To all those new to repairing Corvettes: We welcome you to the sport, learn you bolt grades. I just found standard bolts where grade 8 bolts should have been. Someone didn't know or didn't care and I am not sure which is scarier. When you put sub-grade bolts in you are making a time bomb death trap. How many sad wrecks that we all have seen are from brakes, axles and such leaving at speed because a soft bolt snapped. We have a responsibility to ourselves, those who ride with us and those we sell cars to to repair it safely. Slap on loud radios and silly wings if you must, but do the critical repairs safe and correct.

 

Just curious, where did you find the bad bolts? Rear spring mount or lower control arm mounts?

 

I don't think GM used anything less than grade 5 everywhere (no grade 2's). Quality control was pretty bad in the 60's and 70's so bolt strength was always overspeced to compensate for the frequent over torque by the workers. Can't go wrong with using grade 8 though (but not the gold hardware store ones.....gotta be black).

Gary

 

What? Nobody ever told me that. I've been buying the gold ones from the auto parts store for years. Those are no good?

 

I think that was purely as a cosmetic preference. Most of the stuff I buy is grade 8 and gold color

 

The difference between the gold color and the black I believe is that the gold will rust
quicker than the black, They are both still Grade 8. Correct me if I'm wrong through.

Riggs.

 

you may be correct there.

 

black is probably black oxide when the gold is a candium(sp) dip?

i used only grade 8 when i rebuilt my 77

 

I was looking for some grade 8 bolts a while back and went to Home Depot. I couldn't find 'em and the guy in the fasteners dept. had no idea what I was talking about. He called for another guy that "knows the dept. better". Didn't have a clue either. Guess I found 2 extra tools at the Depot!

 

never trust color or what someone says, learn to look at the marks on the head of the bolt, do a search for bolt grades and they will explain it to you. the marks on the head are there for a reason, and never blindly replace one bolt with another even of better grade, a grade 8 is hard and stronger but more brittle so know your application before you choose your bolts

 

Where do you need to use Grade 8? I'm just trying to remember the repairs I have done on the vette. I don't think I used a grade 8 bolt when I clamped that soup can around my broken exhaust pipe.

 

The bolts that hold the calipers on, a mixture of 8s and 2s. One was actually so long they put a wad of washers on it to fit.

 

Grade 8 bolts come in a variety of finishes. Some are Zinc, Clear Zinc, Blue Zinc, Yellow Zinc, Yellow Chromate, Black Oxide, (hot and cold process). The color is just varying levels of corrosion protection and cosmetics. The important thing is the strength. Head Markings!

Use the right bolt for the application.

Keep Stainless away from critical, High Torque uses such as suspension and head bolts. These will stretch or shear and fail.

 

Grades:
Grades are denoted by head markings. Grade 8 is the hardest, Grade 2 the softest. The process is to form the fastener, then heat it in a furnace to re-align the grain boundaries and quench it very quickly in a bath of cooler oil to drop the temp. The quenching freezes the grain structure and makes the part very hard. Harder fasteners can be torqued to higher load than softer ones without failure (usually failure is that the head pops off). Do not mistake hardness blindly for "strength". A metal file is very hard, but it will shatter into a thousand pieces if you drop it on the floor - hard, but not strong. Harder is always brittler, which is why we anneal them by reheating after quenching. This process restores some of the ductility to material. Coatings do not effect hardness for the most part.

Coatings:
Color is usually used as a shortcut to differentiate coatings, but that is all it is. Yellow is usually Zinc/Yellow and generally denotes Hexavalent Chrome, something we phased out years ago in favor of "Trivalent Zinc" because the Cr6 is so bad for the environment. Both have a layer of zinc covered with a layer of clear chromate. These are typically in the 48 hrs to white rust/ 96 hrs to red rust. "chrome" would give you better resistance in the salt spray chamber, stainless the best. Black oxide, Zinc/Black, Zinc/Olive, JS400, E-Coat, etc will give you substantially more but these are not going to be found in your hardware store (I can get them if you need them). Remember, the color is usually a shortcut. It could just as easily be dye as a different product. most of your home depot fasteners are Zinc/Yellow Chromate and are Cr6 and therefore aweful for the environment. These are cheap, however, because they do not meet the newer RoHS or other specs.

Next we can all discuss breakstem rivets! (kidding...)

 

Glad I came from a machinist.

 

Perhaps 3, for even entering a Home Despot...


just kidding

 

I have used nothing but grade 8 since I started playing with these cars. I don't have room to stock 8's, 5's and so on. I have a large supply of varying sizes of grade 8. I have not seen any rusting issues with the "gold" bolts I have used & I have gotten caught in some real down pours the past 2 years.

 

I get my Grade 8 and 5 stuff from Lowes. I find the selection they have is so much better than Home Depot. Plus if you mess with late model stuff that is metric they have that as well at Lowes.

 

yes, but ours only has course thread bolts. The ones I needed were a 7/16 20 and all the hardware stores had was a 7/16 14

I think I get madder when they have something close but not quite right than when they have nothing at all

 

Besides bolts not being torqued down on the transmission, rear end & front suspension, this struck me the most. (Garage pretends to be the best US car garage in Belgium)....

Both engine mounts where fixed with threaded studs & 2 nuts .. glad I saw it 'during my while I'm at its'

Nick