SUGGESTION ON REAR AXLE!!!

[jreyes]

I OWN A 1972 F100, ORIGINALY IT WAS A STRAIGHT SIX 240 ENGINE. NOW IT IS A 351M 400 WITH A C6 TRANNY.....OUT OF A 1979 F150. SO MY QUESTION IS, SINCE I CHANGE ALL THE FRONT SUSPENTION OUT OF THE 1979 TO INTALL IN THE 1972 SHOULD YOU GUYS RECOMMEND TO CHANGE THE REAR AXLE SINCE IS SHORTER THEN THE 1979 OR SHOULD I LEAVE THE ORIGINAL REAR AXLE?

PLEASE HELP ON THIS DESICION, WHICH REAR AXLE IS BETTER TO KEEP IN MY 1972?

[fordman]

the 79 axle will be wider. so that will line up the front tires with the back ones. and the rear end wil match the speedo gear in the transmission. but the perches wont line up unless you cut them off and move them to fit your springs.

[ToughOldFord]

You should also take the gearing of each axle into consideration, use the gearing that matches YOUR DRIVING STYLE AND INTENDED TRUCK USE. *Ahem*  

[jreyes]

WELL THATS PART OF MY QUESTION TOO, WHICH IS BETTER FOR ME TO USE THE ORIGINAL OR THE 1979 ONE?

WITH THE ORIGINAL THE TRUCK WHEEL KEEP SPINING ALOT BUT THAT ONE OF THE THING I AM CONSERN, WITH THE 1979 WILL IT SPIN LESS AND WILL IT TAKE OFF FASTER?

[td]

WELL THATS PART OF MY QUESTION TOO, WHICH IS BETTER FOR ME TO USE THE ORIGINAL OR THE 1979 ONE?

WITH THE ORIGINAL THE TRUCK WHEEL KEEP SPINING ALOT BUT THAT ONE OF THE THING I AM CONSERN, WITH THE 1979 WILL IT SPIN LESS AND WILL IT TAKE OFF FASTER?

we need to know the ratio's of each rear end to help you

the one that is in your truck is probably a 350 ratio if it was a original 6 cylinder truck

[Redcap]

Without ratios, we can't really make a decision.  If they happen to be the same ratio, I'd use the narrower '72 rearend.

Oh, and...

[fordman]

???WHAT???

[papabug71]

I agree, it all depends on the gear ratios & how you are going to drive the truck. (Daily driver, street truck, drag truck etc.)

Also,

The '72 rear end will have 28 spline axles & the '79 rear end will have 31 spline axles.

Some say the 31 spline axles are stronger than the 28's, but its a toss up.

[BobbyFord]

Some 72's have 31 spline.

[FORDification]

Some 72's have 31 spline.

It's my understanding that the '72s with 31-spline axles actually have a 9-3/8" rearend, not a 9". The 9-3/8 pumpkin can fit a 9" housing, with a little clearancing work inside the housing.

[Fordnatic]

The 31 splines are much stronger-the axle does not neck down at all on a 31 spline.  I searched and found 31 spline axles for the original narrower rear-ends on both my bumps.