aamir007

Hello friends, I have a 93 sc400 in excellent condition. recently I was out of the country for about 6 months and when i came back i drove the car and noticed a very bad front end vibration when i go over bumps or un even roads. The mechanic changed the inner and outer tie rods, all front end bushing, engine mounts, transmission mount, but the vibration remains there. Although its less noticeable after changing all these parts. The car runs smooth on nice paved roads otherwise but on bumps the steering wheels vibrates. As soon as it hits a pot hole or a dip i feel the vibration. The mechanic is now clueless.The wheels are balanced and tires are fairly new. Any suggestions on what the cause is? Thanks

chnk

iTrader: (12)

i would like to know this alo, my sc does the same thing

SaintLouSC

Lower control arm and steering rack bushings? Pretty common wear items.

m1k3yg

sway bar bushings and links?

horent135

iTrader: (10)

Most likely control arms if not, then it wheel balance

Ali SC3

iTrader: (10)

could be early sign of steering rack bushings.
if you havent done your lower control bushings you should check them.
check the uppers also its less common but can go out.

if you have aftermarket wheels on try the stock ones and see if it still does it.

GamblerZ

I would check the steering rack for wear as well, along with all your bushings.

An oft overlooked item that can contribute to vibration (aside from poorly balanced wheels) is warped rotors. "Warped rotors" can be overused to diagnose vibration problems, but in short, causes for this can be one or all of the following:

- the hub and wheel flange are not flat and in a good condition
- the wheel bolts/lugs or hat mounting hardware is not
a. in good condition
b. installed correctly
c. tightened uniformly and in the correct order to the recommended torque specification

Too many times I have seen wheel & tire shops use an air wrench to tighten wheels without hand checking lug torque to spec. Simply put, over tightening of the wheel lugs can translate into a warped brake rotor after a few good heat cycles.

However, given that most of you seem to be experiencing this following a bump leads me to believe that it is a steering rack issue, deteriorating suspension bushings, or both.

Dougspeed

iTrader: (2)

You say that the car rides perfectly smooth on nice paved roads and you only feel vibrations on rougher roads. That seems pretty normal to me on the SC. If it were an issue with tire balance, warped rotors, etc, then it would do it all the time regardless of the surfaces you're driving on. The steering on the SC is just a bit more sensitive than most any other car I've driven with regards to pavement being driven on. I've yet to drive an SC that doesn't do this. Reducing the tire pressure helps smooth out some of the vibrations for me, especially if you have it pumped up to a higher psi.

aamir007

Here is the update. All bushings, engine and transmission mounts are replaced. New inner and outer tie rod ends. Tires are fairly new . I have an NSX, G35 coupe and a 740i and my beloved SC400. The steering on my SC is the best between all cars. Never ever before it gave me any problems. The only thing that I did not mention was that for almost 6 months I did not drive the car and it sat outside in extreme temperatures. These symptoms started after the car came out of hybernation. The only thing that I have not replaced is the front hub/bearing. I do hear a faint clicking noise when I hit the brakes. Could that be an issue. Secondly how much is the hub assembly and where should I get it. All previous parts are from Lexus OEM. This vibration is most annoying. My cars are my passion and all are in immaculate condition. Moreover my SC is now my daily driver. Any further suggestions?

Tabaka

iTrader: (8)

Your tires developed a flat spot with the 3,000lbs car sitting in the same position in different climates over the six month history. Take the wheels off of your G35 and install them on the SC. Let me know if it still feels the same.

Dougspeed

iTrader: (2)

^^ this. Flat spotted tires won't affect the balancing of the tires so it will show up as balanced on the machine but will still give you bad vibrations.

aamir007

Thanks for all the replies. I changed the tires, swapped the wheels off my G35 but the vibration remains. Next step i am taking is to change the rotors even though the vibration is persisitent now and not only when i hit the brake. The only other thing remaining is the hub and the spindle. Any suggestions on where to get them from, other than the dealer. I need help desperately. Over $1500 spent on the changing the front bushing, engine mounts, tie rods, tires etc. I truly want to choke my mechanic on replacing all these parts and the car still shakes as before. Your expert opinions will be appreciated. Thank you very much.