For those of you who like to be creative, you might find it interesting
that I shortened my driveshaft without the use of a special shop or
fancy tools. Here's what I did.
First I figured out how much I'd need to remove from the driveshaft. A
little over an inch. I took a standard piece of paper, wrapped it
around the shaft, and drew a cut line around the shaft. I positioned
this line about an inch away from the u-joint yoke weld. I figured that
I'd re-insert the yoke into the shortened shaft, and doing it this way
would be a whole lot easier then trying to cut out of the center of the
shaft.
Taking my trusty 4.5" angle grinder I started cutting on the line while
rotating the driveshaft. I did it somewhat cautiously because I wasn't
sure what I'd run into, not knowing how long the u-joint flange went up
into the shaft. What I found was that the shaft is made of thin steel,
and in about a minute I'd cut completely through the shaft.
I looked at the yoke end to see how long it was. I'd hoped it was a
long taper, making alignment easier when I put it all back together
again. Instead, I found it to only be about a half inch long, with a
good bit of taper. Hmm, not going to be as easy as I'd hoped for when I
put it back together. So be it.
At this point I remembered that I had *not* marked the shaft and yoke
prior to cutting it. Blast! Stare at it, fit it back together, cuss
how smoothly I'd made the cut, and guess. It would have been better to
know, but guessing worked out fine in the end.
I carefully cut the little piece of driveshaft pipe remaining on the
yoke. I did this by cutting the weld itself. Again, the 4.5" angle
grinder in one hand, the yoke in the other, cut gently while spinning
the yoke. Worked just fine. Interesting how much of the weld failed to
penetrate the yoke at all. Only about half the weld actually joined the
hollow tube to the u-joint yoke.
Reassembly time!
Put the yoke into the driveshaft, stand it up on the floor, whack the
yoke with a hammer, driving it into the tube, jamming it a bit to hold
it in place.
Now comes alignment of the u-joint yoke in the shaft. I laid the shaft
on some scrap steel pieces and would then rotate the shaft and measure
the clearance between the yoke flanges and the work surface. I could
have used fancy calipers and such, but instead, I used wrenches and
sockets. As in find a wrench that would just fit under the flange,
rotate the driveshaft and see if the same wrench would fit on the other
side. Take the trusty hammer and whack the yoke until it aligned. For
measuring alignment across the yoke, I set a 1/2" extension in it, and
measured clearances to it. Whack as necessary. Took only a few minutes
to get the yoke aligned quite closely on the four points.
Now, while I was undoubtedly off by a few thousand, that was all I was
off by. So too probably was the original driveshaft. I figured I could
compensate for it with balancing weight, as they did in the original
manufacturing of the shaft. More on that later.
Weld the yoke in place. I could have used a MIG, but I liked the idea
of torch welding a thin walled tube to a very solid block of steel. The
challenge appealed to me. MIG welding it would have been a cake walk,
but torch work here would require some serious finessing to prevent
burning the tubing off while actually penetrating the solid yoke mass.
Took quite a bit of gas, but it was done, and done well.
All right, the driveshaft is now complete and a little more then an inch
shorter! Put in the u-joint and attach it to the car. It fits, and I
feel so successful.
I'd figured on doing a final balancing with hose clamps, if needed.
Since the shaft was cut at the end, there would be very little risk of
having the shaft off center and out of round. What off centering I
could have would be at the yoke end, and could be compensated for with
just a little bit of mass. Hence, the hose clamp(s). I was also
gambling that it would not need any balance work, since the shaft had
very little in the way of weights welded onto it, and because the Locost
Super 7 building book discusses doing driveshafts the way I describe,
and says very little problem with balance has been encountered.
So it's test drive time. For various other reasons, I didn't just go
out on the road, but had the car up on stands. So I ran it that way.
With the wheels and hubs off the car, there is no vibration! Success!
Redline the engine in 4th gear overdrive, and there is still no
vibration, and the new boot on the front cv joint is holding (whew!).
Throughout the entire rpm range of the driveshaft, there is no
vibration, so no balancing of the shaft was required. Yippee! Double
Yippee!!
On the road, there is a touch of vibration, but that's almost assuredly
the wheels, which have never been balanced by me in the years I've owned
them. Some hard clutch dumps and such to make sure the weld will hold,
and it does. I'd figured it would, because of the way the stresses are
applied to it, but it's nice to see the evidence.
So there it is, cut your own driveshaft, and save about a hundred bucks,
as well as having fun doing it. By all means, have a shop do it if it's
beyond you. But if you're just a bit resourceful, it can easily be
done. You're welcome to inspect it if you'd like at Carlisle this year.
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