1965 upper shock bolt finish

[Eugene B.]

Members,
The 1965 TIM & JG (page 150) states that the upper shock mount thin hex nut is cadmium or zinc plated. It also states that the lock washer is installed between the bolt head and shock bracket. No problem.

Question: The JG does not document the finish on the bolt and lock washer, only the thin nut. Perhaps other C2 Judging Guides are more explicit.

As always, your comments and advice are greatly appreciated.

Regards,
Gene

[Loren L.]

The rear upper shock bolt appears in

various AIMs and Parts Books, carrying a variety of #s - but by the Fall 1967 parts book, it is listed as #3815933 - little detective work reveals that it is ALSO LISTED in Gr 0.662 as the Special Perfromance balancer bolt, which I have seen in both Silver Zinc and Gold Zinc plating. FWIW

[Joe L.]

Re: The rear upper shock bolt appears in

Loren and Gene-----

The original bolt used in PRODUCTION for the upper rear shock mounting for all 1963 through 1970 Corvettes was GM #3824692. This bolt was 7/16-20 X 2-3/16". It was a non-indented head, SAE grade 8 (6 radial line) bolt and the finish was black oxide. This particular bolt was NEVER available in SERVICE from GM.

The GM #3815933 bolt is a SERVICE replacement bolt which can be used for this application and has been, at times, catalogued by GM for this application. Its primary application, since 1963, has been as the balancer bolt used for certain small block applications as Loren has found. This bolt is 7/16-20 X 2-1/4". It's, consequently, close enough to the original that it works fine. This bolt is also a non-indented head, SAE grade 8 bolt. However, it differs from the original bolt in 3 ways.

First, the finish is zinc plated, although early examples of this bolt may have been black phosphate. Second, the thread length of this bolt is a little different than the original 3824692, but this causes no problems for the shock application. Third, this bolt has a hole drilled across the flats of the head for a safety wire installation. So, while it's 100% functional for the application, it's configuration and appearance is somewhat different.

[Mike M.]

Re: 1965 upper shock bolt finish

Gene: if you go withn the service replacement botl, solder the hole shut, treat it to black oxide finish and i'll bet the judges won't catch it. mike

[Eugene B.]

Re: 1965 upper shock bolt finish

Gents,
I will retrieve the original bolts from the electroplater before he rains clear zinc (silver) on them. I was in a hurry to get them in today's plate.

I should have realized that they were black phosphate. The TIM & JG let me down!

Thanks a lot, gentlemen.

Gene

[Joe L.]

Re: 1965 upper shock bolt finish

Mike and Gene-----

Even simpler is to purchase a hardware store grade 8 bolt of 2-1/4" length (or, longer and cut off the excess). If the bolt is black phosphate finished, as many are, just leave it the way it is. I don't think that anyone's going to discern the difference between black oxide and black phosphate with only the bolt head to look at.

If the bolt is zinc plated, remove the plating by immersing the bolt is a conatiner of muriatic acid (the kind used for swimming pool pH control). It won't take long for the zinc to be removed. Then, paint the bolt with the black oxide paint available from Quanta. Don't apply the paint too thick or it will look like paint----use VERY light coats until you just get the surface all covered. Finally, after air drying, place the bolts in an aluminum foil wrapping and bake them at about 450 degrees F for about 1-1/2 hours. Presto--- bolts virtually indistinguishable from the originals.

[Joe L.]

Re: 1965 upper shock bolt finish

Gene-----

The bolts weren't originally black phosphate; they were black oxide.

As far as the replating of parts goes, if you're having any high strength bolts or fastners re-finished, then the plater has to take special steps with these parts to avoid hydrogen embrittlement. This is a phenomenon that occurs as a result of the electroplating process and it seriously weakens the fastner. You should never use any fastner that is and needs to be of the high strength variety after replating UNLESS the special protocols to eliminate the hydrogen embrittlement problem have been followed subsequent to the electroplating. If your plater does not understand what this is all about and/or does not have the capability of doing this, then either find another plater that does or don't have the fastners electroplated.

Having fastners that look as-new is very nice. Having fastners that don't fail is even nicer.

[Mike M.]

Re: 1965 upper shock bolt finish

joe; years ago i took some parts up to the kitchen(believe they were eastwood painted exhaust manifolds) for a short oven baking.my better half of 37 years informed me that there'd be no vittles if i stunk up her kitchen. with tale between my legs and un-rx'd manifolds in hand, i put my butt in reverse and had pork chops and hominy that evening.manifolds had to wait for initial engine fire-up to cure.mike

[Joe L.]

Re: 1965 upper shock bolt finish

Mike-----

Using the kitchen oven carries with it certain risks of destroying relationships and possibilities of retribution. The aluminum foil wrapping, if it's tightly wrapped, will minimize the offending odors and prevent the "unsightly" automotive parts from being visible in the oven. If all else fails, a cheap toaster oven can be procured and used as a "curing oven" for small parts.

[Eugene B.]

Re: Hydrogen embrittlement

Joe,
Thank you for your response to my post. I'm interested in learning more about the hydrogen embrittlement phenomena. I will ask the plater if he takes any steps to prevent it.

Would plating the spindle support/lower shock mount forging be a bad idea? As far a weakening the part, I mean. I would imagine that it takes plenty of abuse.

Also, thanks for the tip on oven-baked black oxide. Sounds yummie! Never seen it on Emiril's show.

Best regards,
Gene

[Joe L.]

Re: Hydrogen embrittlement

Gene------

Hydrogen embrittlement is a phenomen that occurs in the electroplating process. Although I've forgotten most of the details of it, basically, it involves the hydrogen released as a normal part of the electroplating process permeating the ferrous material of a piece electroplated. Once the hydrogen ions (or molecules, I forget which in this case) get into the metal, the metal is seriously weakened. It occurs in all electroplating of ferrous parts but for non-structural or non-high strength pieces, it doesn't really affect any important quality of the item. For high strength parts or alloy steel parts, it will reduce the strength considerably.

Subsequent to electro-plating, high strength parts must be treated to eliminate and release the hydrogen. This involves baking the parts in a specific cycle of temperatures and time periods. I've forgotten the details, if I ever knew them.

The use of electroless plating processes avoids the hydrogen embrittlement phenomenon completely. Originally, this process was limited to nickel plating, but I think that it's been expanded now to other metal finishes. It's more expensive, though, since the chemicals used in it are a lot more expensive than the total cost of electroplating chemicals + electrical power consumed in the process. Also, the cost to treat the chemical waste residues before discharge to a wastewater collection system is very high. So, not as many platers offer this type of plating.

The spindle support is not a forged piece. It is a piece manufactured from cast nodular iron. I wouldn't even consider electroplating this part due to the above-referenced. Plus, none were ever originally so-finished.

[Eugene B.]

Re: Hydrogen embrittlement

Joe,
Thank you for your response. I did confuse you though. I asked about the lower shock mount forged piece, not the spindle support. The '65 JG states that it is cadmium or zinc plated.

Thanks again,
Gene

[Joe L.]

Re: Hydrogen embrittlement

Gene----

The shock mount shafts are forged pieces. They can be replated but MUST be treated using the procedures that I generally described to avoid weakening due to hydrogen embrittlement.

[John H.]

Re: Hydrogen embrittlement

We had an interesting (?) example of hydrogen embrittlement a few years ago in my assembly plant. Most OEM fasteners these days are zinc-plated, and the spec calls for annealing them after plating (as it always has) to avoid hydrogen embrittlement. Suddenly one day we had a bunch of the heads on self-tapping screws that secure brake and fuel line clips start "popping off" cars all through the system, from the Chassis Line all the way to the Final Line; you'd hear a "pop" that sounded like a .22 pistol, and a bolt head would come flying across the aisle. Turned out that particular lot of screws had somehow bypassed the annealing operation and got shipped without it, and the stress under the screw head after torquing was enough to metallurgically fail the hydrogen-embrittled fasteners. Had to contain several hundred cars and change all the fuel and brake line clip screws - not a fun project.

Been to a car show recently and seen the number of "chromed" fasteners in critical areas on modified cars? Lots of them haven't been annealed - scary stuff.

[Craig S.]

Re: Hydrogen embrittlement

Joe - I would then assume the brake caliper mounting brackets need the same anealing process after plating then?....Craig