December 28, 2013

Shortening a Drive Shaft

The 40 Ford needed an inch and a half taken out of its drive shaft. Many people think stuff like this is the sole domain of professionals, but with a little planing - and some attention to detail - it can be done with your basic shop tools.

First thing I did was throw together a couple simple stands - making it easier to hold, turn and work on:   1) Cut 2 - 6" pieces of rod and 2 - 6" pieces of something to weld them to:

2) Round the edges and bend them evenly in the middle. 
I just put them in the vice and hit them with the 2lb sledge.

3) Weld them together....

Now that you have a place to set the DS on and work with, you'll want to MARK the location of the yoke arms. That is, draw a line along the tube to ensure you insert the yoke in the same position after it is cut and re-inserted.

With that done, double-check your measures. Go back under the car and be sure you measured from the correct place on the rear end pinion yoke to the transmission end. You will need to take into account how far the U-joint sits from the yoke and the rubber seal on the tranny.

I measured how much I needed to cut and marked it on the DS in several spots around the tube, then ran a line all the way around by holding the marker and turning the DS on the stands. You can also use a sheet of paper held square, or a larger hose clamp to mark an even line.

** You'll notice how I elected NOT to remove the U-joint. While removal is recommended, you can get away with not removing it  - if you protect it well. I used foil paper - folded 4 times and taped to the joint.

I then set up the chop saw and propped up the stands on 2x4's to get the tube even and square with the blade. You could use a cut-off wheel or a bandsaw to cut it, but you need to be careful. Cutting it square is the critical operation. Take your time and leave a little more rather than a little less - you can cut or file it down afterwards.

Be sure to make the first cut AWAY from the U-joint yoke, as it gets inserted into the tube portion and you want to retain that part:

With the chop saw, I also scored the old weld at the yoke base to ease the removal of the balance of the tube:

By scoring it at the old weld, then cutting the tube portion with a hacksaw, the unneeded piece came off the yoke easily. You may need to slowly cut, or score a little at a time, until the tube portion can be removed.

The next step is not shown in detail, but is critical. The end of the tube needs to be SQUARE. If you did a good job marking and cutting, it should be square, or close to it, but you need to triple check it. Either use a Combination-square as shown, or stand the tube up in it's cut end and use a steel square to check the end for square. File or grind a little if required to get it perfectly square (=/- 1/32nd should be good).

Once you are satisfied you have the end square, chamfer the outside edge and de-burr the inside edge. Finally, clean up the yoke end that will be re-inserted. Use a grinder to remove any weld that may be in the way and a gridner or course sandpaper to clean up the yoke insert. Take your time with this entire operation.

You can now re-insert the yoke into the tube. ou should need to hammer it gently to seat it. Don't seat it all the way home - you'll want 1/8th of an inch to ensure its square - and to seat your weld.

With the yoke inserted - and clocked as before - check square again. Tap one side or the other to get it right on.

Then, once you are satisfied it is "dead on", attach your ground clamp and put a spot weld on either side of the tube (opposite from each other). As shown, I used a set of panel vice grips for a place to clamp the ground. Later I changed to a magnet. With a tack on either side, you can re-check for square and still move it a little if required. Once satisfied, tack it on the other 2 sides, then weld it solid, in 1 inch runs, alternating sides, until it's welded all around. Lastly, Run a bead over top of that one all the way around.

If you've taken your time - and rechecked for square often, you should be VERY close to perfect. You can now either use it, keeping an ear and eye out for any odd vibrations, or you can take it to have it balanced. They will check it in a lathe-like machine and either tap it, or add weights, to get it balanced.

The DS was re-installed and checked for fit. Perfect!

After having done a few now, I am quite certain this one will be good for moving the car around. At some point though, it will get pulled for a high speed balance.

Cheers - and good luck!