How to measure 9" axle shafts

[snick]

I have acquired 2 sets (one wild horses set and one Yukon set) of aftermarket 31 spline EB rear axle shafts in parts lots that I purchased. I know that both sets are for big bearing housings so I've narrowed it down to 3 out of the 4 possible EB housings. The following measurements are what I've found for the axle shaft lengths per viperwolf1's post on a different thread from many years back.

66-75 (SMALL BRG) (28 SPLINE) 1 3/4" BRAKE R.H..29.62"
66-75 (SMALL BRG) (28 SPLINE) 1 3/4" BRAKE L.H..27.25"

66-75 (LARGE BRG) (28 SPLINE) 1 3/4" BRAKE R.H..29.31"
66-75 (LARGE BRG) (28 SPLINE) 1 3/4" BRAKE L.H..26.94"

74-75 (LARGE BRG) (28 SPLINE) 2 1/2" BRAKE R.H..29.75"
74-75 (LARGE BRG) (28 SPLINE) 2 1/2" BRAKE L.H..27.25"

76-77 (LARGE BRG) (28 SPLINE) 2 1/4" BRAKE R.H..29.68"
76-77 (LARGE BRG) (28 SPLINE) 2 1/4" BRAKE L.H..27.25"

My question is: Are the measurements above from the outer surface of the axle flange closest to the wheel or the inner inner axle flange surface or something else? Or is there an easier way to determine which housings these axle shafts were made for just by looking at them (they don't have axle retainers installed and they don't have any packaging/markings that I can see on them)?

 

[DirtDonk]

I'll look those up compared to ours to see if you can use our method. But no matter how it works out, be aware that different companies still use different points on the outer flange area for their measurements.
For example Wilwood uses a different point on the axle to determine which brake setup to use.

They all seem to use the very end of the splines on the inner end, but then use different locations on the outer. Some use the "bearing offset" location which is the stopping point (shoulder) on the axle shaft itself.
Others use the inside of the flange, and still others use the outside edge of the flange (edit: We use the same "outside the flange" location that Ford does in it's charts). Not a big difference there, but enough to throw off the measurements!

Unfortunately, your numbers don't coincide consistently with ours.
For example, we use the full outside of the flange distance, and for the '76/'77 axles, the right side is 29.68 (which is consistent with yours) and the left side as 27.18 (which is not the same as yours).

Same for the '74/75 setup. The same 29.75" long dimension, but a 27.37 short.

For the earlier small and large bearings, both of our measurements are different from your chart.
The large bearing '66 to '75 are 29.5" and 27.12" respectively.

So use your own best judgement. Maybe those discrepancies are not enough to cause a problem, or maybe they are. But ours are taken from outside of flange to tip of splines.

Paul

 

[Viperwolf1]

The overall length is not as critical as the brake offset and bearing size. There is some leeway on the length. Usually there is more than enough spline to fully engage the diff side gears but if it's too long it can contact the cross pin. Brake offset is measured from outer surface of flange to outer edge of bearing. It's something like 2 3/8" on the 76-77 axles, and 1 3/4" or 2" on the earlier big bearing/big brake axles. I don't have any small bearing axles to measure.

 

[snick]

Thank you for your responses, great info and really appreciate it.

One more question - I'm going to run explorer discs on my 74 9" EB housing (I'm well aware many believe the performance gains are minimal and not worth the cost/effort over just keeping the rear drums but I've decided that's the route I'm taking). In my explorer rear disc search, I came across this post by Sykanr0ng:

"If you are ordering custom axles you can probably get the raised part that centers the rotors made larger so you don't need the spacers.
Wild Horses does that with their disc brake kit."

Can someone please post a picture of this raised part? Do all Wild Horses 31 spline axles have this raised portion or just the axles that come in their 73-75 9" housing 31 spline axle upgrade kit with explorer disc brakes? If my 31 spline WH axle set (assuming they are the correct length 31 spline shafts for the 73-75 medium duty 9" housing) has this raised part, I do not need the spacers, correct?

 

[DirtDonk]

Most, and perhaps all axle shafts are going to have the raised part. I believe the portion of the axle that was being referenced would be what I think I correctly call the "register" and is the center of the axle wheel flange.
You can see it on your own axles, or the axles in this image here: https://www.wildhorses4x4.com/produ..._7475yr_Lg_Bearing_10in_Drum/bronco_rear_axle
These registers are perhaps used in the machining process, but primarily to help locate the drums on the exact center of the flange would be my guess. Rather than relying on the wheel studs, the holes for which are probably slightly loose fitting by necessity.

If our custom shafts for the brake kit were actually cut from cores made to hold the same diameter as the stock replacement axles in order to allow the stock stuff to be fitted, then the same spacer ring should do the job for you too. The Explorer rotors were never designed to go on to an old 9-inch rear axle, hence the need for a spacer.

I don't know any of that for a fact, but it's probably close to the truth.
If you already have your Explorer discs you could test any of those theories by sliding the rotor over the wheel flange and see how it fits.
I was not aware of anyone needing the shimming with stock axle shafts from your year. Perhaps the early adopters of the Explorer setup just never bothered. Maybe it's a common thing, but I don't remember discussing it.

We no longer sell that kit, but may still have some rings if you end up needing them for your application.
First things first though. Trial fit your rotors and see what happens.

Paul