Rear spring outer bolts/castle nut

[Ronald L.]

Re: Rear spring outer bolts/castle nut

The finish on the C bolts is more than black oxide, it has an organic base to it that provides much better (longer) corrosion protection. I would be very surprised to find any original chassis bolt in black oxide. Black phos, yes, and they rusted fast. At best they were a 96 hour salt spray bolt meaning in less that a year of normal use they were rusty.

[Don L.]

Re: Rear spring outer bolts/castle nut

Don, Music to my ears! Where is your lab? I'll donate the RBW's that I took off that I see are sold by a MI supplier. As far as other old bolts, I'll have to ask my source and are there other willing to donate old bolts to the cause?

Southfield MI. Call me at (248) 736-9798. The guys in the lab tell me that they'll have to make a fixture for the tensile test. The material analysis will be easier.

[Rich C.]

Re: Rear spring outer bolts/castle nut

My two cents: bought a pair in GM bags around '91 or so. They are black, large C,5 lines, about 6 5/16", 3/4" of thread. #458982, Made in USA! Did I mention I survived having one break while driving? Choose your bolts carefully, if it happened at speed, me and vette would have been toast.

[Joe L.]

Re: Black phosphate vs. Black oxide? Why one vs the other

Ron,

Do you know if both black phosphate and black oxide treatment were used for chassis bolts, nuts, washers, during the C2 and C3 era? If both were used, what was the likely criterion that dictated one vs. the other? Was there more black phosphate during the C2 era vs. the C3 era? Or vice versa?

Thanks,

Gary

Gary-----


Black oxide was rarely, if ever, used on GM fasteners. Black oxide is a very smooth, almost shiny black finish. If you have ever seen ARP fasteners, they are usually finished in black oxide. If you carefully examine these and then think about what GM fasteners you've ever seen that appeared like this, I think you'll come up none.

The only fastener on a Corvette that I can think of that MIGHT have been black oxide are the front spindle-to-steering arm bolts on C3's and I'm far from sure about these.

The vast majority, if not all, black fasteners seen on Corvettes are black phosphate. As Ron mentions, some are an organo-phosphate. These often have a somewhat smoother appearance than plain black phosphate.

As far as I know, black oxide is a much more expensive finish than any form of black phosphate.

[Joe L.]

Re: Rear spring outer bolts/castle nut

My two cents: bought a pair in GM bags around '91 or so. They are black, large C,5 lines, about 6 5/16", 3/4" of thread. #458982, Made in USA! Did I mention I survived having one break while driving? Choose your bolts carefully, if it happened at speed, me and vette would have been toast.

Rich-----


This is why GM always recommended that the spring end bolts be replaced any time they were removed from the car for any reason.

It's also why GMSPO once supplied a SPRING UNIT which consisted of bolts, cushions, inner retainers, outer retainers, slotted nuts, and cotter pins. This unit encouraged the replacement of ALL the referenced parts. Unfortunately, the SPRING UNIT is no longer available from GM.

[Ronald L.]

Re: Rear spring outer bolts/castle nut

Joe,


Black oxide is cheap aggressive smelly and dirty, nothing more that a caustic solution at high temperature that turns the ferrous surface to FeO, a form of iron oxide that is black in color. Over time some of that with just the humidity in the air turns to Fe2O3 Fe3O4 and other derivatives that have reddish yellow and orange hues and it is that which give the original BB oil caps their greenish hue. I am working with a local shop and have been able to "re-color" the oil caps.

Now as far as corrosion resistance - nada.

It would never have been used as you stated in ANY known chassis application where exposure to salt was known.

The chemicals going into black phos, by the nature they are more complex, do cost a little more. Again, corrosion resistance of those parts are 96 hours at best. Organo Phos - moves the needle into the range of acceptability and then we get into those highly zinc loaded organo coating that last 400 hours our more.

We will be real interested to see the tensile test result.

Anyone have an old bolt to donate to the cause?

Like the flip side to the one that broke?

[Patrick H.]

Re: Rear spring outer bolts/castle nut

Rich-----


This is why GM always recommended that the spring end bolts be replaced any time they were removed from the car for any reason.

It's also why GMSPO once supplied a SPRING UNIT which consisted of bolts, cushions, inner retainers, outer retainers, slotted nuts, and cotter pins. This unit encouraged the replacement of ALL the referenced parts. Unfortunately, the SPRING UNIT is no longer available from GM.

I've got one, and the label even says spring unit. Checked it last evening - 5 lines on the bolt.