Hi, so i have a 2000 Sierra, 4.0 5 speed. I am trying to figure out if the previous owner regeared it. It should have come with 3.73 new as the build sheet and tags on the diff's indicate
I have 31's on it that measure at 30".
By looking at the gear ratio calculator on grimjeeper.com which I have read that I can trust, something does not seem right.
At 2500 Rpm I am running exactly 75 mph
At 3000 rpm I am running exactly 90 mph
In 5th gear. Nv3500 tranny.
With 3.73 I should be going 85 mph at 2500 rpm and 102 mph at 3000 rpm according to the calculator. Can anyone confirm or dispute this?
With 4.11 gears I should be 77 mph at 2500 rpm and 92 mph at 3000 rpm according to this calculator, only 2 mph off of my actual speeds leading me to believe I have 4.11 gears.
My speedo tracks almost exactly with my gps as well as those radar activated speed limit signs that flash my speed at me as I drive by.
What do all of you experienced guys think of this?
Do you agree that the speeds at the given rpm indicate 4.11? Can anyone with similar tranny and tire size advise me if this sounds right?
I am getting ready to go to 33" tires and lockers , and looking into regearing. That is why I was looking at the charts and gear ratio calculators and noticed that something does not seem to add up. I am hoping to find that I already have 4.11 gears.
Would someone regear and leave the 3.73 tags on the diff's?
Thanks in advance for your help! This site is such a wealth of information and knowledge!
1. Open the diff and count the number of teeth on both ring and pinion and do the math.
2. Jack up the rear axle so the tires are off the ground. Mark your tire and your driveshaft so you can count the number of revolutions.
I have 4:56 gears. When my tire turns one full turn, the drive shaft spins ~4 1/2 times...so if you spin yours and it goes around ~3 3/4 times, then you have 3:73's....a little more than 4 turns then you have 4:11's.
Realize it is driveshaft rotations to two full tire rotations with locked Diffy jack up both and one full rotation on both sides but with open Diffy jack up only one side and count for two full tire rotations on one side
If you jack up both with open other side rotates some and count is garbage
Dont use 5th gear to calculate. Comparing the transmission gear ratios for 5th are different, some list it as .73(grims), others have .78 ratio. Use 4th gear which has a 1:1 ratio
Using a few other sites that allows to manually input the numbers, Grimms 5th gear ratio likely is not listed correctly or not calculating properly. Even attempting to manually input the ratios on Grimms do not generate different results for 5th gear, be it .73 vs manually entered .78.
Hmm, well I think tis broke now. It stopped generating any numbers (closed browsers/cleared history/changed browser ).