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Speedo Gear in 205

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by sserven, Oct 22, 2006.

  1. sserven

    sserven Registered Member

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    I've got a 205 with a fixed yoke output for the rear driveshaft. The housing on the back of the 205 where the speedometer gears are at isn't working for me. Most 205's I've seen have the cable going in the top passenger side of this housing. Well mine it goes in the lower driver side. I disconected the rear drive shaft and turned it to see if the gear was turning with the cable unhooked, it wasn't.

    So next I used a big socket and took out the piece that keeps the gear in. I turned the driveshaft and held the end of the gear further up and then it would turn. But when I put the piece that keeps the gear in, back in, it put the end of the gear in a lower position and then it wouldn't turn again.

    Could I possibly have the wrong gear in this thing? It's not the original tranny and t-case so it's possible the gears were swapped at some point. If thats the case, where would I be able to find the correct gear?
     
  2. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    As far as i can remember the drive gear is sandwhiched between the output shaft and the yoke. Try putting a few thin shims in then tighten the yoke back down and see if that fixes it.
     
  3. Jimbo*

    Jimbo* 1/2 ton status

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    4x4 High has it; There's two different output shafts for the 205. One has a splined speedo gear and the other is smooth. I would bet that your yoke is a bit loose, and not creating enough friction to keep the speedo gear driven.
    Try tightening the rear yoke first, if that doesn't do it, you'll have to remove it and install a couple thin shims.
    Jimbo
     
  4. sserven

    sserven Registered Member

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    I might have explained this wrong. The red colored gear that is inbetween the t-case output shaft and the yoke isn't the problem. It turns when the driveshaft is turning. It is the gear that runs off that and connects to the spedo cable is where I think my problem is. This is the gear that you swap if you've changed axle ratio's or tire sizes to get the speedometer back to correct speed.

    This is the gear that works when I hold it up (closer to the gears between the output shaft and yoke), but when it put the piece that holds it in, back in, then it acts like it isn't making contact and therefore isn't turning.

    I was wondering if different years of 205's use different sized gears for the speedo cable?

    This picture might help.
    http://www.transmissioncenter.net/64_38cutawayspeedogear.jpg
    The green gear turns fine, its the gear below it that it drives is what I'm having trouble with getting it to turn.
    [​IMG][​IMG]
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    I know on the automatics the "sleeve" (piece that holds the driven gear you are talking about/showing in that pic) is different based on speedometer combos, two different sizes IIRC, due to the different driven gear sizes.

    Wasn't aware the 205's were setup like that, but not surprising either.
     
  6. Jimbo*

    Jimbo* 1/2 ton status

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    Send me your address, and I'll send you an extra speedo drive gear--that way you'll know you have the right gear set, and if it doesn't work, it's something else.
    Jimbo
     
  7. sserven

    sserven Registered Member

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    I've got a few friends who would probably have different gears I could try instead of having you ship one across the country. Hopefully in another week or so, we'll be done picking corn and then I'll have time to see what my friends have that i could swap in and try.

    I have noticed that all the driven gears I find for sale on the internet and ebay look like they are plastic and the one that is in mine is a 100% metal gear. I really haven't been able to find anyplace that sells a metal one like mine. Maybe the dealership sells them?
     
  8. Jimbo*

    Jimbo* 1/2 ton status

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    All the 205 driven gears I've seen are metal, and I've seen both metal and plastic drive gears. In fact, all the drive gears have been 7 tooth, it's the driven gears that are different.
    Post up a pic of yours, and maybe we can figure it out.
    Jimbo
     
  9. sserven

    sserven Registered Member

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    I found the problem. The red gear, the driver, is bad. The threads on it are not all there. It makes sense now. When I bought the truck, the spedo cable had rested on the exhaust and melted and wouldn't turn. Therefore when it was connected to the metal gear, driven, it would have eaten up the plastic, drive, gear. I've seen a few places where I can get the red gear so I'll get one of those and that should solve it.

    Here are some pics, thanks for the help everyone!

    DRIVE GEAR.jpg
    DRIVEN GEAR.jpg
    speedo hook up.jpg

    The cell phone camera with flash really helped.

    DRIVE GEAR.jpg

    DRIVEN GEAR.jpg

    speedo hook up.jpg
     
  10. 425 Xpedition

    425 Xpedition 1/2 ton status

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    In picture #3 can anyone tell me about the "black box" in the speedo cable? My truck has the box also and have always wondered what it was for.:confused:
     
  11. dyeager535

    dyeager535 1 ton status Premium Member

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    Ratio adapter. Instead of changing the speedometer gears, GM went that route for some time, in some applications. Varying ratios obviously, typically stamped into the outside of the adapter somewhere.
     
  12. 425 Xpedition

    425 Xpedition 1/2 ton status

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    Kinda what I thought, but wasn't sure.:doah:
     
  13. sserven

    sserven Registered Member

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    My original setup with factory 4.56 gears didn't have that black thing, but the truck I swapped axles with was an 89 1 ton 4 door with 3.73's and it had the black thing, so took it along with the axles.

    Also, the red plastic gear that I'm replacing was $25 on ebay, but the local chevy dealer can get it from a wharehouse in chicago for $6.98.
     

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