I noticed these cracks in my right front steering knuckle when I was changing my brake pads/rotors. The red arrows show the extent of the cracks that don't show up well in the photo. None of these cracks extend around the corners of the steering knuckle so I don't know if they are just surface cracks or something more serious.

The steering knuckle looks like it has some sort of surface treatment, paint maybe (?), so I'm hoping these cracks are only surface.

Opinions?

 

Looks like surface from that picture.

 

Forged part, i believe mine looks the same. I have also bent one too, adds camber when you bend the upper area, great for CS autocross and Spec Z

 

Really looks more like a surface defect probably due from the cracking in the die it was cast in. The dies usually develop cracks like that over time and it will show in the casting. The die is obviously in its later stages of use because to the right of the hole you can see weld marks where it has been repaired.

The coating you are referring to is probably the release agent they used on the die.

I worked in aluminum casting industry for years as a Quality Engineer and thats a typical die cast part and surface appearance

Below is example of die thermal cracks - they can either make a recessed looking crack or a protruding flash line depending on the flow characteristics of the die.

Probably since that is a hot spot in the die some material is pulled out when it separates, mirroring the die crack into the casting. you can see some other places on the part that had some pulled out as well. Also looks like a heavy flash line on the edges indicating that die was probably nearing a service. Heavier die release also is a good indicator of that, explaining the excessive staining you refer to as "surface treatment or paint".

In other words, it looks fine, if you want to see if its really a crack, mag particle or dye penetrant is the only real nondestructive way to do it.

But again, I dont think its a crack.

 

no worries there man its just surface

 

Surface

 

Thanks guys.

 

The inside surface of my nismo diff cover looked 1000x worse. All surface cracks.

 

Definitely looks like surface cracks!