Topic: 1968 San Jose GT 390 Fastback Need to make my car a roller question

[bullitt68]

So it looks like I am going to (reluctantly) make my car a roller after all so my painter can mock up the sheet metal and do the final body work before blowing the car apart again and painting it. I was entertaining the idea of using all of my restored suspension parts to make it a roller, but have decided that I would prefer to use old suspension parts instead, so as to keep my freshly restored parts nice and clean as the fine body shop dust will get into all those parts. Then when the car comes home from paint, I can install fresh new parts that are ready to go.

I am looking to confirm what are my diff options as I am looking to source and old used diff locally and may have access to a '66 diff. I am just not sure if they are interchangeable and will work for my purposes. My understanding is that the earlier diff's are a little narrower, so I would like to confirm if I can use a '66 diff and it will mount right up to my leaf springs.

Thanks any advice greatly appreciated

[RoyceP]

I don't think you will find a 31 spline '66 differential, so that means no way to use the 31 spline axles that you have. 1966 Mustang 28 spline axles are too short so that would not work either.

There were 9" rear differentials in many Ford and Mercury products in 1966. Most are 28 spline and most would fit and work fine if there were 28 spline axles from a 1967 - 70 Mustang or Cougar to use with that differential.

[bullitt68]

I don't think you will find a 31 spline '66 differential, so that means no way to use the 31 spline axles that you have. 1966 Mustang 28 spline axles are too short so that would not work either.

There were 9" rear differentials in many Ford and Mercury products in 1966. Most are 28 spline and most would fit and work fine if there were 28 spline axles from a 1967 - 70 Mustang or Cougar to use with that differential.

Hi Royce. Sorry if I did not explain myself correctly. I am looking to just use an entire diff, so I don't have to use the one I just restored. So I am looking to confirm if a '66 diff would mount on the leaf springs on my car to make it a roller. I have a friend who cam let me use his '66 unit. If it fits great, otherwise I will have to look for another option.

Thanks

[DTruitt]

The spring perch distance was different on a 65-66 vs. a 67-68.  I would look for an 8 inch rear out of a 67-68 as the easiest solution.  I think 69-70 have the same spring perch distance.

Danny

[bullitt68]

The spring perch distance was different on a 65-66 vs. a 67-68.  I would look for an 8 inch rear out of a 67-68 as the easiest solution.  I think 69-70 have the same spring perch distance.

Danny

Great thanks

[Bossbill]

All 65 to 73 Mustang spring perches are about 43 inches apart. Fairlanes are different.

The total oveall widths are different from outside of axle (where wheel bolts on) to outside of axle on the various years of the Mustang.

So as a roller, the early diff would work.

[bullitt68]

All 65 to 73 Mustang spring perches are about 43 inches apart. Fairlanes are different.

The total oveall widths are different from outside of axle (where wheel bolts on) to outside of axle on the various years of the Mustang.

So as a roller, the early diff would work.

Great thanks Bill that is great news. Now I can save my restored diff & suspension as it would get fifty in the body shop

[Bossbill]

I think the discussion got hung up on nomenclature. Spring (perch) spacing is not often discussed -- we normally talk about axle flange to axle flange (overall) widths. And those are different across many years.

Another interesting tidbit along this line is that the front and rear frame rails are the same distance apart from at least 65-70. That's why most Mustang rear axles will bolt in there as they are hung from the rails. The later axles will have issues in an earlier car due to overall width and tire fouling at the arches. But the perches will line up.

My rotisserie bolts up on the front frame rails of a 65/66 just as well as it does on my 67 (through the bumper bracket holes).
On the rear the rotisserie will bolt up, but the bumper holes are arranged differently, but at the same spacing.

I have a Versailles 9" axle in my 65 street car.

[bullitt68]

I think the discussion got hung up on nomenclature. Spring (perch) spacing is not often discussed -- we normally talk about axle flange to axle flange (overall) widths. And those are different across many years.

Another interesting tidbit along this line is that the front and rear frame rails are the same distance apart from at least 65-70. That's why most Mustang rear axles will bolt in there as they are hung from the rails. The later axles will have issues in an earlier car due to overall width and tire fouling at the arches. But the perches will line up.

My rotisserie bolts up on the front frame rails of a 65/66 just as well as it does on my 67 (through the bumper bracket holes).
On the rear the rotisserie will bolt up, but the bumper holes are arranged differently, but at the same spacing.

I have a Versailles 9" axle in my 65 street car.

Thanks Bill looking forward to making this thing a roller as it has been on the cart for about a year it seems