Shimmy when braking


#1

hello. i have a 1992 lexus ls400 which for the most part is in very good condition.i bought it used and noticed a shimmy in the braking and when reaching speeds of about 65=75mph.i have replaced tires which have effectively taken away the high speed shaking in the steering wheel. i have replaced the rotors and pads, tie rod ends and steering rack. bearings seem fine. i haven’t been able to get rid of the shimmy when i apply the brakes at about 40 mph and up. i get a hard shaking in the front end which feels like something is going to fall off. i’ve had it up in the air and examined 3 times and the mechanic is not finding any problems. is there an inherant problem with this year? what suggestions might i try to alleviate this. thanks for anything. jim


#2

Take the car to a totally different mechanic. If this mechanic you are speaking of is trying to diagnose the source of brake shimmy while he has it in the air (without touching or driving the car) then the only thing he is capable of is changing tires - and I doubt his ability to do that. The shimmy only comes when you are breaking, then it can only be the brake rotors or the wheel bearings. when you had the tires replaced, you had the tires balanced and that is what took care of the high speed shakeing. New tires off the shelf have to be balanced, and then it has to be done periodically. Anyway, you’re talking about two different problems and I think the remaining problem is the brake rotors. If it was the wheel bearings you would have known for sure by now - the tire assembly would have fallen off. Take the car to a reputable shop and have them turn the rotors and also replace the brake bads. The best shop you are going to find is one that probably looks like a hole in the wall, but it has consistent business. It will also have a low shop rate per hour. Basically your going to be looking for a mechanic who has bought his own shop and is not part of a chain store - he has very low overhead and he keeps his shop rates low because he makes more by bulk business and not by chance. The chain stores will have people who will work for them for nothing because they have to pay the franchise and therefore have a high overhead.


#3

thanky you beefy, i will try someone else. i had suspected the rotors even though they are brand new.


#4

I think the car should be put on the rack and a magnetic base dial indicator used to check rotor run-out.
It’s possible that the car could have a warped hub due to a wreck in the past, large pothole, or having struck a curb hard.
This can tweak the hub and will in turn throw the rotors off a bit.

If this is the case, then new hubs are in order or (depending on the price) it is possible to surface the hub flanges.
I’ve assume here that both the front and rear brakes have been done?