Rear gear ratio check

[93/96 f-body]

Hi refresh my memory on how to check your rear gear ratios.I jacked my car up and marked the yoke and rotated the tire.Per one revolution of the tire it spun four full turns.It has a posi rear.My seedo is off 5mph so i need to figure out the ratios to correct the problem and i'm getting new rims and tires.The guy i bought from thought 373 where what the previous owner installed thanks For any help.

[Rob B (shoebox)]

That's how you do it (make sure both rear wheels are off the ground). You need to be very precise, so you don't confuse 3.73s with 4.11s.

[LarryMow]

someone once told me that the ratio is stamped into a axle tube...not sure on how true this is though...didnt some of them come with a ratio tag bolted on the rearend cover too? yeah i know, if both were true, dont do any good if the original owner changed the gears. but still i was just wondering

[Injuneer]

I've never seen the factory stamp or tag the gear ratio on the 4th Gens. They put that data on the build tag.... GU2, GU5, etc. And it wouldn't help him anyway... appears someone has changed the gears, since neither 3.73 or 4.11 gears were installed at the factory on a 4th Gen.

At what indicated or actual speed is the speedo off by 5 MPH? Its going to be "off" a different number of MPH at each different speed..... the error is a percentage, not a fixed number of MPH.

[93/96 f-body]

I knew it was off when i purchased it and when i put it on the road it was apparent.I dorve buy the local speed check they place around town.

[93/96 f-body]

My father in law told me since both wheels spun @ the same time count the half turns which would have been 8 divide by 2 which would be 411 gears.I just want to nail this down.My ss had 342 ratios and i was talking to a guy who swapped his 342 for 373 and eventually to 410 gears.He said there wasn't much of a difference between 342 and 373.Well after having the ss theres a big difference in this car i use 5 & 6 all the time.Thanks for anymore help you guys rule.

[fastTa]

If you want to be sure, pull the cover and look at the face of the pinion gear. It will be stamped with the number of ring gear and pinion gear teeth which is how the rear axle ratio is calculated.

For example on a 3.23 gear ratio, you will see 42 -13. 42/13 = 3.23:1

[Rob B (shoebox)]

If you want to be sure, pull the cover and look at the face of the pinion gear. It will be stamped with the number of ring gear and pinion gear teeth which is how the rear axle ratio is calculated.

For example on a 3.23 gear ratio, you will see 42 -13. 42/13 = 3.23:1

Like this :

[fastTa]

Like this :

Just like that!

[MarkFL]

I'm thoroughly impressed...many folks on the net want to use expressions like 3:73 or 4:10 when they mean 3.73:1 and 4.10:1 respectively and I just want to force them to drive their fbody for a day with 3:73 rear gears...I doubt they would ever forget that!!