69 Caliper Mounting Bolt Washers

[Michael C.]

I've seen previous posts regarding caliper mounting bolts, but haven't seen anything about the washers. I purchased new calipers from a supplier sometimes praised here and they came with a set of bolts and washers. The bolts are black (oxide or phosphate?) and the washers appear to be zinc plated. My old washers are so corroded I can't tell what there were originally. Thoughts?
Thanks,
Mike

[Ron G.]

Re: 69 Caliper Mounting Bolt Washers

Michael,

My thoughts are that they are either black oxide or black phosphate.

- Ron

[Joe L.]

Re: 69 Caliper Mounting Bolt Washers

Front caliper bolts-----GM #186645-----phosphate or phosphate-organic

Rear caliper bolts------GM #3843384----phosphate or phosphate-organic

Lock washers------GM #103328----plain steel

So, what's phosphate-organic finish? It's kind of a "shiny" appearing phosphate finish with a more "brownish" coloration.

[David B.]

Re: 69 Caliper Mounting Bolt Washers

GM #186645 is 7/16 - 20 x 1 1/4 Plain

[Joe L.]

Re: 69 Caliper Mounting Bolt Washers

GM #186645 is 7/16 - 20 x 1 1/4 Plain

David-------


In that case, either the original bolts on my car were not the specified 186645 or the finish spec was changed before my car was built. The bolts on my car were definitely black phosphate or phosphate-organic.

[David B.]

Re: 69 Caliper Mounting Bolt Washers

Kind of thought there would be a question about that. GM Engineering spec. is pretty precise. The part # for a phosphate coated bolt
7/16 - 20 x 1 1/4 is # 9425339. Agree something is off target! If phosphate used why not use phosphate lockwasher #123153 also.

[Joe L.]

Re: 69 Caliper Mounting Bolt Washers

Kind of thought there would be a question about that. GM Engineering spec. is pretty precise. The part # for a phosphate coated bolt
7/16 - 20 x 1 1/4 is # 9425339. Agree something is off target! If phosphate used why not use phosphate lockwasher #123153 also.

David-----

It could be that the GM #9425339 bolt was the bolt actually used despite what the AIM says.

As far as the lock washer goes, GM often used plain finish lock washers in a fastening system that otherwise included phosphate finished fasteners. Why I've never been able to figure out.