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

So basically there is really no fix too the drive line problem without creating another problem.
I think I will just save my money and stick with a few vibs and the stock shaft.

 

Yes, that's correct. Which is why I think that if you have a double cardan just after the carrier bearing it will smooth things out.

Don't get all negative Nancy on us. Each situation is a bit unique and you just have to science the fuck out of it. I'm learning along the way.

 

Isn't that what @1MK did and fail on him?
Or did I miss something along the way?

 

He did but broke it because his builder used a smaller diameter spline shaft. Otherwise it seems as though the results were more than satisfactory.

 

Whew.....okay.
good to hear.

 

I'm sure the driveshaft I had made would be fine on a street truck or very mild offroader.

PS, it's for sale!

 

4:56 gears and zero vibes 0-100 mph ( with corrected speedo btw ) the gears don't matter at all only rpm's of the shaft matter and you should have zero issues until you are near redline anyway. Your drive line shop should have a cross reference chart that shows exactly what diameter & wall thickness is needed to support what length of shaft at specific rpm's.

It can really only be two things :

1. They did not use sufficient wall thickness to prevent " drive shaft death wobble ".

2. It is not balanced properly and you are picking up harmonic vibes at certain rpm's.

Tons of people are using 1 piece double cardon shafts with zero vibes, you need to keep digging to find the real problem. Did you get the shaft from Tom Woods ?

 

Actually, I just measured....3.5" diameter. So yeah, I guess that may be an issue there. And your statement, "gears don't matter" is incorrect. The differential gears determine how fast the drive shaft has to spin to allow the vehicle to achieve a certain speed. This is why i was fine on 3.73 stock gearing but the 4.56 gears forced the shaft to spin much much quicker.

But I think you're right, the 3.5" diameter definitely isn't helping and it may even be out of balance. The vibrations don't appear to be harmonic because they got increasingly worse. Either way, the one I have is going back and I'll be pursuing a modified two piece shaft locally. I plan to see if the shop local to me can modify mine without using a smaller diameter input spline. If they can, I'll do it. If not, I may bug @1MK to try out the one he had made.

 

Couldn't you send it back to Tom and have him make it thicker?

 

Maybe. But that may or may not solve the issue. And I'm wondering why that wasn't mentioned when i was on the phone with them last week. I need to call and find out. In any event, I believe a two piece drive shaft with double cardan and carrier bearing support in the middle is the BEST solution if done right. You will have the ability to spin the shaft faster with the support yet still have compliance for the pinion angle fluctuations. PLUS, you get back a little ground clearance. Maybe not enough to make a huge difference but every bit counts. I'll be making some calls in the morning.

 

you misinterpreted my statement...or my shitty explanation - i tried to specify it is the RPM's of the driveshaft itself not the rpm's of your motor. ..the only variable is at what motor rpm's you hit what driveline rpm's...make sense ? the only difference gears make is at what engine rpm you hit what drive shaft rpm. Either way with a properly spec'd driveshaft you will have zero issues.

 

My driveshaft comes in tomorrow. If it doesn't work I'll toss a few more hundred at it and give aluminum a shot.

 

Here's my dumbshit question of the night. Why would you Regear? Crawl rig build?

 

For sale

 

My first driveline I lengthend was bigger in diameter but smaller in wall thickness. Which I didn't realize until I twisted it almost 45 degrees on the Rubicon a couple of years ago. Didn't break though... it was an interesting drive home. (I also broke a main leaf in the front too!) I carry a spacer and a stock length driveline now and a front leaf pack.

My new driveline is much thicker still using the stock yokes though so hopefully the u-joints are the week point and Ill just have spares.

This is on my '85 pickup

 

How much lift did you have? I might be interested...

 

Pros/cons of this as opposed to a single shaft?

 

Great info! I have some vibs from 30 to 35 mph. I will look into this refinement. Thank you.

 

So why isn't this offered on 2wd or pre-runner's? I skimmed the whole thread and couldn't find the answer