I bought this car recently, it’s a 2005 Infiniti G35x, in decent condition but there is a knocking sound when I hit the breaks. Breaks are brand new but this rod underneath my car is rusted. Does anyone know what it’s called? I’ve seen a stay bracket/Compression Rod Stay but not sure if thats what the rod is or just the bracket it connects to..

 

It's a subframe connector / stay brace. People use different names for a lot of this stuff.

There's the big triangle one on the front under the engine, the big "W" shaped one at the end of the driveshaft tunnel, and two smaller ones near the rear tires. All 4 are prone to rusting, just grab it with your hands and see if the metal is separated at the welds.

I think your picture is one of the two on the rear subframe, they're typically called the "rear stay" it's the last picture I'm linking.

If this clunking sound started immediately after replacing your brakes it's not the subframe braces though, it's probably something on one of the brake corners that got overlooked.

 

Thank you! That brace is actually on both sides of the front of my car and not the back, I think that was a big reason for my confusion. It’s completely rusted so I’ll have to replace it either way but i’ll get my brakes looked at again and see if anything was missed. Thanks!

 

If it's not actually rusted through completely and broken off you can just get under the car with a can of Rustoleum automotive undercarriage spray and repaint it, just use a piece of cardboard behind it to catch overspray. Usually a piece about the side of a large envelope works for me.

The Rustoleum undercarriage spray will stay a little flexible in the future, works great, factory it's just painted and as the chassis flexes it cracks the paint and then it rusts.

 

Does it only knock when braking? Not when going over washboard bumps? Do you have any shaking of the steering wheel if braking firmly at highway speeds? There are lots of things that can clunk in the front end of our X's. The lower ball joint in the steering knuckle, the ball joint or the bushing in the compression rod that is held on by that stay in your picture, the sway bar end links have all made clunks for me when going over bumps. Completely blown out bushings on the transverse link gave me a huge wobble/clunking when braking hard at high speeds. If you raise just one front wheel and can push/pull on the wheel/tire at 3-9 and get any movement, you can see what's worn out. If you can put a long bar under the tire and lift up, you might be able to get a clunk from a worn out ball joint. Diagnosing clunks can be tough.