Thursday, January 30, 2014


I suppose. We're talking differentials here--specifically, Ford 7.5" and 8.8" differentials.

I'm not a fan of taking the higher-the-number-the-better approach. Making choices based on higher numbers is for insurance companies and people who don't know any better. And it tends to be the more expensive approach. Yet, for those who care to know, a 5.45X39 round shoots farther, faster, and more accurately than a 7.62X39 round. So there's that.

When I purchased a used axle unit to replace the damaged unit in my pickup, I thought I was purchasing an axle with a 7.5" differential. I drove up to Nordstrom's Automotive in Garretson, SD last week, strapped the axle to a carrier attached to Dolly's hitch--Dolly is the name of my '89 Oldsmobile Delta 88, named after its previous owner--and carefully drove home.

When I had my neighbor help me carry the axle into my garage, I couldn't help but notice how heavy the thing was. It seemed heavier than it should have been, as I'm under the impression that a 7.5" differential axle weighs about 120 pounds (I don't know if that includes the axle shafts and the gears, or just the housing). The 8.8" differential axles weigh 50-80 pounds more than the 7.5" axles. Looking back--and having removed the old axle from my pickup all by my lonesome--that difference in weight sounds about right.

The stupid thing is, I didn't notice the difference between the two units until I was removing the old axle. Every time I looked down at it, I couldn't help but think that it looked small. Then it hit me...the differential on the old axle was smaller. The differential on the new unit was downright cavernous by comparison:

8.8" on top, 7.5" on bottom.
Oooh...that's not a bingo. That's an 8.8" differential. One call to Nordstrom's revealed that yes, a mistake was made, and they were very accommodating regarding the issue. I'd do business with them again without hesitation. But I'd bring a tape measure. And my wits.

Back to the axle differences. The numbers 7.5 and 8.8 refer to the ring gear size in inches. As evidenced by the above photo, there is also a difference in the differential cases. But there's also a big difference in the size of the pinion gears:

7.5" and 8.8". Free axle to the first person to name the movie on the TV!

So what does this mean? I don't see myself hauling any semi trailers anytime soon, but it should make for a stronger differential. That's not really necessary, as the 3.0L engine wasn't the cause of the old differential's failure, and I wouldn't bother trying to tow much more than a pop-up camper or boat with my pickup anyway. But bigger is bigger, and it should make for a differential that outlasts the rest of the pickup once it's assembled and installed in its new home.