Single (and Two) Piece Driveshaft = Vibes....BE GONE!!!

Jesus. Took you two hours? This is at most a 30 minute job. Lol, great job and good to see you are happy. Hopefully it is still working out trouble free for you.

 

Don't know if you've gotten a reply to this yet because I haven't looked, but your issue is that you are not aligning up your center bearing to the correct angle to do away with the vibes. None of this would be an issue if you would do that.

 

Trust me, I've been there, tried it a million different ways. I had an original CB with a drop kit. Didn't work. I tried a new CB. Didn't work. Tried the new CB with 4 different length spacers that I machined out of solid aluminum bar. Didn't work. All I was able to accomplish was having the vibes move throughout the speed range.

 

So is the diameter of the shaft best to be 4inchs and not 3.5? Or does the wall thickness of the tube provide the same effect. Does the 4 inch use bigger parts or is the metal tube really another half inch thicker

 

Like I said, OCD. 2 hours from opening box, setting up jack stands getting tools out, drinking beer, etc. From loosening first bolt on oem DS to tightening last one on new DS was probably 45 min. I just took my time. It could definitely be done quicker. And yes, so far so good. Zero issues.

 

4" is vastly superior from what I know. Thicker wall may help some too but I believe most of the benefit is from the diameter.

I'm with you. When doing something for the first time I really take it slow; even if it's easy. Half the time I spend down there is looking at other crap under the truck and making sure it's proper.

 

Check out the attached link...

http://pstds.com/critical-speed-chart/

 

My next step of advice would be to take it to a driveshaft shop locally and see if they can determine if the angles are spot on or not. Something is causing it to be this way, and if you can rule out the DS as one of the culprits then maybe you can get to isolating where it is originating from.

Where did you get those spacers from btw?

 

TW driveshaft came in last night. Took me about 15 min. to switch it out on the ground. Driveline vibrations are gone. I'll be happy until it's time for 4.56s, then it's back to the drawing board.

 

Hell yeah! Glad it did it for you! If my solution works then I'll let you know what the next step is when you go to 4.56 gears!

 

I made them out of solid aluminum bar. Chopped them to length and then used a drill press my friend had in his shop. I made two different lengths. Solid aluminum is probably overkill but if I was going to do it I was going to do it right.

 

When you pick this modified shaft up, can you please get the part number for the companion flange they used to mount on the original midship stub shaft? I've spent the better part of 10 hours searching through Spicer catalogs looking for a companion flange for a 1.181x26 spline form and my local shop nor myself can find one. I'm getting a DC joint installed just like you are, but I'm being told that they're going to need to change the midship stub shaft, which I was hoping to avoid due to additional cost and complexity of the situation. I'm also leery of going down in joint strength to 1310 from the 1330 that the rest of the shaft utilizes so I'm having a 1330 DC joint installed.

Hate the single piece didn't work out after the regear. It was honestly a surprise to me that it worked from the beginning.

 

If he has the correct drive shaft 4:56 gears will not make a shits difference...didn't we cover this already kids ?

 

If you have the correct 4" OD shaft you better cut that cross member out before the driveshaft makes sweet sweet prison style love to it...

 

Yes, this..
This is exactly what I've been talking about. Math, science, geometry, measure twice, cut once etc

 

Can it be unbolted? I would want my fab guy to make a replacement that clears the shaft. I'm happy with the very minor vibes I have now, just looking down the road cause it will get worse...

 

Anyone done the single shaft with the 6speed auto? They are 4.10 gears not 3.73 so I assume there vibration level would start before the 3.73 auto

 

Exactly what I went through. They ended up making one with a 23 spline midship hub and it sheered in half. I contacted at least a dozen driveline shops and no-one has anything 26 spline.

 

Agreed with you both. I'm VERY curious to see what this guy comes up with tomorrow and I'll be sure to let you know what he uses if he does it right. I too am scratching my head but the very last thing I said to him on the phone was, "Now I want to make sure, you're not compromising strength on this right? Same diameter stub shaft and everything? I'll be using this primarily offroad so I need it to be just as strong". He said yep, won't be an issue. So yeah, I guess tomorrow we will see what he heck this guy comes up with I guess.

 

So I've actually done the math....but it doesn't sound like you have. Maybe I've done it wrong so would you care to check my work?

Last time I checked, the critical speed for a Style A steel shaft, 4" in diameter, that is 68" long...is 2839RPM. MAX operating speed is 3191RPM. I calculated those values on Dana's website. http://www2.dana.com/expert/wc.dll?hvtss~decrits~series

Now, the next part I cheated a bit to figure out the shaft speed at a given ground speed. I used an engine RPM calculator in reverse. Stuck in tire size (33.25"), differential gearing (4.56), and then used 1 as the final transmission ratio. Using 1 as the final drive ratio would mean the engine would spin at the same speed as the drive shaft; right? When you plug those numbers in, if you want to go 80mph the drive shaft would need to spin 3686RPM to achieve that speed. Nearly 500RPM faster than its safe operating range. And that's with a fairly large tire size. If the tires are smaller, the shaft would need to spin even faster. Here's the calculator I used (bottom of the page).
http://www.csgnetwork.com/multirpmcalc.html

So tell me again how a 4.56 gears won't "make a shits difference" because my math doesn't work the same as yours apparently. Either that or I've totally botched something up which is 100% possible.