Odd Vibration, But Not From Brakes

[probabli]

1995 GS300, 100,000 miles, no accidents, bought new.

The front vibrates when braking. Even the shifter handle on the console vibrates like mad. Rotors, of course, but don't think so. Rotors were turned twice to of no avail. Then I replaced with new rotors and brake pads. The pins on the calipers were also well lubricated. Same problem again. Then onward to suspension. No apparent problem, as checked out by a garage (although I still have reservations on that). The brake paddle does not vibrate when the symptoms occurs and the car drives beautifully straight and vibration free. The problem occurs only when braking, and seems to come from one side (although I am not positive on that) and the car does not pull to either side. Also, the antilock brake light does not indicate any problem. The tires do not have abnormal wear. Some people mentioned Universal joint, but there is no noise or any abnormal sensation while driving. Master cylinder? Brake boost? Brakes do not lock or is there any loss of braking. Antilock brake still? The problem is not noticeable when braking from 20 mph or under. But braking from 40, the vibrations are definitely there. Thanks for your help in advance.

[ColinBarber]

steering joints?

[jmorris]

I have a 1990 LS400 with exactly the same symptoms. Has any one found a solution to this problem yet?

[rhaines]

engine mounts going soft ????

[andybriggs]

Take it to a Lexus dealer....

For a guess:

Warped disks

Ball joints/bushes

[yoshi]

I checked the service manual, nothing obvious in there.

I take it you've checked the discs aren't warped?

Yoshi

www.lexusvertex.com

[jmorris]

I have turned all 4 rotors, replaced the rear trailing arm bushings, replaced the ball joints (lower), replaced an upper differential mounting pad that was cracked, checked the engine mounts and checked the transmission mount. I visually checked the steering links and the front lower strut rods and could not detect any play there. So far nothing has helped. I did notice that after the rotors were turned that one front rotor has .003 inches of runout. I doubt that would be enough to cause the problem since new performance rotors have +/- .002 inch specs.

[ColinBarber]

Have you checked for play in the steering rack?

[maneesh]

I've got a similar issue with my LS400. I thought the front discs were warped, so I replaced them. Problem still there. Funnily enough, it isn't there all the time.

Before the problem occured the steering rack had already been changed under warranty.

I then changed the upper front control arms (bushes were split), but problem still there.

Now I'm changing all anti-roll bar bushes, strut bar cushions, front lower control arms, both engine mounts, transmission mount.

I'll provide feedback once the car is back. I'm confident it's a suspension issue rather than a braking issue.

[jmorris]

I am very interested in the results of those repairs. I would be helpful if you could have the technician comment on which parts show the most wear.

Thanks.

[jmorris]

I am happy to report that the violent shaking of the shifter and on occasion, the steering wheel while braking at speeds over 40 MPH has been solved. Apparently machining the rotors twice in 6 months by two different shops did not correct a "fat spot" in one of the front rotors. Upon rechecking the rotors, I found that one rotor had an area that was .0035 inches thicker than the rest of the rotor. I replaced the bad rotor with a new brembo rotor and the shaking is completely gone.

[ColinBarber]

Glad to hear it's all sorted out now. Shame the people who machined your rotors didn't do a good job, would have saved a lot of hassle.

[Rob]

I replaced the bad rotor with a new Brembo rotor and the shaking is completely gone.

i am hoping that you have not replaced just ONE rotor and that u have changed them as a set???????

[Monster-Mat]

well i would never have recomended machining the discs anyway, once a disc is warped...............its always warped!!

if you have warped discs .change them