Vibration at 70 MPH...

Hello, and thanks for reading this post.

I have a 2001 Cherokee with 3.5" Rubicon Express lift, 32" tires, 4.56 gears, aftermarket control arms, Rock Hard 4x4 rear bumper/tire carrier, SYE kit, cv driveshaft, and rear axle shims.

Before the SYE kit and axle shims, it had a bad vibration from the drivetrain at almost any speed. With SYE and shims, it is smooth as glass through around 67 MPH. At around 70 MPH, a vibration appears like flipping a switch. The vibration is worse if I am on the throttle, but it is still there even if I take my foot off the throttle, as long as the speed is above 70.

It is an almost resonant vibration, it sounds like it could be tire noise, but it really comes and goes like flipping a switch at around 70 MPH.

What could it be?

Did you install new u-joints? TREs good, tires balanced, ball joints good?
Just brainstorming.

32's and your smooth through 67, be glad. But seriously Kujito is on the right track i think.

Man, I would just drive 67 and be done with it. On my last XJ(99) I hunted down vibrations for almost the whole time I owned it. It literally drove me crazy. I had an SYE, new driveshafts, shims, new axle u-joints, adjustable control arms, etc... and still couldn't get it down. I have since bought a different daily driver and bought an old cheap XJ for the trails.

I bet your pinion angles are out of wack. Either the front or rear. You'll have to pick up an angle finder if you don't already have one, and make sure they're within spec.

I have the same exact problem and know exactly what you're talking about. All joints and hubs are pretty new and the rear pinion is perfect. The front is a different story. At 6.5"s I had to find a happy medium between pinion angle a castor.

Mine starts the vibs just above 65.

You drive a lifted XJ. Mine vibed at 70 stock. I think your lucky it doesnt start earlier. Its a brick that wasnt meant to go that fast..thats why the speedo only goes to 85.

Lets get some real details! What transfer case?Who's SYE kit?What driveshaft?What axle?What are your driveshaft/pinion angles?Who's gears(and who set them up)?
Have you removed the front to eliminate it?
BTW:Have you corrected your speedo gears?

mine vibes pretty good after 55/60 ish.
i just picked up some 4* shims and ill see if there is a difference.