28 or 31 Spline Axles in my 9\" Rear?

Is there any way to ID the axles based on the application? Or a visual inspection of the axle flange? I'm looking to buy a 3.50:1 posi for my rear, but don't know which axle I have. [img]/phpBB/images/smiles/icon_confused.gif[/img] Any suggestions would be helpful...I can pull an axle if necessary, but would rather wait until it's time to change the diff.

Application: '79 F150 Supercab Shortbed, 2WD, 302, AT, w/o towing package.

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[addsig]

Really no way to tell for sure on yours. Pull a wheel & the drum & 4 nuts & you're there. Most likely a 28.
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As a general rule (on 73-79 trucks) if it's a 2x4 with a 300 or 302 it had 28 splines, and all 4x4s and anything with a 351 or bigger engine had 31 splines. Not sure what the Supercabs used though. Shouldn't take that long to check.
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Ford doesnt let us make rules [img]/phpBB/images/smiles/icon_smile.gif[/img] I've got 2 trailers made from half ton 73's, one was a 360 truck, the other a 300. Both have 31 spline 3.25 setups. Just give an axle a yank, and take a look. Better to be safe than sorry. But being a supercab, I'd be willing to bet 31 spline.
[addsig]

its fairly easy to tell what spline count you have. first remove the rear tire and brake drum. you should see 4 nuts that appear to hold the backing plate on the axle tube. if they are 9/16 you have a 28 spline axle. if they are 11/16 you have a 31 spline axle. check out the page in the tech department reguarding ford 9's

I've heard the size of the nut theory works on which bearing size you have but on my 71 it has the 11/16" nuts and it's a 28 spline. We've done alot of swapping of center chunks here in the truck club I belong to in NC and all the earlier 67-72 trucks have had 28 spline regardless of the bolt sizes
Clint
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here is site that will help you out with all your 9" questions www.quickperformance.com/ninecase.htm .hope this helps it did for me