Spedo way out - The 1947 - Present Chevrolet & GMC Truck Message Board Network

hopelessredneck · 11-26-2011, 07:24 PM

My 1978 gmc is an oshowa ont truck and my tires are nothing huge or small but my spedo is 30kmh out when i do 110kmh it shows 80kmh any idea why????

raceman6135 · 11-26-2011, 07:45 PM

Did this happen suddenly? Or has it always been inaccurate?

If it's always been that way, then the driven and/or drive gears for the speedometer, inside the transmission, need to be changed in order to correct the speedometer's calibration.

If, however, your speedometer was correct before and now is wrong with no changes being done, I have no idea. Sometimes a speedometer will act erratically if the drive cable or speedometer head are worn out, but that's all I can think of.

11-26-2011, 07:24 PM	#1
hopelessredneck Registered User Join Date: Aug 2009 Location: Vancouver, BC Posts: 147	Spedo way out My 1978 gmc is an oshowa ont truck and my tires are nothing huge or small but my spedo is 30kmh out when i do 110kmh it shows 80kmh any idea why????

11-26-2011, 07:45 PM	#2
raceman6135 Dino burner Join Date: Nov 2002 Location: Calgary, Alberta, Canada Posts: 602	Re: Spedo way out Did this happen suddenly? Or has it always been inaccurate? If it's always been that way, then the driven and/or drive gears for the speedometer, inside the transmission, need to be changed in order to correct the speedometer's calibration. If, however, your speedometer was correct before and now is wrong with no changes being done, I have no idea. Sometimes a speedometer will act erratically if the drive cable or speedometer head are worn out, but that's all I can think of.



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.