I'm going to suggest you forget about the tap, ("die", actually, but that's picking nits). We've all done that at some point in our careers, and even if you could find the right die, which will be expensive, it's not going to clean up threads that it can't thread onto to begin with. You'll end up with it cross-threaded and it will wreck the threads even worse. Instead, what you want to find is a thread file. You'll find them at hardware stores, and possibly Sears and Harbor Freight Tools. They're about 1/2" square, about 10" long, and have four different tooth spacings on each end, so you get eight different files in one tool. One of them will have the teeth spaced right for your shaft. Start with the file resting on mostly good threads and cutting on just one or two bad ones. The good threads will hold the teeth in the proper position over the bad ones. Take a few strokes, then work your way out toward the end of the shaft. Once they all look okay in that area, rotate the shaft a little and continue around it like that. You'll be amazed at how nicely it will clean up those threads.
There is another type of tool that I've seen, but when I've needed it, they were nowhere to be found. Even the guys who drive the tool trucks around don't carry 'em. That's a die like you want but it's split into two pieces. That way you can place them over the shaft on a section of good threads, hold it together with a socket, then run it off over the bad threads. If you find one of those, then you'll have to get the right size and thread. You can make one of these too with another nut. You'll spend all day with a hacksaw because those nuts are hardened on the outside, but you'll end up with kind of the same thing. You can walk it off just like that tool, but these threads aren't designed for cutting or cleaning threads like the tool is. You may get only one or two uses out of it, but what more do you need? The other problem is if the nut walks over the damaged threads, it will usually just press them down rather than removing metal, and that can still leave it difficult to get a good nut to go on. Where this works is when the threads in the nut can push the threads on the shaft sideways to move them back to where they're supposed to be.
If you pursue this idea, thanks to the metal removed by the hacksaw, the nut will fit tighter on the shaft IF you can hold it together with a slightly smaller socket. That means you'll have to grind a little off the other sides of the nut so that smaller socket will fit onto it. Try to run the nut off with a hand ratchet first so you have some control over any sideways forces. Stick a screwdriver into one of the cooling slots in the middle of the brake rotor to hold the shaft from spinning. Most of the time this will clean up the threads. If you just can't get it to run all the way off, there's no harm in resorting to air tools since you have nothing else to lose.
As for the replacement nut, just head to any salvage yard. You're likely to find one laying inside a car that someone has already removed the half shaft or transmission from. The exception is if your vehicle uses a "torque-to-yield" nut, commonly called a "one-time-use" nut. On those the threads are expected to peel and stretch when it is torqued, and you're supposed to use a new nut every time. If you have that style, the new bearing would have come with a new nut or there would be a note to that effect in the box, or the parts store guy would have tried to sell you a new nut. You can still use old nuts for these other tricks, but install a new nut to finish the job.
One word of warning though, and this pertains to any car with this type of wheel bearing. Don't place any vehicle weight on that bearing unless the axle nut is torqued to specs. Doing so will instantly make it noisy and it will make a buzzing noise that sounds like an airplane engine. You'll want a click-type torque wrench because the value is pretty critical to the life of the bearing. I remember that most Chrysler products and some GM vehicles call for 180 foot pounds, but some GM vehicles specify as much as 240 foot pounds. You won't get accurate enough with a beam-type torque wrench, and there's no way anyone can guess how much to tighten those nuts without a torque wrench.
Also keep in mind there's going to be a lot of unused, exposed threads on the shaft after the nut is installed. If the threads are messed up just on the end of the shaft, you can just grind them down with a small angle grinder. That takes some experience, and probably a few swear words, but that is acceptable as long as there's enough threads left that the nut can be tightened to the proper torque value.
Thursday, September 18th, 2014 AT 9:28 PM