rear end gear ratio

Hey all. I'm trying to figure out the gear ratio on my rear end. I googled a how to and read to jack up one side leaving the other tire on the ground. Then put a piece of tape on the tire and driveshaft as a marker. Rotate the wheel 10 times and count how many times the driveshaft rotates. So a buddy helped me out and off we went. the driveshaft rotated 15 times. I thought you just divided the rotations into one another but theres no way I've got a 1.50 rear end gear.

Obviously I'm doing something wrong here but I can't figure it out.

Thanks for any help. NAES

 

Turn it till the tire goes 1 revolution only. Take the drive shaft revolutions and double it (assuming one wheel is locked).

 

Probably at around a 3.0:1 gear.

 

Rotate the tire (2) times, count the driveline revolutions.

 

Rotate tire ten times, divide shaft revs by 5... or as Marty said.

 

I like to mark both tires and the drive shaft. then i pick it up and walk it one revolution of the tires while counting the drive shaft turns.

 

This is probably a lot simpler than what I said. My head hurts now.

 

I think we just broke a record (6) views and (5) responses!

 

this same question got a lot of discussion about 5 times, pull the cover and count the teeth

 

try a search here - lots of info already posted

 

I've tried all the methods and sometimes you get goofy readings, like half of what you think the ratio should be. The only method I have found that I can use is to put a mark on the tire while the car is sitting on the ground, and also put a mark on the driveshaft or yoke. Then roll the car straight forward and have someone watch the tire turn while you watch the driveshaft. When the tire makes one exact revolution total up how many revolutions the driveshaft made. That is your ratio. (example: 1 wheel turn and 4 driveshaft turns = 4.1 gear ratio)

It is the only consistently accurate method I have found, but that is just me.


Don

 

Don,

The mental picture of that procedure makes me chuckle..........not that it's wrong....it's not........just funny!

I do agree it should work accurately.

Ray

 

That is the hard way.
But if you like hard ways, do this:

Go through a flying measured mile with the transmission in high (1:1) and the engine at 2,000 RPM. Time it with a stopwatch.
Multiply the seconds by your rear tire diameter in inches.
Divide by 605.
Voila !!

 

The biggest obstacle is talking a skinny friend to actually lay under the car and count revolutions while you push the car over him !

Don

 

I definitely wouldn't fit under the vehicle unless it was a jacked up 4x4. I'm big boned you know.

 

That counts me out, too, Don!

 

3.0 ratio. If you turn one tire 10 times, it's like turning both tires 5 times...and 15 divided by 5 is 3.0

 

No mommy, make them stop, my brain hurts.

 

how about rotate 20 times and divide by 10?

 

I posted the same exact question a few months ago. Everyone said "pull the cover and count the teeth." So I did, and it turned out to be a 3.73 rear end which is exactly what the rotating method had been telling me but I didn't believe it because the car was supposed to have a 2.56 in it.
One tire revolution = 3 3/4 drive shaft revolutions = 3.73 rear end.
I cannot think of any good reason to rotate the tire more then one time, and if the other tire is on the ground you don't need to multiply or divide anything. Rolling the car would work exactly the same.

 

If you turn one tire two revolutions OR two tires one revolution, you don't have to do any math, you just have to count driveshaft turns. But that's kind of complicated for some guys to understand, apparently

 

Yeah, it really confuses me, and I have 20 years of education........I did the 10th grade twice.

Don

 

Always believe the "tooth count".......

4TTRUK

 

Here's how my pappy taught me years ago---

Jack up one tire.

Mark tire and driveshaft.

Turn tire 20 times

count driveshaft turns

estimate fraction of last turn.

for example -- 30 and almost another driveshaft revolution>>3.08

a hair over 41>>4.11

doesn't work for locked, etc.

 

Jim, I agree wholeheartedly with your last sentence. I can't believe how many different, conflicting, difficult solutions are offered up any time this question is posted.

I don't normally have anyone around to count driveshaft revolutions while I spin the wheel, so here's what I do. I jack up the drivers side and turn that wheel 1 3/8 turns, then lower it, jack up the passenger side, and rotate that wheel 5/8 of a turn. I weld 6 nails to the driveshaft in a radial arrangement, spaced at 60 degree intervals, and tie my dog underneath the car next to the driveshaft. He howls every time the a nail hits him in the ass, so I simply count the number of times he howls, divide by 6, and that's pretty damn close to my gear ratio. I could weld 10 nails to the driveshaft, but I love my dog.......

 

spewed coffee. Thanks for the laugh, Ebbsspeed!

 

Read this thread http://www.jalopyjournal.com/forum/showthread.php?t=677320

 

OUCH my big blue head!!!!!Good one Ebbsspeed!!!!

 

now if you have an open diff and turn the driveshaft and only one wheels spins(like the brake is tight on one side) then the spinning wheel is going twice the speed than the if two wheels spin. You will then need to multiply the drive shaft rotation num ber by 2 to get the correct rear gear ratio....does your head hurt yet?

 

You just turn the driveshaft so that one wheel makes two revolutions, and count the number of times you turn the driveshaft. That number is the gear ratio.

No math needed, ever, if you turn both wheels one revolution, OR turn only one wheel two revolutions.

You can put your slide rule away.