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Hagerty
Hagerty Employee

What it really takes to cut and weld a drive shaft | Redline Update

If you watched our last two updates, you saw Davin swap a T5 transmission into our 1946 Ford pickup. Part of that process was getting a new driveshaft to fit the new length of the T5. So, we thought we'd take you behind the scenes with Dan at Valley Truck and see what it takes to make a custom-fit drive shaft.
https://www.hagerty.com/media/videos/what-it-really-takes-to-cut-and-weld-a-drive-shaft/
4 REPLIES 4
GBRBill
New Driver

A couple of additional points/corrections to this otherwise good video.
First, the caps and yokes were welded on the original driveshaft not because the snap ring grooves were worn out as stated. They don't really wear out. It was because the yokes themselves were worn out. The u-joint caps are a very tight press fit into the yokes. This is because the u-joint caps should be stationary. If they start spinning, this is a bad thing. The needle roller bearings are supposed to be spinning between the trunnion on the u-joint and the cap. Not the cap in the yoke. Yes you can weld them as in this video but it is what I call a bush fix. You can inspect you existing driveshaft to see if this is happening by the shiny spot on the cap. As it rotates, it rubs on the snap ring polishing it up. If you see shiny spots on the cap on an older driveshaft that covered with surface rust, this is what is happening. Plan on repairing or replacing the shaft.
Second thing, the video skipped a step concerning the balancing. The initial straightening of the shaft in the video was correct. You press all of the parts together and then you use a dial indicator to reduce the runout to as close to zero as possible. Certainly less than .005". What the video didn't show is that after you weld the bits together, you again check the straightness. This is because the heat of the welding usually warps the shaft a bit so this second step is required. You straighten the shaft by selectively applying heat to various parts of the shaft. This is the art part of building driveshafts. Some driveshaft shops skip this step and compensate by hanging/welding big honking weights on the shaft to try and compensate for the shaft not being straight. Some perspective, if you have more than .025' runout, you cannot put enough weights on the shaft to balance it. If you have a shaft in which someone has double, triple and even quadrupled stacked weights on it, they didn't bother to straighten it enough to start with.
Third, measuring the driveshaft. First some terminology. What you are measuring is what is called the neutral measurement or similarly the 'flange to flange' measurement. You will sound like you know what you are talking about when you go see the driveshaft professional. Video emphasized that you needed to have the vehicle sitting on the floor with it's suspension at a neutral height. This is correct for certain types of suspensions - such as leaf sprung suspensions. This doesn't apply to swing arms suspensions - fixed length radius or trailing arms. In theory the driveshaft will not change length thru the entire length of the suspension travel with this type. It actually does a very small amount but this is from suspension bushing compression, not the function of the suspension movement. Which reminds me, when giving a shop your flange to flange/neutral measurement, it does not need to be to the fourth decimal point. Plus or minus an eighth of an inch is fine. Identical vehicles can sometimes vary by +/- 1/4 inch! This is one of the functions of the slip yoke. As I tell people these vehicles are not airplanes so tolerances can vary.
Related to F to F measurements, bear in mind that there are two kinds of ends on driveshafts/transmission and differentials. The video showed end yokes. You can also have flanges - pinion flanges on the diff and output flanges on the transmission or transfer case. You measure differently depending upon what you have. An end yoke, like in the video, you measure from the center of the u-joint to the center of the u-joint. This is usually called the neutral measurement. If you have yokes, you measure from the face of the flange to the face of the other flange - hence the term F to F measurement. Some applications have both so adjust your measuring appropriately.
Lastly before I write a book, driveshaft component quality can vary. In our shop we use only genuine American made Spicer and Neapco components. What I call generic offshore stuff is available and is cheaper so if you want a top quality shaft ask. It will cost more but it is a better shaft.
uweschmidt
Advanced Driver

A fine demonstation of Skill and Know How
deckerbilt
Intermediate Driver

I'm surprised he doesn't face the cut end of the tube in a lathe before pressing it together.
For the ultimate in yoke alignment, use the protractor-level on one end, lock rotation on that end, and then use the SAME protractor-level in the SAME orientation on the opposite end. Removes any inaccuracy of the measuring device from the procedure.
Also would be a lot better if the metal was prepped and primed before painting it. I've found that some premium car manufacturers (such as Mercedes) paint their suspension components before assembly and things look a lot better underneath the vehicle as the years pass. (sorry for being a critic)
hyperv6
Engineer

It takes the guy down the street that has the right tools to cut and balance it right. 

A man must know his limitations.