740 Speedometer Sending Unit Question

Discussion in 'Volvo 740' started by Jamie, Jun 12, 2006.

  1. Jamie

    Jamie Guest

    Howdy folks,
    Yesterday I tried to find the cause of my speedometer issue. It has a
    mind of its own. Usually only kicks in after driving down the highway
    at speed for a short while.

    I pulled the dash first and disconnected and reconnected everything. I
    reinstalled it and no change. Next, I removed the pan hard rod from
    the rear and unplugged the electrical connector from the sending unit
    on the differential. The ends of both wires were exposed, so I cleaned
    them and the connector with throttle body cleaner. From there I applied
    liquid electrical tape, plus electrical tape over the bare wiring. The
    wires did not appear to be broken.

    I reconnected the unit and still it does not work. I am thinking my
    next step is to remove the unit from the differential, but I do not
    know what I will be looking for.

    Any suggestions?

    Thanks!
    Jamie

    1987 740 GLE
     
    Jamie, Jun 12, 2006
    #1
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  2. Jamie

    Jamie Guest

    I didn't take apart the speedo or any components on the cluster, I just
    unplugged the wires and reconnected them in case they were loose.

    I wonder which end should I dig into the guts first - behind the dash,
    or at the chunk? BTW- where exactly are the wires to the speedo on the
    dash?

    Can ya'll help me out from memory?

    As I recall, from the drivers side going left to right are:

    1) a multi pin connector on the lower left.

    2) A yellow wire going high center with a plastic lock cover.

    3) A brown/white wire going low, just right of center onto 1 of 2 pins.
    I use the lower pin.

    4) A multi-pin connector to the low right

    5) A multi pin connector off to the high right.

    6) There is also a 3 wire set (3 or 4 - can't remember), in a weird,
    hard to disconnect plastic housing. It looks like you open the plastic
    connector downward and back the wires out. I could not get this off and
    did not want to break it. It was just to the lower right of the speedo
    on the rear.

    Can ya'll tell me what any or all of these wires do and which are for
    my speedo?

    Thanks
     
    Jamie, Jun 12, 2006
    #2
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  3. Jamie

    Guest

  4. Jamie

    Jamie Guest

    Thanks. I've read through all of these and while very informative, I
    was hoping someone could give me a more descriptive answer on what I
    should see when I remove the sending unit from the differential.

    This gives a good detail of the wiring, but not much about the inner
    workings at the 'chunk'. Haynes talks about using a feeler gauge to
    determine the correct distance when installing a new unit.

    I wasn't sure if there were any tell-tale signs of problems once you
    remove the sending unit.


    wrote:
    > this might help
    >
    > http://www.brickboard.com/FAQ/700-900/ElectricalInstruments.htm#SpeedometerFluctuates
     
    Jamie, Jun 12, 2006
    #4
  5. Jamie

    User Guest

    In article <>,
    says...
    > Thanks. I've read through all of these and while very informative, I
    > was hoping someone could give me a more descriptive answer on what I
    > should see when I remove the sending unit from the differential.
    >
    > This gives a good detail of the wiring, but not much about the inner
    > workings at the 'chunk'. Haynes talks about using a feeler gauge to
    > determine the correct distance when installing a new unit.
    >
    > I wasn't sure if there were any tell-tale signs of problems once you
    > remove the sending unit.
    >
    >
    > wrote:
    > > this might help
    > >
    > > http://www.brickboard.com/FAQ/700-900/ElectricalInstruments.htm#SpeedometerFluctuates

    >
    >

    There is a tone ring, or shutter wheel fixed to the ring gear carrier.
    The pick up is a simple coil wrapped around a permanent magnetplaced in
    a brass can and molded shut with plastic to form a seal and a plug
    connector. The sensor is shimmed from below and held in place by a
    threaded cap while it is sealed with an oil ring. The sensors only go
    bad when the car is hit from behind driving the panhard rod into the
    molded plastic and breaking it or the diff cover or both. Or if
    something inside differential literally blows up. If you had to name one
    piece on a Volvo that is absolutely bulletproof you have found it.

    Now if you have ABS on the car the signal from the vehicle speed sensor
    goes to a divider/multiplier circuit where the AC signal from the speed
    sensor is split. One portion is converted to a square wave for use by
    the ABS controller and the frequency adjusted for that use, IIRC the
    tone ring for the hubs is 72 teeth and the ring on the differential is
    48, the other half goes directly to the speedo head. The 4 pin plug that
    connects to the speedo is the other end of the speed sensor wires, the
    Gn/W, Bn wire twisted pair plus a R/Bl switched B+ and a SB-.

    If you jack up the rear of the car enough that the rear wheels can spin
    free you should be able to read a good AC signal from the sensor wires
    with the cluster removed. There should be very little amplitude change
    but some increase from wheels turning at idle, but a substantial
    increase in frequency with each increasing change in rear wheel speed.
    If the signal is there and reliable then the speedo needs to be repaired
    or replaced.

    Bob

    --
    The goal when driving is to miss the maximum number of objects.
     
    User, Jun 13, 2006
    #5
  6. Jamie

    Jamie Guest

    Well, lots done and still no speedometer:

    1) Removed and inspected the sending unit. Reinstalled - did not know
    how to test it.

    2) Cut off two-wire connector to sending unit, removed each wire-end
    from the connector and rebuilt the wiring using a butt connector
    installed in each hole with replacement 12 gauge wiring. I reinstalled
    connector with new wires and re-wired wiring.

    3) Removed the dash and inspected all connectors

    4) Checked ground wires around left foot side of driver's floor. There
    was an assembly that had dismounted from the chassis, so I remounted
    it.

    5) Checked fuses.

    Everything else on the dash works - the odometer, tach, fuel -
    everything but the speedo.

    (sigh).


    Jamie wrote:
    > Thanks. I've read through all of these and while very informative, I
    > was hoping someone could give me a more descriptive answer on what I
    > should see when I remove the sending unit from the differential.
    >
    > This gives a good detail of the wiring, but not much about the inner
    > workings at the 'chunk'. Haynes talks about using a feeler gauge to
    > determine the correct distance when installing a new unit.
    >
    > I wasn't sure if there were any tell-tale signs of problems once you
    > remove the sending unit.
    >
    >
    > wrote:
    > > this might help
    > >
    > > http://www.brickboard.com/FAQ/700-900/ElectricalInstruments.htm#SpeedometerFluctuates
     
    Jamie, Jun 13, 2006
    #6
  7. Jamie

    James Sweet Guest

    Jamie wrote:
    > Well, lots done and still no speedometer:
    >
    > 1) Removed and inspected the sending unit. Reinstalled - did not know
    > how to test it.
    >


    Measure it with an ohm meter, unless it's open circuit then it's
    probably fine. As someone else mentioned, all it is is a coil.

    > 2) Cut off two-wire connector to sending unit, removed each wire-end
    > from the connector and rebuilt the wiring using a butt connector
    > installed in each hole with replacement 12 gauge wiring. I reinstalled
    > connector with new wires and re-wired wiring.
    >
    > 3) Removed the dash and inspected all connectors
    >
    > 4) Checked ground wires around left foot side of driver's floor. There
    > was an assembly that had dismounted from the chassis, so I remounted
    > it.
    >
    > 5) Checked fuses.
    >
    > Everything else on the dash works - the odometer, tach, fuel -
    > everything but the speedo.
    >
    > (sigh).
    >


    And the odometer and cruise control don't work either I assume?
     
    James Sweet, Jun 13, 2006
    #7
  8. Jamie

    Jamie Guest

    The odometer is fine, works well. The cruise works if/when the speedo
    kicks in.

    Everything works fine, only the speedo doesn't work.


    James Sweet wrote:
    > Jamie wrote:
    > > Well, lots done and still no speedometer:
    > >
    > > 1) Removed and inspected the sending unit. Reinstalled - did not know
    > > how to test it.
    > >

    >
    > Measure it with an ohm meter, unless it's open circuit then it's
    > probably fine. As someone else mentioned, all it is is a coil.
    >
    > > 2) Cut off two-wire connector to sending unit, removed each wire-end
    > > from the connector and rebuilt the wiring using a butt connector
    > > installed in each hole with replacement 12 gauge wiring. I reinstalled
    > > connector with new wires and re-wired wiring.
    > >
    > > 3) Removed the dash and inspected all connectors
    > >
    > > 4) Checked ground wires around left foot side of driver's floor. There
    > > was an assembly that had dismounted from the chassis, so I remounted
    > > it.
    > >
    > > 5) Checked fuses.
    > >
    > > Everything else on the dash works - the odometer, tach, fuel -
    > > everything but the speedo.
    > >
    > > (sigh).
    > >

    >
    > And the odometer and cruise control don't work either I assume?
     
    Jamie, Jun 13, 2006
    #8
  9. Jamie

    Guest

    Go to a U Pull It and yank out another cluster, if all else fails.
     
    , Jun 13, 2006
    #9
  10. Jamie

    Jamie Guest

    What is giving me fits is the yellow wire is on pretty tight and I
    didn't remove it out of fear of breaking it.

    The only other set I cannot remove is I think the speedo set, a small
    cluster of wires in a cube (not like the parallel snap-ons), that are
    on the lower corner of the speedo. I can't see how these are clipped
    in. I want to pull the cluster and inspect the back side, but I mainly
    fear I will break this one cluster of wires.

    Can anyone tell me how these are removed?

    Thanks.

    Jamie


    Jamie wrote:
    > The odometer is fine, works well. The cruise works if/when the speedo
    > kicks in.
    >
    > Everything works fine, only the speedo doesn't work.
    >
    >
    > James Sweet wrote:
    > > Jamie wrote:
    > > > Well, lots done and still no speedometer:
    > > >
    > > > 1) Removed and inspected the sending unit. Reinstalled - did not know
    > > > how to test it.
    > > >

    > >
    > > Measure it with an ohm meter, unless it's open circuit then it's
    > > probably fine. As someone else mentioned, all it is is a coil.
    > >
    > > > 2) Cut off two-wire connector to sending unit, removed each wire-end
    > > > from the connector and rebuilt the wiring using a butt connector
    > > > installed in each hole with replacement 12 gauge wiring. I reinstalled
    > > > connector with new wires and re-wired wiring.
    > > >
    > > > 3) Removed the dash and inspected all connectors
    > > >
    > > > 4) Checked ground wires around left foot side of driver's floor. There
    > > > was an assembly that had dismounted from the chassis, so I remounted
    > > > it.
    > > >
    > > > 5) Checked fuses.
    > > >
    > > > Everything else on the dash works - the odometer, tach, fuel -
    > > > everything but the speedo.
    > > >
    > > > (sigh).
    > > >

    > >
    > > And the odometer and cruise control don't work either I assume?
     
    Jamie, Jun 13, 2006
    #10
  11. Jamie

    Jamie Guest

    Here are some photos:

    -- the sending unit connector with bare wires

    -- the sending unit connector with some liquid electrical tape

    -- the sending unit connector cut off and rebuilt

    -- an assembly near the driver's foot that has a snap on I guess for a
    ground

    http://pg.photos.yahoo.com/ph/jamiebabineaux/album?.dir=/cc79scd

    That about covers it so far...



    Jamie wrote:
    > What is giving me fits is the yellow wire is on pretty tight and I
    > didn't remove it out of fear of breaking it.
    >
    > The only other set I cannot remove is I think the speedo set, a small
    > cluster of wires in a cube (not like the parallel snap-ons), that are
    > on the lower corner of the speedo. I can't see how these are clipped
    > in. I want to pull the cluster and inspect the back side, but I mainly
    > fear I will break this one cluster of wires.
    >
    > Can anyone tell me how these are removed?
    >
    > Thanks.
    >
    > Jamie
    >
    >
    > Jamie wrote:
    > > The odometer is fine, works well. The cruise works if/when the speedo
    > > kicks in.
    > >
    > > Everything works fine, only the speedo doesn't work.
    > >
    > >
    > > James Sweet wrote:
    > > > Jamie wrote:
    > > > > Well, lots done and still no speedometer:
    > > > >
    > > > > 1) Removed and inspected the sending unit. Reinstalled - did not know
    > > > > how to test it.
    > > > >
    > > >
    > > > Measure it with an ohm meter, unless it's open circuit then it's
    > > > probably fine. As someone else mentioned, all it is is a coil.
    > > >
    > > > > 2) Cut off two-wire connector to sending unit, removed each wire-end
    > > > > from the connector and rebuilt the wiring using a butt connector
    > > > > installed in each hole with replacement 12 gauge wiring. I reinstalled
    > > > > connector with new wires and re-wired wiring.
    > > > >
    > > > > 3) Removed the dash and inspected all connectors
    > > > >
    > > > > 4) Checked ground wires around left foot side of driver's floor. There
    > > > > was an assembly that had dismounted from the chassis, so I remounted
    > > > > it.
    > > > >
    > > > > 5) Checked fuses.
    > > > >
    > > > > Everything else on the dash works - the odometer, tach, fuel -
    > > > > everything but the speedo.
    > > > >
    > > > > (sigh).
    > > > >
    > > >
    > > > And the odometer and cruise control don't work either I assume?
     
    Jamie, Jun 13, 2006
    #11
  12. Jamie

    Jamie Guest

    OK, today the speedo decided it wanted to work. Let's see how long it
    lasts...

    I am beginning to think Volvo has a 24 hour rule. It seems like when I
    adjust something, it doesn't take effect for 24 hours, then it works.
     
    Jamie, Jun 13, 2006
    #12
  13. Jamie

    Jamie Guest

    Went out for lunch -- no speedo.

    C'est la vie.


    Jamie wrote:
    > OK, today the speedo decided it wanted to work. Let's see how long it
    > lasts...
    >
    > I am beginning to think Volvo has a 24 hour rule. It seems like when I
    > adjust something, it doesn't take effect for 24 hours, then it works.
     
    Jamie, Jun 13, 2006
    #13
  14. Jamie

    James Sweet Guest

    Jamie wrote:
    > The odometer is fine, works well. The cruise works if/when the speedo
    > kicks in.
    >
    > Everything works fine, only the speedo doesn't work.
    >
    >


    Then the problem is obviously in the speedometer itself, the same sensor
    and wiring drives both. I had to fix one which had some cracked solder
    joints on the circuit board inside.
     
    James Sweet, Jun 18, 2006
    #14
  15. Jamie

    Jamie Guest

    Thanks James.
    Can you tell me exactly how to remove what I think are the speedo
    cables from the cluster. It's the only group of wires like that. The
    multi-pin clips just unclip, and singles wires just unclip, but this
    one little group of 3-4 wires on the bottom right goes into a cube
    shaped white-plastic housing. I can't tell if the whole housing just
    unclips or I have to open the housing to release the wires or what.

    This is preventing me from removing the cluster entirely. I really wish
    I had a diagram that told me what every wire on the back of that
    cluster went to. In an easy to read format.

    Thanks.
    Jamie


    James Sweet wrote:
    > Jamie wrote:
    > > The odometer is fine, works well. The cruise works if/when the speedo
    > > kicks in.
    > >
    > > Everything works fine, only the speedo doesn't work.
    > >
    > >

    >
    > Then the problem is obviously in the speedometer itself, the same sensor
    > and wiring drives both. I had to fix one which had some cracked solder
    > joints on the circuit board inside.
     
    Jamie, Jun 18, 2006
    #15
  16. Jamie

    Arnold Guest

    Hi Jamie, take a look at this link. I believe the wires you are talking
    about do not go through the wire harness, I think they are jumpers soldered
    between 2 places on the cluster itself.

    Take a look at this link.

    http://www.brickboard.com/FAQ/700-900/ElectricalInstruments.htm#740InstrumentClusterRemoval

    "Jamie" <> wrote in message
    news:...
    > Thanks James.
    > Can you tell me exactly how to remove what I think are the speedo
    > cables from the cluster. It's the only group of wires like that. The
    > multi-pin clips just unclip, and singles wires just unclip, but this
    > one little group of 3-4 wires on the bottom right goes into a cube
    > shaped white-plastic housing. I can't tell if the whole housing just
    > unclips or I have to open the housing to release the wires or what.
    >
    > This is preventing me from removing the cluster entirely. I really wish
    > I had a diagram that told me what every wire on the back of that
    > cluster went to. In an easy to read format.
    >
    > Thanks.
    > Jamie
    >
    >
    > James Sweet wrote:
    > > Jamie wrote:
    > > > The odometer is fine, works well. The cruise works if/when the speedo
    > > > kicks in.
    > > >
    > > > Everything works fine, only the speedo doesn't work.
    > > >
    > > >

    > >
    > > Then the problem is obviously in the speedometer itself, the same sensor
    > > and wiring drives both. I had to fix one which had some cracked solder
    > > joints on the circuit board inside.

    >
     
    Arnold, Jun 18, 2006
    #16
  17. Jamie

    James Sweet Guest

    Arnold wrote:
    > Hi Jamie, take a look at this link. I believe the wires you are talking
    > about do not go through the wire harness, I think they are jumpers soldered
    > between 2 places on the cluster itself.
    >
    > Take a look at this link.
    >
    > http://www.brickboard.com/FAQ/700-900/ElectricalInstruments.htm#740InstrumentClusterRemoval
    >



    That's for a newer car with a different cluster, I don't recall there
    being anything unusual in the wiring of 700 series clusters though, I've
    had a number of them apart before but not recently.
     
    James Sweet, Jun 19, 2006
    #17
  18. Jamie

    Jamie Guest

    Thanks Arnold. I had seen this page before, but I read it more
    carefully this time and see the section about the capacitor. I just
    hope I can remove the speedo wires without breaking them.

    Thanks again,
    Jamie


    Arnold wrote:
    > Hi Jamie, take a look at this link. I believe the wires you are talking
    > about do not go through the wire harness, I think they are jumpers soldered
    > between 2 places on the cluster itself.
    >
    > Take a look at this link.
    >
    > http://www.brickboard.com/FAQ/700-900/ElectricalInstruments.htm#740InstrumentClusterRemoval
    >
    > "Jamie" <> wrote in message
    > news:...
    > > Thanks James.
    > > Can you tell me exactly how to remove what I think are the speedo
    > > cables from the cluster. It's the only group of wires like that. The
    > > multi-pin clips just unclip, and singles wires just unclip, but this
    > > one little group of 3-4 wires on the bottom right goes into a cube
    > > shaped white-plastic housing. I can't tell if the whole housing just
    > > unclips or I have to open the housing to release the wires or what.
    > >
    > > This is preventing me from removing the cluster entirely. I really wish
    > > I had a diagram that told me what every wire on the back of that
    > > cluster went to. In an easy to read format.
    > >
    > > Thanks.
    > > Jamie
    > >
    > >
    > > James Sweet wrote:
    > > > Jamie wrote:
    > > > > The odometer is fine, works well. The cruise works if/when the speedo
    > > > > kicks in.
    > > > >
    > > > > Everything works fine, only the speedo doesn't work.
    > > > >
    > > > >
    > > >
    > > > Then the problem is obviously in the speedometer itself, the same sensor
    > > > and wiring drives both. I had to fix one which had some cracked solder
    > > > joints on the circuit board inside.

    > >
     
    Jamie, Jun 19, 2006
    #18
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