8 hours ago in Project Cars
Preparing our Miata for a theme.
been working on the '11 Challenge car and I need to shorten the half shafts.
My thoughts are, since a RWD driveshaft is a hollow tube with the joint ends welded on, would it be okay to cut and weld a hollow half shaft at the spline end?
They appear to be welded from the OEM, so I'm thinking why can't I do the same thing.
Short answer: no.
Unless you can just shorten it by grinding a bit off the existing splines, no, they'll break right along the heat-affected zone of the weld. Unless of course you're running big axles with little power, but I assumed otherwise :)
The "big" hot rod axle guys will cut and spline shafts for you for a fair price. I have used a couple from Strange and was not unhappy.
Pictures would help, but I think if you HAD to shorten an axle shaft, I'd do it in the middle. Taper both sides so they're pointy (think crayon point, not spear point) then butt them together and slowly build up your weld material on both sides. After they've been built up to the original shaft diameter, grind/machine off the extra and put a sleeve over the joint, then weld the ends of the sleeve. This sort of welding is pretty tricky; I used to know a few guys in Detroit that were good enough to do repairs like this in the plant, but the parts still failed sometimes.
A better option might be to cut to length and have a machine shop re-roll the splines in place, but it would still need to be heat treated to toughen up the splines I think.
Of course your best option (budget and time notwithstanding) is a shaft of the proper length.
I'd do it near the inner CV joint, a few inches outboard. Cut the axle tube, shorten the outer part.
I'd chuck each half in the lathe - 3 jaw chuck is accurate enough - and clean up the interior bore a little. Face the end to a 45 degree bevel.
Again, in the lathe, make a tubular internal couple that's a light interference fit in the axle half interior bores you just cleaned up.
Heat an axle half - MAPP gas is plenty - and drive the coupler halfway in - let it cool and repeat w/ the other half.
Now - drill a few holes - perhaps 5/16" through the axle halves and a little bit into the coupler. Plug weld these. Run a good, deep bead around the V-groove.
Just a serving suggestion. Let us know how you end up doing it and how it works out.
If you have a lathe, get a live center for one end, butt the pieces together, then weld it like that, rotating the assembly by hand. ie the lathe acts as a fixture to hold everything in alignment.
Didn't Bryce do this on the Fiero? Only I believe he shortend his by taking apart the CV joint itself and mixing and matching parts from different axles to get the length and spline count needed. No welding needed.
In reply to motomoron: A friend did some the exact same way on a FWD Corvair engine special ice racer.
They way I did it: Chuck each half in a lathe, drill & tapa fine 1/2" thread in each with a generous chamfer on the end. Put a 1/2 -20 stud in one, loctite, screw the other half in.
Now you have two pieces threaded together with a big "V" in the center. TIG the V full.
mock up is just started so I'm not really sure if there isn't a usable shaft from something else, it will definately need to be shortened though.
Where is Jensenman.. He did this on his abomination. The process was pretty close to what Dan describes. IIRC it worked well for the autox but failed on the sticky drag strip after a few launches.
Also get your instant access to the digital edition of Grassroots Motorsports Magazine!Learn More