Front Axle Shaft Repair

[Matt Wilson]

Greetings to all,

Both front axle shafts in my '49 Power Wagon are in need of repair. The seal and bushing surfaces have some corrosion on them. Some of it is light surface rust, while some of it's deeper than that. For the seal region in particular, I'd like to repair the shafts to make them smooth again. The bushing region may not need to be quite as perfect, but still fairly smooth with no raised areas, I would think.

It may be possible to polish the seal areas down, but in the event it's not possible to do so and remain within the required diameter range, then I think it will require machining down the surface, then building it up by some means, followed by machining to the correct final diameter, while leaving a polished surface. Alternatively, I could buy a different set of shafts, preferably NOS, but considering that NOS parts are getting harder to find and new ones are not being made, I would rather repair my existing shafts, depending on the price to do so and depending on whether it can be done without compromising the strength of the shafts.

If building up the surface is required, then one option might be to take the shaft to a shop I know, where the gentleman welds and grinds crankshafts. I had him do this on a crankshaft recently, and he does beautiful work. The only concern is whether it will mess up the heat treat of the axle shafts and thereby weaken them. I don't know if the crankshaft process is applicable to axle shafts.

Another option is to take the the shafts some place where they can apply a molten spray of some kind. I've heard that there are processes like this that will not adversely affect the heat treat, but I don't know specifically what type of process this is, or where to find a place capable of doing it.

And then there may be other paths to take.

I'd appreciate any input.

Thanks.

[Greg Coffin]

The process you are looking for is known as spray welding. You can probably find someone in your area that can build up the shafts and turn/grind them back to spec. The spray welding process should not harm the heat treatment of the steel, but I'm sure the welder could give you better info. Let us know how it goes.

[Matt Wilson]

Thanks, Greg. I've heard of spray welding, but I wasn't sure if that is what would be best for this situation or not. I will call around and see if I can find a place that will do it. There are also other molten spray coatings that can provide a hard surface, but I'm not sure of the pro's and con's of these.

I took some measurements of the shafts last night, and found that the bearing/seal areas of both outer shafts are at or beyond the wear limits listed in one of my repair manuals, depending on where exactly they are measured. The two inner shafts are within wear limits, but are at or beyond the minimum new part dimensions, meaning the might be ok from a dimensional standpoint, but they are corroded over a sizable area, making them unsuitable for use with a seal.

If the diameters on these shafts are worn (especially the outer shafts), then I wonder how much the thrust surfaces are worn, but I don't have published dimensions for these. I could put the shafts and bushing back in the axle assembly, then install the spindles and see how much axial play there is, and that would tell me if the thrust surfaces are worn.

[Matt Wilson]

Well, as it turns out, I was able to clean up the corrosion on the inner axle shafts. I am fortunate enough to have an Atlas lathe, so I put each shaft in it, and polished for a bit until the rust was gone. Under magnification, one shaft has a very slight amount of pitting, so slight, in fact, that it's hard to see, even when magnified. I may work on that just a bit more, but otherwise, they look great. I was lucky enough to find that the new neoprene seals seem to contact the shafts in a different place compared to the original leather seals. The original location is where most of the rust had formed.

I took multiple diameter measurements and found the inner shafts to be at the lower end of the new part tolerance range, for the most part, with one spot being just a tick below that. These measurements didn't change measurably as a result of polishing. So I think I'll use them, and not replace or repair them. The outer shafts are quite a bit more worn, being right at, or slightly below, the wear limit shown in the M37 manual, although they are very smooth. Since these do not directly contact the seals and are separated from them by the tracta joint, I'm fairly confident they won't impact the seal durability., so I plan just to use them.

Three bushings are within new part limits, while the fourth showed a taper on the inner diameter, which I think was there from manufacture, since there was no sign of wear. so I'm replacing it. Considering that I won't be running the truck in four wheel drive very much (hardly ever, to be honest), I think this will work ok. I have locking hubs, so I will be able to keep the front drive train disengaged nearly all the time. If I decide to make the occasional offroad jaunt, then I'm willing to accept the risk that the looseness of the joints will compromise the seals.