70 Rear bumper brackets and hardware finish

[Bill L.]

Were all the rear bumper brackets the dipped semi gloss black?

Were all the mounting bolts the black/gray phosphate?

Were the bumper mounting bolts on the outside all a Cadmium finish?

Thanks as always


Bill

[Alan S.]

Re: 70 Rear bumper brackets and hardware finish

Hi Bill,
The TIM/JG indicates that the brackets are semi-gloss black like you stated and I'd think they had been dipped.
You're also right about the bracket to bumper bolts, the JG descrbes them as cad plated. It goes on to describe the bracket to frame bolts as black oxide, not phosphate. The black oxide has a bit of a different appearance than the black (manganese) phosphate.
Regards,
Alan

The black oxide finish is VERY easy to do at home with quite remarkable results.

[Bill L.]

Re: 70 Rear bumper brackets and hardware finish

The bolts look great. Whose product did you use?

Also, are the lock and flat washers natural or cad plated?

I am constantly amazed at all your pictures Alan.

Hi Bill,
The TIM/JG indicates that the brackets are semi-gloss black like you stated and I'd think they had been dipped.
You're also right about the bracket to bumper bolts, the JG descrbes them as cad plated. It goes on to describe the bracket to frame bolts as black oxide, not phosphate. The black oxide has a bit of a different appearance than the black (manganese) phosphate.
Regards,
Alan

The black oxide finish is VERY easy to do at home with quite remarkable results.

[Edward J.]

Re: 70 Rear bumper brackets and hardware finish

Were the bumper mounting bolts on the outside all a Cadmium finish?


Bill, my 72 has the rear outside bolts with the TR marking and they are cad. plated

Thanks as always


Bill[/QUOTE]

[Pat M.]

Re: 70 Rear bumper brackets and hardware finish

I am constantly amazed at all your pictures Alan.

Me too. All of the things in Alan's photos always look perfect.

[Alan S.]

Re: 70 Rear bumper brackets and hardware finish

Hi Bill and Pat,
Thanks for the compliments.
I've been very fortunate that the vast majority of the parts on my 71 were restorable. Those bolts were done with the Caswell Black Oxide materials. The blackening goes very quickly after the parts are prepped and scrupulously cleaned. They also supply a sealer that you dip the parts in immediately after they come out of the bath. The sealer gives them a good appearance and protects the oxide, but I've found it takes about 3 days to dry so the fasteners can be handled.
I'm also setting up Caswell's small copy cad/ zinc system. It's more involved than the oxide, but I'm hoping for good results based on what I've read here on the board. I'm redoing fasteners that I plated with an even smaller tin/zinc system about 10 years ago.
About the rear bumper bracket washers and nuts.... I'm not sure of their finish; perhaps someone else can help you with a reply!
Regards,
Alan

[John H.]

Re: 70 Rear bumper brackets and hardware finish

Alan -

Nobody likes to hear this, but I seriously doubt that any Corvette bumper bolt was EVER finished in black oxide; that was a VERY expensive premium fastener finish, and it's unlikely that the bumper release engineer would ever get that premium cost past either the fastener engineers or the cost guys. I think you'll find they were originally phosphate & oil, which was pretty much the GM standard for bolts.

[Ron G.]

Re: 70 Rear bumper brackets and hardware finish

My experience has been that all the brackets were originally dip plated and the hardware for 1970 thru mid 1971 was black oxide. From mid 71 thru 1972 you will start to see silver cadmium. This is for the rears, not the front.

[Alan S.]

Re: 70 Rear bumper brackets and hardware finish

Hi John,
I'm surprised about your description of the the 2 finishes.
In doing the small batches I'm doing these days it seems the oxide process is faster and takes less precise control than the phosphate process. I realize that may not be true in production sized operation.
I certainly value your experience and thus opinion!
Regards,
Alan

[Bill L.]

Re: 70 Rear bumper brackets and hardware finish

Just to clarify.

All hardware on the underside, including all washers, is either black oxide or phosphate. All hardware on the outside, including washers, is either phosphate or cad?

Alan, I would be happy to bring my fasteners to you to perfect your plating before you do yours

Thanks, Bill

[Bill L.]

Re: 70 Rear bumper brackets and hardware finish

I also just noticed that I have three different headmarks. M, A, and RBW. All appear original.

Bill

[G A.]

Re: 70 Rear bumper brackets and hardware finish

Alan -

Nobody likes to hear this, but I seriously doubt that any Corvette bumper bolt was EVER finished in black oxide; that was a VERY expensive premium fastener finish, and it's unlikely that the bumper release engineer would ever get that premium cost past either the fastener engineers or the cost guys. I think you'll find they were originally phosphate & oil, which was pretty much the GM standard for bolts.

Mine is an October 10 1969 production and I just finished doing the front bumper attaching hardware. All the bolts under the car were, I'm 98% certain, black phosphate (it has a distinctive way of coming off while cleaning the bolt with a wire wheel). The finish was still in pretty good shape due to the low usage of the car. Headmarks were A, M, RBW and the difficult to describe 'Bowtie'.

Alan, I've been phosphating for about two weeks now and it goes a whole lot faster than the cad stuff.

Dan

[Alan S.]

Re: 70 Rear bumper brackets and hardware finish

Hi Dan,
I too have found the phosphating (should we be calling it Parkerizing?) to be quite a straightforward process. Of all the finishes I tried to do on my hardware over the long period of restoration, it seems to be holding up the best.
The original tin/zinc process I tried wasn't very successful; but what I'm learning about the various parts of the process now gives me hope I can do something with a more 'original' and long lasting appearance. Just learning about the effect of the voltage and amperage on the plating has opened my eyes. I had SO many things going on with the car at once during that period that I realize I didn't put enough study into the plating I was doing. That was close to 20 years ago and I didn't have the Internet, (did it even exist?); and had little to no contact with other restorers.
It's really interesting to still be curious about how 'stuff' is done!
Regards,
Alan

[Alan S.]

Re: 70 Rear bumper brackets and hardware finish

Hi Bill,
I may take you up on your offer/request..... if YOU do the prep!!!!
Regards,
Alan

[Bill L.]

Re: 70 Rear bumper brackets and hardware finish

Hi Bill,
I may take you up on your offer/request..... if YOU do the prep!!!!
Regards,
Alan

Thanks Alan.

By prep I assumes that means a piece of hardware that is bare steel.

Bill