Vibration Source - Tires or ???

I've had a very high frequency vibration in Lulu for a while now. Start to notice it at about 50mph. I always assumed it was the rear driveshaft out of balance, but wasn't 100% sure.

On Saturday, I replaced my transmission mount and t-case mount, hoping this might solve a little of this vibration and a few other things. When I got it all finished up, I took her out to the highway to see if anything changed.

It was a little smoother at 50mph, but it was definitely still there. I decided to see if I could "push past" the vibration at a higher speed. So, we eased on up to about 60, and the vibration started to decline. By 65 mph, it was gone. I went on up to 70 to see if it was just a fluke, but no vibration - just smooth and comfortable. 70 was about as fast as I wanted to go, so I backed off. Sure enough, as I came back through that 50-60mph range, the vibration was there again.

Would this be the tires, since it's not a constant vibration, or could it still be the driveshaft? I'm sorta puzzled now... :?

 

Sounds like it could be the tires. Not sure if it would cause a vibration but you might want to make sure the DS is in phase (where the yokes are lined up the same)

 

x2

 

Tim, I think DS. I have the same issue with my 38. 33s, no lift and a T-98 thats been lowered about 3/4". Only shows up about 58mph and is fairly constant after that. Can you feel it in the shifters? If so, then I would definately suspect driveline...

 

Had this problem on my Chevelle and it was tires. Might try and rotate as Sparky said as troubleshooting? Definately would not discount what Patrick says though. More in the steering wheel or just general vibration?

 

Do any of the shifters vibrate?

 

More just general vibration. I can feel it through the seat, and I notice it alot in the mirror. It'll vibrate so fast that everything behind you gets blurry. Not much coming through the steering wheel.

Since it won't cost anything, I'll rotate the tires and see if that helps anything.

I've just read some stuff lately (it might have even been on here) about how inaccurate the normal balancing proceedure is for tires, especially for bigger mud terrain tires. I asked the shop to only put the weights on the inside, so that added to my suspicion.

 

Bringing this back up, as I think I might have discovered the problem.

I pulled the rear driveshaft, since I'm replacing the clutch right now. I noticed that the u-joints are slightly out of phase. I tried rotating one end, but even if I move the splines by one tooth, the ends are even further out of alighnment.

In the pictures below - the first shows that one end doesn't sit flush on the table, when the other end is sitting flush. The second shows the other end, and the third is an overall shot so you can get an idea of the perspective.

I have three questions:

1. Are both u-joint suppose to be exactly in-phase, or is there a slight "margin of error" with driveshafts?

2. If this is a normal "margin of error", can that be corrected for by balancing the unit (there are currently no weights on the DS, leading me to believe that it has never been balanced)?

3. Do you think this slight difference in the two ends would even cause vibrations?

 

Twisted driveline. It's out of phase. Need new drivline.

 

1> yes
2> maybe
3> maybe
if it were me, I would go have it checked to see if it is twisted/bent
even if it's not, i think I would have the yokes centered and the shaft balanced
ymmv

 

You might be able to take it to the DS shop and see what they say. I would say that it needs to be dead on, but that is a very minimal twist. They may be able to counter act it with some weights. If you have a fleetpride nearby they have always done good work for me.

 

Twisted, but to prove it to yourself you might try this: Puts some nuts and washers on your output yoke to hold the brake drum on, then drive around some using the front axle. Found that my rear shaft caused all sort of vibrations that went away when it wasn't there.

 

Thanks guys. Looks like I'll be in the market for a driveshaft now...

 

Call Tom Woods Tim.
You wont be sorry when you see his product.

 

Just when I see the price tag, right?!!!

I think I'll just get a used shaft from the junkyard or from a member, add my new ujoints, and have it balanced the DS shop. Probably cost me a total of $50. As opposed to $150 for a new custom DS local, or even more from Tom Woods.

Remember - Lulu is going to be sold pretty soon. No need dropping more $$ than necessary at this point.

Thanks for the advise guys!