Hey, guys. I know it's been a while since I've been on, but I've been trying to trace down every possibility of my harsh vibration at highway speeds. I'm really thinking it is suspension/steering components being worn, but thought of a couple other things....

First, we're talking about the '93 here. Got a 3" Rough Country lift w/ t-case lowering kit. I know when you lift a vehicle, it changes the camber and caster of the front end. I removed my front driveshaft for now, so caster's not really in the question, right? Camber, however....How much could that influence vibrations?

My other thought is the harmonic balancer going bad. I'm not sure what to look for on this, but it's just a thought of something going bad. What do you guys think about this?

One last thing that's off topic....I think I have an exhaust leak at the manifold gasket. Dripping some water on the middle of the manifold with the engine running made some air bubbles next to the bolt, which I checked to be the correct torque. Think it's time to pull the intake and exhaust and replace the gaskets?

 

ANYTHING can cause bad vibrations. Unbalanced wheels, bad u-joint, bad steering stabilizer, etc.


As far as camber and caster, the only thing that can change the camber on our solid axle XJ's is a bad ball joint, bent axle, bent yolk, etc. Its not adjustable and a lift wont change it. The knuckle is fixed to the axle.


Caster on the other hand WILL be changed by a lift.


If your camber is TRULY off you need to get an alignment measurement and correct it with an offset upper ball joint.


Honestly, I doubt you have a camber problem but stranger things have happened.


I don't think you can solve a caster problem by pulling the driveshaft, but Im not 100% on that. I thought only adjusting the control arms could do that.

 

Correct, the driveshaft has nothing to do with steering geometry.

 

First thing to check for is out-of-balance tires. Tires unevenly worn/cupped. Mud terrain tread will always be rougher on highway. Separated tires. Bent wheels.

Then U-joints, rear only for now in your case. Bent drive shaft. Rear axle bearings. Broken teeth in differential gears.

Misalignment usually will not cause a vibration by itself. Put that on the back burner for now.

Not meaning to be harsh, but it sounds like you're only been theorizing at this point without actually doing anything about it. You gotta start somewhere. A vibration like you are describing shows that something is wrong and you'd better fix it real soon or you'll be sorry.

 

tires are the first place to start, pull them off mark where they were and bring them to a shop to be balanced. have them check for shifted belts bent rims poor tire inflation. yada yada. remount them and test. if the problem continues replace the steering stabilizer, and if you notice a difference, while the tires are off the ground, inspect the front end for play in tie rod ends, ball joints, track bar, control arms (should check anyway when you pull the tires off for rotation and balance, i always balance the tires i rotate to the front). did you ever shim the rear diff? the rear drive shaft U joints should be as straight as possible even with a drop(search drive line geometry). the front drive shaft will not effect caster but caster will effect pinion angle, and pinion angle takes precedent over caster angle. if you have not gotten a SYE then no matter what you do because of the lift the driveshaft has pulled out some from the TC and the slip joint is infamous for causing a vibration, doesn't matter if you have a drop and shimmed it , if the driveshaft isn't all the way on the TC you will get vibes and possible noise. report back after you have done some work and let us know.

 

Front drive shaft in this case cannot be a factor. He said in his post it was removed at this time.

 

i know and i made no mention of the front driveshaft being the cause but he asked and you wrote about the front shaft and it's relation to caster but i'm hoping OP plans on putting it back in. and it's also a good tip to whoever else may come across the thread

 

Oh and as for the exhaust question you best plan replacing the exhaust manifold as they know to crack... now would also be the time to replace the front pipe if you are one of the unlucky few to have the "crush" in it

 

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Few?

 

Sir: You need to reread your own post #5. Half of what you said was talking about the front drive shaft.

 

Jack the car up off the ground and run it up to where it vibrates. Should help narrow things down. Set it up safe though. You're not looking for the bubbles, just a drop in motor rpms. Few? My 99 had and my 94 has the dent. I think all 4.0 at least 90-99 have it. Not sure about renix. Some people say it's for clearance, others say it's there to get the cat to heat up faster for emissions. Either way it sucks and should not be there.

 

That. Check those things first before chasing the less-likely alternatives.

 

How are his drive line vibrations going to cause bubbles and a drop in RPMs?

Obviously, the dent does not suck because the engineers designed it that way. It's there for a purpose and is supposed to be there. How are you more qualified than them?

 

oh are you referring to that one line there which is the only time i make any mention of a front drive shaft please take notice that there is no mention of any sort of vibration.after i go on to talk about an sye referring to the rear shaft. i was simply addressing his concern with the front driveshaft in relation to caster angle. and as for the exhaust the dent is there for emissions purposes not for performance purposes. you dont need to be an engineer to know that any restriction in the exhaust is bad for performance.... this is why people port the heads and polish the exhaust ports often follwed by installing polished (referring to the inside not the outside) exhaust manifolds/headers. also why you see most high quality performance exhausts use mandrel bends (less restriction.) removing the crush wont magically turn the jeep into a horsepower god but it certainly does not hurt it.

and as for my "few" comment so maybe i under exaggerated a little bit lol. probably should have gone with "one of the many". does anyone know what years they actually stopped doing that with the XJ? is it 99? or did they run it all the way til the end?

and in reference to spinning the tires be sure the the jack stands are supporting the axles and not supporting the body to maintain as close to normal "ride height" as possible.

 

Quote: " you dont need to be an engineer to know that any restriction in the exhaust is bad for performance...."

Nope. Wrong again. A certain amount of backpressure is useful for scavenging the cylinders for the next charge.