How do I know if a 9" is 28 or 31 splines?

[Britt]

A friend has a 9" out of a 70 somthin f-100 and he doesnt know what gears or how many splines it is. How do I tell?

 

[taylor4g63]

pull the axles out and count the splines....

to tell the gear ratio, there should be a tag on there somewhere that says what it is. If theres not then you could get an estimate by seeing how many times you have to turn the driveshaft for the wheels to rotate 1 full time...if it takes 3 times, then you have a 3.00 gear.

 

[Lswhat]

i thought the trucks came with 31 plines. just my two cents.

 

[HistoricMustang]

I also believe most trucks in that era had 31 splines. My '69 did.

If it is a complete set up pull the axle and count the splines.

HistoricMustang
www.historicmustang.com

 

[MCABOSS]

31 spline axle ID

Pull the hub cap/center cap off the wheel. Look at the center opening of the wheel at the axle. A 31 spline axle will have two holes about 1/4 inch in diameter. A 28 spline axle has what looks like a hollowed out area at the end of the axle but no holes.

 

[vrooom]

by seeing how many times you have to turn the driveshaft for the wheels to rotate 1 full time...if it takes 3 times, then you have a 3.00 gear.
.

I thought you had to divide by two?

 

[mustangfb66]

I agree with what MCABOSS said. That is what one of the guys working at Currie told me as well.

Efren

 

[vrooom]

http://classicbroncos.com/gearratio.shtml

.....you don’t have room to move the rig, here is another way to do it. Instead of pushing the rig just jack up on rear tire and rotate it one full turn with vehicle in neutral. Count the number of wraps and times it by 2. The total is what you use to figure the gear ratio. Note this procedure will only work with open diffs.

 

[Edbert]

If it came out of a 65-70 Mustang is is a 28 (not so sure about the big bodies). To my knowlege FoMoCo did not put 31s into any passenger cars during that era, but all large bearing 9" axles had the 31s (trucks/vans/broncos).

 

[MCABOSS]

31 splines

If it came out of a 65-70 Mustang is is a 28 (not so sure about the big bodies). To my knowlege FoMoCo did not put 31s into any passenger cars during that era, but all large bearing 9" axles had the 31s (trucks/vans/broncos).

Not true!! all BOSSes and any car ordered with a drag pac has 31 spline axles.