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Coverting from mechanical speedo to electric (AND KEEP THE VSS)

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by fortcollinsram, Jan 31, 2003.

  1. fortcollinsram

    fortcollinsram 1/2 ton status

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    Okay, I have a 1987 K5...it has the mechanical speedo that is driven by a gear off the t-case tail-housing... The speedo cable also drive the VSS box that converts the mechanical motion into an electric signal for the ECM...Well, my speedo cable is broken, my speedometer has a busted needle and I WANNA CONVERT TO AN ELECTRIC SPEEDO..What all is involved? Can I just get like a conversion mdule to send the VSS signal to the ecm and a signal to a NEW Autometer speedo?

    Thanks gang...

    Chris
     
  2. u2slow

    u2slow 1/2 ton status

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    I think you will need an ECM from a truck that had a VSS. You will also need a t-case that uses a VSS - that may require an NP241 or an extremely rare '91 NP205.

    89-93 Dodge diesels used this funny contraption... Don't know what it puts out for a signal though.
    [​IMG]
     
  3. fortcollinsram

    fortcollinsram 1/2 ton status

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    isn't the ECM the same for all TBI 350 truck (the 7747) mine just gets the VSS signal from a different place than the later model ones...at least that is my understanding of it...Didn't Steve Fox have something to convert his 203/205 doubler to a VSS for the speedo and ECM?

    Chris
     
  4. u2slow

    u2slow 1/2 ton status

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    If not the ECM, then the PROM chip must be different. Many 87-90 R/V trucks without cruise, and with a SM465 or TH400 have no VSS of any kind whatsoever.

    There's probably some aftermarket fixes, but I'm not knowledgeable in that department. I have found some interesting fixes on the web though...
    NP205 with VSS
     
  5. Marshall

    Marshall 1/2 ton status

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    I have a NP241 case and i wanted to use it on my 87 Jimmy, i also need to either go electric speedo or just put the speedo gears in the 241(since its an electric speedo t-case)Does anyone know which might be easier,i have heard that the 241 C is a really good case is this true and why?which ECM is in an 88-91 Is it the same as the 7477

    Thanks, Marshall

    350/TBI/3.73Gov-Lock/31"s/208
     
  6. ZonkRat

    ZonkRat 1/2 ton status

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    241 is good case.Better reduction {2.72}.Put good skid plate under it.Can't beat on it like cast iron.Broke one cause I ran dry of fluid.They need a fixed yoke rear instead of slip joint.Old {85}205 slipyoke will fit and it uses 1350 series joint. /forums/images/graemlins/crazy.gif /forums/images/graemlins/truck.gif /forums/images/graemlins/thumb.gif
     
  7. dyeager535

    dyeager535 1 ton status Premium Member

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    </font><blockquote><font class="small">In reply to:</font><hr />
    Many 87-90 R/V trucks without cruise, and with a SM465 or TH400 have no VSS of any kind whatsoever.


    [/ QUOTE ]

    That isn't true. If the truck is TBI, it requires (and has) VSS /forums/images/graemlins/smile.gif

    I believe that if the original poster checks with jags that run (website URL?) you will find various methods of getting the VSS and Speedo outputs you need.
     
  8. u2slow

    u2slow 1/2 ton status

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    </font><blockquote><font class="small">In reply to:</font><hr />
    That isn't true. If the truck is TBI, it requires (and has) VSS

    [/ QUOTE ]

    No. I've torn two trucks completely apart that had TBI and no VSS. One was an '87 K30 with sm465/NP205. Two was an '89 Suburban with TH400 and NP241. Both had cable speedos. Neither had the VSS buffer box.

    The '89 Suburban TBI harness and accessories went into a Jeep for the sole reason that it did not require a VSS. The guy had tried with a different harness and ECM, and ran into problems since it required the VSS, which his Dana 300 did not have.
     
  9. dyeager535

    dyeager535 1 ton status Premium Member

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    I was gonna post and say you were full of crap to be honest, but I can't /forums/images/graemlins/smile.gif

    I checked out MJ's wiring diagrams for the '89 'burb, and sure enough, no reference of VSS wires on the ECM pinout. Diesel on the other hand, does. Go figure!

    Sorry for my mistake. Can't believe GM ran without VSS for those years, guess that's one reason everyone is pissed at the SUV's poor mileage. GM could/can cut corners, so they do.
     

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