Hi i have a 2000 chevy blazer LS and I have a problem with the lower or upper control arm. When I brake from the front nothing happens, everything is normal. But when I back up a thud is heard. I put the vehicle on drive and I arrive at a stop sign and again the dull noise occurs and this from the driver's side. Same thing when I reverse what is the problem? Can anyone help me. Thank you!

 

It sounds like you likely have it narrowed down to a front end component. There are many ways these could fail such that you get clunks. Off the top of my head I'd think a bad control arm bushing but you'd have to jack up the front and visually check all the parts. You will also have to wiggle all the parts by grabbing the wheels and seeing if anything is loose. Keep in mind that some of the parts are under tension due to the springs so this is were the visual inspection comes in.

 

Is your 2000 Blazer LS 2WD OR 4WD ? This answer helps you get accurate info.