Which Diff to upgrade to?

[Dr Terry]

The 9-inch Ford diff is not that strong in stock form. OK, it's tougher than a 10-bolt Holden Large Salisbury, but it's not the be-all & end-all.

My B06 One-Tonner with 308 TH400, even in standard form was a bit hard on diffs back in the 80s. Yes, it was driven hard & did a lot of towing, but didn't do any burnouts. I killed 3 standard diffs, then changed to a 3.25 9-inch.

The side carrier bearings went noisy within 1 year & then the pinion seal began leaking badly, the diff guy said that this was commonplace, so I spent big $$$ having it overhauled.

Less than 18-months later it began making very strange noises so it out it came again. The 'hat' part of the centre carrier had cracked & separated, right around the outside thru the centreline of the crown wheel retaining bolts. Again this was a "common" failure so I had it upgraded with a aftermarket billet hat, the original was just cast iron. I do less mileage in it these days & it has held together. By the way, the original 28-spline axles are still in there today. The conversion involved using Holden axles & brakes with the Ford centre.

When we were drag racing, the 9-inch was the thing to have, but again all 9-inch diffs are not equal. In our Monaro we went thru 28-spline thin axles, 28-spline thick axles, 31-spline GT-HO axles, & then finally 35-spline aftermarket items (Mark Williams) & a billet one-piece spool to replace the standard LSD centre, before we stopped picking up broken diff pieces & spending money over & over again. This was a 10-sec sedan SS/A car, not far removed from a street car, it wasn't a Pro-Stocker or Door-Slammer.

Good alternatives for use in a Sandman would be an M75, M78 or M80 out of a late Holden or Falcon. More commonplace & cheaper than an overhauled 9-inch Ford unit.

Another conversion I've seen is the fitting of B-W gears & hemisphere to a standard Holden Salisbury housing. It is stronger than the original & the parts are plentiful, as some of the 10-bolt bits are getting scarce. It also looks concours original from the outside.

Dr Terry