69 caliper fasteners

[Mark A.]

Hi,
Would someone please help me with 2 questions? On the front brake calipers for my 69, what is the factory correct finish for the caliper to bracket mounting bolts? Also what is the correct finish for the 2 bolts that hold the caliper halves together? My judging manual doesn't say, and I don't want to guess and be wrong. Thanks for the help. Also if someone knows of a more detailed manual that may be available let me know. Mark

[Sal C.]

IMO black oxide *NM*

[Chuck S.]

Re: 69 caliper fasteners

My observation, which is often compromised on chassis parts, was that the caliper mounting bolts were black phosphate.

I once ran across a reputable vendor at Bloomington selling the same length, same 6Line M headstamped bolts out of a small nail keg. They were black phosphate, and probably NOS surplus...I bought a handfull. I know of at least one other headstamp: 6Line Double Circle. I have two of each headstamp; probably each pair was used to mount the caliper on one side of the car.

For judging purposes, my opinion is the average judging team does not have the time to closely examine every black fastener finish to see it it's black oxide or black phosphate. If you have OCD correctness, then make'em black phosphate. If absolute correctness is not that important to you, then I doubt any black finish will hurt you in judging...but, I've been wrong before.

[Chuck S.]

Headstamps...Those Two Were The Fronts

The rear caliper bolt headstamps were all 6Line with like an hourglass laying on it's side, or a horizontal rectangle with all four sides pushed in...if that makes any sense.

[Terry M.]

69 caliper fasteners -- DANGER Red Rider

DO NOT have these bolts refinished. These are critical fasteners and reusing the old fasteners, refinished or not, is questionable. Refinished fasteners, without specialized treatment, can often be weaker than new fasteners. Brake and suspension fasteners should not be weaker than the original specifications. Replacement fasteners often will have black finish -- it usually comes with the grade eight (six lines) specification. It is the heat treatment that is required to get that grade eight strength that makes them black. Don't endanger your safety, and that of others for the sake of a few judging points -- use new fasteners even if they are not the same headmark or color.

[Chuck S.]

Re: 69 caliper fasteners -- DANGER Red Rider

Terry, the only fastener refinishing concerns I'm aware of is not annealing after zinc plating; hydrogen is absorbed into the steel during electroplating, causing cracks and ultimately failure well below the original rated strength if the fasteners are not heated after plating to drive off the hydrogen.

Are there similar problems for black finished fasteners? As far as I know, black oxide and black phosphate are external chemical reactions on the surface of the fasteners. Inability to refinish original fasteners would render most restorations nearly unsuitable for NCRS judging IMO.

[Terry M.]

Re: 69 caliper fasteners -- DANGER Red Rider

Chuck,

It has been about forty years since I worked in the metallurgy field, but I am sure it is not just zinc plating that causes hydrogen embirttlement. I am pretty sure chrome plating will also cause it. I believe any process that uses electron deposition in hydrochloric acid risks hydrogen embrittlement. I am aware that hydrogen can be released by annealing, but I don't think it is a place for amateurs, which I am, to be experimenting.

Does the black finish use processes which can cause hydrogen embrittlement? I'm not sure, but I would suggest it is a risk one would want to clarify with a plater or a metallurgist before re-finishing old fasteners.

Please note the references to phosphating and pickeling in this material:

http://en.wikipedia.org/wiki/Hydrogen_embrittlement

[Patrick H.]

Re: 69 caliper fasteners -- DANGER Red Rider

Terry,

Your danger alarm sounds like you've been reading Jack H's posts.

Anyway, on my 72, the left front caliper started leaking after my drive to the Indiana Regional and back. I removed the caliper and easily put the seal lip back in place. I had the caliper-to-bracket bolt in my hand, and wondered what to do. Yes, it's a Bowtie car, but it was so rusty...

I ran it for a couple hours in old "green diamonds" in my tumbler, followed by crushed walnut shells. The sucker looked like new. I put some Pre-Lube 6 on it, and reinstalled it. Yes, the bolts look "different" than the rest of the brake area because they're now black. But, no problems with annealment or anything else.

See "after" picture below.

Patrick

[Terry M.]

Re: 69 caliper fasteners -- DANGER Red Rider

The process you used avoids those metallurgical nasty issues, and may even be less expensive than plating. I believe there are cold processes that will darken metals without the risk of hydrogen embrittlement. Weapons enthusiasts use some of these cold processes in their work.

I have reservations about reusing old fasteners in some of these critical applications, even if they are not refinished in any way. If one knows the history of the fastener, and is reusing it for the first time that is one thing. Many of us have cars whose history is not so clear, and we are not in a position to know how many times a fastener has been reused and if it was over torqued by Bubba in a previous lifetime. In the latter case new high quality fasteners seem to me to be the best.

I have hopes that someone who is trained as a metallurgist will chime in and either verify my cautions or alley them.

[Patrick H.]

Re: 69 caliper fasteners -- DANGER Red Rider

Interesting you comment about "weapons enthusiasts" and metal darkening. I was just paging through my latest flyer from Midway and noting which products I wanted to purchase and test to make a "better" more durable black finish for my Corvette parts.

http://www.midwayusa.com

Patrick

[Joe L.]

Re: IMO black oxide

Sal-----

I agree, too. I believe that the caliper-to-bracket retaining bolts were black oxide for both front and rear (the bolts were different front and rear due to a slightly different length but they had the same headmarking and were both black oxide). The bolts used for the rear calipers were the same as those used for the rear spindle flange. I have never seen any of these bolts that were anything but black oxide. Also, the part numbers for the bolts were the same from 1965 right through 1982. Of course, the specs could have allowed a choice of finishes (e.g. black oxide or black phosphate), but if any that were black phosphate-finished were ever made, I've never seen one.

The caliper half clamp bolts are another matter. I have seen these in both black oxide and black phosphate. Generally, I believe that "earlier" were black oxide and "later" were black phosphate.

[Chuck S.]

What We Need...

Is someone with access to an engineering materials lab to do some tensile pull tests of plated, phosphated, oxided, and control specimen for us.

I accept the proffered warning and recognize the potential risk...It's memory will no doubt increase the "pucker" factor during the first shakedown cruise and forever thereafter. Others must take whatever action they deem necessary to guarantee their own personal safety.

Frankly, I have problems believing that surface chemical processes such as phosphating, pickling, and even muriatic acid cleaning will have a serious impact on fastener metallurgy like electroplating. Electroplating puts a driving force into the system, and causes charged particles to flow onto and INTO the metal specimen. In a surface reaction, there is no force to drive the hydrogen into the metal...the path of least resistance for the atomic hydrogen is up through the liquid bath to the atmosphere.

Wikipedia is a wonderful resource but not infallible...sometimes I suspect they get their facts scrambled. I had a recent experience during a debate over Mobil 1, where someone quoted Wikipedia as saying Mobil 1 was no longer a true synthetic oil because it only had a few percent of synthetic components. It only took a quick check of the MSDS sheet to reveal that the few percent they apparently referenced as synthetic was organic additives, and the other 93 percent was synthetic paramins.

[Chuck S.]

Re: IMO black oxide

When confronted with differing opinions from TWO really smart guys in this stuff, I may have to admit I might have made a mistaken observation because of corrosion. Rusty black phosphate looks pretty much the same as rusty black oxide, and that was early in my restoration education.

Typically, I would now expect black high strength (grade 8 ) fasteners to be black oxide.

[Terry M.]

[Michael H.]

Re: What We Need...

Terry,

Here's a link to a previous discussion on the subject of hydrogen embrittlement. John Hinckleys response at the end is especially interesting.

https://www.ncrs.org/forum/archive25.cgi?review=212379