VIBRATION! someone please help!!

[ih8getnstuck]

Ok, I just bought a 92 YJ with a 4.0 5speed, 2 1/2" lift, and 31" m/t baja claw radials. When you take off in 1st gear, there is a bad vibration in the drivetrain somewhere. It also does it half way through 2nd. After you get up to speed it stops. It also does it when you accelerate hard. Going down the highway it is smooth, just when you put it under a load does it vibrate. Ive put new motor mounts, a poly trans mount, and a poly torque arm mount on the trans as well and it didnt fix the problem. The u joint are in good shape also. Im starting to think that maybe it is in the transmision it self but I dont know, Im running out of ideas and its starting to get expensive, but what on a jeep isnt! Does anyone know what this might be?

[Jeepr]

could be the angle of the rear driveshaft. With the short driveshaft and a lift they vibrate sometimes. Is there a drop in the crossmember? You can see if there are spacers between the skid plate and the frame.

I have had Jeeps that developed a vibration with as little as a 1" lift. It can be solved with either a slip yoke eliminator kit (SYE) or dropping the crossmember down an inch or so.

Good luck, I hope that helps.

[lah2420]

All I did was put new stock springs on mine and it started a vibration. The new springs lifted it about 2 inches over what it had run for years. I ended up having to put in a 1 inch transfer case drop. All vibration went away. It was a cheap fix too.

[TwistedCopper]

It sdounds like the driveshaft angle as said above. Are the rear springs shimmed to help correct the DS angle? That may be needed if there is already a TC lowering kit installed. If a TC drop isn't installed, you very well may need both to make it right.

Fortunately, these are relatively easy and also inexpensive fixes.

[ih8getnstuck]

But if it was the driveline angle, wouldnt it do it all of the time or get worse the faster i went? It seems to just do it below 10mph and when your on the gas. It doesnt have a trans/transfer lower kit on it, it still has the stock rubber bustings in there, which are smashed pretty flat by the way. Ill try it anyways, cant hurt. Is there any way to tell how muck lift is on here, I was told it was a 2 1/2" but I think its more like 3". Is there two points that I can mesure from on the suspension to compare to the stock suspension mesurements to find the difference?

[Bounty__Hunter]

A bad ujoint angle generally causes a vibration that increases with speed.

How bad is the vibration? The poly mounts will transmit a LOT more natural driveline vibration into the jeep that you wouldn't otherwise feel with rubber mounts, or at speed as you describe.

[ih8getnstuck]

It was the same before the new mounts. It feels like a cap is gone from one of the ujoints. Its that bad!, almost like a shutter. But only at low speeds under acceleration than smooths out after about 10mph. Im going to lower the t-case and see if that stops it, Ill keep ya'll updated. Thanks guys.

[Bounty__Hunter]

Before you lower the TC, grab an angle finder and check the angle of the TC output and the rear pinion yoke. Let us know what you find and we'll help on how best to correct it.

Just guessing on the fix won't be as effective as knowing what the problem is first.

[slo-wrench44]

go to the rubicon express web site. and down load the instructions for their 4.5" lift. it will tell you the proper way to shim the rear axle. i dont remember what it was but there is a couple of different shims that will fix different problems. accelerating deceleration and just chugging along have different shims to fix it

[ih8getnstuck]

Ok, just to update everyone, I never even thought to look and I feel an idiot. Who ever installed this lift put wedges in the rear and had the pinion angle kicked way to high. I took the wedges out and checked the angles on the rear end and the transfer case. The rear end is 10 degrees and the transfer is 7 degrees. Ive already put like a 1/2" transfer case drop on it. The rear shackles are 1" shackles and the fronts are stock shackles, the guy I bought it from said that it sit lower in the rear about 1", so he put lift shackles in the rear. Im guessing because of the hard top is why it sits a little lower in the rear. Anyways, Im assuming thats where Im getting the extra degrees in the rear from. I was just wondering if that 3 degrees off is going to effect anything. Oh yea, the vibration is gone by the way.

[Ragtopman]

I had a problem with the add shackles giving me a vibration once I got rid of them no trouble

Heres a post for you http://www.jeepz.com/forum/showthread.php?t=15168 (Vibe question w/research)