MACH 1 Rear

[johnrem46]

I have a 1969 Mach 1 with a 351W.. I am looking to replace the rear with a posi and would like to know how you can tell the size of the rear 8in or 9in. Also how do you know the number of splines 28,31 ect ect... Does anyone have a good supplier

 

[ratio411]

The easiest way is to look at the bolts that hold the center section into the housing.
If all can be accessed with a socket, then it is an 8"
If one obviously needs an open end wrench to remove, it is a 9".
If it is an 8", then you have 28 splines.
A 31 spline 9" has some marks to tell, I don't remember them exactly. I think there are 2 bumps cast into the wheel mounting hub. There is also a difference in the holes around the stud flange where you access the backing bolts.
Someone else will have to clarify.
Dave

 

[96 DOHC Cobra]

If the car is a real Mach 1, it would have come from the factory with a nine inch rear. Since all Mach 1's had at least 351ci motors, they all got nine inch rears.

 

[dolfan87]

If the car is a real Mach 1, it would have come from the factory with a nine inch rear. Since all Mach 1's had at least 351ci motors, they all got nine inch rears.

And to add to this, VERY few came with 31 spline axles.

87

 

[Max Power]

Only Drag Paks, Bosses and special orders got 31 spliners, for the most part.

 

[bnickel]

Only Drag Paks, Bosses and special orders got 31 spliners, for the most part.

and not even all of those, although in rare cases other cars got 31 spline axles. i once heard of a 69 351w 2bbl grande having 31 spline 3.00 open rearend, why maybe the assembly line was out of 28 spline rears that day

 

[ratio411]

That is how Ford did things...
Don't have an 8", throw in a 9"...

 

[Max Power]

They did a lot of parts swapping when the assmbly line ran out of parts. I've heard some pretty cool stories.

I imagine that 2bbl windsor never even made those 31 spliners sweat!