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Did search, no real answer... Speedo Recalibration effort!!!!

Discussion in 'The Garage' started by Batmanjr, Apr 27, 2003.

  1. Batmanjr

    Batmanjr 1/2 ton status

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    Alright, I figured out after alot of reading that it is highly necessary for the idle to be set right on my 87 Blazer with a ECM, that the computer be able to know what speed I'm going! SOOOO, I need to fix my gears in my 205! Here is my problem, I swaped a 205 out for the 208 behind the 700r4, I have no idea what gears it had in the truck it used to be in, but the METAL gear that comes out of the tailshaft has an "H" stamped in it and 18 teeth.... I have 4:10s now with 38" tires, I soon plan on running 4:56 or 5:13 but I have to come up with the cash to do so, so who know how long that will take... The bottom line is that I'm probably looking at doing this twice, so I need to understand how to do it! Where can I get info or can someone explain the formula for me to use to decide on what to change!??? Where is this infamous "Plastic" gear that is supposed to be color coded, and what exactly am I changing??? Thanks /forums/images/graemlins/ears.gif
     
  2. Okiemuddog

    Okiemuddog 1/2 ton status

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    Bruce,
    Try Speed-o-calculator, it is hosted by bowtieoverdrives.com. I ma not sure if the gears in the 205 are the same as the 700 or not, but should give you an idea of what gear you need. /forums/images/graemlins/thumb.gif

    Krennen
     
  3. amm888

    amm888 1/2 ton status

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  4. amm888

    amm888 1/2 ton status

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    i just checked out the site...and i don't understand what you do once you get your answer?
     
  5. Batmanjr

    Batmanjr 1/2 ton status

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    I found this as well, but it says I need an 8 count drive gear!!!! Does this sound correct? I tried to count the teeth on the gear in my transfer and it seemed to look brown in color and have 5 teeth... This could be way off though!!!! All I know is that the driven gear in my hand looks way differnt than all those I've seen on the 700r4 sites and it's the only one that I've ever heard of being metal!!! I'm about to take the tailhousing off just to see... It's midnight and I know there's a thousand other things I should be doing! but here goes..... /forums/images/graemlins/thumb.gif
     
  6. dyeager535

    dyeager535 1 ton status Premium Member

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    Good luck with this.

    Believe the 241 reluctor ring/205 swap is your only choice. Do a search for "205 vss" and I bet you find it. There are exactly *2* driven gears available for the 205 in '85/86, I doubt there was much more than that number ever offered, thats why the adapters were popular. There are no plastic gears in the 205, thats why you can't find them. Guess thats the way a transfercase should be. No plastic, and 100% iron:)

    Only other option is probably a bolt on VSS AFTER getting an adapter that corrects the speedo gear output, but I bet thats more costly/time consuming than doing the 241 reluctor ring fix.
     
  7. Batmanjr

    Batmanjr 1/2 ton status

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    Dyeger, tell me more about this 241 rel???? ring replacement...

    I finally got the drive gear out and the thing has 7 gears...... Perfect according to the calculator for 4.5 and 5.13 gears! I hope!

    Now what! It is metal and I have no idea where to go to find info on this setup!!!!! Thanks To anyone with more info! Bruce /forums/images/graemlins/ears.gif
     
  8. Triaged

    Triaged 1/2 ton status

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    Go to the 1st gen forum and search some of Steve_Chin's posts on the subject!
     
  9. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Excuse my ignorance here. I'm on the learning curve with the FI. I didn't think the VSS was used on the TBI till 90 with the 241 came out. I thought the VSS was in the speedometer if it had one at all from 87-90. I know my 88 Burb (now it's a 454 so maybe different) does not have a VSS at the tranny. I was looking at it last night. Only wire on the whole tranny was the kick down wire.
    As such a Speedo shop should be able to provide and little device that screws into the Speedo drive that will adjust for the gearing. This will get the Speedo acurate and should cure the signal problem to the ECU.
     
  10. Batmanjr

    Batmanjr 1/2 ton status

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    According to my Chiltons manual, the vss on the 87 models are located on the back of the speedometer itself... I haven't pulled it off yet, but it says that in order to set the idle adjustment, the ecm must read above 40 moh and then count back the steps on the TPS in order to set the 0 setting, or idle.... That's what the book says, I also found out that the metal gears I have will be perfect for when the 4:88 gears go in and they will be perfectly accurate, so I'm simply going to put the thing back together and deal till I do the gear swap! Thanks all for the input! /forums/images/graemlins/thumb.gif
     
  11. dyeager535

    dyeager535 1 ton status Premium Member

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    I'd be curious what you find when/if you pull your gauge cluster out.

    You are right, everyone says that manual trans trucks did not have VSS, which seems to indicate even on auto trucks it wasn't used by the ECM, but it just seems odd not to. At least to me. Others have apparently found the same thing, no VSS, but I'm still just a bit hesitant to believe there is NO VSS.
     

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