Lexus SC430 :: Shaking Occur Anywhere Between 55 To 70 Mph

I thought I'd post an update about my front end shakes that I've been working on eliminating since I bought my SC. They used to occur anywhere between 55-70 mph. The remaining shake occurs around 65-70 mph. I should mention that when I added H&R 25mm wheel spacers in the back and 20mm spacers in the front. I had the shakes both before and after adding the spacers though. The following list is what I've done over the past couple of years to try to eliminate my shakes:

1) New tires - Bridgestone Potenza's, nice tires, better ride.
2) Replacement, chrome, OEM wheels. Look nice.
3) Road force balancing.
4) Steering rack was replaced with a rebuilt unit because the old one was leaking. Came with inner tie rods and I put on new outer tie rods at the same time. No change in shaking.
5) Daizen polyurethane lower control arm #2 bushings.
6) Daizen upper control arm and lower control arm bushings.
7) Daizen steering rack polyurethane bushings. Still not perfect, but this made a huge difference.

I did the steering rack bushings today. I've really, really developed a dislike for Lexus steering bushings!

Some background: I had issues with my '01 LS430 steering bushings @ 85K miles. My only choice was to replace them with OEM. I should have replaced them at 50K. They were really, really awful. The interesting thing, though, is that they physically looked pretty good. The result is amazing; nice and tight.

The bushing design of the SC is essentially the same as the LS. But luckily we have more choices with our steering rack bushings than the LS crowd. I began to hang around the GS guys because their front end is quite similar. The '98-'05 GS430 uses the same steering rack and bushings as our SC. Sewell sells both OEM and an aftermarket polyurethane solution for around $30 complete.

At this point my SC tracks very, very well. The polyurethane suspension bushings probably add a bit of harshness to my ride but I don't find it objectionable and it's a reasonable tradeoff for the added precision in the front end. I don't believe that the polyurethane steering rack bushings have any tradeoffs at all. The remaining shake that I'm experiencing is pretty darn subtle but I'm not done. I'm going to rotate the tires tomorrow and see if anything changes. I'm also looking at toe in. My front tire wear tells me that I don't have enough. I've been running factory settings but I'm going to experiment with a bit more toe due to the additional road forces created by the wheel spacers. I don't give up easily!