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Vibration woes *update* fixed

gone huntin

gone huntin

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Coldwater, MS
Since I installed my 14bff and my "new" driveshaft in my 'burb I've had a very annoying vibration. I installed the 14b first, I drove it almost a week with the stock shaft that was now 2" too short. I did not feel a vibration then, but I never got it on the interstate like that either. I then took a driveshaft that was 2" too long to the driveshaft shop and had it shortened to my desired length, but they did not balance it. I installed the "new" shaft and went for a test drive. I had a terrible vibration from 40mph-up, so I pulled it back out and took it back. They balanced it and said that it required 1.5 oz. of weight, 1 up front and .5 at the rear, both were opposite of the factory weights. I re-installed the driveshaft and took off down the road and all was well.......so I thought.
We took it out of town and pulled my 16' trailer with 3 atvs on it to LBL 200 miles away. At 55mph and up I still had a vibration, not nearly as bad, but it was noticeable. After driving it 400 miles like that I had to replace both the TC tailhousing seal and my pinion seal. So, once again I pulled the driveshaft out and sent it back to the shop with my wife, as I had to work. They checked it again and said it was perfectly balanced and had no bends in it. The shaft has new Spicer joints in it (1/2ton to 3/4ton in rear).
I went by my local tranny/diff. shop to see what they thought and they said that a bearing would have to be chewed up pretty bad in the rear diff. to cause such a vibration, and I checked all of the bearings before I installed the rear end.
I almost forgot, the sound/feel of the vibration changes with accelerator pedal pressure, if you coast it makes a louder noise and if you let off completely it changes again.
Any ideas? This is not a tire vibration, it's too "fast" for that. I do have 4" of lift and 33's.
 
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dont forget the bearing race in the tcase behind the seal. and as for the shaft, thay are stupid. you need to remove all old weights and then rebalence. the new is just counteracting the old and looks like crap and is a wast of space on the shaft. if this is a slip on the shaft then is the ujoints out of fase on the slip to shaft? if not slip shaft ignore this question. just a few things to check over.
 
The driveshaft is @ 11deg. with the yoke at the t-case being about 5deg. and the rear being about 7deg.,with the tapered blocks in the rear the driveshaft is almost straight with the pinion. I did not have this vibration with the ten bolt rear or the previous shaft and the 4' lift was there with both of these. The new shaft is only 2" longer than stock. The lift pulled the yoke out of the t-case an inch and the 14b pulled it out another inch.
 
Can you post pics of your driveshaft installation? Your pinion should not aim directly at your tcase unless you have a double cardian style shaft. You should have equal but opposite angles between the shaft/tcase and the shaft/pinion.
 
I exagerated(sp?) a bit about them being almost straight, but it does tilt up a bit. I could not get a good reading on the rear end, but it is slightly more tilted up than the t-case yoke is down. My driveshaft is 55.5 inches end to end without the yoke.
 
I would suggest getting an angle finder ASAP and checking your angles. They are very cheap at Harbor Frieght (and good enough quality to do what you need). You should have the pinion turned down about 1* more than the angle on the tcase. This will allow for them to be equal when the axle rotates up under acceleration. Sounds to me like the problem could likely be in your driveshaft angles.
 
I did check them with an angle guage, I forgot I had one in my tool box. I just couldn't get a good place to check it at the rear with the d-shaft in it. The front IS 5deg. and the shaft itself is 11deg., so wouldn't that make the rear 6deg? The angles are the same as what they were with the 10 bolt in there and I had no vibrations then,or do the 14b have more angle at the perches? Also it only does it after 55-60mph.
 
Is you ujoint sitting correctly in the pinion yolk. Sometimes the cups want to sit on the centering tabs on the yolk. That does make it vibrate at that speed.
 
ok, wasn't sure if the 14FF went in with a lift at the same time... Next place to check is your 14FF if the 10 bolt didnt have a problem. Did you check the pinion bearings? They are kinda hard to see even with the rear cover off.
 
Yes, they are seated properly, and the driveshaft was properly phased when it was rewelded.
 
I removed the pinion carrier and looked at the bearings as best I could. I spun the pinion while holding the pinion carrier and it all felt smooth. Jhellwig, yes it is.
 
That's not what I wanted to hear! Believe me, it did cross my mind to just put the 10 bolt back in it. I still think it's with the driveshaft. I forgot to mention that everytime I put it in gear I get a "tink" sound from the driveshaft like you were hitting it with a hammer. Usually that means ujoints, but they're new and tight, checked 'em twice.
 
I think it may be the pinion angle. If the tcase is at 5* then you should want the pinion to be at 4* so when you drive, it rotates up to 5-6* equel to tcase( for single ujoints). Thats what I have read while tring to get rid of my vibes. :burb:
 
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