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Trans speedo gear?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by TPI86, Jun 22, 2000.

  1. TPI86

    TPI86 1/2 ton status

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    Has anyone done any research on the speedometer gears located at the transmition. I have a 86 K5 with 33 x 12.5 tires, 700R4, 3.42 gears. I am using a TPI with speed density system that uses the pulses from the speedometer gear. I know my speedometer is off-does anyone have any information for the correct gear to correct my speed? ANY HELP WOULD BE GREATLY APRECIATED.
     
  2. jimmyjack

    jimmyjack 1/2 ton status

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    Is it in the transmission or the transfer case? I have an 83 and its in the tail shaft of the t case. Not sure about the TPI tho.
    creepin and crawlin
    jim
     
  3. TPI86

    TPI86 1/2 ton status

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    Your correct it is at the tail section of transfer case. I know it is a small plastic gear, just looking for the correct one.
     
  4. 72junker

    72junker Registered Member

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    there was a post on this a few days ago. Someone said that the teeth = 2mph, so if you're 10mph over you go with 5 more or less teeth, I can't remember which was. Check the last few days of posts for more info.
     
  5. jimmyjack

    jimmyjack 1/2 ton status

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    That was a reply to a post of mine but I forget when I wrote it sooooooo.
     
  6. dumbfounded

    dumbfounded 1/2 ton status

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    I believe on my TPI system in my vette that the computer doesn't change engine systems in relation to vehicle speed. The TPI is set around exhaust (rich or lean conditions) It takes engine sensors and adjusts accordingly. IE: increase throttle, throttle position sensor see's, bumps timing, increases injector duration (more fuel), checks O2 sensor to maintain fuel/air ratio. The speed sensor I believe is mainly for lockup torque converters, shift light on manuals, and on vettes it uses this to compute mpg, mileage left on tank etc (separate computer but same sensor) I don't believe that it cares as far as the engine is concearned. OBD II system on I believe 96 or 97 and newer is a whole other ball game though. It takes everything seriously. So performance gains are harder but in your TPI sys you can disconnect any sensor (acting like sensor failure) and system will go into "limp" mode. It will guess what the sensor is supposed to be reading by going off other sensors. The engine will run like crap but you can "limp" it home. This is what happens when the "service engine soon" light is for. It let's you know you have a problem with the fuel injection. Some cases you can't notice a difference other than fuel economy, but in other cases it will run terrible. So other than your speedo don't worry it won't hurt anything unless you have a lock up torque converter and it's trying to lock up at too low of speeds. Even then it will take more throttle to take off and then it will probably see to great of throttle and unlock, then it's just an annoyance.....

    Wasn't me.............
     

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