The rear differential was dropped off at the driveline shop for a rebuild.  They made quick work of the dis-assembly and inspection process.  Unfortunately they immediately noticed that the housing had a crack.  I later learned that this is not all that uncommon with the standard  versions of the Ford 9″ rear end.  Ford used a housing made of nodular iron on their differentials used behind their higher performance engines such as the 428 Cobra Jet or the Boss 429 to resist this cracking problem.   But mine was cast iron and needed to be replaced.  Val did some quick checking on the Web and found a complete differential, rebuilt and ready to go.  That lead failed to pan out as it was built for 31 spline axles and my car had 28 spline axles.  Next he located a used housing on Craigslist.  There are also several vendors that sell new housings that are much stronger than the stock original.  In the end he found somebody that he knew in the local Mustang club who had one for sale.  He picked it up and dropped it off at the driveline shop so that they could continue with the rebuild.

***Update***

Several weeks later the differential is still in the driveline shop. First Val had to order the clutches and metal washers to repair the traction lock.  Then there was a mix up regarding who is ordering the rebuild kit.  Val ordered that as well and delivered it to the rebuild shop.  The person performing the rebuild was unavailable for a few days due to a family emergency.  When he returned to work he spent some time trying to get a good gear mesh pattern on the ring and pinion, only to discover that the ring and pinion needed to be replaced.  So Val ordered a new ring and pinion.  It’s been almost another week since I last heard the bad news about the ring and pinion.  Hopefully the differential is almost complete.

In the mean time Val has been working on some rust repair as well as cleaning and repainting the rear end housing.  He sent me some pictures which I am posting below.

Cleaned differential housing

Painted housing, axles, brake drums, and backing plates.

Rusted trunk drop off

Repaired trunk drop off

Rusted rear floor cut out

Patched rear floor

***Update 2***
I heard from Val and the differential is back from the driveline shop. That means that next week he will finish up the rear end rebuild and move on to the clutch, subframe connectors, and the brake power booster. If all goes as planned the car should be completed in about one more week. I’ve got my fingers and toes crossed, but I won’t be shocked if if ends up taking two weeks instead of one.

Here are some additional pictures of the rebuilt and painted differential

Rebuilt and installed differential

Cleaned and painted brake backing plate (rear view)

Cleaned and painted brake backing plate (front view)