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Easy Question?? Rear End Ratio

1163 Views 4 Replies 4 Participants Last post by  bigblok86ranger
Is there a way to tell the rear end gear ratio with out pulling it apart and counting the teeth?

Here is my issue. @ 70 mph the car is tact'ing @ ~3100. Tires are 315/35/17 (approx. 25 inches).

I have a 5 speed, but not sure what the 5th gear is either. I guess I am trying to figure that out as well.

Any help would be greatly appreciated.


PS my friend has what we thought was the same set up however he tact's at approx 2400, I am not sure if it is a different 5th gear or a different rear end.
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jack it up and turn the passager side tire and count how many times the driveshaft turns. if it turns 3.5 = 3.55 if it turns alittle more be 3.73 or a little less around 3.27 and so on

Thank you for the quick response. That is what I thought. I just did that, looks like 3.55, is there anyway to check each gear of the tranny? It doesnt make sense to me to have a 1:1 5th gear (calculations I found online)
4th will be 1:1 5th will be .7x
Can figure it out based on RPM in 4th at a given speed and RPM in 5th at same given speed. 5th gear RPM divided by 4th gear RPM should get you your answer.
That sounds like too many rpm's to be 3.55's especially with an overdrive trans. I just put the info into tci's calcultor figuring a .7 overdrive and comes up with a 4.70 ratio. If the rpm's you are listing is in 4th;1:1 then comes out to 3.29 so that would mean 3.27's.
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