Hey everybody. I was woundering if someone could help me out abit. Im trying to find out what my rear axle ratio is. I have the engine and tranny out of the car and its up on jacks so i mark a spot on the rear wheel and one on the yoke. The tire will make 3/4 of a turn for every full revolution of the yoke. One web sight i read said that the tire would make more turns than the yoke. I am obviously doing something wrong here. Can anybody tell me what it is?  

Your ring & pinion gear ratio is figured by the number of teeth on the ring devided by the number of teeth on the pinion.Nothing else will have the same accuracy.  

So i have to take off the pan and count the teath on both gears. I have never had the pan off a rear end before. will i have to pull the ring and pinion out to count the teath on them?  

you can estimate it by turning the wheels, and counting how many times the yoke turns.  For example...my Cutlass has a 3.73 in it.  So for every one revolution of the wheel, the yoke will turn a little less than 4 times.

I think you've miss counted...as that would leave you with approximately a 1.33 gear set.  Lowest I know of is in the 2.50 range.

Whatever website you got that information from...never go there again.  The only time the wheel turns more times than the pinion...is when its overdriven.  Rear ends are not overdriven...only transmissions.  The pinion should turn more times than the wheel does.  

could you walk me though the math you used to come up w/ the 1.33 gearset?  

1/.75

One turn of the pinion divided by .75 turns of the wheel

my car has a 3.73

3.73 turns of the pinion divided by 1 turn of the wheel.  

The number of teeth on the gears are usually stamped on the ring gear. Just pull the diff cover and you will find a number on the ring gear.  If I remember right, my firebird had 41:15 stamped on the ring gear. 41/15= 2.73 which is about what I expected based on MPH to RPM calculators.  I haven't pulled the cover on my Centurion, but the book says it has a 2.93 ratio and if I remember right gave the numbers as 41:14 which equal 2.9857 ~ 2.93.  

I haven't looked it up in a long time, but for the tire turning method if the vehicle doesn't have positraction don't you have to multiply the number of yoke rotations by two (or is it divide?) because the other half of the rotation is used up in the opposite side tire spinning the other way?

It is an elco so probably should have positraction, but doubling that number would give you a 2.66, which ballparks it in reality. Being mid-'70s and figuring some measuring error it probably is a 2.73 but that is just a guess.  

Thats a good question  All of my cars have posi...so I really don't know...  

All these inaccurate calculations and uncertantys.For the time spent,its just as easy to pull the cover(the diff. fluid prob.needs changed anyway)check it the right way and do a visual inspection while its open.The cost of 2 bottles gear lube and a tube of silicone RTV,and posi aditive if needed,and you know what you have.And yes,If he does it the halfassed way on a open diff.,its gotta be multiplied by 2,cause the diff is a 1/2 split in rotation.It is also needed to have a friend hold the other side still,or adjust the brake out tight to hold the tire still to avoid more uncertantys from movement.  

My perferred halfassed method is drive at 60mph or some known speed (assuming accurate speedo or GPS it) see what rpm you're pulling, then punch the info into a gear calculator. All you need is RPM, MPH, and tire size or diameter depending on the calculator.  Assuming for some torque converter loss it'll get you in the neighborhood.  

Ah,somebodys gettin simple now.No work involved there,just a cruise down the road and a tachometer,if he's got one.As I like your taste in cars,I like your train of thought,make it easy! Afterall if its gonna be halfassed,why make it hard to do?  

Oh yeah, I guess it's worth mentioning, to read the ratio stamp doesn't require the removal of pinion or ring gear, just the diff cover. It is stamped on the side of the ring gear.  

Who said a thing about taking the gears out,HELLO FORREST.Just inspecting them through rotation in the housing.And I dont know how many axles youve been into for repair in time,but in the 100 or so ive been through Ive NEVER seen a # on a gear other than a part referance#(which isnt always stamped in the gear)and Ive yet to find 1 that in any way other than a referance book or contacting GM or Ford has a corelation to the # of teeth on that gear. Dodge Ive not been through,Dana makes those axles right the first time.I must be inexperienced with these matter's,I suppose. And you prob have never came accross an axle were the tag was missing,right.A Ford or GM factory tag missing? Never.  

Calm down, jeez. I'm amazed you missed this out of the hundred or so you've done. Your're right, I have very little differential experience, BUT I do know what I saw on my Firebird. Plain as day, pointed out by the Transmission guy to me at the GM Dealership I worked for.  Here is a website with a nice picture showing exactly what I saw:

http://www.nastyz28.com/2gcog/rearaxle.html





Looks like a 15 41 to me, which is.........2.73! I've yet to have a car with the original diff tag on it. After 30+ years they tend to either disappear or the gears get replaced with a different ratio.

And Gord himself asked if he would need to pull the gears, I thought it would be kind to clearly answer "No". At least this picture should also serve to show him what to look for too.

Here's a few more for good measure:

http://www.pirate4x4.com/tech/billavista/PR-ARB/articles/Yukon_14b_Gear_Review/IMG_3191.jpg       45-11

http://www.oldsmobility.com/10boltPont-rebuild.htm    Fig.5  

Well theres a first for all.I just put the 14 bolt in mine 3 months ago and have no # even vaige to the tooth count on either gear.And yes they are oem.As to the part of Gord asking about removal,I guiss sometimes I may need to explain a statement better.So,Gord,if you choose to do an inspection while the car is of the ground,just use some mineral spirits to wash the gears(wont hurt a thing)so you can see the componants clearly.You dont have too baith them,just a soked rag wiping the friction areas.Look for "blueing" as this indicates overheated areas which may need attention.Rock a tire back and forth a slight bit to see the "slop" in the differential's spider gears,should be little or none you can see off the naked eye.This is a critical wear point on "open" diff's.The pin gets worn on the thrust side causing the "slop" and can break under loads as any mechanic whose been around awhile has seen.When they go out,youll be buying an axle or rebuilding that 1.The spider repair kit is around $100,quite a  difference in price compared to replacing it all.