My speedometer reads 80 when I'm going 55 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

R&R · 07-07-2002, 08:16 AM

My speedometer reads 80 when I'm going 55. Please tell me the problem and solution. Thanks

da-burb · 07-07-2002, 09:57 AM

What is not original to the truck, the rear end or the transmission. Something was swapped. There are 2 gears in the tailhousing of the transmission that take into consideration your gear ratio and tire size to give you the correct speed reading. You will need to know which size the driven gear is. This will be the one that is at the end of your speedo cable indide the tailhousing. Then take a look at this web page and it will help you figure out what gear you need to get the correct reading.
http://www.novaresource.org/speedo.htm

bigjimzlll · 07-07-2002, 10:46 AM

have you changed tire size? going from a tall tire to a short tire can change your speed dramatically...i went from a 29 in tall to a 27 inch tall and now im 8 mph off...

07-07-2002, 08:16 AM	#1
R&R Registered User Join Date: Jun 2002 Location: Dallas Posts: 31	My speedometer reads 80 when I'm going 55 My speedometer reads 80 when I'm going 55. Please tell me the problem and solution. Thanks __________________ '68 C/10, SWB, 396/350, PS, PB, A/C '68 C/10, SWB, 400sb/350

07-07-2002, 09:57 AM	#2
da-burb "Ochre Ogre" Join Date: Apr 2000 Location: Springfield, MN Posts: 3,558	What is not original to the truck, the rear end or the transmission. Something was swapped. There are 2 gears in the tailhousing of the transmission that take into consideration your gear ratio and tire size to give you the correct speed reading. You will need to know which size the driven gear is. This will be the one that is at the end of your speedo cable indide the tailhousing. Then take a look at this web page and it will help you figure out what gear you need to get the correct reading. http://www.novaresource.org/speedo.htm __________________ Bowtie Truck Stop Inc. Mid-West GM Truck Restoration Parts Supplier Your Key Parts, Auto Metal Direct, Dynacorn, and Goodmark dealer. like us @ www.facebook.com/BowtieTruckStop 1971 C-10 Suburban (Ochre) 1971 K-10 Suburban (Ochre) 1972 C-10 Suburban (Ochre) 1972 K-20 Suburban (Yellow- that just aint right!) Springfield, Minnesota 56087

07-07-2002, 10:46 AM	#3
bigjimzlll Senior Member Join Date: Dec 2001 Location: Redding,CA...USA Posts: 4,736	have you changed tire size? going from a tall tire to a short tire can change your speed dramatically...i went from a 29 in tall to a 27 inch tall and now im 8 mph off... __________________ It's called "drag racing" if they called it "tic..tic..WHAM!..BANG! F*&K!!!", they'd have to keep the magazines under the counter with the other men's publications click the clicky to join the site.... http://67-72chevytrucks.com/vboard/payments.php 67 lwb..first hotrod in 25 years..540 best ET is 9.45 @ 141.44 Anderson,CA



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