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1990 electronic speedo cable tp NP205

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by CK5, Dec 20, 2001.

  1. CK5

    CK5 In my underwear Administrator Premium Member GMOTM Winner Author

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    I think I may have this info at home but might as well ask again. When I do the doubler I need to go from a NP241 to NP205 speedo cable, my 1990 has the electronic speedo the 205 mechanical, someone posted a place that sells the correction that I need, anyone?

    Steve

    Director of Global Expansion
     
  2. GRINCH

    GRINCH 1/2 ton status

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    I may be wrong here but, Since the 1990 uses a DRAC (under dash by ashtray) which is wired to the ECM and the 241 how will a mechanical one convert? Wouldn't you have to just put the sensor in the 205?

    The Few, The Proud, The K5 Blazer
     
  3. HarryH3

    HarryH3 1 ton status Author

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    Here's a few places that sell different types of speedo adapters for EFI conversions and such:

    www.painlesswiring.com
    <a target="_blank" href=http://www.jagsthatrun.com/Pages/SpeedSensors_Speedometer.html>http://www.jagsthatrun.com/Pages/SpeedSensors_Speedometer.html</a>

    <font color=black>HarryH3 - '75 K5</font color=black>
    <a target="_blank" href=http://www.angelfire.com/super/ThunderTruck>www.angelfire.com/super/ThunderTruck</a>
    It's a great day to be alive...
     
  4. JROSS

    JROSS 1/2 ton status

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  5. 90blzr

    90blzr 1/2 ton status

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    clicky.: <a target="_blank" href=http://www.speedometershop.com/cru-pag.htm>http://www.speedometershop.com/cru-pag.htm</a>
     
  6. Russ

    Russ 1/2 ton status

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    Steve,
    I went through all this back when I put the doubler in my 90 model. I talked to most all of the major speedo places and could not find any kind of conversion short of rewiring the dash or converting to manual speedo. I finally took the tail section of the 205 and had a hole tapped in it for the VSS from the 241. I bought a new exciter ring from GM for about $15 and had it bored out to fit the 205 output shaft. It basicly just replaced the mechanical speedo gear. I just welded a cap over the mechanical speedo adapter so it wouldn't leak oil and left it in the case. When it was all put together it worked great and has been working for about a year now.
    Russ
     
  7. pcorssmit

    pcorssmit 1/2 ton status

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    Couldn't you use parts out of a '90-'91 1 ton with a 205? Or were they still mechanical.

    Another thought: I have no idea if they use the same type of pulse or would be physically interchangeable, but my Dodge uses a gear-driven speed sensor that goes in the t-case similar to a traditional rear wheel drive GM car speedo gear drive (I think thats how the 4x4 ones are too, just can't picture it in my head).

    Of course it would be cheap to convert to a mechanical speedo.

    Pete

    '83 K5, 350 TBI (ex 6.2), 700R4, NP208, Dana 60/14 bolt, 4.56s, Detroits, 3" lift, 15-39.5x15 TSLs
    '97 Dodge 2500 4x4 CC LB Sport, Cummins 5 spd
     
  8. Russ

    Russ 1/2 ton status

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    Pete,
    The problem with converting to a mechanical speedo was that the computer needed the VSS signal. Don't ask me why, I am no computer guy, but my Check Engine light would not go out and the Idle was screwed up without the VSS hooked up.
    There is only one year of chevy one ton truck that uses the 205 with a VSS. The 91 crewcab SRW truck. Finding one of those was impossible, even Parts Mike could not locate one of the tailcones that I could put my VSS into. Chevy quit making that part a few years ago.
    I checked with all of those speedo shops listed previously in this post and even had some of them send parts out to me that did not work, for some reason the GM VSS for the TBI trucks was a different pulse than everything else out there and nothing would work. I imagine one of the electronic guys on here could probably figure something out, but I pretty well exhausted everything that I could think of prior to having the machine work done. I never expected the speedometer to be the most complicated part of the Doubler when I went to put it in.
    Russ
     
  9. pcorssmit

    pcorssmit 1/2 ton status

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    Its been a few years since I did my TBI conversion, but I thought all TBI motors used the 2-pulse speed sensors (as opposed to the 4 pulse). The trucks had speed sensors starting in the early 80's for electronic cruise control, it is optically triggered off a ring on the back of the speedo. I run the stock speedo in mine. I don't know how integrated the abs stuff is with the engine ecm, I never had a need to look into it. Hmmm. Anyways, the speed sensor in the mechanical speedo trucks is i a little box that is kind of loose under the dash, I think the part that actually goes to the back of the speedo has 3 wire on it (possibly a 3-wire ribbon type wire).

    Pete

    '83 K5, 350 TBI (ex 6.2), 700R4, NP208, Dana 60/14 bolt, 4.56s, Detroits, 3" lift, 15-39.5x15 TSLs
    '97 Dodge 2500 4x4 CC LB Sport, Cummins 5 spd
     
  10. Russ

    Russ 1/2 ton status

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    Pete,
    I never got into the wiring under the dash. I would have to look up the notes that I was taking from back then to remember what the pulse was. I did talk to Howell, Jagsthatrun, and that speed shop in Arizona and they all told me that they did not make a manual to electronic converter for the TBI model VSS. They had all but that particular one. Once it gets into the elctronics side of it, I start getting lost so there may be a solution that I did not think of.
    Russ
     
  11. K5 NUTT

    K5 NUTT 1/2 ton status

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    Howell EFI...2 pulse vss...screws right onto the Np205 output....2 wire weatherpack outlet...$80.

    Azblazer

    1979 K5 350 TBI
    1976 K5 Chalet
    If it ain't got arizona pinstriping.....you ain't wheelin the pee outa her!
     
  12. Russ

    Russ 1/2 ton status

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    I bought that one. It didn't work. I sent it back.
    Russ
     
  13. CK5

    CK5 In my underwear Administrator Premium Member GMOTM Winner Author

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    I was afraid of this, thank's for the info Russ, I will prolly contact you a little later on as I get into this some more.

    Steve

    Director of Global Expansion
     
  14. Eric78K5

    Eric78K5 1/2 ton status

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    Is an 89 electronic or mechanical?

    Eric78K5
    K5-Because Size Matters!
     
  15. CK5

    CK5 In my underwear Administrator Premium Member GMOTM Winner Author

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    mechanical

    Steve

    Director of Global Expansion
     
  16. Kyle89K5

    Kyle89K5 1/2 ton status

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    How about finding a wrecked 89 blazer or sub and stripping the stuff to go back to mech?

    Kyle
    89K5
     
  17. CK5

    CK5 In my underwear Administrator Premium Member GMOTM Winner Author

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    From the other post, I think the ECM needs the signal from the VSS to properly run the TBI, but not totaly sure on all of this.

    Steve

    Director of Global Expansion
     
  18. Russ

    Russ 1/2 ton status

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    No problem, Hopefully you will think of something that I did not. What I did works fine, just not as clean as I would have liked it to be.
    Russ
     
  19. blazer72

    blazer72 1/2 ton status

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    The ECM uses VSS to tell if the truck is moving or not. this along with a switch on the shifting system tells the system when it should up the motor RPM based on load. The vdo senser or the autometer senser for the elec. speedo will work but will not give you the right speedo reading. There is a GM part that replaces the speedo cable drive that will work and Yes it is in the JTR book. Also Panless Wiring sells the senser.

    72 Blazer 400TPI NV4500 NP203/205, 6 bolt FF14
    01 Suburban 8100 2500 4X4
     
  20. pcorssmit

    pcorssmit 1/2 ton status

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    So, the '90 and up TBI computers require a different vss signal that the '87-'89 trucks?

    Pete

    '83 K5, 350 TBI (ex 6.2), 700R4, NP208, Dana 60/14 bolt, 4.56s, Detroits, 3" lift, 15-39.5x15 TSLs
    '97 Dodge 2500 4x4 CC LB Sport, Cummins 5 spd
     

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