High frequency vibration chasing

[MarsChariot]

Starting to chase a buzz-like vibration, so I thought I would cast for suggestions. The vibration is high-frequency, and my guess is drive line. But the drive shaft is fairly new. Still has stickers on it. No looseness or slop at all. U-joints are seated properly, nothing obvious. The vibration starts cutting in around 40ish on smooth pavement. Almost feels like the buzz you get from some mud treads, but I am running ATs, also fairly new, so not hard or worn. Tight motor mounts and transmission mounts.
There is leak starting on the pinion seal. Any chance that something is going wonky on the pinion? Will a tired harmonic balancer with cracked rubber give a noticeable buzz-like vibration? C4 seems o.k., and was recently rebuilt. THis started in the last month or so and nothing has been done in the time immediately before it started, so it doesn't seem like anything I did. Just searching now. So looking for suggestions for chasing strategies.

 

[Broncobowsher]

Those can be had to chase. Few thoughts.
Centering ball in the CV? if you ever over angled the CV you may have bound/bent stuff in the CV. The U-joints will be good, the little ball in the middle.
Have you gone for a drive without the rear driveshaft, in front wheel drive?

 

[MarsChariot]

Broncobowsher, A drive in front wheel drive only does seem like the best test for drive line issues. Unless I have bigger issues with the front drive shaft! Which has been known to happen. I may just give that a try, though.

 

[valveamp]

I second Broncobowsher on the CV ball. I had a very similar problem to yours, a high frequency buzz/vibration. One day at an intersection, starting out from a red light, I felt a large "thump" followed by a lot of "clunking" as I moved off. Managed to get it into a nearby parking lot. The CV joint broke, not completely, but enough. That ball was a mess. I just installed a front locker and, for some reason, the front hubs were not locking in, so I couldn't use front wheel drive either. Had to have it towed in, then ordered 2 new driveshafts, front and rear.

 

[surfer-b]

Have you tried disconnecting the rear driveshaft from the T-case and running it up to where you normally feel the vibration, this may eliminate from the t-case forward. I would guess its prob in the rear pinion bearing since the seal is leaking. Some of the newer scan tools will actually detect vibration frequency, the one I used was a Pico scope, a friend of mine is a mechanic at Toyota dealer, I went to the dealer on a Sat when he was not busy and he hooked it up, this scan tool is really good. Here is a good vid about vibration and the Pico scope tool, its more about the tool but will give you a good idea of what could be the problem.

https://www.youtube.com/watch?v=cAB9NBDYWxY

 

[Justafordguy]

If the rear pinion seal is leaking you better check into that. If the bearing is going out or the yoke is loose it can cause a vibration for sure.

 

[MarsChariot]

Great suggestions. But the more you guys talk the more I see money slipping out of my wallet! I will see what I can find out. I eyeballed the ball on the CV and did not see anything outrageous, although I did see a little scouring on the shiny surface. The coincidence of the pinion leak and the increasing vibration does sound mighty suspicious though. I will post back when I find out something. Nothing is ever so bad that (a) it can't get worse real quick (favorite expression of a friend), and (2) nothing is so bad that it can't soak up all the money thrown at it.

 

[DirtDonk]

You can't see vibration causing failures unless they're pretty catastrophic.
Another way to see if it's the shaft components would be to grease them. Especially the female fitting on the CV centering yoke.

Paul

 

[MarsChariot]

To finish this thread: I took the rear drive shaft off and did the test with just the front drive shaft and the vibration was not noticeable. In looking at the rear drive shaft on the bench I could just feel a slight looseness at the centering ball of the double cardon. So I took it to my local drive shaft repair place and had them re-do the U-joints and the centering ball on the double cardon. They thought that it was not ready for replacement yet, but I thought it was based on the high-frequency vibration and the ever-so-slight looseness. On installing the repaired shaft, the vibration is no longer there. Moral of the story: We Bronco types are very sensitive to drive shaft tolerances! If you are a Bronco driver and it feels like a drive shaft vibration, it probably is. Thanks for the suggestions and input.