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Tech Tips
Driveshaft repairs
Driveshaft
fun
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| TECH TIPS WITH BEN |
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| How to do driveshaft repairs at home |
Imagine this scenario, the night before the Big 4WD event and as usual (at least for me) you are making major changes to your rig's drive line and/or suspension, etc. You fire up the trusty Hi-lift jack to see just how much extra drop travel said changes have netted you, and "boirk" the slip yoke in your stock drive shaft separates and the slip spline falls in the dirt. What's a wheeler to do? Limit wheel travel?!! Unthinkable. Create a new drive shaft of the correct length to span the distance between the pumpkin and the t-case - entirely possible! Now before I start revealing the secrets of drive shaft tech, some caveats are in order. First, a possession of good to excellent welding skills is a definite must, cause when you think of it, you are making a part that will spin as fast, if not faster (overdrive) as the crankshaft of your engine. Having it come apart on the highway will surely create a racket if not a wreck. So if your welding skills are not top-notch, get a pro to do your shafts for you.
If you are still with me, the process for lengthening (or shortening) a shaft is not entirely too complicated providing the parts you need are readily available. If you are like me and your garage is piled to the rafters with 4x4 stuff, this should not pose a problem. If not, get out to the wreckers and buy up a few used shafts (get ones with the same tubing diameter as what you currently have). They can usually be purchased fairly cheaply, but always look to make sure the fixed end has been drilled for a center (this sometimes involves some major crud scrapping on a used shaft).
If the shaft doesn't have a center, leave it for somebody else and find one that does. The slip spline end pretty much always has a center drilled in the end of it. Also with a used shaft, check to make sure the tube isn't dented, bent, and doesn't have a spiral crease in it from somebody else's 4x4 adventure.
Hint: check out vehicles like Ford vans or Chevy station wagons for a good supply of lightly used tubing or sometimes a long wheelbase shaft can be swapped for a slightly longer shaft in a short wheel base vehicle. Also, one can swap Import to Domestic to connect stock parts.
With any project, it is nearly always easier to cut something shorter than it is to lengthen it. So sometimes, depending on the particular vehicle, a rear shaft can become a front with a new tube acquired for the rear, etc., (without getting too specific).
So now you're probably thinking "why don't I just pony up the dough to get it done by somebody else and leave it at that?" Because I am a cheap bastard, that's why.
So here is how to do it. You will need:
- dead blow hammer/soft faced
- Mig welder (over 90 amps)
- dial indicator and mag base (get a decent one)
- hacksaw or mini-grinder (with cutting disc)
- cutting torch or a propane torch (with mapp gas)
- file (half round single cut is best)
- bucket of water and a rag
- various hand tools
- some sort of jig
to put the staff between centers, for example a wood lathe, a length of tubing welded up into your own personal drive shaft jig.
The length of the jig is determined by the maximum shaft you want to build. So the next task is to measure the current shaft and cycle the suspension through its total range of travel to determine how much longer or shorter the shaft has to be. I always measure the shaft from weld to weld and then check the total travel of the slip yoke on the slip spline to try to center the travel range on the spines to ensure the shaft doesn't bottom or overextend.
So no we know the length of the shaft we want to build. Now all we need to do is separate the parts we are going to keep off our old shaft and add the parts from the new shaft to get what we want. The easiest and best way to cut the new tube to length is with a properly checked and squared up chop saw, but if it is simply too darned late at night to fire up that baby, a hose clamp and a hacksaw will do (use a 32 tooth blade and use the hose clamp tightened around the tube to ensure a square cut). De-burr with the half round file in and out.
Now we are faced with having to remove welds from one or both ends of the shaft parts. When you cut the old tube off rememaer that the slip spline and fixed yoke only extend into the tube 3/4 - 1" (19 - 25mm for you import folks). Cut it off about 1.25" from the center of the weld to give you some tube to play with. The absolute best way to remove the welds from drive shaft parts is with a metal lathe but if you are lathe impaired, a file or mini-grinder will do, just be extremely careful to cut only through the tube and not into the slip spline or fixed yoke. Also make sure that all old paint, grease, and crud are removed from the parts to ensure a sound weld with good penetration.
Now that you have clean parts, a tube of the correct length (less 1/8" for welding purposes) the welding jig and assorted other stuff, you must check to see if the u-joints are in phase. This is very important as some pretty serious vibration can occur if it is not taken care of properly. If you have a good flat metal workbench or even the tube of the welding jig,
assemble the parts with a rubber mallet or a chunk of wood and a regular hammer and check to see that the "ears" of the fixed yoke and the slip yoke are exactly in line. By placing the staff on the flat surface and giving it a good "eye balling" mark on the slip yoke and spline where they fit together. When you go to weld the shaft after phasing, make sure that there is a gap between the shoulder of the former welded area and the tube of approximately 1/16" to allow for welding penetration and pre-welding alignment.
Place the shaft in the jig
and using the dial indicator, true it to within .010 using a rubber mallet. With just one dial indicator and mag base you will have to move it back and forth quite a bit to get it true enough to weld. When truing a shaft before welding, always make sure that you get the tube down to bare metal with some sandpaper where you are dialing to ensure the needle on the dial indicator doesn't jump around too much. When it is true to .010" or better, T.I.R. (Total Indicator Reading) we are ready to weld.
Now comes the fun part.
We know that heat expands things. The relatively thin tubing of a drive shaft is no exception. It expands more than you might think, so take the time to loosen the adjustment of your jig before you start - not so much that your assembly will fall out, but enough that it can expand without binding up. Now with all the regular welding precautions in place (mask, gloves, etc.) you have to strike an arc with the Mig handle in one hand and rotate the drive shaft with the other hand until you have welded a nice uniform bead around the entire circumference with no minimal overlap (this is easier said that done - practice, practice, practice). If you are welding both ends of the drive shaft, it's time now to re-check the unwelded end for trueness and weld it as well.
Now that the welding is done, use a nice wet rag to cool off the tube and weld so we can determine a base point for truing the shaft. Truing a shaft is where the true artistry (pun intended) comes in. You may find that a shaft that was within .010 TIR before welding is no where near that after welding. Well don't lose hope yet because this is where that torch set or propane torch with mapp gas cylinder comes in. The basic idea is to heat an area of the tube to just red hot and cool it rapidly causing the tubing to shrink.
With the shaft in the jig rotate it until you find the part of the shaft near the weld with the highest indicator reading and mark it with a paint pen or chalk. Move the dial away and then take the torch and heat a small area near the weld about the size of a quarter to just red hot but not more. Now move the torch away and take a very wet rag and hold it on the heated area quenching it rapidly. Reinstall the dial indicator and rate your progress. You will have to move back and forth from one weld to another doing this a little at a time until proper trueness .007 is reached.
As I have said before, this entire process takes practice and as always it is best if you are unsure about anything, don't risk it - get it done by a pro.
Now a word about balancing. If the shaft is within .005" - .007" TIR it shouldn't need balancing.
If the shafts you make are for front use or spare rear use don't bother getting the shaft balanced. But if it is to be used in the rear for on road use, go spend the bucks to get it properly balanced. The bearings in your pinion and t-case output will thank you for it.
So, in closing, do try this at home but only if you feel your welding and patience is up to the task. And before you try this on a driveshaft that has to get you home, practice on some old junk to get the technique down.
That's it! Happy welding.
Ben Olson |
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