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Bouncing/Incorrect speedometer

Discussion in 'Chevy C/K Truck Forum' started by knexster, Feb 27, 2012.

  1. knexster

    knexster New Member

    When I am stopped is the only time my speedometer is correct, the moment i accelerate and reach maybe 10mph it says im at 80. It will then flick up and down speratically while I drive. I believe its the speed sensor but I want to confirm my truck has a speed sensor and that is what is causing my problem.
  2. rileyjr16

    rileyjr16 Rockstar 3 Years 1000 Posts

    You do have a speed sensor I just forgot if its in the trans area or around the front tires which I will have to check. That could most likely be your problem.

    ---------- Post added at 04:20 AM ---------- Previous post was at 04:14 AM ----------

    It is on your trans.
  3. knexster

    knexster New Member

    Super awesome so I have to go diving into my transmission right? gonna go buy the sensor tomorrow can't wait to know how fast im going everywhere lol
  4. knexster

    knexster New Member

    changed my speed sensor, it stl jumps to 80 upon accelerating forward at all...., what to do what to do..
  5. knexster

    knexster New Member

  6. Josh

    Josh Member 100 Posts

    i take it this transmission is the 4l60. is it 4wd or 2wd. i just replaced my vss on mine. fixed it. its possible the connector is dirty. clean all the terminals.
  7. okysmokey911

    okysmokey911 Rockstar 100 Posts

    Ah yes I was having this issue which was frustrating as hell. My speedometer would read correctly and if I hit either the right or left blinker, it would bounce around like crazy. After a while my speedo stopped working completely. There are only two things that I could think of that would be causing this. 1. you have a bad vssb ( vehicle speed sensor buffer ). This is located behind the glove box near your ecu. It will be encased in a white plastic housing. 2. There is an electrical issue. My problem was that the main positive wire going to my starter had rubbed raw and was rubbing against the frame which caused a whole lot of electrical issues, and fried my vssb. My advice would be to take your vssb out and go to a junk yard and find one that matches. I got lucky and found two vssb's and one of them ended up being the correct one. If you get the wrong one your speed sensor will be off. Pretty much impossible to find these things online, and I wouldnt want to know what a dealership would charge you, cost me about 10 dollars from the junkyard. It's a very frustrating thing to diagnose, so I hope that my advice helps you. The only other thing it could be is that somehow your instrument panel has gone bad ( I tried switching that out too) but I would lean more towards the previous things I mentioned. If none of this helps you, let me know I might be able to walk you through some other things to try. Good luck.
  8. rileyjr16

    rileyjr16 Rockstar 3 Years 1000 Posts

    My dad said his problem on Old Blue was the ECM itself but he got his from the dealership...$$$$$$$.
  9. knexster

    knexster New Member

    Sounds like I have a vssb issue because when I use my blinker it will twitch from 80 to like 50 back to 80.... the search begins, any recommendations on what I can pull from?
  10. okysmokey911

    okysmokey911 Rockstar 100 Posts

    Wow yeah sounds like the exact same problem. Honestly I would check both the grounds and positive lines going to the starter and make sure none of them have exposed wires. It's possible that your vssb is still good and this is causing your problem. If those check out okay then yes I would go ahead and change out the vssb. I believe you can pull from any 89- 98 style truck, but like I said it may take a few to get the right one. Best advice I can give you is to take the white plastic housing of the vssb which will have a model number on it and try to match it to something from the junkyard. I'd say that I would send you my two extra ones I pulled from other vehicles, but somebody broke in to my truck and stole all my old parts and tools haha.

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