1967 power brake booster discoloration

[Michael C.]

Over the winter something has happened to my power brake booster. Looking at it today I noticed blotchy, sorta gray in color specs, on the unit itself. It is not rust. Believe it or not it , it looks moldy , but it is not mold. The plating on the booster is cadium dichromate. I tried using some rust removal solvent and 0000 steel wool on a small spot. It somewhat helped, not to my satisfaction and it took the color off of the booster. Question is , what is this stuff ?? How do you get it off without screwing up the color of the booster and how do I get the color back onto the spot I messed up ??? Sure would appreciate any ideas. Thank You Mike Chase

[Gerard F.]

Re: 1967 power brake booster discoloration

Not sure what exactly the spots are but it was probably something acid which dissolved the dichromate protective finish, and brought it back to the zinc or cad plating on the booster. If it is gray with white powder, that is how zinc corrodes.

An acid rust remover will dissolve the dichromate finish, which is simply a dichromate reaction on fresh zinc or cad. I use muriatic acid cut 2 to 1, to completely strip dichromate from parts to be replated with zinc in my hobby replating kit.

If you now have a lot of spots and rub off of the dichromate, you should probably go to a replater. You might get by with stripping the dichromate, buffing the part to a bright shiny zinc finish and then dipping into yellow chromate, if you still have the plating intact. Dichromate reacts with the zinc or cad plating only. There are paint coatings out there, but there is nothing like the original plating finish.

Jerry Fuccillo
#42179

[Michael C.]

Re: 1967 power brake booster discoloration

Jerry , thank you for your response. Mike Chase