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Originally Posted by 68 ReNay
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but my question is this, should the speed be off a consistent number of MPH's, regardless of speed, or does the difference increase with speed?
i checked mine out and here's what i discovered:
(left side number is actual MPH, right side number is my speedo reading)
30mph - 30mph
35mph - 37mph
40mph - 43mph
45mph - 49mph
50mph - 55mph
55mph - 62mph
60mph - 67mph
65mph - 73mph
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Quote:
Originally Posted by 68 ReNay
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mrein3, i never did like math and i don't really know what the significance of being off by a constant 10% means (in order to fix the problem) in your post.
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You were wondering why you're not off by a constant number of miles per hour. And you're right. You're not off by a constant number of miles per hour but you are off by a constant percentage of miles per hour. Most likely this is caused by you or a previous owner putting on the wrong sized set of tires.
This incorrect mph reading is totally correctible. The "signal" for the speedo is generated by a gear set in the transmission behind where your cable screws in. There are links on the internet where you type in your tire size and rear end gear ratio and the program or spread sheet tells you what two colors you need for the gears in the speedo signal generator.
Since you've replaced the cable and speedometer already, and since this gear set is the only moving part left in the system, if your needle still bounces, I'd revisit the cable.
Another thing to consider is the lube you used on the cable. I don't know how cold it gets in Kansas but here in Minnesota a good way to make your needle to bounce is to put lube on it that gets hard in the cold then drive it on a cold day.