Vintage Mustang Forums banner

1 - 7 of 7 Posts

·
Moderator
Joined
·
4,129 Posts
Discussion Starter #1
In my travels over the years I have collected two 9 inch differentials. One is a 3.25 posi with C7AW-023 on the housing. The other one came from a 64 1/2 Mustang K coupe. It is a 3.89 conventional with C1AW and below those letters is 4025C on the housing. I was hoping that I could make the 3.89 into a posi, but upon closer inspection it does not look possible. Am I correct that the conventional and posi gears are not compatible? The other question is the 3.89 out of the 64 1/2 K Mustang worth anything? I would like to get a 3.50 or 3.89 Posi for my Mustang. The rear end is the one thing that I have never upgraded over the years. KBF 8 days and counting... fd

1967 GT coupe been in my garage since 1974
1993 Ranger ExtCab 4.0L daily driver
1996 Aerostar wifes ride
Those that know it all are willing to learn something new, those that think that they know
it all don't know anything.
 

·
Registered
Joined
·
391 Posts
There are kits that allow you to convert your 9" 3.89:1 open rear end to a locker without taking it fully apart within an hours worth of labor as it sits on your workbench. They quote a mornings labor with having to remove and re-install in your car.

I am looking for a 9" 3.25:1 posi in usable condition. Is that something we could discuss?

Russ

http://albums.photopoint.com/j/View?u=1595962&a=12199293&p=44358030&Sequence=0&res=high.JPG
 

·
Moderator
Joined
·
4,129 Posts
Discussion Starter #3
My 3.25 posi is all there, but usable is not exactly a word that I would use describe it. My dad took it to Toms differentials to check it out. They took it apart and said that it is fine, and that is the way that it was returned to me. So now it is in a box in pieces and has been that way for many years. I wish that I could remember why Tom returned it to me in a box, but that was over 17 years ago. But if you are still interested in looking at what I have let me know. I will be at KBF next Sunday. If I can convert my 3.89 into a posi than I have no use for the 3.25. And unless I hit the lottery tonight money is always an issue when it comes to buying parts for my "Toy". fd

1967 GT coupe been in my garage since 1974
1993 Ranger ExtCab 4.0L daily driver
1996 Aerostar wifes ride
Those that know it all are willing to learn something new, those that think that they know it all don't know anything.
 
G

·
Guest
Joined
·
0 Posts
As long as both units are 9" centers, there is no difference in posi gears from conventional, you just have to change the gears from the standard open spool onto the posi spool-they are bolted on, and of course change the pinion gear.If you use the search feature there was a good post that detailed the removal and installation process to do this correctly on the old forum.What you may be seeing on the 3.89 stup up is the fact that the ring gear is actually only 8 3/4" in diameter, not a true 9".The ring gears will interchange from spool to spool, but everything will have to be setup acordingly.If you have the entire housing and center with axle from the 64.5 HIPO I would say it would be worth some good $$ to the right person.Do you have the tag still? Early correct 9" mustang housings with narrowed tubes are hard to find-only used on HIPO cars.The center is special only if it is an N case-should be a C4AW casting number on it-it will have two horizontal ribs on the outside of case, as opposed to the C7 case which would have only one.Also I believe if it is and Ncase you will find it have a daytona pinion support-bolts to front of case behind the driveshaft yoke, it should also have a C4 part number.The hipo center by the way should be 28 spline which might make changing a bit more complicted if the posi center spool is 31 spline.If you have the tag numbers or further casting numbers off of pinion supports-numbers are stamped into front face of support, post them.I may have some pictures as well to help identify.

1967 S code GT Deluxe Coupe 65B
1966 Convertible 76B 289 4 speed

Descendent of Francois Seguin dit Laderoute,
Soldier Regiment d' Carignan, New France 1665-1668
 

·
Moderator
Joined
·
4,129 Posts
Discussion Starter #5
I only have the differential, the axle housing and axle shafts are something else that I will need but I'm going to worry about that after I have a good posi differential. And I also do not have any of the tags :( The 3.89 was free so I can not complain, and I almost bought the 64 1/2 K car. I remember looking at the axle code on the door of the car. She had the differential replaced and left it behind when she moved. My brother in law moved in there and did not want the diff and gave it to me. Also I just measured the thickness of the ring gear and it is 1.375 in thick (1 3/8) and the posi ring gear is 1.030 (1 1/32). On the 3.89 gear is stamped U.S.A. C3AW 4210C <> 1-651 shift No. 3 On the differential case cover is C2AW 4206 on the differential case cover is DIF 21 and on the differential case is 31 DIF. I am going by the names of these as shown in my 1967 shop manual. Thanks for your help, fd

1967 GT coupe been in my garage since 1974
1993 Ranger ExtCab 4.0L daily driver
1996 Aerostar wifes ride
Those that know it all are willing to learn something new, those that think that they know it all don't know anything.
 

·
Registered
Joined
·
391 Posts
If you are interested in parting with the 9" 3.25:1 posi pumpkin, then I am interested in it. My '67 vert currently has 9" 3.25:1 open pumpkin. Given the car has an extremely strong 351W engine and I let my adult children use the car on occasion, I would worry about them getting in over their head with a locking rear. A posi has much softer traction control and less likely to put an inexperienced driver in over their head.

Locking rears are the preferred drag or track racing pumpkin. I think many four-wheel drives use them because of durability. If you are interested, let me know, and then we can strike an arrangement at Knott's.

Damn, I've been looking forward to Knott's since last year.

Russ

http://albums.photopoint.com/j/View?u=1595962&a=12199293&p=44358030&Sequence=0&res=high.JPG
 
G

·
Guest
Joined
·
0 Posts
You have noticed the different thickness of the gears-this is another good way to spot a good ratio visually without counting the teeth-the beefier the gear(its thickness) the better the performance ratio.As ratios go from 3.00 to 3.50 for example the gear thickness increases quite alot and is easity visible to the naked eye, a 3.89 will indeed be quite a bit beefier than a 3.25.By the way if the 3.25 is a 28 spline posi out of a car, they are very diserable, most of the ones you find are of the 31 spline variety-often found in trucks.I am going to be working on a page to give visual id's and tag numbers eventually, here is what I have of the visual part now, click on link below to take you there:
http://www.geocities.com/kevinstang66/Ninecase.htm

1967 S code GT Deluxe Coupe 65B
1966 Convertible 76B 289 4 speed

Descendent of Francois Seguin dit Laderoute,
Soldier Regiment d' Carignan, New France 1665-1668
 
1 - 7 of 7 Posts
Top