You need them, all 12 of 'em...don't ask why, just replace them if lost.

https://www.partzilla.com/product/honda/45128-ME2-003

 

If Mr Honda put them there, they are undoubtedly required. No compromise in the braking dept for me.

 

Might add that the center of the one on the right in the above pic looks a bit eccentric. I'd be replacing that one as well, and looking carefully at the rest. Make sure the discs are properly torqued when reinstalling 'em (clean the grunge off of the old washers or your torque specs won't be accurate).

 

I would have to disagree with this statement. Quite a few people dont reuse the paper washers. Either they lose a couple and dont want to spend the money or dont understand why they're there in the first place. I would either use them all or none at all. I have heard they are there as noise reducer for the disc.

 

These washers aren’t just bits of paper are they ?

Mr Honda obviously developed and worked out the correct bolt arrangement and pressure distribution for our brakes, but if he possibly decided that vibration, temperature variations and other factors could have a NOT meaningless effect on the possible torque settings of bolts in that area, and
he then decided to use washers then who am I to argue.
I don’t know exactly why he wanted them but he did, and I wouldn’t waste my time trying to second guess in this situation.




I can understand a little of the argument to not bother with them but can’t understand at all the swerving of the minor cost of just replacing the lot and putting it back together as designed.
Just my thoughts.

 

OK...let's end this.

The washers are there to center the disc in the caliper. Without it, the disc is being forced out of its proper plane of orientation whenever the brake is applied, resulting in significantly reduced braking force and majorly uneven brake pad wear. It also helps reduce heat transfer from the disc to the hub.

Do not install the discs without them, and if you have any that are beat-up or worn, replace them.

 

It says in the description, shim, so it's needed for proper spacing as stated above.
I would say that more importantly is that when not installed, you would have a hard surface mounted to another hard surface and when the brake is applied, it would sing.
Those things are cheap enough so replace them with new. You have done so much work on the wheel so far so don't cheap out, install new.

 

I read somewhere their main purpose is insulate heat from the hub and to keep the disc from "singing". But to center the rotors in the calipers, no. The calipers float so they will center themselves on the rotors.

 

I'd be concerned that, towards the end of the pad life, that uneven wear of the disc and pads might be an issue without the washers. So yeah, my previous post is likely a bit hyperbolic. Heat transfer & noise is more likely the main reason.