98 LS400 vibration above 72 mph

[w140amg]

I bought a 98 LS4 and it is smooth until about 72 mph. Above 72 or 73, a massive vibration starts, feels like its from the rear of the car. 

It appears to go away under load (accelerator down), but it returns and is shaky.  Rattles the rear deck.  Sort of like going over the highway rumble strips to prevent drivers from diIg off the road.  But the vibration is more spaced out.

i searched the forum, but I don't see what may be relevant.  It's not balancing or alignment bc the car will temporarily go without shaking at 72 and above.  Starts vibrating depending on the accelerator input and coasting.

any ideas?

1 Engine mount and 1 transmission  mount replaced at 272,849 on 11/2012.  2 strut rod replaced at 235k on 3/2009.

Currently has 304k miles.  Thanks!

 

 

 

[billydpowell]

check your drive shaft cushions, differential mounts and ALL your rear suspension (and I dont mean to just LOOK at them)  prize around on them like they are going 75mph. 

You might look on club lexus for 98 LS400 severe rear vibration  

https://www.clublexus.com/forums/ls-1st-and-2nd-gen-1990-2000/484366-98-ls400-severe-rear-vibration.html

[w140amg]

New continental tires, and balancing fixed it.

[WaveRunner]

I had the same issue on my 1998. Previous owner had cheap tires. I had those balanced but still vibrated a little. I put new Michelins and it went away. I noticed though going 95 MPH or more the car would shake. Make sure your tire pressure is around 34/35 PSI. I had mine at the in car panel recommendation of 29 which is fine for slow driving but not for highway. High speed needs firmer tires.

[Lexus_DK]

On 7/25/2017 at 10:35 AM, billydpowell said:

check your drive shaft cushions, differential mounts and ALL your rear suspension (and I dont mean to just LOOK at them)  prize around on them like they are going 75mph. 

You might look on club lexus for 98 LS400 severe rear vibration  

https://www.clublexus.com/forums/ls-1st-and-2nd-gen-1990-2000/484366-98-ls400-severe-rear-vibration.html

I'd check the differential mount rubber bushings. Possibly worn and cracked. If anything try rotating the wheels to see if it changes the vibration.

[vissine]

On 9/22/2017 at 2:46 AM, WaveRunner said:

I had the same issue on my 1998. Previous owner had cheap tires. I had those balanced but still vibrated a little. I put new Michelins and it went away. I noticed though going 95 MPH or more the car would shake. Make sure your tire pressure is around 34/35 PSI. I had mine at the in car panel recommendation of 29 which is fine for slow driving but not for highway. High speed needs firmer tires.

I keep tires at 29 psi, never had vibration for highway speed.

[WaveRunner]

On 9/24/2017 at 7:47 PM, vissine said:

I keep tires at 29 psi, never had vibration for highway speed.

Interesting. The panel in the car recommends 29 but the Lexus dealer sets it to 34/35 PSI. Not sure if that is what fixed my highway vibration but it is gone over 90 MPH.