9" Rear End Questions

I am planning to buy a posi third member for a 9" differential from a 1972 Lincoln Mark IV. They guy wants to know if it is for sure a 9" and if it is a 28 or 31 spline. Does anyone know? I am pretty sure it is 9 inch but do now know how to tell about the splines without pulling the axle. Anyone know how or have a place to find tech specs for Ford rear ends? :

JR  

The easiest way to tell an 8-inch from a 9-inch is the bottom most two studs on the housing that retain the center section. On an 8-inch you can place a socket over the nut, on a 9-inch you have to use a boxed end wrench to access the two nuts.

As for spline count, I believe (but don't qoute me) the 31 spline axles are identified by the axle end having two machined or cast dots in them, though 28-splines can to (it's best to pull the axle)...

Here's a great site with visual help:
http://www.maliburacing.com/ford_9_inch/ford_nine_inch.htm

HTH...
Mark  
Mark Houlahan
Editor
Modified Mustangs & Fords Magazine

1965 FFR Roadster 427W/TKO-600
1966 Mustang 289-4V/C4
1968 Mustang 4.6L Three-Valve/5R55S auto
1990 Mustang 347/AOD
1998 Escort 2.0L SOHC/F4E-111 Auto
2002 Explorer Sport Trac 4.0L V-6/5R55 Auto

The dots or slots on the ends of the axles are an unreliable indicator.  You will have to pull the axle and count to be 100% sure.  
1967 Falcon 4 door 351C-4V
1970 Mustang 351C-2V
http://raceabilene.com/kelly/hotrod
Owner built, owner abused.

I would like to know the factory axle length (not housing width) for 64 1/2 to 66 Mustang 9" rear and the length for the 67 to 70 Mustang. Was a 31 spline axle offered before 69? If so, what years & length.  

All 1972 Lincoln Mark IV had 9" rears.  Chances are pretty good it's a 28 spline as well as it wasn't a performance vehicle.  First year of the lower compression engines, etc.  

If you buy this 72 rear end I would be willing to swap you rear ends for 74' 9" that has the larger bearings and will accept the larger 31 spline axles, but it would have to be complete with SURETRAC pick-up sensor and reluctor on the driveshaft.  Or could you pass there info on to me please.  

HotRodLincoln,

I have a 1972 MarkIV that I purchase already Hot Rodded up. With exception of the stock diff 2.73 gear.
I pulled the pig this weekend. The shafts are 31 spline and there is some sort of sensor on the pinion.
Is the sensor for the cruise control ? I didn't think they had ABS systems in 1972 ?

I just dropped the Pig off at D&R drivleine. The told me they've never seen a Ford 9" like this before. They think I may have a problem getting 4.10 gears ?