Ive got a 1970 Monte Carlo that i recently replaced several parts in the front end (Bushings, shocks, springs, rotors, brake pads, ball joints) When i put it all back together i had a larger black washer left over that came off the spindle.

After looking around online it looks like it goes around the spindle between it and the backing plate. Is this a critical piece? Looks to me like its just to prevent noise, but id like to know before i tear it all apart again to put it back.

Any help is appreciated!

 

I would think that it is there to keep dirt and grime out, protect the bearing and take up any play when it's all tightened up. I would put it back in if it were me. I dont know exactly what it's for but this is my best guess.