1968 GT350 Axle Spline count

[Corey Bowcutt]

Again thank you so much for the help!

[TLea]

Actually a 3.89 car could have SPEC case. Might be easier to find than a no N nodular

[Corey Bowcutt]

So now I need to know what an SPEC case is?  Is the one I pictured in previous reply an SPEC case?

[gt350hr]

  Corey,
      The case you are looking for 'might" have a 7M xx  date code on it. the casting number on the inside MUST say C4AW 4025B or simply C4AWB . This is the ONLY casting number that is original for your car. It would NOT have an N on the front as that was added in late '68 for '69 productiom.  The pinion retainer is as Pete ( Coralsnake's photo shows. The C5AW letters are below the surface , NOT raised . If you are only concerned with function, the one you are being sold will "function" but again is not the "as produced" version. I believe the guys here are concerned about  spending potential big bucks on an incorrect assembly. IF the M 3.50 diff has the proper case and bearing retainer you would be money ahead by simply having the gear set changed. 7M cases are out there. Your car is a bit too late for a SPEC ( where the date code is normally) case but it "is" possible as TLea suggested. The Axle tag would say C8ZX-? Check the Coralsnake site for the specific suffix. You can't go wrong with the information on his site.
     Randy

[Corey Bowcutt]

Thank you Randy.  I go on The Coral Snake web site all the time but it is amazing even with that how much I miss and do not know.  This is all great information.  This weekend I am going to check and see what case I currently have in my car and I will go from there.
Until this discussion I knew I had a 3.50:1 gear but I had no idea there were so many nuances with the case.

[gt350hr]

  Hopefully the 3.50 was put in your original diff and you will only need a gear replacement .

[Bob Gaines]

  Hopefully the 3.50 was put in your original diff and you will only need a gear replacement .

Ever see any N type web cases (no "N") with a late 1968 date ? I was told about a Dec 1968 dated casting but thought they were all "N" marked by then.

[papa scoops]

you can make a "N" with some jb weld, I know people that have. phred

[Corey Bowcutt]

I could not stand the suspense of waiting for the weekend to find out if the 3rd member in my car was correct or not.  So last night on my way home I stopped in and looked at my car.  I was very relieved to find the gear casing and pinion retainer are correct for my car.  It even has the tag on it which is hard to read because it has all been painted black.  Returning it to the correct color and possible gear ratio will be a job for another day.

Once again this Forum really helped me out!  Thank you all.

[gt350hr]

   Corey ,
      Looks like response #18 was "spot on" LOL.  As with many situations there are patterns for parts in certain ranges and yours fit into one I was familiar with. Nice that you still have the original tag on your original diff. Every picture shows the correct parts , original to your car. Before "I" pulled it, I would verify that the ratio is 3.5 not 3.89 unless you are certain for some reason. Mark "a" tire and the driveshaft. Turn the drive shaft , not the tire to determine how many turns are needed for one revolution of the  tire. If you turn the tire instead ( on an open diff) the spider gears might turn and throw the count off.
     Glad your curiosity got to you and you found "all the right stuff".
      Randy

[Corey Bowcutt]

Randy,

That is very interesting.  When I did the check for gear ratio I was turning the tire and counting the shaft.  I will do it the other way and see what happens.  It would be crazy if all along I had exactly what I was suppose to have gear wise.  It would not all be for nothing since I did learn a whole bunch about 3rd members in 68 Shelby's.

Corey

[68stangcjfb]

7M21. The same date housing that was in my brothers April 25th Mustang with 4.30s and my May 11th Torino GT with 3.91s.

[Bob Gaines]

Randy,

That is very interesting.  When I did the check for gear ratio I was turning the tire and counting the shaft.  I will do it the other way and see what happens.  It would be crazy if all along I had exactly what I was suppose to have gear wise.  It would not all be for nothing since I did learn a whole bunch about 3rd members in 68 Shelby's.

Corey

FYI a 3.50 gear is much more street friendly then the 3.89.  If it turns out that is a 3.50 I would be torn with going to the trouble to change just for the reason of it not being original . It is not like anyone could tell looking at the car. Is everything else visually on the car 100% correct? If not then shouldn't be a big deal. If you find it is a 3.89 then all good. Ether way I think you are in very good shape. Just my opinion ,others may think differently.      

[gt350hr]

7M21. The same date housing that was in my brothers April 25th Mustang with 4.30s and my May 11th Torino GT with 3.91s.

     Drum to drum axle assemblies were built at the axle plant per requisitions that could be for a hundred or more , the same went for component parts used on them.  As you have noted there can be some large  "ranges" in dates of parts used. The casting plant "req" may have been for a thousand (or more) castings and it took a week to macing the "run" . They ship to the assembly plant and get built as third members ( more time) and then into complete drum to drum assemblies , get palletized , and finally shipped to the car assembly plant.  This is one of the reasons there is a "manufacturing date" on the axle tag as well. Your case has a wide range while another could have a real close one. I-we have seen both cases on original unmolested applications.
     Randy

[TLea]

7M21. The same date housing that was in my brothers April 25th Mustang with 4.30s and my May 11th Torino GT with 3.91s.

never seen nodular casting between 7M and 8D. I've seen original 7M cases in June cars