Hello, I don't know if anyone here has had this problem before. I have a '98 GS400, and my buddy has a '00 GS300. We both have the same problem. When the breaks are hit hard at slow speeds in reverse or forward, or when turning the steering wheel at very slow speeds, there is a knocking sound that comes from the front of the car. seems as if the front right side. Iwas told that it's the caliper bracket by a mechanic, who disassembled my bracket and showed me it was shaking a little bit. After he assembled it together when I drive and go over bumps with my front right wheel it's as if my shock is brocken, i can now literally hear my caliper shaking underneath my car. SO obviously the caliper bracket was NOT the problem, but now is. The knocking sound is one that is similar to one which the door makes when opened the whole way. If someone has experienced this, please tell me what this could be. I just don't want to go to Lexus and pay like $120 for 15 minutes of work (since they charge by the hour). Thank you

 

I was with you up till here... i had an Acura TL which had the same issue. What it ended up was the pad support plate. As the pad slid on it back and forth it made a sound at very slow speed like you described above. What i did to get rid of the sound was to just grease it. I put some grease on it and the sound went away.

Not sure on this, hopefully the person put the caliper back correctly and nothing is loose. I attached the diagram of it which shows where the pad support plate is located. Hope this helps.

 

Don't forget the struts. In the history report from Lexus on my GS there was a repair made for a thumping sound on the right front. Lexus R and R the front struts under warranty and no sound no more. Sorry I can't be any more specific than that.