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Mech speedo???

Discussion in 'The Garage' started by shaun, Jan 31, 2005.

  1. shaun

    shaun 1/2 ton status

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    I have a 241 from an 89 3/4ton suburban. The question I have is I am preeping my truck for a drive from CA to NC and I have no speedo. I was going to put a Mech speedo but my tcase has an electric plug for the speedo an the tail end. Is there an adapter I can buy so I can use a manual speedo. Or do I have to buy the universal gm plug for an electric speedo and a electric speedo. Does anyone have that plug or any suggestions.
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    Going to have to get an adapter or I assume tear down the one you have and replace the output stuff relating to VSS.

    NP241 is going to be a 40 pulse VSS, check with www.jagsthatrun.com and see if they have a 40 pulse VSS generator.

    IMO the tear down/output swap is the best option. If you go the generator route (if they are even available) then you have to deal with speedometer gears to compensate for your gears, ratio, etc. to make the speedo read right.
     
  3. K5Jimmy

    K5Jimmy 1/2 ton status

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    If I'm understanding correctly...doesn't a 90 have the Elec speedo? I know they changed from Mech to elec about mid 89. I have the mech type in my 89.

    Guessing a yard won't let you cannibalize a complete TC. An alternative may be to convert your TC to mech.

    You'd need the snap rings, worm gear for the shaft, oil pump housing, driven gear w/housing (part ya screw the cable onto)...the tailshaft housing should be the same. Sounds like a lot more than it really is. Replace the tone ring with the plastic worm gear, different housing.... Prolly a 45 min job because of that sob snap ring against the bearing on the housing.

    If you go that route...Buy an Extra Snap ring at the housing....They are a common breakage prob on 241's....I was told that by more than one rebuild/tranny shop...I bought 4 for $1 each....the dealer wants $8ea, and Napa don't got 'em

    If I misunderstood, and you need to convert from mech to elec, you would just do the opposite.

    Exploded view of my 241 came from www.motivegear.com ...they are wholesale only...good picture, tho

    I got my parts from National Drivetrain 1-800-507-4327...they ship from Chi and Atl www.nationaldrivetrain.com

    As for the Gears and Ratio....Someone recently posted about how to figure this and what color went to what ratio....someone with a speedy connection could find this pretty easy....it was very straightforward and super simple the way they described it, and they had a link that was really spot on.

    Found it.... http://www.tciauto.com/components/speedometer_gears.htm
     
    Last edited: Jan 31, 2005
  4. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    I have found this bored today and curious . They don't have a pic up yet , and I have never heard of this place before . http://www.terf.com/SpeedChangerMechanicalPage.htm

    I am looking for more . If something like this is true and works , then mechanical speedo trucks like mine can use any np241 :thinking:
     
  5. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    Found another , pricey Clicky
    This turns electric signal to mechanical drive , works with most aftermarket speedos ( I am sure GM ones with an adapter if it doesn't already work ) , but its 300 bucks , not cheap :(
    [​IMG]
     
  6. dyeager535

    dyeager535 1 ton status Premium Member

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    I believe someone over on thirdgen.org had come up with something like this as well. I do know that it works with digital speedometers, but thats about all I know.

    I would suspect it can't be too hard to find NP241 VSS parts that you'd need for the swap, heck, can probably find someone that is trying to go mechanical to trade with.
     
  7. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    Dorian , he wants to go from electrical transfercase to a mechanical gauge instead :D
     
  8. dyeager535

    dyeager535 1 ton status Premium Member

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    I understand what he wants to do, (which is get advice/opinions) I'm putting another option on the table that I think makes more sense.

    No one has bothered to worry about VSS either have they? All the DRAC wiring, would have to be rewired for cruise, ECM VSS, and ABS to work if you go with mech. drive, and I have a feeling making ABS work with cable drive is a LOT more complex than using a DRAC.

    1989 t-case he says, with 1990 truck.

    So, with that scenario, we have a mechanical speedo case, with digital speedometer gauge.

    He may want to go electric case to mechanical speedo, but for the prices that have been posted so far, I think swapping the parts to electric speedo 241 makes a lot more sense. You leave everything alone but the case, and the truck works exactly the way it was supposed to, with no off the wall parts. Already stated that tearing the back half of the 241 apart isn't too tough, and they are common cases, so it should be a no-brainer.

    I know which route I'd take. Oh wait, I have already. :)
     
  9. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    I wouldn't bother with it either , just knew it could be done :D
     
  10. shaun

    shaun 1/2 ton status

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    I guess i should give more info on the truck. It is a 1990 jimmy frame and body. 85 3/4ton running gear, rebuilt 350 (carbed w/ no emission), t400, 89 elrctric speedo 241, painless wiring, all autometer gauges. No VSS, cruise, ecm, abs....

    It is just a barebones rocks/sand truck.
     
  11. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    Well , just keep looking or shell out some coin , or just buy another case to use for parts and save the leftovers if you break a chain or something . I knwo transfercases are simple :k5: :k5:
     

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