GMC Differential Woes

This evening I decided to clean up the rear differential housing for the GMC. It seems like I have been on the verge of this chore for months but for the life of me I couldn't figure out why I hadn't done it. Then I looked at my blog. Oh yeah, I was working.

The great thing about the blog is that I can forget what I have been doing and still have a record of it.

First I had to beat out the bear chases for the pinion. I used a 24" piece of rebar and a framing hammer. The next step would have been either removing the wheel bearings and seals and then finally I would begin the de-grunging process.

At this point I noticed something that derailed the process. I was looking at the bottom of the differential housing when I noticed what appeared to be a weld. Having never really looked closely at the bottom on the housing, I inspected it further. And then I looked inside.

The differential housing had apparently been broken at one point and the hole was big enough to put a baseball through it. The broken piece had then been welded back into place. I could imagine this had probably been done after dark one fall evening in the front yard of a single-wide.

Perhaps this was the location of the leak resulted in the differential only having about a quart of fluid in it. Perhaps.

Regardless, I think it is time to hit the salvage yards and attempt to locate a replacement GM 12 bolt housing. The complete carrier assembly is fine.

My guess is the 12 both was originally a locker. At some point it "blew up" resulting in a cracked housing and the total annihilation of the carrier. The housing was welded back and a replacement carrier was dropped in.

According to the code stamped on the axle, the differential was originally a 1/2 ton 3.73:1 from a 1972 pickup, so the housing is probably original. The gears I found inside were 3.07:1. I like the 3.07:1 ratio because it will provide better MPG at highway speeds.

It will probably be a few weeks before I can round up another diff housing. I already have plans for the next few weekends.