Our lovely Highway systems has uncovered a beautiful issue. At 70 even an expansion joint causes a violent shutter that feels like it'll rattle your fillings out. I replaced the coil-overs and it calmed it down but it's still there. Slow down to 60 and it goes away. I have never had any vehicle have this issue before and I'm at a loss of where to even begin to go next. Everything feels firm and tight with no play. Any ideas would help.

 

From what I've read, coilovers generally suck. Car came with coil and shocks (or air struts in my UL), I believe, and non-OE is not same. One other crazy thought: make sure tires are nor seriously overinflated. Brother-in-law inflated his to 65psi by "feel" and thought his struts all failed. Nice mechanic set him straight without charge.

 

Stock replacements. Mine's a base model so thank God I don't have to deal with the Air System.

 

Check stabiliser bar "D" bushes(not drop links) F & R for wear, allowing metal to metal contact.

In many cases, using a pry bar will not find this problem, as the force that can be applied by this method is unable to replicate the force of a sharp bump at high speed.

Since changing my front bar bushes 10 years ago with poly bushes just after purchasing my 2004 Mitsubishi Diamante that source of noise has not returned.

Also, the firmer handling gained from the upgraded bushes is a big plus.

Firmer poly bushes, whilst providing more harshness that stock factory rubber bushes, are still better than putting up with metal to metal contact from worn out stock bushes.

If you can do the work yourself, the cost should be less than $100 to replace F & R.

Don't forget the lube.

 

check your control arm bushings

 

that's the first thing I thought but I kinda dismissed them as the problem based on my experience with my '69 elCamino. It had no bushings left in any of it's A-arms and still didn't do that. But I did look them over just be positive. They appear ok. Appreciate the advice nonetheless.

 

I fixed a "highway speed bump causing a big steering shake" by replacing steering rack bushings. Steering rack bushings, 2 per side

45516-50030 Drivers side
45516-50040 Pass side

Lexus does not sell these individually for 2004-06 so you have to look under 2001-03 to find them...but they do fit all years. No alignment required after swapping.