RR Axle keyway regrind

Red Mark

Red Mark

Junior Member
Hi, All
Sometime ago I recall hearing of someone toying with the idea of regrinding or EDM'ing a new keyway on the taper opposite a stressed or damaged RR axle keyway. Is anyone aware if this was tried and if so, was it successful? Who is doing it and how much does it run?
I know, don't be so cheap & just buy a new axle. But, seems like you would replace both while you were at it to the tune of around $600 for the axles plus everything else and alot of work. This alternative has the potential to be done economically without complete dissassembly of an otherwise well functioning rear end. Thanks as usual for the feedback.
 
You would either have to mill a stepped key. Lets say....1/4" on the one side, for the brake drum, by 5/16" for the keyway in the axle. By the time you cost out for the maching of the axle and milling of the keyway in the axle, you are well on the way of paying for a new axle. A person would still have to justify to tooling cost for a portable mill.
 
There can be a problem with fixing only one half of the keyways, like fixing the axle keyway and not the hub keyway. If there has been slop in the bad keyway for a time then the key itself has been rocking slightly and wearing on the good keyway. So you really have to look at both of them, possibly enlarging both to 5/16" so you get a good key to keyway fit.
This would be a better alternative than fixing one side only and then making a step key to fit.
 
Let me see if I understand this, you can enlarge the keyway in the axle toa ccept a larger key? Then would you have to enlarge the hub keyway as well?

Thanks,

Mike
 
They should both be the same.

The only drawback would be possible weakening of the axle by taking out 1/16" inch more.
Maybe an engineer-machinist could weigh in on this with more advice?
 
Timothy Kelly said:
Enlarge the axle to accept a larger key. Then create a custom key that is stepped; larger for the axle and standard for the hub.
Click to expand...

McMaster Carr has oversized and or stepped key stock, I haven't researched the exact sizes but I have filed and fitted keys and keyways with success. I haven't done this on really worn our keyways. I wouldn't be afraid to do one that was out 1/16". I do have a milling machine to size new keys. BUT after fitting the key I would torque to min 175 Ft. lbs. I always use new axle nuts. One my modified I tighten to 200 ft lbs min. Most keyway damage is caused by axle nuts loosening. This is one thing that should be checked periodically
 
Since the tapered axle holds the hub on by friction of the tapered hub and axle and not really the key, I would think a recut would work fine.
 
Assuming the taper surface is still reasonably good,
just mill a new keyway opposite the old one. Takes about 20 minutes.
THEN, LAP THE TAPER TO THE HUB. Very important!!
If you can get at least 80% surface it should last for years.
 
A morse 9 to1 taper is designed to be a self locking taper. The key is only there as a failsafe. It is not supposed to handle the load. These tapers are pretty much standard on propeller shafts for boats. Any marine mechanic worth his salt will always lap the propeller on to the shaft taper. If you were to paint a blue trace on to the taper then install the prop, or in your case the hub assembly you would probably be amazed at how little actual contact there is between the two surfaces. Lapping the two together with valve grinding compound and applying the proper torque, will almost enable you to throw away the key. I think two keyways might weaken the taper. I think the Mcmaster Carr step keyway is the hot lick. As to machine work You will probably have to disassemble the rear, or find a real good friend machinist to chuck up your whole rear in his machine of choice. What about fitting the oversize step key to your wallowed out keyway, a little grinder work, a little file work, I'll bet thats how it was done down on the farm in the good old days. Hope it all works out Rich
 
You can probably fix it with a ball peen hammer right on the car.
The keystock gradually "moves" the metal (of the axle) over a slight bit and folds it away till the slot appears worn except usually all the metal is still intact...just shifted over abit.
(This won't work if there's a chunk missing)
If no metal is missing, simply support the underside with a heavy hand dolly and tap-tap-tap with a small hammer to move the folded metal back where it came from. I did this with 2 axles, first try...easy as pie... and I fit the keystock nice and tight without picking up a file.
It's easier than you think.
 
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