rear drive line vibration???

[Scratch]

I think I've norrowed the majority of my vibration to the rear drive line.
I shift the TJ into front only(flipped 300) high and drove home today without most of the vibrations I normally have.
I have adjusted the pinion angle in the rear from right on to several degrees both above and below and every where in between with very little change on the vibrations. I did this with one twist increments of my uppers.
I'm wondering is the torque to the front evened out a vibration that may be there or if it is indeed the rear drive line.
I have also tested for run out on the Dana 300 output and it was off by only 2 or 3 thousandths so I don't think that is the problem.
I could really use some direction here.
My setup is:
AW4
flipped dana300
8.8
RE LA 4.5
1.25 BL and MML
Any suggestions?
Thanks
BOb

[ChrisK]

Have you had the driveshaft balance checked?

Don't you love the fact that the flipped 300 can do front wheel drive only? I've been told the Atlas can't do this.

Chris

[Scratch]

yep, I think it is real cool. I really like the flipped 300.
My sifters had the slightest of a rattle in them so I took them off and slid the little bushing off and put a couple wraps of tephlon tap around them. I put it all back together and no more rattle. I love when a fix is simple.

I have had the front drive shaft rechecked but not the rear. I may have to do that. IT has recently been rebuilt by a VERY competent shop so I' leaning away from that but you never know.
Bob

[DanB98TJ]

Besides balance, make sure the driveshaft yokes are "phased" correctly - even being off a slight amount can cause bad vibes.

We chased vibes on my dad's '32 Ford for months and finally tracked it to the yokes being a little out of phase - it was a new, custom-built shaft, too. The vibes were bad enough that it wiped out the U-joints in a relatively short period of time.

Chris - I thought the Atlas could do front only? I dunno - I always thought that was one of the benefits of an Atlas, but maybe I have it confused with something else - woudn't be the first time.

[Robert J. Yates]

Originally posted by Scratch
I have had the front drive shaft rechecked but not the rear. I may have to do that. IT has recently been rebuilt by a VERY competent shop so I' leaning away from that but you never know.
Bob

Wouldn't be the first time that happened I had a brand new driveshaft delivered to me that was incorrectly balanced

You also might want to check your tires and rims - I've chased what I thought were driveline vibes only to find that my tires and wheels were incorrectly balanced.

[Stu Olson]

Yep....what Robert said.

I had a "very competent shop" retube my front driveshaft. It came back missing needle bearings in a couple of the u-joint caps. But everyone told me how good they were..... I guess my standards were higher than most folks!

[Jeff Weston]

My driveshaft from RE came out of balance as well. I had Wenko fix it and replaced the RE SYE (bad splines on two different flanges) with a Currie and have been good to go since.
With the Jeep in park, do you get much play between the joints? Have you pulled the shaft and taken a look under the caps? If they're scored, it's time to replace them.

FWIW, my last vibe which drove me absolutely nuts was due to the onboardair bracket flexing and acting like a springboard. I welded in a few gussets and it's been fine since. I say that so that you don't overlook something else which may be causing the vibes. Is there plenty of room around the tranny, not hitting the tub under torque?

[Scratch]

Another idea that came to me last night.
It has become worse since removing .5" of the mml that was 1.5 inches. I forgot that I had done that. I know what an idiot. I'm refinancing the house right now and my mind is definately somewhere else.
I thought it was just pinion angle but it might need the more down angle of the aditional mml. I just thought the motor was really angle before. Maybe I'll add some washers and see if it goes away before building new motor mounts.
BOb

[TJRON]

I would PULL the rear drive shaft to eliminate the balance and bent output shaft possibilities.

[Scratch]

I've already done that and put a dial indicator on the tail shaft.
WIth the flange on it was between 2 and 3 thousanths off. I don't know what that should be for the Dana 300 but that isn't much and discounted it as my problem.
If anyone thinks thats alot I'll recheck it.
BOb

[TObject]

Make sure everything is tight. I had a driveline vibration for months, until we figured out that it was caused by the loose yoke on the transfer case output shaft.

[TJRON]

Originally posted by Scratch
I've already done that and put a dial indicator on the tail shaft.
WIth the flange on it was between 2 and 3 thousanths off. I don't know what that should be for the Dana 300 but that isn't much and discounted it as my problem.
If anyone thinks thats alot I'll recheck it.
BOb

I was thinking drive it with no rear drive shaft.

[Scratch]

Ron ,with the flipped dana 300 I just shift out of RWD and shift to front only.
When I do this almost all of the vibs go away.
I don't know if it is because the vibration is in the rear or if because the torque added to the front drive line stablizes it, thus reducing the vibes.
Bob

[TJRON]

It sounds like some of your vibes are definitely coming from the transfer case back to the wheels.
Your driveshaft and output shaft are still turning even though no torque is on them. Possibly if you remove the driveshaft all your vibes will be gone.
That's what I would try.
I don't remember how bad my output was bent but it was very slight. I replaced it and the problem was cured. I wish I could remember how many thousandths off it was.

[Cement_guy]

Originally posted by ChrisK


Don't you love the fact that the flipped 300 can do front wheel drive only? I've been told the Atlas can't do this.

Chris

I believe the Atlas II can do low front only, but not high front only, if I understood Robin properly.

[speaceman]

I second what TO said. Make sure everything is tight.

I had a rear driveline vibration that got steadily worse over a couple of months. Kept checking everything only to find that the rear straps were loose and the rear ujoint was about to go.

After replaceing the ujoint, no more noise or vibes.

[Daless2]

Hi Bob,

A quick way to help find out if that rear drive shaft is out of balance is to put a stainless steel hose clamp around the drive shaft and tighten it down. Drive it around a bit and observe the vibration. Then rotate the clamp on the drive shaft. If you do this a few times and the problem either gets better or worse as you rotate it around the DS, the odds are the shaft is out of balance.

Also, I don't know how recently you have been inside your 8.8 differential cover. But is it possible the ring gear bolts (one or more) have backed out on you? This would certainly cause a vibration under load that would be more pronounced then when just driving around in Front Wheel Drive.


Chris, your right on the Atlas.

While it will do Front Wheel Drive only, it will only do it in Low Range.

Frank