suprasoup

Whats up,

I have a 96 LS400 with 150k and I am experiencing some bad vibration at speeds 60mph+. I have replaced the strut rods, tires, transmission mount, driveshaft coupler's. At this point I am trying to figure out what to try next. The car will vibrate at high speed regardless of being in gear or neutral. It does seem to vibrate more under load but will still vibrate when off the gas. I know the shocks/struts need to be replaced but I don't think they would cause this kind of issue. The parts I have used are all OEM. Any feedback or recommendations is much appreciated.

Thanks

timmy0tool

iTrader: (7)

what made you replace the driveshaft coupler? that is a rotating mass that needs to be balanced.

next, i would suspect the bad shocks combined with new (or unbalanced) tires.

suprasoup

I replaced both coupler's as my vibration is speed related and the old ones had a few cracks. This did improve the way the car drives but did not resolve the vibration.

The tires were balanced at time of install. (I had the vibration before installing new tires)

I just didn't think the shocks would cause a vibration at higher speeds and not do it all the time.

400fanboy

Vibration in sync with the speed you're traveling says it's something rotational, either in the wheels or in the driveline. First step is to find where it's coming from, then you hone in further on that area doing more testing.

If it persists even while in neutral it's behind the transmission. But - just to rule it out, is there a vibration when you rev the engine to 2000rpm while in park\neutral? This should rule out motor mounts.

Did the source move or change at all when you got new tires and had the wheels re-balanced? This should rule out if it's wheels\tires.

Is the vibration coming from the steering wheel or the seat? This will tell you front\back.

suprasoup

No vibration while in park or neutral when reving.

I did not notice a change in the vibration after the tire change.

I can feel the vibration throughout the car however more so in the seats and floor while slightly feeling it in the steering wheel. The passenger seat will vibrate pretty bad with no one on it while on the interstate.

Thanks

Losiracer2

try checking for play in the control arms in the rear. My 99' LS with 155k had tons of slop in the rear UCA bushings causing at least a 1/2" of side to side movement when under load. I still also have to replace my knuckle bushings as those have play as well.

Could also be bad wheel bearings in the rear if you have play, but you have to be careful as what I thought were bad wheel bearings, was just the knuckle bushings and UCAs.

400fanboy

If it's speed-related vibration (aka the frequency of the vibration is in sync with the mph you're going), give the tires\wheels a real close look. Get them road-force balanced which is the next level above a normal balance.

If that isn't it, then take a good hard look at all your bushings. There are a ton down there. Get your fingers in there and really push into the ones that allow it to see if they may visually look fine, but are degraded internally. Give the arms good yanks to see if there are play in addition to the normal tire testing.

I too am chasing down a phantom chassis vibration that's proved quite elusive. Could be wheel bearings, could be upper control arms... not really sure.

I'm out of ideas though - best of luck.

plexus914

Same here - high speed vibration in the steering wheel and from time to time slight wandering.
Maybe new original equipment (OE) upper control arms in the front will help. Bushings might be weakened after 150k and 24 years.
I am currently in the process of changing the Beck & Arnley (Made in China) wishbones in the front to OE ones.
Parts replaced so far:. New stabilizer bar bushings & links, strut rods, lower ball joints, brake discs & pads in the front
Future will tell.

suprasoup

I took the rear wheels off and found that the trailing arms bushings were torn up, more so on the side attaching to the wheel hub. I bought new bushings for the trailing arms. I will report back once I swap them out. The other bushings seem ok via yanking and poking around however you cannot really see the inside of the bushings on most of the parts as they are in a tight space. If this doesn't fix it I will begin removing other bushings for inspection.

I may get the tires road force balanced as well.

Thanks for all the suggestions.