77 rear end, 28 or 31 spline?

[SeaVee]

Can you tell without cracking it open? Stock 77 rear end axle tag says 3.50 9

 

[.94 OR]

You can pull an axle out by removing 4 bolts from inside the rear brake. Not as simple as reading a tag, but easier than dropping the chunk out, which you would have to pull both axles anyway.

 

[okie4570]

All 66-77 bronco 9" rears came with 28 spline. Doesn't mean that there's not 31 in there now though lol

 

[m_m70]

Stock 77 rear end

If it's stock, it's 28 spline.

 

[SeaVee]

Thanks guys

 

[Johnnyb]

If it's stock, it's 28 spline.

I thought that U152 had factory 31 spline?

 

[Broncobowsher]

I thought that U152 had factory 31 spline?

Nope.

Factory Bronco is always 28 spline. End of story.

But there have been a LOT of upgraded axles to 31 spline over the years. It can be done with stock axles that are cut and resplined, so everything looks stock in the end. But this was never done by Ford. The 31 spline never existed in a Bronco until they went full size in '78.

 

[Jdgephar]

Look at the number of dots on the end of the shaft. 2 dots is 31 spline.

Sent from my SM-S916U using Tapatalk

 

[DirtDonk]

Is that a universal protocol, or just for certain years of Ford vendors? Certainly unlikely that all the aftermarket manufacturers follow that.
Where exactly are the dots, and how big/deep are they?

Paul

 

[SeaVee]

Yep-28. Thanks again

 

[jamesroney]

Is that a universal protocol, or just for certain years of Ford vendors? Certainly unlikely that all the aftermarket manufacturers follow that.
Where exactly are the dots, and how big/deep are they?

Paul

It is the protocol for the Intermediate Car High performance axle ONLY, from 67-70. Specifically Boss and Cobra Jet Mustang. If you see a 9 inch in a Mustang with the 2 dots, then you got a 31 spline shaft. (The 28 spline had an open shaped raw casting index)

During the manufacturing process, you need a way to hold and index the raw forging during manufacturing. Since there is no spatial reference on the blank. So they machine a feature that allows for centering and indexing. (so that you can drill all of the holes for the lug pattern, etc.

Every Bronco used the same 2 dot index mechanism. So they LOOK like a high performance axle...but they are not. I don't know how many times I have been told that the 2 dots meant 31 spline. In a Bronco, 2 dots is meaningless.

 

[DirtDonk]

Thanks. I wondered if those two registration holes (if that’s what they can be called?) were what was being referred to. Seems like there are a lot of aftermarket axles though, that don’t have even those.
Pretty sure we touched on this subject about 10 years ago. Or maybe more.

 

[Broncobowsher]

It is the protocol for the Intermediate Car High performance axle ONLY, from 67-70. Specifically Boss and Cobra Jet Mustang. If you see a 9 inch in a Mustang with the 2 dots, then you got a 31 spline shaft. (The 28 spline had an open shaped raw casting index)

During the manufacturing process, you need a way to hold and index the raw forging during manufacturing. Since there is no spatial reference on the blank. So they machine a feature that allows for centering and indexing. (so that you can drill all of the holes for the lug pattern, etc.

Every Bronco used the same 2 dot index mechanism. So they LOOK like a high performance axle...but they are not. I don't know how many times I have been told that the 2 dots meant 31 spline. In a Bronco, 2 dots is meaningless.

I was thinking that was the case. Didn't know about the 1/2 dot car thing, so that's new. Always thought the trucks were two, but getting out of my realm. I learned that early 70s F150 9" were 28 spline and the later ones all went to 31 spline. Forgot the cutoff for that.