Northern Virginia Jeepers Association

Open Discussion (Club Members and Non-Members) => Jeep Tech Talk => Topic started by: packinnova on September 12, 2017, 04:29:36 PM



Title: Driveline Vibrations - yeah I know theres threads all over the interwebs
Post by: packinnova on September 12, 2017, 04:29:36 PM
Bad baad baaad, bad vibrations... :s

Jeep:
1997 TJ
4.5" Suspension lift
SYE and rear double cardan
Adjustable rear upper control arms and pinion angle set at about a half a degree high from 0.  IE it's damn near a straight shot from rear pinion to the yoke on the sye.
4.56 gears and Eaton E-Lockers front and rear.
Recently cut, lengthened, and rebalanced front driveshaft.

So I'm having vibrations over 50mph now.  I originally had them at 35, but fixing the pinion angle in the rear got me up to 45ish without vibes.  45 and up it started vibrating again.

Front drive shaft removed...NO NOTICEABLE VIBES AT ALL up to 70 tested.  Driveshaft in, vibes return at 45ish.  Took it to a shop and they said the splines were bad in the front and it was too short.  They cut the shaft from the yokes, welded in a longer shaft one, rebalanced and bolted the shaft back up.  Now it's good up to about 50ish and gets considerably worse by the time I hit 55.

Same deal.  Remove front drive shaft, no vibes.  Shop now claiming has something to do with having the lockers in the front and the driveshaft always spinning now.  I call BS as I had that EXACT set of lockers in the other Jeep I have with a 2.5" lift, but stock front driveshaft and there were ZERO vibes.  I find it hard to believe it's all due to the lockers and it's never going away.  I kid you not, they said just drive it without the front driveshaft from now on or put in manual locking hubs up front.

Help...  Ideas, theories etc... all accepted at this point. :?


Title: Re:
Post by: sirjames186 on September 12, 2017, 06:33:48 PM
I know the front shaft has a cv/double cardan but is the pinion angle right on that on too?

Also u joints all good?

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Title: Re: Driveline Vibrations - yeah I know theres threads all over the interwebs
Post by: RFH_98TJ on September 13, 2017, 09:08:18 AM
Took it to a shop and.... cut the shaft .... rebalanced

What shop did you use that was qualified to do this?  I'm wondering about your rebalance.

Also, did you just do this lift and now have vibrations, or was it running smooth and just started out of nowhere?


Title: Re: Driveline Vibrations - yeah I know theres threads all over the interwebs
Post by: I6CJ7 on September 13, 2017, 10:08:57 AM
That doesn't make sense, the front driveshaft isn't spinning while in 2wd going down the road. The only things spinning up front are the axle shafts. Since you don't have selectable hubs. Make sure your engine and trans/Tcase mounts are all in good shape and tight.  My friend said he was having bad driveline vibes in his TJ. i peeked under and his skidplate was ripped out of the frame rail on the passenger side from rust in the frame.

You could try adding 200lbs or so to the front or rear and see if that changes the vibes at all. My CJ7 starts to vibrate at 67mph in the rear because i know the pinion angle is off. when i recently went to the beach with a hitch rack, and 200lb+ cooler, it was enough weight to squat the rear and change the pinion angle enough to cure the vibes.


Title: Re: Driveline Vibrations - yeah I know theres threads all over the interwebs
Post by: RFH_98TJ on September 13, 2017, 11:16:06 AM
On the TJs the front axle and driveshaft always spins, it is just "driven" only when in 4WD.

That said, remove the front shaft to see if it goes away again.  If it does, it would obviously be the DS since your locker and front axles are always spinning and would rule these out.  Your DS would then be most likely out of balance, bent, or have bad u-joints.  Or a mix of these.


Title: Re: Driveline Vibrations - yeah I know theres threads all over the interwebs
Post by: zuke on September 13, 2017, 11:17:50 AM
That doesn't make sense, the front driveshaft isn't spinning while in 2wd going down the road.

The front drive shaft does spin on a TJ in 2wd, the axle isn't disconnected from it or the axle shafts, the only disconnection is in the transfer case.

If the driveshaft is truly all good, how about the Front yoke and bearings on the Transfer Case?


Title: Re: Driveline Vibrations - yeah I know theres threads all over the interwebs
Post by: RFH_98TJ on September 13, 2017, 11:24:10 AM
how about the Front yoke and bearings on the Transfer Case?

Good point!


Title: Re: Driveline Vibrations - yeah I know theres threads all over the interwebs
Post by: highlandercj-7 on September 13, 2017, 02:20:17 PM
That was my next logical step Zuke. If the shaft is good then the slop would more than likely have to be there at the t-case.


Title: Re: Driveline Vibrations - yeah I know theres threads all over the interwebs
Post by: cwkann on September 14, 2017, 01:27:34 PM
Have you borrowed a front from someone that doesn't have vibrations?  If you put one in from someone that doesn't have an issue, it is the shaft.  If you still get them, it is something else and the shop lied.....    :?  Unless there is something special about yours, that would deduct one thing anyway.