How to determine the rear end gear ratio? Not for a T but for a 56 Chevy. My friend rotates the drive shaft 2 times and the rear wheel rotates 1.16 times. This does not give me a ratio that comes close to the standard rear end ratios found in these cars. So, what are we (he) doing wrong or better yet, how to determine the gear ratio???
Least confusing and safest way on a vehicle with exposed driveshaft. Block securely ahead and behind 3 tires and jack up one of the rears just off the ground. Handbrake off and transmission out of gear.( sounds like you have done this part) Rotate the driveshaft counting the number of revolutions until the wheel has made exactly 2 complete revolutions. The driveshaft turns will be the commonly used ratio number examples: 4.11 or 3.76 or 2.73 etc.
If the 1.16 is accurate, divide by four (2 for the two turns and 2 for one wheel on the ground) and take the inverse of that and you get 3.45:1, which at least is within a reasonable range.
Roar
I am a little confused. Will go out to look at my friends car chassis tomorrow and do an accurate count doing the method described here.
Thank you.
With one wheel off the ground, the differential cuts the ration in half. So two turns gave you 1.16 turns of the wheel. One turn would give you 0.58 turns of the wheel. Your ratio is then 2*(1/.58) or 3.45 as Roar stated above.
Not to be picky, but if this is the normal Chevy rear axle, I believe it should be 1.17 not 1.16.
Jim's 220HP Bel Air was bought new in '57 with a 3.55:1. It was three on the tree and would scoot along well.
Ok, went out to my friends house and did an accurate count:
2 turns of the wheel gave 3.5 revolutions of the drive shaft.
This ratio gives me 1.75:1 so how do you figure out the supposed "real" ratio? Times 2 would give me 3.50 ??????????????????
That equates to the 2.29 gear ratio. Nice highway ratio for gas mileage.
2 X (1/.875)= 2.29
Reread my last sentence. 3.5 is your rear end ratio. Due to accuracy of measurements it is probably the 3.55 that John spoke of.