1969 Trailing Arm hardware finishes

[Kevin S.]

First time posting here,

I have the trailing arms off of my 1969 Coupe, standard suspension, L-46 4-speed and I am trying to determine what the correct NCRS finishes should be for the following items:

My NCRS book 5th edition (p. 219-220) states trailing arms are held to frame with long zinc-plated bolts with a flat washer on each side of the frame. A split-ring lock washer and a natural-finish cotter pin secure the castellated nut.

Question on long pivot bolt:
Is the term zinc-plated equal to zinc phosphate medium gray parkerize finish? Or, is zinc-plated suppose to be zinc chromate shiny silver electroplating as the finish?

Question on the washers and nut:
I am also unsure of the finish for the two flat washers, the split-ring lock washer, and the castellated nut. Are these all the same finish as the long pivot bolt and they should match the pivot bolt finish whether that is medium gray zinc phosphate parkerize finish or zinc chromate shiny silver electroplate finish?

Question on the rear trailing arm alignment shims:
I was of the opinion that medium gray zinc phosphate finish would be the correct finish for the groups of trailing arm shims and would be closest to "natural steel". Again, my NCRS book says there were no stainless steel trailing arm bolt and shims so I am interpreting that to mean that the long pivot arm bolt and the shims should not be a shiny silver finish; therefore, go with medium gray zinc phosphate parkerize finish on the long pivot bolt and the rear alignment shims?

Thank you in advance for the finish clarifications on my trailing arm hardware.

Kevin

[Patrick H.]

Re: 1969 Trailing Arm hardware finishes

Original hardware was a dull (non-polished) zinc finish. What you buy now from Lowe's or Paragon or most places is a very shiny zinc finish, and sometimes looks more like chrome than zinc. For a correct restoration they are much too shiny.
You can make a shiny finish into a correct dull one using vinegar or a similar mild acid.

Zinc phosphate is flat or dull medium gray, and does not look like zinc plating. They are completely different.

None of these finishes truly appear like a natural non-coated finish.

[Joe L.]

Re: 1969 Trailing Arm hardware finishes

First time posting here,

I have the trailing arms off of my 1969 Coupe, standard suspension, L-46 4-speed and I am trying to determine what the correct NCRS finishes should be for the following items:

My NCRS book 5th edition (p. 219-220) states trailing arms are held to frame with long zinc-plated bolts with a flat washer on each side of the frame. A split-ring lock washer and a natural-finish cotter pin secure the castellated nut.

Question on long pivot bolt:
Is the term zinc-plated equal to zinc phosphate medium gray parkerize finish? Or, is zinc-plated suppose to be zinc chromate shiny silver electroplating as the finish?

Question on the washers and nut:
I am also unsure of the finish for the two flat washers, the split-ring lock washer, and the castellated nut. Are these all the same finish as the long pivot bolt and they should match the pivot bolt finish whether that is medium gray zinc phosphate parkerize finish or zinc chromate shiny silver electroplate finish?

Question on the rear trailing arm alignment shims:
I was of the opinion that medium gray zinc phosphate finish would be the correct finish for the groups of trailing arm shims and would be closest to "natural steel". Again, my NCRS book says there were no stainless steel trailing arm bolt and shims so I am interpreting that to mean that the long pivot arm bolt and the shims should not be a shiny silver finish; therefore, go with medium gray zinc phosphate parkerize finish on the long pivot bolt and the rear alignment shims?

Thank you in advance for the finish clarifications on my trailing arm hardware.

Kevin

Kevin------


Bolt was as Patrick described (dull zinc plated). Flat washers were also dull zinc. Split lock washer was "plain" finish. Cotter pin was also plain finish.

While most slotted nuts used on a Corvette were "plain" finish, the trailing arm slotted nuts were an exception. These were a dull zinc, like the bolts and flat washers.

[Terry M.]

Re: 1969 Trailing Arm hardware finishes

Kevin
Welcome to the Tech Board

In your 1968-69 TIM&JG 5th Edition you will find a Glossary beginning on page 247. It describes Cadmium, Cadmium Dichromate and Zinc finishes. Now days, for reasons cited the Cadmium section, Zinc is used for the base of Dichromate when that gold toned finish is desired. In manufacturing the finish is specified for the corrosion protection desired and not for the color finish as we judge it.

There are other terms in the glossary that may be found useful. And for those looking at more recent, and potentially future, early C3 Manuals this Glossary is found in other 1968-69 recent editions and in the 1970-72 TIM&JG recent editions as well.

[Gary B.]

[Kevin S.]

Re: 1969 Trailing Arm hardware finishes

Hey Patrick,

I'll try a test on some dummy parts that I can media blast and do a little trial and error experimenting.

I can do both zinc electroplating and zinc phosphate parkerizing. I might be able to land somewhere between shiny silver zinc plating and dull gray. I'm also familiar with distilled white vinegar to reduce the sheen on parts and have used vinegar to change part colors from silver to gray to almost black depending on how long they soak.

Appreciate the help.

Kevin

[Kevin S.]

Re: 1969 Trailing Arm hardware finishes

Hi Joe,

I media blasted the split-ring lock washers, new cotter pins, and castellated nuts. They are all a dull silver finish at the moment after media blasting. I keep talking myself into circles in terms of what "natural" and "plain" finish is. I know that I need to put some kind of coating back on them to prevent them all from rusting in the future.

Am on the right thought process to use a very short zinc phosphate parkerize process (like 1 minute) to give them some color and some protective coating to prevent future rust? Or, is there something better that I can put onto freshly media blasted parts that keeps them "natural" or "plain" looking? Maybe just a very light coat of Fluid Film is all I need to keep them "natural" and also protected from future rusting.

Thanks for your input.

Kevin

[Patrick H.]

Re: 1969 Trailing Arm hardware finishes

Rather than media blast, which leaves a rough finish, using acid to remove non-original zinc plating leaves a smooth natural finish.
Blasted finishes are not plain or natural. And, natural finishes can even appear shiny!

For larger parts or even some smaller ones, a light coat of matte clear can help. Otherwise using CRC-350 or similar heavy oil can protect a finish to some degree.

[Kevin S.]

Re: 1969 Trailing Arm hardware finishes

Hey Patrick,
Thanks so much for the follow-up info. I also have a small parts vibratory tumbler which I can use to smooth the media blasted surfaces. I think I have everything I need to get the parts clean and smooth. I really love this hobby. I have learned so much doing this restoration.

I will buy the CRC SP-350 corrosion inhibitor today and use that on bare parts to prevent future rusting. Honestly, the car has never seen a rain drop so the CRC SP-350 should last many years if not decades. Thanks for the recommendation.

Kind Regards,

Kevin

[Kevin S.]

Re: 1969 Trailing Arm hardware finishes

Hi Terry,
It was one of those I looked but did not see moments. I've been in that glossary section dozens and dozens of times looking for other things like bolt and head mark types, never even noticed the cadmium, cadmium dichromate, and zinc finish descriptions. Feeling a bit foolish today.


You guys have all been so very helpful. Thank you.

[Terry M.]

Re: 1969 Trailing Arm hardware finishes

Hi Terry,
It was one of those I looked but did not see moments. I've been in that glossary section dozens and dozens of times looking for other things like bolt and head mark types, never even noticed the cadmium, cadmium dichromate, and zinc finish descriptions. Feeling a bit foolish today.


You guys have all been so very helpful. Thank you.

No worries Kevin. I am always looking for opportunities to make the TIM&JG better and I wanted to be sure we had addressed these items someplace in the manual. Your questions gave me a chance to review the section. Thanks.