Causes of speedometer error? - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 01-30-2000, 05:35 PM Thread Starter
 
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Causes of speedometer error?

My S10 is currently running a 10 - 15% error rate on the speedometer. When I had my 4spd manual rebuild I asked the guy who did the work if he could fix it with a new speedomter drive unit on the tranny. He looked and said that it was not possible to get one to correct that rate of error. I'm running 195/75/14's and the math for speedometer error says that running 235/75/15 tires would fix the problem. This would seem to indicate a rear end with numericly higher ratio.

What could be causing this error? Could it be the display unit in the cab or is it the rear end ratio I'm running. It's been like this since I bought it.

--Drew
83 S10 Ext Cab
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post #2 of (permalink) Old 01-30-2000, 05:44 PM
 
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Re: Causes of speedometer error?

I think that if it's got the original ratio, and original size tires, it should be right... I think that whether the rear diff gears are higher or lower, depends on whether it's 10-15% higher than it should be or lower...

Tim
"The_Sandman_454"

[img]/wwwthreads_images/icons/cool.gif[/img] '79 Suburban 4x4 454, 6" lift, 35x12.5s & '85 GMC S15 4x4
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post #3 of (permalink) Old 01-30-2000, 06:37 PM Thread Starter
 
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Re: Causes of speedometer error?

When I'm running at an actual speed of 100km/hr my indicated speed is 113km/hr. It's like I'm running 4.11 gears when the correct ratio should be 3.73. Those aren't my ratios (I don't think), but they do match my error % almost exactly.

BTW, What was a normal rear end ratio on the early models? (2WD, 4spd Manual)

--Drew
83 S10 Ext Cab
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post #4 of (permalink) Old 01-30-2000, 08:29 PM
 
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Re: Causes of speedometer error?

Not sure... I'd guess somewhere around 3.42, 3.07 or somewhere near there... As a factory option my truck has 3.73's... [img]/wwwthreads_images/icons/crazy.gif[/img]

Tim
"The_Sandman_454"

[img]/wwwthreads_images/icons/cool.gif[/img] '79 Suburban 4x4 454, 6" lift, 35x12.5s & '85 GMC S15 4x4
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