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Bad Vibration from Rear

Vehicle trembles badly between 45-50 mph, not too bad above that. 150,000 mi; extremely well maintained. Have spent $2,500 on new driveshaft, differential fluid, two wheel alignments, all tires rotated and rebalanced, new front shocks and strut bushings (rear checked fine). Had dealer, two others check it out along the way, still doing it. Can you help save me from insanity or insolvency? All ideas welcome. Seems to be getting worse. Steering wheel not vibrating, just seat. Out-of-round tires never mentioned as I recall. Thank you.

did you have the new drive shaft ballanced? What about the u-joints, have you had those replaced, lubed, anything like that?

Thanx for the reply. New driveshaft was from Lexus so I presume it is balanced. I did not mention but there were also new u-joints installed. (I once had u-joints break on a '56 Chevy while doing 40mph; an experience one never forgets.) It’s just that the vibration is so noticeable in the 45-50 area, speeding or slowing. Any more thoughts appreciated.

the only other things I can think of are if it has rear cv joints, or if the rear antisway brace/stabilizer is loose, or if the tires are delaminating but that last usually causes a wobble all over the speed range. I am stummped, but this reply will bump you up so others can get in on this tread who may well know more about it than I do.

What Is The Model-Year Of This Lexus LS 400 ? Is The Problem While Accelerating ?

Has anybody looked for Lexus Technical Service Bulletins ?
I see a Lexus Technical Service Bulletin # DL002-96 (April, 1996) that helps technicians improve the LS 400 " . . . driving smoothness when accelerating from approximately 35 m.p.h."

Part of the bulletin discusses the addition of a dynamic damper to the vehicle’s stabilizer bracket and it looks like a new differential mount cushion.

Anyhow, this must have been a problem (They issued a TSB.), how big a problem I don’t know. If this sounds like it describes your vehicle then maybe you could find a “mature” Lexus technician who can remember making this modification to an LS 400 or two “back in the day”.

Also, if you’re interested have somebody find and discuss the bulletin with you. There’s a production effective VIN, although no stated model-years, so you’d have to be sure you don’t already have a model with this mod.


This is awesome and I never use that word. Whether or not any of these tips apply or not, we’ll see. I’ve written them down and will return to my trusted dealer and independent mechanic to run these past them. But this support and the suggestions are what’s awesome. It’s a '98 LS400 and if you’ve got time to kill, it’s my car at the web site.
Thanx to both of you. I’ll follow up and if any of these suggestions solve it, I’ll send you a check for a case of beer. Honest. I’m tired of my ass buzzing when I’m driving down a smooth road. As I mentioned in my initial reply, it happens accelerating or slowing. Thanx again.