While driving, i'm getting a knocking sound that increases with speed (from 0 - whenever). The car is also experiencing vibration at highway speeds.

I'm thinking there is a problem with the driveshaft, but haven't gotten underneath the car to check.

What are the likely culprits for this bad behavior?

Center Driveshaft bearing?
Motor or transmission mounts?
Differential?

If anyone has experience with this kind of problem, please chime in. If you know the costs for the repair (parts $) and how long it should take to perform it, please post that too.

Thanks guys

 

Could be an unbalanced driveshaft but that is not common on the SC's, but could happen if the driveshaft took a big hit or something...I would check the motor and tranny mounts first...Then maybe the differential and or drive shaft joints..... How many miles are on your car?

 

Lift the car and push up on the driveshaft. If it moves, then its the center bearing. Get a used driveshaft from one of the guys in the parts section.

If it doesnt move, then go to any lexus dealer and get a xmission mount for $75. If it doesnt fix the problem, well... you needed one anyway

 

I've got about 132,000 on the car

and 14 years later i am sure it will need a tranny mount

I'll check those out. I haven't heard of the shaft joints going bad on these cars that often, is it very common?

 

Would any or all of the suggested fixes apply to a w58 5-speed. I've got vibration that comes on in the ~85mph level. Put in a n/a lsd and then it started.

 

i had a similar problem mike. turns out to be my diff. does it feel like it wants to lock up like a welded diff and makes a lot of nasty noises? i hope its not.

 

the knocking sound is really consistent with the wheel speed, so i don't think it's on the diff side. Seems to drive and handle just fine...except for the

ko ko ko ko ko ko kokokokokokokokokkkkkkkkkkkkkkkkkkkkkk

knocking sound + vibration

 

could be one of the rubber flex discs at each end of the drive shaft-- I had a bmw 5 series that did exactly the same thing-- and all it was was a flex disc--

Cheap repair...

 

Bump this because I'm having the same problem. Could anyone chime in?

 

Check the center bearing bolts. They could be loose from the lsd install. I have see it happen.