So i have new tires, re balanced, wheels run true, checked all bushings and joints in the suspension.
from 65 mph onwards I have an oscillating vibration. Does it in drive or neautral.
The frequency doesnt change, only the amplitude of the vibrations.

6 seconds smooth, 3seconds vibrate.
Best way to describe it is an ocean wave, it builds, peaks then gradually dies down within 3-4 seconds, and then smooth as glass for 6-7 seconds.

I can be doing 60, 70, 80 mph. Same time frame for the "ebb and flow" of the vibration.
Drive or neutral, 3,4,5th gear all same thing.

Wheel bearings and hubs are good and tight. dont feel it in the steerign wheel, rather the whole bottom/base of the car.

I did a quick hand jiggle fo the driveshaft and it appeared solid, maybe I should pull it and inspect better.

Im thinking either the center U joint, or perhaps the hanger bearing itself? (degraded rubber).

Anyone experience something like this?

 

Everybody always says motor and transmission mounts. And it could be the flex joints or what you mention too.

 

trans mount is brand new, engine mounts are original, however it would not be the engine mounts as it is a speed dependent vibration and not RPM or load.
Rubber couplers at trans and yoke look to be in good condition. I see the U joint is "non serviceable" as it is staked in there, Im sure with a press i could get it out.
However, last night again I inspected the shaft with it on the car, jiggled and twisted it aroudn with my hands, all seems tight. I have had bad u joints on my truck and you can clearly tell when they are starting to go bad. Maybe the carrier bearing is seizing up at some point int the shafts rotation? I should put it in neutral and try rotating it to feel abnormalities.

 

I have the same issue. I also have new motor and tranny mounts.

Curious to see what fixes it.

My rear diff has a bad seal as well, and leaks fluid. It makes a hum on the high way. One day I'll change out the diff.

 

flex joints are possible but unlikely as you would start feeling the vibration far sooner than 65mph.

The LS400 is VERY sensitive to wheel balance, and often times older balancing hardware and/or lazy technicians will be inaccurate enough to cause the issues you described. Try having your wheels/tires balanced with a "Road Force" balancer, they have a much finer tolerance.

 

I've had tires with blisters on the tread or bruises on side walls that can cause vibration, also there are CV shafts at the rear, and the rubber mounts for the rear end. Jack each wheel off the ground and turn them use a block of wood near the tire to see if it runs true.

 

wheels all run true, actually jsut replaced a rear tire because old one had a hop to it and shook the entire rear real hard. wheels run true.
I agree about wheel balance especially with my large width wheels. Everyone claims to have the best road force balancers, but they always shake. \
I have only found 1 shop near me that was able to balance my tires. Funny, you take the tire to a shop they mount and balance on road force. take the same tire directly to the other shop and they say its all out of balance and needs a new one.
I just remembered, my front tire was balanced by the "bad" shop (shop is fine, they jsut cant seem to balance this specific set of wheels). I will take it to my "good" shop for them to balance it.
I dont think its front tire as the vibration is felt much lower in the car, the floorboards it seems, and the wheel does not shake. But...either way I will re balance it.

Actually I noticed my right front UCA BJ was toast. a good 1/4" of play on it when compressing it with a channel lock. Swapping that tomorrow. Again...dont think that is causing the vibration issue, but it needs to be adressed regardless. other side was done by the PO at some point and is good and tight. right side appears to be OEM.

 

You are running hubcentric rings, right?

 

^yessir. I make sure to also tighten the acorn nuts in a star pattern slowly to make sure the wheel is perfectly centered around the stud. Like I said, the wheels themselves all run true.

I also suspect since i run -4 deg camber in the rear, wich weights placed on the outermost part of the barrel, it does not run in line with the forward rotational motion of the tire, (think motorcyle wheel when you corner-hyroscopic effect wants to return the wheels upright).

That may have an effect on balance.
The one shop I mentioned that does a good job balancing always ends up putting a good decent amounf of weight as close to the center of the wheel as they can, and the outer barel barely has anything at all if any at times. Vs most other shops just stick it on the inside barrel-which coul result in vibration on excessive negative camber wheels.

But....these wheels were balanced by the good shop.
Well see how the new FRUCA performs tonight after the swap.

PS, do I torque the inside bolts with the wheel at ride height or full droop?

 

Try taking it to a wheel balancing shop which "shaves" a little tread off the tire as they high-speed balance it...

 

It's not just wheel balance but it's differences in strength along the sidewalls that cause vibration at high speeds and camber will make it worse. It could be balanced perfectly and turning true but you'll still feel vibration sometimes. That's why a good road force balancer is sometimes needed to counter these affects. If you take a road force balanced tire to a standard balancer it's going to show it as being way off even though it's not. For what it's worth, your rotors can also cause imbalance in the hubs. When I replaced all 4 rotors I noticed a big difference, and when I swapped out the front strut bushings it took care of the rest. I still feel a slight vibration at 75+ but rarely go that fast so I left it there. I'm pretty sure a road force balance would take care of it (currently running a standard dynamic balance).

 

front strut rods and Tie rods and rear carrier arm bushings can also cause issues if the bushings are dead/dying or there is play in the joints (tie rods)

 

Oscillations as you describe are generally caused by two (or more) different frequencies (vibrations) that roll through alternate periods of reinforcement, then cancellation. The longer the period of time between peaks, means the two sources are nearly identical frequency, which produces the most noticeable harmonics (also the most destructive, if it coincides with the natural oscillation frequency of the mechanical assembly). So, what's all this got to do with you?
In your case, this may take some experimentation, because eliminating just one of those sources of vibration might make your problem better, only to have it pop up again at a different speed. These things are a science unto themselves, and require sophisticated tools to investigate mechanical oscillations in large equipment. Unfortunately, there aren't many shortcuts when it comes to dynamic interactions between multiple moving parts. Swapping tires around may provide some clues. Good luck.

 

The Lexus LS400 shop manual dedicates several.pages to drive shaft alignment and angularity.

If the differential housing to body bushings have never been replaced, if not worn by mileage, then certainly expired by age.

Ditto for center bearing (rubber)

Whoever is performing work, have them show you a Lexus shop manual. If they can't produce one or relevant sections then don't let them touch your car.

 

well, i replaced the front right upper control arm. the vibration got a little better, but still definitly present.
I had the "good shop" rebalance the wheel and...smooth as butter!
Again, very strange as they all claim to have the best road force balancers..maybe the tech is putting in the wrong specs for the wheels at the "bad" shop?

Very happy to have finally gotten it to an acceptable level. Its not butter smooth, and it never will be as they are stretched 19s on wide wheels, but there are no vibrations, and certainly no oscillating ones.
It is smooth till about 90mph, havent gone or need to go faster than that.

My main concern is at 70-75 mph as thats where the car spends nearly all of its time.