[MV] The Cheap Mechanic- Differential Overhaul Update

Lee Ethridge (leeethridge@ibm.net)
Fri, 19 Dec 1997 07:32:50 -0600

I'm back with a few tips from what I've learned, and with a few
questions about what I haven't learned.

The axle housing is now completely stripped of its associated parts, and
I've been working on rust removal for awhile.

I tried using a cylinder ridge reamer to clean the rust out of the axle
tubes. There are a number of reasons this isn't a good idea. My axle
tubes had a fairly rough weld along their entire length on the inside.
This weld ate the abrasive off the reamer in no time. Also, as Alan
Bowes pointed out, the scratches left behind by the reamer could lead to
cracking of the tubes.

I found that I was able to remove most of the loose rust with a
Scotch-Brite (plastic abrasive) pad wrapped around a long wood-boring
spade bit on my electric drill.

I also tried phosphoric acid. The instructions on the container (it was
packaged as a rust removal product) said not to leave it on the surface
more than 30 minutes. Unfortunately, it had just begun to work in a few
spots when the time was up, and I had to wash it off. I was frustrated
that the marketer didn't see fit to explain the consequences of leaving
the rust remover in place longer than 30 minutes.

I've been working on removing the undercoating. This Jeep was
undercoated in 1982 with Ziebart. Since then, I've sprayed it with
undercoat a couple of additional times. In the places where I was able
to get through the undercoat, using brake cleaner, I find shiny metal.
This speaks well for undercoating, I think, but undercoating does look

I used the car wash trick for pressure washing the axle housing. It's
probably not as good as a real pressure washer, but it's cheaper, and it
did a fair job of cleaning up some things. Still, I've spent a lot of
time with a wire brush and several cans of brake cleaner.

The bearing cups came out fairly easily. The cups for the pinion shaft
bearings were removed with a two foot piece of small diameter steel
pipe, that I used as a drift. Expect to ruin the shims behind the cup
if you do this.

(I have a pair of brass drifts for installing new bearing cups. Brass
drifts can be used to install bearing cups if you're careful. Steel
drifts tend to dent the cups. I once paid a guy $20 to press bearings
into some hubs for me. When I got there, I found that his "press" was a
big hammer and a steel drift. The dents were significant.)

The tough part at this point is removing the bearing cones. I've been
working on the pinion shaft bearing with a bearing separator and a
hammer. It's sometimes possible to drive a bearing off a shaft this
way. Remember that if there are threads on the shaft, that you should
probably put a nut on the shaft to protect the threads before you start
hammering. Use care and common sense. It's still pretty easy to ruin a
shaft this way.

Since hammering the bearing off the shaft (which worked fine for the
transmission and transfer case I overhauled last year) didn't work, I'll
probably move on to attaching the hub puller to the bearing separator.
(Get the Harbor Freight and Northern Hydraulics catalogs for reasonable
sources for bearing separators, hub pullers, etc.)

I'm told that it may be necessary to cut the bearing off the shaft. My
father-in-law says he can do this with a cutting torch without damaging
or overheating the shaft. As a mere mortal, though, I'll have to try
something else. Maybe a high-speed grinder (that's a Moto-tool to me)
with a cut-off wheel would do the trick. I'm also thinking about trying
to heat the bearing or cool the shaft enough to loosen it, but I'm
afraid I'll heat-damage the shaft if I apply a torch to the bearing.


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