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TwoFiftyShifter · 01-09-2011, 02:05 AM

I think you have your gears wrong.... a 3.73 rear should run way lower than 3500RPM at 55MPH... as per this calculator, and a conservative guess that you have only 27" tires, your running about 2600rpm at 55 with 3.73s. You speedo may be way off due to a gear change, as I put you at 5.13 gears to get 3500rpm at 55.

http://www.csgnetwork.com/multirpmcalc.html

Back to the tranny, those 2 first gear numbers arent much different. These trucks came with a creeper box 4 speed, which had I think a 6.55 1st gear and was good for 10mph tach'd out, so either one of those would be fine, and in a truck, the 3.27 1st would be preferable and with a 3.73 should roll out to 30mph or so.

Still you either don't have anything close to 3.73, or your speedo is WAY off and when it is indicating 55 your doing 75....

01-09-2011, 02:05 AM	#2
TwoFiftyShifter Registered User Join Date: Nov 2008 Location: Gwinnett GA Posts: 1,803	Re: 5-speed "deep thoughts..." I think you have your gears wrong.... a 3.73 rear should run way lower than 3500RPM at 55MPH... as per this calculator, and a conservative guess that you have only 27" tires, your running about 2600rpm at 55 with 3.73s. You speedo may be way off due to a gear change, as I put you at 5.13 gears to get 3500rpm at 55. http://www.csgnetwork.com/multirpmcalc.html Back to the tranny, those 2 first gear numbers arent much different. These trucks came with a creeper box 4 speed, which had I think a 6.55 1st gear and was good for 10mph tach'd out, so either one of those would be fine, and in a truck, the 3.27 1st would be preferable and with a 3.73 should roll out to 30mph or so. Still you either don't have anything close to 3.73, or your speedo is WAY off and when it is indicating 55 your doing 75.... __________________ 1982 K10 SWB 1987 V20 - Sold - Doh! Last edited by TwoFiftyShifter; 01-09-2011 at 02:06 AM.