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Thread: Speedometer jumping around...What gives?

  1. #1
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    Speedometer jumping around...What gives?

    I noticed this today on my way home from work. Pretty much does not matter what speed, the speedo needle will jump around while going down the road. Very wierd... what could cause this?

  2. #2
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    Quote Originally Posted by phils89sc View Post
    I noticed this today on my way home from work. Pretty much does not matter what speed, the speedo needle will jump around while going down the road. Very wierd... what could cause this?
    speedo cable stretches over time. I don't think ours are adjustable. Read the Haynes. I would get a new cable. It goes from your cluster to your trans. Get familiar and change it. Does it hop up and down? Then it is stretched. IF it measures speed then doesn't (intermittent) then it could just be coming lose out of the back. Either way pull the cluster and check it. It is a push/pull and twist like a spring loaded small light bulb.

  3. #3
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    These cars don't have speedometer cables they are electronic. First thing I would do is check the connector to the sensor on the transmission. When it isn't making a good connection this will happen. I wish I could describe which sensor it is, mine has yellow on it and looks unique.

    Chris
    Me-89 SC 5-speed 1.7 Autorotor twin screw over 443rwhp 20psi
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  4. #4
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    Quote Originally Posted by mywhite89 View Post
    These cars don't have speedometer cables they are electronic. First thing I would do is check the connector to the sensor on the transmission. When it isn't making a good connection this will happen. I wish I could describe which sensor it is, mine has yellow on it and looks unique.

    Chris
    Can the sensor be cleaned? Connector cleaned? I knew about the cable thing, just didn't want to be the first to say anything :-)

  5. #5
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    Could be

    I believe the electronic sensor actually take the place of the cable in that is attaches at the same place a normal cable would attach to, but engages the output shaft teeth and transfers that RPM into a pulse the EEC can then output to the gauge. So.........

    Perhaps some of the teeth on the speedo gear are stripped and making the reading jump all over the place.

    It could also be the motor in the gauge cluster is just getting old and will not keep a steady MPH, I had to gently tap on my gauge cluster for a while to get my Speedo to start reading anything, then it would be fine until the car stoppped again.

    Smitty
    Venetian Blue 1995 5 Spd...............No ET
    Orange Crush Pearl 1995 Auto SC........11.175 @ 121.85 MPH
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  6. #6
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    Just pull the connector apart and see how it looks. To a point you may be able to clean it. The tab that locks the connector to the sensor on my car is broke , it used to come unplugged every once in a while. In the process the speedo would go irratic on me until it unplugged all the way. The plastic gear inside the tranny may cause the same issue, but I have never experienced this on one of my cars.

    Chris
    Me-89 SC 5-speed 1.7 Autorotor twin screw over 443rwhp 20psi
    Her-95 SC auto 1.7 KB 400rwhp 17psi
    my email

  7. #7
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    Usually it is the speed sensor or the cluster.
    Alan

  8. #8
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    Here is a picture with the speedo sensor location on the M5R2. The AOD is in a similar location and looks the same.

    It has a fork and bolt that hold the assembly into the trans housing. Very easy to remove and check the plastic gear while you're checking the connector.
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  9. #9
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    thanks

    thanks for the update on the drive -by-wire speedo system. I did not know. It can only be sending unit or the plastic piece in the trans. The receiver is the EEC and we don't want to go there. Sorry for the cable info. My 93 cobra had one. These SC's are truly way before their time. That is why I love them.

    Linc

  10. #10
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    Just a shot in the dark here.....

    Have you tried cleaning the battery posts and battery connectors...

  11. #11
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    I will try that tomorrow. Hey Eddie, interested in another 5 speed SC or XR7?

  12. #12
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    You bet....

    Price and location....

  13. #13
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    Hey guys I got a question about this sensor so I didnt want to make a new post. I am putting in a new transmission and everything seems right except for the cable that actually plugs into the sensor. It looks like it has a little metal piece that is spring loaded and you can push up and down, but then it has threads like it screws into something? I dont know if it is broke or if its just me, but I cant figure it out for the life of me.

  14. #14
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    Quote Originally Posted by cyoder View Post
    Hey guys I got a question about this sensor so I didnt want to make a new post. I am putting in a new transmission and everything seems right except for the cable that actually plugs into the sensor. It looks like it has a little metal piece that is spring loaded and you can push up and down, but then it has threads like it screws into something? I dont know if it is broke or if its just me, but I cant figure it out for the life of me.
    There is no cable that plugs into the sensor. There is a gear that goes on the end toward the transmission an electrical connector on the other end.
    SCCoA Member#: 2515
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  15. #15
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    Oh ok. What does this cable go to then? I dont know if I posted the pic right so bare with me here.
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