S2kstephen

Try replacing the steering rack bushings:


I spent hundreds of dollars on replacing wheels, tires, mounting/balancing, alignments, lower suspension bushings....$40 later it's smooth as butter.

leone

Did you ask owner why he replaced the shocks with only 26,000 miles?

Byescott

He said the Lexus dealer recommended he do so as one had a small leak. They claimed the miles normally don’t cause them to fail but age.

Byescott

Well the owner called me tonight said problem was solved. Took car to suspension shop and in about 10 minutes they found right front rim was bent. He has ordered a replacement rim. I am going back to test drive it again on Tuesday. If the ride is smooth the wife and I will be proud owners of an 06 SC 430.

Harold57

Very cool, good luck.

VVV1493

As I am having brakes serviced, bushings replaced on all four wheels my mechanic discovered on my 2005 that the seals or boots on the Caliper Guide Pin was torn in 2 places. Allowing moisture in and the pin to rust and wear as photographed. The left being the normal one. My tires are BF Goodrich and new. And the shocks were all replaced with OEM recently. With further research on O'Reilly's website we discovered it can seize up which contributes to the vibration. But immediately upon seeing it he was certain it was the culprit. I hope this helps anyone with this issue.
PS: Mine vibrated at 60 and 80.

On the left normal wear and tare. On the right is the one with two years in the seal and the damage lack of lubrication caused. So it can be very bad. Through reading other sites of Lexus owners and clubs we also garnered that it isn't unique to sc430 it's common in the brand. And we're it not for having the bushings and brakes serviced we would not have caught it. Hope it is of assistance.

Harold57

So VVV1493, I gather your vibrations are now gone?

Wilson2000

While this is a common problem with the brand, as you said, I wouldn't expect it to cause a vibration between 60-80 mph. What I would expect it to do is cause vibration and noise while braking at any speed, and perhaps, brake noise at all speeds if the pin was frozen and not allowing the caliper to "float." A corroded or frozen pin will prevent the calipers from settling into a central, even position as the brakes are applied and as the pads clamp down on the rotor. Also, any braking vibration due to a slightly warped rotor would be vastly exaggerated as well.

jimisbell

I CURED THE 55 MPH SHIMMY
My car shimmyed at 50 to 60 MPH and also porposed on undulating highway.
I replaced all four wheels and tires. They needed to go from the purchase day, anyway. The shimmy is GONE. I suspect a bent wheel. I now have a surpluss set of five wheels and three with usable tires. Are they worth anything (OEM 2006)?
The porposing is still there so obviously they are not related problems. I am now going to replace rear shocks.

Harold57

That's good to see Jim. I haven't seen the term "porposed" before.

jimisbell

i suppose you could talk to my spell checker, she may know what she had in mind. My prefered spelling would be porpoise. i.e. nose down, nose up, repeat threee times.....etc.

jimisbell

I just bit the bullet and spent $800 for a full set of of 4 (front and back) OEM Lexus shocks. I hope at that price all the porpoise is gone. The first ones lasted 180,000 miles.so I have high hopes that these will outlive me.

doobs

Jim,

Would it make more sense to do a set of Coilovers from MeisterR? The ZetaCRD units for our cars is $1000.

I find my '07 with <50k miles on it has a lot of lift/squat (porpoising as you call it?) under hard acceleration. Pretty certain the shocks are not worm out.

The Coliovers seem allow for a great deal more latitude in setting the suspension up exactly as you want it. It's the direction I'm going go to when space/time/money allow.

Just sayin'....

jimisbell

When I refer to porpoising I am not refering to "squat" I am referting to a porpoise like oscillation that goes on for seveeral cycles when the rear end hits a dip in the pavement att speeds above 30 MPH. Like a porpoise swims.

I have examined the situation and see no good reason to go with an aftermarket solution for a problem that can be fixed with OEM parts when the aftermarked solution costs 25% MORE than OEM. Also the life of the aftermarket solution is not known and I KNOW that the OEM parts lasted 180,000 miles!!!

tmakogon

In my case the shimmy, also at 60MPH, also went away at <50 or >70, was caused by alignment. Once aligned and perfect, the steering wheel vibration disappeared.

So many possible causes, including bent wheel, off-balance wheel, deformed non-original wheel centralizer, worn steering bushing, worn suspension bushing, etc. etc.
The same is observed in many cars. When all is perfect, there is no shimmy, but if one thing isn't perfect there is shimmy (steering wheel vibration).
This similarity suggests this is a system design property.

The front stock springs could have a resonance frequency around 60MPH.
If the front stock springs are the root cause, this is Lexus' engineers shame.

If any of us here is a mechanical engineer (or if anyone here took middle school physics) they could help calculate the spring characteristics which would cause the spring resonance (or natural frequency) of a wheel rotating at 60MPH with wheel size 245-40-18 (or whatever the wheel size is).
I'll take a stab but I'm not a mechanical engineer.

A search for 2454018 tells me the tire is 653.2mm diameter. So at 60MPH wheel rotates at about 13 Hz.
A search for SC430 wheel mass tells me wheel is 37lbs.
A search for 2454018 micheline pilot sport mass tells me tire is 23 lbs.
A search for SC430 front spring mass is 5.7 lbs.
A search for SC430 front shock mass is 6 lbs.
Sums to about 66lbs (30kg) sprung weight of the front wheel with half shock and half spring.
A search for spring natural frequency calculator tells me that 30kg has a first natural frequency of 13Hz if spring is about 200 N/mm or 20 kg/mm.
Don't know if this number makes any sense to suspension specialists.
Perhaps at some next harmonic the resonance could occur with stock springs around 60MPH. If frequency is half of that, 6.5 Hz, the spring should be 5 kg/mm.
This means that if the stock front springs happen to be 5 kg/mm, the first harmonic would be at 30 MPH, which is too slow to notice. Next resonance at 60MPH.

Anyone know what the stock spring kg/mm rating is? Stock spring is 48131-24600 but nobody mentions the stiffness.
Any engineers/suspension modders here?
Anyone experience 60MPH shimmy with non-stock front springs?


Edit: Found this reference that stock front springs are 4.8. The puzzle seems to match. Stock front springs resonate at about 58MPH (and also at 29, 87, 116 and 145 MPH).