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| | | | Joined: Apr 2013 Posts: 62 Wrench Fetcher | | Wrench Fetcher Joined: Apr 2013 Posts: 62 | 1953 3100 1/2-ton with 216ci
the 216 is numbers matched to the year, i have the factory three-on-the-tree transmission, with the factory closed-drive shaft and the rear differential carrier has all the mounting and brake line hardware to tell me that it's factory..
ALSO: my tires are 235/60/15
however, i've recently replaced my speedometer with a new one (cable as well) from classicparts.
on my last couple road tests, my speedometer is telling me i'm topping out at ~52mph.. i immediately knew something was up, since my old 216 is only getting 90psi on all cylinders, and it's just nonsensical to think i could get that speed with all factory gear.
so i got a speedometer app on my phone, (checked it for accuracy in a newer car) and checked my speed. i'm actually going 5mph slower than the speedometer is telling me (at all speeds).. the odometer is off by roughly +2/10ths of a mile as well. all the basic "calculate your rear axle ratio" tricks require an open driveshaft, so i'm wondering if anybody knows another way for me to calculate my gear ratio without popping open the carrier?
i'm guessing my gear ratio would have to be in the 3's:1 area, right? i'm supposed to have 4.11:1
TLDR; factory engine, trans and brand new speedo+cable..speedo is +5mph, how do i figure out my gear ratio?
Last edited by gmtjr; 03/23/2014 1:16 AM.
| | | | | Joined: May 2005 Posts: 8,983 Sir Searchalot | | Sir Searchalot Joined: May 2005 Posts: 8,983 | If it's easier to pull the diff cover, read the stamp or count the teeth. Actually that is THE only way to be sure.
Manual says 4.11: 37 ring, 9 pinion.
Does not make sense that it's off by a constant and not a percentage? GPS or Speedo error?
"i'm actually going 5mph slower than the speedometer is telling me (at all speeds).."
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
| | | | | Joined: May 2006 Posts: 8,351 'Bolter | | 'Bolter Joined: May 2006 Posts: 8,351 | Sounds like you have the 4.11 gear, what is causing the main problem with the speedometer/lack of speed issue are the tires. 235/60/15 are much smaller in diameter than the oem tire (26" vs 29"). That will cause the speedo to read off, plus limit the top end, as the shorter tire will be the same as if you put a lower gear ratio in the differential. To improve the speed issue, there is a 3.55 gearset available from Patrick's, or you could go with a taller tire.
Bill Burmeister
| | | | | Joined: Apr 2013 Posts: 62 Wrench Fetcher | | Wrench Fetcher Joined: Apr 2013 Posts: 62 | Sounds like you have the 4.11 gear, what is causing the main problem with the speedometer/lack of speed issue are the tires. 235/60/15 are much smaller in diameter than the oem tire (26" vs 29"). That will cause the speedo to read off, plus limit the top end, as the shorter tire will be the same as if you put a lower gear ratio in the differential. To improve the speed issue, there is a 3.55 gearset available from Patrick's, or you could go with a taller tire. cool, thanks for the speedy response. i've been scouring the books and i can't find the OEM tire size, though.. http://chevy.oldcarmanualproject.com/chevyresto/53155.htm not sure what measurements they're taking there EDIT: nevermind, i guess 6.5 is 6.5inch width with a 100% aspect ratio.. so my 235/60s are 2 inches shorter..!
Last edited by gmtjr; 03/23/2014 2:10 AM.
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