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Discussion Starter #1
I'd like to upgrade my rear axles to 31 splines on my 68 which has a stock small bearing rear end. I know it requires a differential or side gear change but does it also require different axle bearings and seals or are both 28 and 31 spline axles the same diameter at the bearing ends?

Thanks,

68Restoman
 

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My understanding is that the 31 spline axle shafts are a larger diameter. This makes sense as otherwise the larger number of splines would actually make the splines weaker and they would tend to strip under torque. In fact, the converse is true, so logic says the diameter of the shaft has to be larger. My response is based on that logic.

With a small bearing style 9 inch rear, you have a larger bearing cap, which makes for a stronger set-up. When I converted from an 8 inch to 9 inch, I went with the small bearing and added 31 spline Moser axle shafts. When doing so, the axle bearings were also changed.

I suggest contacting Moser or checking out their website to get an authoritative answer to your question. Other resources would be Currie and Drive Train Specialties.

good luck.
 

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A small Ford bearing is a small Ford bearing. It doesn't matter if it's going in an 8" a 9", it's on a 28 spline or a 31 spline axle. It's all the same. The difference between a 31 spline axle and a 28 spline is all after the bearing surface (28 splines taper down more than a 31).

Same with the seal ... same seal ... small Ford is still small Ford. The seal is made to seal on the axle, just inside the bearing ... on the bearing surface before the taper.

That said, it would make zero sense to me, not to use new bearings and seals.

How do I know all this? I just converted from an 8" open rear to a 9" 3.50, 31 spline traction-lok last weekend. This is in my '69 using a stock '67-'70 Mustang 9" housing (small Ford).
 

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John I'm glad you said that. Reading this post had me worried. A couple of years ago I dropped $300 on a 3.25 9 inch 31 spline tracloc differential and just found a tapered 9 inch housing for it that came out of a 69 mustang. I was going to have the housing cut down to fit in my 66 and invest in the axles backing plates, bearings, seals, brakes etc. for it. Reading this post had me worried that I had the wrong housing and had wasted my money on it. From what I read in your reply, my tapered 69 housing should work fine with 31 spline axles once I get it sized to fit the width of my 66. Correct? ::
 

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Actually the 31 spline axle used another ring pressed on after the bearing for the seal to ride. If you do not have this ring, not manufactured by Ford any longer, you can use the 28 spline seal however it will eventually where a ring in the axle.

Mike
 

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A 28 spline carrier can ot be converted to 31 unless you bor ethe end of the case for the larger axle. The 31 spline side gear or soder gears will fit in the case but the axle will not. One can convert a 31 splne carrier to a 28 if needed.
 

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I agree, and hopefully, no one interpretted me as saying you can use a 28 spline carrier with 31 spline axles, as that simply won't work.

I'm just saying the axle bearings, seals, and housing are the same for the 28 spline vs. 31 spline. At least this is the case with aftermarket axles (I bought Superior 31 spline axles). I've never had a factory 31 spline, so can't comment on those axles.
 

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Discussion Starter #8
I'm actually going to replace the carrier alltogether with a Truetrac unit so in my case that won't be a problem, thanks for the heads up though...

68Restoman
 

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Discussion Starter #9
Hey John, do you have the part number for those axles? Also, did you just reuse the axle studs or did you buy aftermarket ones and if so what brand? I plan on making an order to Summit here soon so any details would be appreciated...

68Restoman
 
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