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Wacky Speedometer


Radar22
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My 2000 HR Imperial speedometer has a mind of its own. I could be going down the road at 40 and it reads 47. I installed a scan gauge and there’s usually a 5-10 mile and hour difference between them with the speedo needle jumpy. I had one of the rear wheel sensors replaced and the others checked out OK. Any help would be appreciated. Merry Xmas to everyone. 

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There should be a ground buss mounted on the firewall.  Most coaches the buss can be accessed from the outside side of the firewall.  

Dash instruments grounds are daisy chained.  Road vibration will cause wires to become loose.  One loose wire causes a lot of crazy issues.  Locate the ground buss for the instruments, loosen all the screws, spray the connection points with WD 40,  tighten the screws.  Clean the main cable feeding the ground buss at both ends.  I purchased small lock washers to install them on the back lugs of each instrument.  Clean Both ends of the main ground cable that comes off the negative post of each bank of batteries.  

IMO, running a separate ground cable to something is a band aid type cure.  Any loose or corroded ground will produce what I call a ground loop.  All the components on a coach whether chassis or house, can will be effected by a ground loop.  The above is what I call prevented maintenance.  

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As I reported earlier on this subject there is a pot variable resister on the back of the speedometer. It is black and has a screwdriver slot in it. Mark its position and rotate the pot back and forth to clean the resistor. Move it back to original position.

Bob U 2000 Dip

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Radar22, just to try and unconfuse things. RobertU may be correct with the pot on the back of the speedometer but not necessarily. Some speedometers have a set of dip switches as they work off of a digital signal and have no pot. When I suggested a "new, dedicated" ground, I meant a new wire from the speedometer directly to the chassis, not necessarily all the way back to the battery. If you simply clean up the ground path to it's original ground buss you may not correct the problem because speedometers are strangely sensitive to poor grounds and the original coach ground buss may have suffered some degradation in its connections over time. In most coaches there exists a daisy chain of ground busses so you can spend a great deal of time getting to and sorting out which one(s) have faulty connections. Yes, this so-called bandaid may be introducing a new ground loop as ChuckB says but, as a Physicist, I'm willing to go out on a limb here and suggest this one additional ground loop, added to already existing ground loops in your coach will not be detrimental, and it may be enough to fix your Wacky Speedometer. Good luck finding a solution.

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To all that have responded to the wacky speedometer post I thank you very much. This spring after things thaw out here in the Northeast or if I venture down south I will attempt to correct the issue. May you all have a Merry Xmas, and a Happy Healthy New Year ! 

 

Marc 

 

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The experience of living in a coach full time for 6 years, provided me with the knowledge that "not detrimental" issues seem to reappear at the most in opportune of a time frame that sometimes leaves one stranded on the side of the road.  When a problem occurred for me, I tried to nip it in the bud so that I can put it to rest down the road so to speak.  

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