I am brand new to this forum and have a problem. My 93 SC400 is overall in superb shape for 201,000 miles but has recently developed a subtle but detectible vibration at speeds over 70. It has It has brand new tires that all road force balance correctly. It has a new transmission mount plus a new center bearing on the drive shaft. This past summer the front lower and rear upper suspension bushings were replaced. The transmission itself was replaced about 35,000 miles ago at the Lexus dealer. The Lexus dealer detects the vibration but says after having addressed the items already mentioned they do not know what is the cause and don't want to start guessing and replacing parts and then end up not solving the problem. They suggest to just let it get worse at which point they expect to be able to diagnose the culprit item. Of course I could do that, but I simply don't like vibrations. That's one of the main reasons I bought a Lexus and spend all the money I have spent to keep it in near perfect mechanical condition. I would really appreciate ideas from anyone out there who has either had a similar problem or has some ideas on what the problem might be or how to find out what the problem is. Thanks in advance for helping me with this.

 

Welcome!!!
Motor mounts?? At 201,000 milies and a '93 they are guaranteed to be toast!

 

Could have been an idiot that did the balancing.......... Did you notice the vibrations after the new tires were put on?

 

yeah vibrations at highway speed through the steering wheel indicate misbalanced tires..., otherwise go with Mkorsu's suggestion.

 

Check the AIR PRESSURES in your tires...!!!!

 

def have a feeling its the motor mounts, they tend to get shot at that many miles...i have a 95 sc400 with 259k miles and the mounts are almost gone no vib. thank god but my friend who specializes in lexus's used tow ork thru dealer for many many many years...told me u will feel sooner or later...cud be other things tho...but most likely motor mounts

 

Thanks. I will have them looked at but I don't think they are the problem, because they have already been replaced twice, the last time in 2004 somewhere around 150,000 miles.

 

Thanks for the idea. Actually, the vibration was there before the tires were replaced, and that was a reason to replace them because they were somewhat cupped and it was believed that that could be the source of the vibration. The new tires actually did improve the situation, it's just that it's not perfect anymore, and unfortunately, I can detect the slightest flaws. I appreciate your taking the time to answer.

 

I appreciate your taking time to respond. Thanks. Actually I didn't make it as clear as I could have. I don't feel the vibration through the wheel at all. What I feel is in the seat of my pants and occasionally through my calf through the accelerator pedal. And when I do feel that slight something in my calf, it sometimes can be under 70 mph. And, it seems like it's worse going up hills, but that isn't always true. Since the center bearing has been replaced, I keep suspecting the drive shaft, but the Lexus dealer understandably does not want to replace that if they can't be sure that's the source. I

 

Thanks for responding and congrats on that many miles. As I've already posted I don't think my problem is in the mounts because they are so relatively new. Speaking of as many miles as you have, I am curious about whether you have used any synthetic lubricants to get that far or have you made it on regular petroleum lubes? My dealer tells me about a number of high mileage cars that haven't used synthetics, but I have wondered whether that was really possible and when I say possible I mean to go that far and have all the drive train components in pretty much excellent condition?