Shorten Your Driveshaft:

Here is a pictorial on how to shorten your driveshaft. You may need to shorten your driveshaft because of a tranny change, rear end change or in my case, because I had no driveshaft at all for the '65 Mustang I am working on. This may be one of those projects people shy away from because they think that there are special procedures, tools or black magic involved. I am here to tell you that I have shortened dozens of driveshafts this very way, and very very few have needed to be balanced.

The car I am working on had no driveshaft at all, so I went to the driveshaft vault and found a suitable core. In this case it was a Ford driveshaft out of an un-known vehicle, but it was a 3" O.D. shaft that had 3 1/4 yokes that would accept 1 1/16" U-joint cups, which is what I would be using. I inspected it for dents and rust or any other damage and deemed it suitable for shortening.

The first step is to measure for the new driveshaft. The procedure I use is to push the slip yoke all the way into the tranny, and pull it out 1 1/4":



With the weight of the vehicle on the springs, I measure from the flat of the rear end yoke:



.......to the center of the front U-joint. In this case the measurement was 51 1/2":



We now need to cut one of the yokes off. I try to cut opposite of the balance weights if I can. I grab my 4 1/2" angle grinder with a thin cut off wheel and cut the edge of the weld towards the center of the shaft. You need to cut only as deep as the tubing is thick so in our case, slightly more that 1/16". It is better to cut a smaller amount than needed than to go too deep:




With the cutting done, the yoke should come right out with a couple of taps of the hammer. If it does not come out, you need to cut a little deeper:



This is the yoke after is is out of the shaft:



We now need to shorten the tube. The shaft I was cutting was 56 " center to center, so 4 1/2" would need to be cut off. I use a thin wall tubing cutter because it cuts perfectly straight. You could use a cut off saw, but make sure that the cut is perfectly square:



Here is the tube after the cut and after de-burring with a file:



The yoke can now be tapped in to the tube and the center to center measurement adjusted. I like to leave about 3 /32" of a gap for welding into. I also place both flats of the end yoke on a flat surface to make sure that they are both in the same plane. You can adjust the yoke wherever you want it with a couple of hammer taps:



The front U-joint and yoke can now be installed, as well as the back U-joint. The driveshaft can now be bolted into the vehicle. At this point you might be thinking,"He forgot to weld the yoke on." I didn't forget, I do this so I can check the run out with a dial indicator. I mount a dial indicator on the rear end, and set it against the drive shaft tube to measure the run out. You can now adjust the run out with a few well placed hammer taps. I try to achieve the smallest amount of run out possible, in this case about .004" which is pretty good. With the driveshaft still bolted in the car, I tack weld it in four places:




The driveshaft can now be removed from the car in order to be welded. I would strongly suggest that you have at least a 185 amp MIG welder for the next step. If you are not comfortable with your welding skills, take it to someone who is qualified to weld it:





A little paint, and we now have a finished driveshaft. As I said before, I have shortened dozens of driveshafts just like I describe, and only a few have needed to be balanced, but even if you need one to be balanced, you have saved a considerable amount of money shortening it yourself:

 

Great tech article and pictures

 

Nice tech!! Very detailed and the pics help alot..

 

Nice tech...thanks!

Of course my first drive shaft was too short, so this wouldn't quite get me off the hook. hehe

 

Great tech , Drive Em !
I really like the pics with the step by step process . Looks like just about anyone can shorten a drive shaft with the post you did . I do agree with you on the welding ! If someone can do all the work and just tack weld it , then they can have someone else to the welding .
Thanks again for the tech Tip ! I will be using this one for sure !

RetroJim

 

very informative. Thanks for posting all the great pictures and descriptions

 

Nice tech, drive 'em! I've done it the same way a several times now. I like to check the runout on a pair of v blocks on the bench too. I've noticed on occasion that sometimes the runout has increased slightly after welding the end back on. You can heat a small spot cherry red on the opposite side of the tube and quench it to shrink that side a few thousandths and bring your runout back in check.

 

Good posting, Great info. I usually do stuff twice.

 

Yep been doing that for years. works great. nice writeup.

 

I did mine like this as well. But before i cut the weld bead to release the yoke, I scribed a line into the drive tube and across the yoke. This allowed me to install the yoke in the exact position it was from the factory.....as a reminder not to screw up the phasing.

Great thread!

 

Wow ...I thought you needed a lathe, great info.

 

Thanks great write up and really apppreciate the pictures

 

Great tech it looks fairly simple to do too.

 

Great tech. Once you do one you'll never take them to a shop again.

 

I too, have shortened many driveshafts by this method and they were all vibration free. If the tubing is ON-CENTER with the true centerline of the cross&roller joint, there will be no vibration. Many factory assembly line D-shafts are not on-center and therefore require the addition of balance weights. I have had to "correct" a few so-called professionally lathe-built D-shafts because of severe off-centered positioning.
As noted by Drive Em, shorten the rear portion of the shaft.
NEVER splice two driveshafts together in the middle.
Oh, BTW those dented driveshafts make excellent exhaust tubing straight pipes or header collector extensions.

 

This is way cool.
It never occurred to me the yoke slipped into the tube...It's like Duh! Why wouldn't it?

 

Thanks for your time doing this,you did a very good job on writing,pics and shop skill,s..2 thumbs up....................YG

 

Personally, I prefer to scribe 3 lines onto the driveshaft the entire length of what needs to be cut off...this way I can perfectly line up the yoke to the stock orientation better than with one scribed line (because 1 scribed line might wander a bit over 6+ inches, so with 3 you can center the lines easier)...

Great tech post though, the pics are fantastic...and I also agree on the welding and runout tips...good job buddy...

 

Great tech post, thanks.

 

Thanks for taking the time to post this tech article, this will go in my tech archive.

 

your threads rule, thanks so much

 

Great post. I like the way you went through it soup to nuts and provided good pictures of each step. I also always thought you needed a lathe.

 

Great tech. Just wanted to add some observations after doing hundreds of shafts. Be careful of some of the GM driveshafts, specifically the one with plastic holding the u-joint in. The ends were not machined at the factory but forged with a slight taper. They are pressed in and then welded. They can be done this way, but take your time, they are a pain. I do not know the specific years of these shafts, but it seems that majority of the GM shafts I get are like this. Hope it helps.

 

So, I have been doing it right.... no really I've always done my own drive shafts...take your time and it'll be just fine.

 

Excellent tech, thank you! that was always a dark art to me.

 

Did you ever hear of putting styrofoam or expanding foam inside the drive shaft ?

Had a driveshaft guy tell me he does it all the time to eliminate harmonics and whip ?

Maybe he was just pulling my leg ?

 

thank man...that helps alot..now I think I can try this myself.

tok

 

I have grasp the idea and I would like to try this the only thing I dont seem to understand is what your calling " measure the run out" let me know what this measures

 

Great tech post. This is one thing I've never tried, but it will happen sooner or later. I just remembered when I was building my first car way back at age 16. I had to have the driveshaft shortened, and a friend told me his Dad could do it. He just cut it in the middle with a chop saw, then cut one side to make the right length, and welded it back together poorly. You could see how crooked it was without even spinning it! I think that driveshaft might still be leaning in the corner in my Dad's garage.

 

The weld yoke presses into the tube with a slight press fit. ( you can install it and remove it with a few light hammer taps) When you tap it into the tube, it may not go in perfectly straight and may be cocked slightly which will not let the tube rotate as true as it can be. Measuring the runout or wobble with the dial indicator will let you "tap" the yoke to where it needs to be with as little runout as possible.