Details on bolt for alternator bracket to wire harness (3952222)

[Mathew S.]

I have not found any details on bolt 3952222, that hold the bracket to the alternator for the wiring harness. About all I found is that it was also used on Vegas. If someone has details on it, it would be appreciated.

[Leif A.]

Re: Details on bolt for alternator bracket to wire harness (3952222)

Mathew,
What year is your car?

[Mathew S.]

[Terry M.]

Re: Details on bolt for alternator bracket to wire harness (3952222)

Is this good enough? It is the best I have in my files.

[Mathew S.]

Re: Details on bolt for alternator bracket to wire harness (3952222)

Terry that is good. Thank you and happy New Years

[Joe L.]

Re: Details on bolt for alternator bracket to wire harness (3952222)

I have not found any details on bolt 3952222, that hold the bracket to the alternator for the wiring harness. About all I found is that it was also used on Vegas. If someone has details on it, it would be appreciated.

Mathew------


This is kind of a strange situation. Bolt GM #3952222 was a special bolt cataloged in GM parts group 2.313 and not also cataloged in standard parts groups. As far as I know, this was a standard hex head bolt of 5/16 X 5/8", GM 280-M material grade, zinc plated. It was released in late 1968, was used in Corvettes for the alternator application from 1969 through 1979 and discontinued without supersession in November, 1988. For the life of me I can't figure out why it was considered a special bolt.

It was also used on 73-74 Vegas, some Chevrolet and GMC pick-up trucks, and some Pontiacs

[Terry M.]

Re: Details on bolt for alternator bracket to wire harness (3952222)

Mathew------


This is kind of a strange situation. Bolt GM #3952222 was a special bolt cataloged in GM parts group 2.313 and not also cataloged in standard parts groups. As far as I know, this was a standard hex head bolt of 5/16 X 5/8", GM 280-M material grade, zinc plated. It was released in late 1968, was used in Corvettes for the alternator application from 1969 through 1979 and discontinued without supersession in November, 1988. For the life of me I can't figure out why it was considered a special bolt.

It was also used on 73-74 Vegas, some Chevrolet and GMC pick-up trucks, and some Pontiacs

Joe,
Isn't 5/8 unusually short for a fastener of this size? If so, that might make it a special fastener.

[Joe L.]

Re: Details on bolt for alternator bracket to wire harness (3952222)

Joe,
Isn't 5/8 unusually short for a fastener of this size? If so, that might make it a special fastener.

Terry------


Yes, it is short. However, GM had at least two other bolts of the same dimensions and configuration. That is standard hex head, 5/16-20 X 5/8", GM 280-M material grade, and zinc finish. The first was GM #180075. This is a standard bolt which has been in the GM parts bin "since the earth was young". The second is GM #355587. This bolt would not have been around, though, in 1969 as it was released about 1973 or 74. It was used for some group 2.313 non-Corvette applications and some passenger car group 3.880 applications. It was later replaced for SERVICE by the 180075 which was discontinued quite some time ago. Neither bolt ever superseded or was succeeded by the 3952222. As far as I can tell, both the 180075 and 355587 were identical to the 3952222. Why GM would have created the 3952222 specification when they already had the 180075 in the parts bin is a mystery to me. And why they would have created the 355587 when they already had the 180075 and 3952222 in the parts bin is also a mystery to me.The part that interests me is that my gut tells me there was a reason but I just can't figure out what it was. That confounds me.

[David B.]

Re: Details on bolt for alternator bracket to wire harness (3952222)

Looking at the photos Terry provided it appears #3952222 not only holds the alternator bracket but is instrumental as an electrical conduit for the wiring system. It would be my guess this is where the 'special" description comes into play. The specific requirement for this fastener would therefore call for a special zinc organic finish probably GM 6173-M (240). Fasteners under hood used for electrical grounding which will be directly against surfaces on aluminum components would all require a specific finish for it's use.
Additionally, I am sure you are aware 3952222 is a chevrolet Motor Division engineered and assigned part # therefore it would not show up in Standard Engineering's list of parts numbers (Standards has their own assigned block of numbers) but 3952222 might show up in Chev. parts books under Grp. 8. Also elementary is the known GM rule that every part must have an assigned part number but in no instance is any part allowed to have 2 part numbers assigned at the same time. With that being understood, the correct description of #180075 is 5/16 -18 X 5/8. There are a lot of short 5/16 bolts with part #s the only difference in all of them is a finish, thread type etc. etc. etc.

[Joe L.]

Re: Details on bolt for alternator bracket to wire harness (3952222)

Looking at the photos Terry provided it appears #3952222 not only holds the alternator bracket but is instrumental as an electrical conduit for the wiring system. It would be my guess this is where the 'special" description comes into play. The specific requirement for this fastener would therefore call for a special zinc organic finish probably GM 6173-M (240). Fasteners under hood used for electrical grounding which will be directly against surfaces on aluminum components would all require a specific finish for it's use.
Additionally, I am sure you are aware 3952222 is a chevrolet Motor Division engineered and assigned part # therefore it would not show up in Standard Engineering's list of parts numbers (Standards has their own assigned block of numbers) but 3952222 might show up in Chev. parts books under Grp. 8. Also elementary is the known GM rule that every part must have an assigned part number but in no instance is any part allowed to have 2 part numbers assigned at the same time. With that being understood, the correct description of #180075 is 5/16 -18 X 5/8. There are a lot of short 5/16 bolts with part #s the only difference in all of them is a finish, thread type etc. etc. etc.

Dave------

It's possible that a finish difference was the reason for the different part number. However, there are many other bolts and fasteners used for "electric conductance" applications in which a standard bolt is used.

Bolts with Chevrolet part numbers may have specific parts group applications. However, while some may not be included in Standard Parts cataloging (like the 3952222), there are many, many with Chevrolet part numbers which are also included in Standard Parts, including the 355587. Sometimes (but not always) the "group of prime use" is notated.

[David B.]

Re: Details on bolt for alternator bracket to wire harness (3952222)

Joe --
You are correct regarding other "standard" bolts and fasteners being used where there is some "electric conduction". The Key factor (determined by a Division's Engineering Section) is how critical is the need for a particular fastener in it's use to maintain "electric conduction". Partially quoting GM rules for fastener design standards: "It is permissible to use other finishes if multiple ground paths are available through mating parts and there is absolute assurance that a ground adequate to permit proper function will exist after assembly"
The bottom line, anyone can obtain a 5/16 X 5/8 bolt from ACE Hardware and it will work BUT in all likelihood it will not come close to meeting engineering specifications particular to that bolt's location on the car.

[Terry M.]

Re: Details on bolt for alternator bracket to wire harness (3952222)

In this situation the fastener doesn't provide the path for electrical conductivity. The current flow would be between the alternator case and the lug of the wire. The fastener just keeps the lug tight against the alternator case.

There is another negative electrical path at the starter, as well as the main negative path through the frame and the engine, if the jumper across the passenger side engine mount is in place. So in this case there are multiple electrical paths available.

IIRC I was once told that the order of the lug and the bracket on my car is not per the assembly manual. I don't have my AIMs handy, so I can't verify my recollection, but in any case the purpose of this fastener is not electrical connectivity but a physical connection. I can understand the need for a special finish for the bolt to reduce corrosion at an electrical connection, but the fastener itself does not conduct electricity.

[Rich P.]

Re: Details on bolt for alternator bracket to wire harness (3952222)

this bolt is unique to this application. It's what I call a thin head alternator bolt. It's 5/16 18 thread 5/8 long 1/2 inch hex but what's unique about it is the thickness of the head is less than half that of a normal flat hex head bolt. You can see it here in this picture the A head marking bolt and in the first picture it's the top right bolt you can see how thin the head is. Their grade 5. Typical head markings are- r b w, a, c h, t r, and and L5

[Joe L.]

Re: Details on bolt for alternator bracket to wire harness (3952222)

this bolt is unique to this application. It's what I call a thin head alternator bolt. It's 5/16 18 thread 5/8 long 1/2 inch hex but what's unique about it is the thickness of the head is less than half that of a normal flat hex head bolt. You can see it here in this picture the A head marking bolt and in the first picture it's the top right bolt you can see how thin the head is. Their grade 5. Typical head markings are- r b w, a, c h, t r, and and L5

Rich------


I do not understand why a thin head bolt would have been required for this application.

[Terry M.]

Re: Details on bolt for alternator bracket to wire harness (3952222)

Rich------


I do not understand why a thin head bolt would have been required for this application.

Is it possible the thin head is to reduce the opportunity for over-torquing the fastener? The threads in the aluminum case, being so short, wouldn't provide much resistance to over torquing, and perhaps the engineers would rather have the socket slip on the short head than pull out the threads in the alternator case.