73 Correct Alternator Support Bracket Adjustment Bolt

[Jimmy P.]

I need to replace the top alternator support bracket adjusting bolt on my 73 L48. In my search I have found that there is more than one type of bolt head marking being used. I want to use an original bolt. I couldn't find any old threads addressing the 73 most were all pre 72. Most of the vendors are selling a repro bolt/washer set with the "WB" marking on the head saying it is correct for 63-77. I'm pretty sure that can't be correct. My car is an April 30th build car. I have checked with two other NCRS member friends of mine with April build cars. One has a bolt with just the "3 lines forming the triangle", one with the "3 lines and an S in the middle". The other has the "3 lines with the letter C with an H in the middle". I also found an original alternator bolt with the "3 lines with the TR" letters in the middle. Which one should I get? Or would any of the three orginals be fine for judging? All three bolts listed here are easily obtainable BTW.
I thought clarification on this would be helpful for other 73 restorers out there with the same issue.

[Edward J.]

Re: 73 Correct Alternator Support Bracket Adjustment Bolt

Jim, My 72 has a WB grade 5 , it has the 3 lines, But like most corvettes they are others, The ones you mention are correct also. Others can be RWB, RSC, There is one more small note the length of the bolt should just reach the last thread on the ear of the alternator( should pretty much flush). and they generally use a split lock washer and thicker than normal washer.

[Joe L.]

Re: 73 Correct Alternator Support Bracket Adjustment Bolt

I need to replace the top alternator support bracket adjusting bolt on my 73 L48. In my search I have found that there is more than one type of bolt head marking being used. I want to use an original bolt. I couldn't find any old threads addressing the 73 most were all pre 72. Most of the vendors are selling a repro bolt/washer set with the "WB" marking on the head saying it is correct for 63-77. I'm pretty sure that can't be correct. My car is an April 30th build car. I have checked with two other NCRS member friends of mine with April build cars. One has a bolt with just the "3 lines forming the triangle". The other has the "3 lines with the letter C with an H in the middle". I also found an original alternator bolt with the "3 lines with the TR" letters in the middle. Which one should I get? Or would any of the three orginals be fine for judging? All three bolts listed here are easily obtainable BTW.
I thought clarafication on this would be helpful for other 73 restorers out there with the same issue.

Jimmy------


The bolt in question is a VERY common size bolt of 5/16-18 X 7/8". It's GM 280-M material grade and zinc plated. It has a trimmed (i.e. non-indented) head. Those things we know about it. As far as the original headmarking is concerned, the ONLY way to know what the headmarking was on your car is to have the known-original bolt. Apparently, you don't have it. That means it will be FOREVER UNKNOWN.

Many manufacturers probably made this size bolt for GM. Any period-correct headmarking will probably be accepted.

[Jimmy P.]

Re: 73 Correct Alternator Support Bracket Adjustment Bolt

Thank you guys, that's what I wanted to know. You are right Joe, my original is long gone.
Also thank you Russ S. and Ralph S. for sharing by email what type bolts your April cars had as well?

[Harmon C.]

Re: 73 Correct Alternator Support Bracket Adjustment Bolt

The bolt should be as others said. The lock washer is black and the washer extra thick cad plated. The washers are usually the problem in this area.