
    * The shorter 39.375" driveshaft. RockAuto has a Dorman unit with serviceable universal joints.
    * Maybe I should re-balance the new Dorman driveshaft ???
    * New axle nuts
    * Wheel bearings. Timken? Other brand?

    Is there anything else I am missing ??
    Is there any advantage to longer wheel studs?
    Other comments?

    And many thanks for all replies

  18. #11
    3,000 rpm - starting to feel the power Rogue's Avatar
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    this what a 1.8 swap can do to a VLSD!
    1992 BnT, 93LE #737, 94M, 95M, 96M, 97PEP, and a few 90s

  19. #12
    Ninja Messiah kung fu jesus's Avatar
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    Is there a 5 speed speedometer gear available to use with a 3.90 Torsen ?

    Timken has been hit or miss on quality. I would look to see if F-A-G or SKG makes bearings for these in the rear. I would definitely consider replacing the hub flanges. Look up rear bearing failures on Miatas for some sobering reading and images.

    Planet Miata sells ( I think they still do anyways ) full upright replacements with new bearings, flanges (?), and optional ARP studs ready to bolt in. Not cheap, but not bad either considering halfshafts can sometimes be stubborn or impossible to remove from the hubs. Your location makes that possibility probable. I knew a guy in California that couldn't get his axles out despite leaving one in a 40T press over night. YMMV.

  20. #13
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