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May 25, 2016, 09:55:43 pm

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Author Topic: Speedo erratic?  (Read 70 times)


  • Grand Gearhead
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  • 2012 Royal Maroon C5 Special
Speedo erratic?
« on: April 01, 2016, 11:54:14 am »
   If your speedo is erratic, the causes can be multiple.
   The RE speedo is mounted vertically, so keep in mind that the speedo spindles and cups want to move DOWN as mounted. The purpose of this exercise is to move the Input Cup DOWN, and if necessary, the Output Cup UP.
   If either spindle shaft is defective (bent/broken) your only option is to replace the spindle or the Speedo Assembly. The following is only applicable if your spindles are straight. DO NOT BEND THE SPINDLES!

   A very thin (.5-.75mm) split spring washer in the input gap, along with a tiny drop of either silicone grease or Teflon lubricant will take up the slack and remain smooth. This is risky, as you could scar the matching bearing faces during installation of the washer and this will make it worse unless you disassemble the spindle assembly first.
   Another way (and the easiest) is to bond a shim to the face of the threaded attachment point (pub?) so the connector won't bottom and force the cable against it's receiver. Measure the in/out movement of the input spindle. Add an equal amount of shim + any additional to just eliminate the pressure on the spindle. The cable socket should be plenty deep enough to accommodate the cable when re-assembled.
  Once the speedo is mounted face up, the input half of the coupling should rest easy, operate smoothly, and the cup should not make contact with the inner cup. If all is good, adding a bit of solder to the stop bar should finish things nicely.
   If contact between the two is still present, you'll need to adjust the output spindle, too.

   STEP TWO, INDICATOR (OUTPUT) SIDE: Only do this if necessary. Have a couple of hemostats available for clamping the spindle, and a dinner fork (or something forked and flat, like a door trim tool) to remove the indicator needle.
   If the indicator spindle has too much axial (up/down) play allowing the cup to make contact the only option is to adjust the play by moving the spindle UP to pull the inner cup away from the lower/outer one.
   a) Move the indicator needle with your finger to a point half way up the scale (50mph/80kmh), then clamp the back side of the spindle to hold it in that position. Clamp the thickest portion closet to the indicator plate to minimize the chance or bending the spindle. I used hemostats with cured silicone sealant applied to the teeth to prevent any damage to the spindle.
   b) CAREFULLY remove the indicator needle by prying it up and off the spindle. You now should be able to note whether there is either a split-collar retainer on the spindle or it is a milled spindle stop. If it is a split collar you can adjust its position on the spindle to take up unnecessary play by CAREFULLY pressing it in toward the indicator plate. DO NOT ALLOW THE SPLIT-COLLAR TO TOUCH THE PLATE! A 3-4mm/5/32" deep socket or ignition wrench box end works nicely.
      If it is a milled stop, it is ok to fabricate a felt washer moistened with penetrating oil to slip underneath it. (The felt washer trick may also be used under a split collar, but the split itself may degrade the felt over time.)
   c) CAREFULLY press the indicator needle onto it's spindle as close to its original position as possible (You might at this point wish to apply a correction for an optimistic speedo, for example set it 5mph/8kmh lower), then remove the clamp from the back side.
   d) Check operation by holding the speedo face up, and spinning the input receptacle, either with the existing cable (I attach it to my Dremel and run at 1000rpm), or by hand. There should now be no contact between the cups, and smooth operation of the indicator needle.

       If there is no contact between cups but the problem persists, the problem(s) could be due to the following:
        a) Worn spindle bushings (Replace Speedo)
        b) Indicator split-collar too tight against indicator plate (should not touch the plate)
        c) Poor cable lubrication (Lube it!)
        d) Worn speedo gear on the wheel hub. (Replace with new, or upgrade to a metal unit).

   Hope this helps.  :)
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