Hey guys i have a 1998 sc400 and i need help. When i am traveling at 40-45 mph i feel a vibration and its only when i am traveling 40-45mph any other speed its smooth. It feels like it is coming from underneath. If you could help in anyway i would greatly appreciate it thanks.

 

The transmission mount is a likely culprit, although I would expect it to be more at highway cruising speeds from what others have said.

 

Should I buy a new mount or should I fix the one that's in there?

 

Similar problem with my 97 5 speed just popped up. It vibrates like crazy it actually felt unsafe so I got onto the access road it still did it just at "safer" speeds like 45-50mph. Is it my transmission mount as well? I also have a high pressure power steering hose leak could that be the culprit? I'm not exaggerating it vibrates so hard the sun block visors shake the steering wheel the shifter **** the seat belts absolutely everything even the sunroof

 

The tranny mount compresses as it breaks down. There's nothing to fix, so it should be replaced if it's worn. Mine still had some life left in it when I replaced it (want a cheap one? ), but you have to remove it to be able to tell and I figured there's no point going to all that trouble without a new one on hand.

ashtray, I would think your motor mounts or suspension components are more likely to blame. I'd be surprised if the transmission mount can cause that much vibration.

 

Get an alignment, check suspension, get a trans mount & make sure your tires have equal pressure in all 4 wheels. But like stated, probably suspension issues. My car currently has 100,8xx. It is a highway warrior. No vibrations. Accept the ones due to road surfaces and the Zeal Coil Overs don't help lol.

Keep us posted.

 

Check the center support bearing on the driveshaft. If you can hear some slight clunking around when shifting from Park to any other gear, OR a quick stab of the throttle, the bearing is worn out. Mine also has an electric car sound coming from the trans tunnel at very slow speeds. While you are under the car, check out the transmission mount as well. Both of these items are common failures. My car needs both.

 

Had this problem on my 92 sc400 and an LS400 1999. Replacing the tranny mount takes about 15 minutes. I think the mount was about $86.

Make sure you take a jack and take the weight off of the mount before you release the bolts.

Easy peasy

 

Thanks! I will check underneath it.

My tires all have the same amount of air and im getting BC coils soon, and Im going to check underneath . I appreciate your help !

I will check both, thanks for the help!

Found one for 56$ brand new thanks a lot!

 

So the issue on my car was that my passenger front brake caliper completely ate $#!T and seized frozen as compressed as it could on the rotor. So basically every time my wheel turned a revolution the caliper would skip or pop open and clamp back down. I have no idea how this happened, probably that cinder block I hit on the damn highway. Anyway, my bearing in that wheel is also shot. Insurance has me covered. Heres to new brakes/rotors and bearings.

 

My SC vibrated at high speeds, so i had the wheels balanced. Viola!

 

Trollololol

 

Usually vibration at a certain speed is caused by a rotational part being out of balance, usually tire/wheel. Could be a separated belt in the tire, bent wheel, bent or out of balance drive shaft. A warped rotor will usually only cause pulsation when brakes are applied, but they can do funky things if they are real bad.

 

Im bout to put on new wheels so will that affect the wheel balance? Also i am going to bring my car to a mechanic so they could lift it and see if the drive shaft is bent. I was thinking it was a tranny mount but this is something new. Thanks for the input

 

If its a constant vibration that progressivly gets worse the faster you go, then its something to do with your wheels (likely balance, but as Ashtray showed us it could be a few other things like a brake caliper).
But if the vibration is only at certain speeds (ie, 40-45 as OP stated) then its likely the transmission mount. I had this same issue in my previous '99 and swapping out the tranny mount cured ALL vibration issues I had. It was a stupid easy job to do, and worth doing on ANY sc over 80k regardless of whether you think you have vibrations or not. Once changed, you car will run even smoother than you thought it did before

..same as the tranny mount, the engine mounts are made the exact same way, so if your tranny mount needs replacing, then likely your engine mounts do too.