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11-30-2011, 04:35 PM
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#1 |
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Registered User
Join Date: Feb 2010
Location: Tacoma, Washington
Posts: 86
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Tire size,rear end, and speedometer
So my speedometer is off by between 10-15 mph over 60mph. My tire size is 275/60/15 on all four corners and if I read right on another site that converts from original size to current I should only be about 1-2% off which unless i'm having a brain fart don't make sense as to why my speedo is so far off. So i'm wondering if someone in the past has changed out the gears in the rearend if that would make a difference and if so anybody have any idea what may be in it? Oh ya and it's in a 72 1/2 ton with 3 spd manual and sbc. Thanks for any help guys. I can't afford a gps speedo right now so I would like to figure out a cheap way to maybe get my speedo close to right.
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Jeramy CURRENTLY OWN, 72 c10 project/driver 2010 Kia Forte Koup SX daily driver 88 cherokee wheeler and dog hauler 2001 drz 400 Miss my 2004 firebolt (stock) and 2001 superhawk with a ton of modifications and many other previous vehicles. |
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11-30-2011, 05:04 PM
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#2 | |
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Registered User
Join Date: Sep 2011
Location: San Jose, California
Posts: 784
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Re: Tire size,rear end, and speedometer
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12-01-2011, 05:11 AM
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#3 | |
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Registered User
Join Date: Feb 2010
Location: Tacoma, Washington
Posts: 86
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Re: Tire size,rear end, and speedometer
Quote:
__________________
Jeramy CURRENTLY OWN, 72 c10 project/driver 2010 Kia Forte Koup SX daily driver 88 cherokee wheeler and dog hauler 2001 drz 400 Miss my 2004 firebolt (stock) and 2001 superhawk with a ton of modifications and many other previous vehicles. |
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12-01-2011, 09:44 AM
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#4 |
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Old member
Join Date: Jan 2002
Location: Liberty, & Garden City S.C. , U.S.
Posts: 19,945
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Re: Tire size,rear end, and speedometer
The old speedo's in these trucks are a good guestment at best. Mine in my 71 never did read right. I used it up until back in August when I bought a GPS one. Have you got a GPS Garmin. If so use it on the map setting and it gives you speed. It's a easy way to check the truck.
The spring inside the speedo after 30 some years is wore out. I suggest a rebuilt one are a new one may or may not help you.  
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1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs. |
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11-30-2011, 05:53 PM
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#5 |
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Registered User
Join Date: Apr 2006
Location: Alabama
Posts: 794
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Re: Tire size,rear end, and speedometer
you can figure your rear end ratio:
Jack up rear end so that tires are off the ground. Mark a line on the driveshaft, another on the tire. Put in nuetral and rotate the tire 1 complete revolution, count the number of times the driveshaft turns.
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