67 alt. brace, base engine w A/C

[Dale S.]

Could some one measure an alt. brace off a 67 base engine with A/C. There are 2 part numbers one for non A/C and one for A/C cars. Jerry F. has the one for non A/C figured out. My belt is longer, but we dont know if it is in the alt. brace length or the diameter of the pulleys. My car has base engine, C-60, K-19,and N- 40. Sure wish I did not throw the old welded one away. Thank you Dale

[Joe L.]

Re: 67 alt. brace, base engine w A/C

Dale-----

According to GM, the GM #3854028 alternator brace used for your with C-60 application was 12-1/6" long with a slot of 2-7/32" length. The brace had a 1/4" offset.

[Dale S.]

Re: 67 alt. brace, base engine w A/C

Thanks again Joe! Dale

[Joe R.]

Re: 67 alt. brace, base engine w A/C

Hi Joe:

I've been following this thread because I have a 67 base engine, A/C, power steering car and my Quanta reproduction belt appears to be too long, since the alternator adjustment bolt is near the outer end of the slot. One guy I know with the same situation in his identical car said that he called Quanta and they sent him a "correct" belt that fit better.

Anyway, this thread made me wonder whether I simply have the wrong alternator brace. Mine measures about 13.7 inches between the two outermost extremes, and the slot is about 3.5 inches.

I'm having trouble interpreting the info in my 1971 Corvette parts book. It looks like the part listed for my car and for Dale's car is the 3884640. The length of this part is listed as about 12.6 inches, with a slot of about 3.2 inches. If the "length" specified in the parts book is actually the center-to-center of the holes, this pretty much matches the length of my brace. However, the slot on my brace is clearly longer than 3.2 inches.

Anyway, can you clarify whether all base engine cars in 1967, regardless of K19 or A/C or power steering, used the same alternator brace? If so, I can check with some friends who have base engine cars and we can compare notes.

[Joe L.]

Re: 67 alt. brace, base engine w A/C

Joe-----

As far as I can tell, only 2 alternator braces were used for 1967 Corvettes with small block. For cars with C-60, the brace was GM #3854028 that was discussed previously. For all other small block applications it was GM #3884640. According to GM this brace is 12-37/64" in length, has a 3-5/32" long slot, and a 17/64" offset.

The "convention" that GM uses for the length specifications for these braces can be frustrating to determine. First of all, they don't specify what the "convention" is. Secondly, I've found that it's not used consistently for all the braces---some are measured one way, others another. The main confusion ALWAYS exists with respect to the total length; the slot length specs and offset specs are usually consistent.

Also, consider this: the GM #3884640 brace was discontinued in December, 1971 and replaced by GM #3826928. The GM #3826928 had also been used earlier for other Chevrolet applications. The 3826928 brace has a GM-specified length of 12-1/8", a slot length of 3-1/2" and a 1-3/16" offset.

Also keep in mind that there were a "jillion" of these braces with different configurations used for all sorts of Chevrolet applications and these can often "wind up" on other applications over the years.

The most frustrating thing of all with respect to these braces? That's easy. RARELY, if ever, did GM ever specify that a part number be stamped on them.

[Gerard F.]

Re: 67 alt. brace, base engine w A/C

Joe,

I think maybe the parts books are reporting x-y dimensions from the GM drawings and I don't quite understand what the offset is. Maybe the offset is an offset from x or y for the beginning or end of the slot.

I'm pretty sure mine is an original 3884640 for a 67 base engine without A/C, and the diagonal dimension outside to outside is 13-3/4", the tangent distance along the slot, outside to outside of curved opening is 3-5/8". If the y axis were the shaft of the brace, the dimension in the y direction would be about 12-1/2" out to out, but the slot on mine in the x direction would still be about 3-1/2".

I wonder if anyone has the GM drawings of those two braces, 3854028 and 3884640?
It would sure clarify those dimensions and how the parts book reports them.

Jerry Fuccillo
#42179

[Joe R.]

Re: 67 alt. brace, base engine w A/C

Hi Jerry:

The alternator brace on my 67 C60 car matches the description of your original and it matches the photo posted by John McRae. This may simply mean that my C60 car has an incorrect alternator brace. I have no doubt that my car is an original C60 car, but the car had a body-off rebuild in 1988 and maybe the alternator brace got changed.

If you still have the Paragon 1779K that you purchased, could you post a photo of it alongside a measuring tape, like John did? I'm curious whether the Paragon 1779K may be more similar to the 3854028 that the AIM calls out for 67 C60 cars, although is sounds like the slot in the Paragon part is too long.

[Joe L.]

Re: 67 alt. brace, base engine w A/C

Jerry-----

Yes, I do believe that the "offset" is the dimension between the "vertical plane" of the slot and the "vertical plane" of the hole. This has been fairly consistent on those that I've measured.

I also wish that we had the drawings on one or more of these braces. Unfortunately, they didn't "get out" before the GM Restoration Parts Program began. Since then, most of these only get out to program licensees and they, obviously, won't share them. It's a real shame since our understanding of the cars could be greatly expanded with access to the drawings and specs of all the components.

What makes it even worse is that although GMRPP licensees are provided the drawings, they don't always make the reproduction parts true to the original specs. And, as far as I know, there is no oversight provided to make sure that they do.

[Joe L.]

Addendum

Joe----

I found another brace used for 1967 small blocks. It's GM #3881816. It was used for 1967 Corvettes with L-79 and without power steering. This brace had a GM-specified length of 12-3/32", a slot length of 4-7/64" and an offset of 17/64". It was discontinued in September, 1975 and replaced by brace GM #361491. That brace was discontinued in September, 1977 and replaced by GM #460754 which remains available to this day. Both of the later braces were also used for 1975+ Corvettes.

[Gerard F.]

Re: 67 alt. brace, base engine w A/C

Joe,

I still have the 1779K on the car and it is in the picture I previously posted:


The slot is 4-3/4" long. If I put my original next to it, the Paragon one extends about 2" beyond my original. Just estimating from my original, the diagonal dimension out to out of the Paragon one should be about 14-1/2".

Dale has a 1779K off the car, maybe he can check my dimensions.

It might be a while before I put my original back on as I'm awaiting a shorter belt and some other parts.

Regards,

Jerry Fuccillo
#42179

[Joe R.]

Re: 67 alt. brace, base engine w A/C

Hi Joe:

I hope you can help me sort out a couple part number issues related to this topic. My problem is that my alternator adjustment bolt is at the very outer end of the adjustment slot. This could be caused by the Quanta reproduction belt being too long or by the brace being too short. After our discussion regarding the braces, I think leading suspect is the belt.

The only parts book I have is the September 1971 Corvette book. This book appears to say that ALL 1967 base engine cars (with or without C60) used the 53 inch 390540 alternator belt.

Per the AIM, though, the base engine without C60 used a 3847710 belt, while the base engine with C60 used a 3798498 belt.

My questions are as follows:

1) Can you confirm that the length for the 3847710 belt called out in the 1967 AIM for non-C60 base engine cars was 53-1/4 inches, as Jerry Fuccillo has stated?

2) What was the length of the 3798498 belt called out in the AIM for 1967 base engine C60 cars?

3) When belt length is specified, is this the dimension measured on the outside surface of the belt?

My tentative conclusion is that the belt length that is correct for my 1967 base engine C60 car is in the range of 53 inches. The reproduction Quanta 3861946 belt that is presently on my car, which they say is correct for 1967 base engine C60, is specified as being 54 inches long, although the outer perimeter actually measures 54-3/4 inches.

In summary, I think my problem is that the Quanta belt is too long, but I want to get my facts together before I call them.

Any clarification you can provide would be much appreciated.

[Joe L.]

Re: 67 alt. brace, base engine w A/C

Joe------

1) GM #3847710 was 53-1/4" in length;

2) GM #3798498 was 57-1/2" in length;

3) I do not know what convention that GM used in specifying belt length.

[Joe R.]

Re: 67 alt. brace, base engine w A/C

Thanks Joe. The 57-1/2" for the 3798498 would be much too long for my setup, so to get things to work right I will probably just use the 3847710.

I'm not sure what the cause of the discrepancy is, since both of the braces called out for the base engine (C60 and non-C60) are about the same length and my brace seems to be in that range.

[Joe L.]

Re: 67 alt. brace, base engine w A/C

Joe-----

The differences in the belt length are not necessarily due to any big difference in the configuration/length of the brace. The C-60 and non C-60 applications may use different pullies which also affects required belt length. I have not checked to see if they are different, but that's ONE of the other reasons that belt lengths may differ.

[Joe R.]

Re: 67 alt. brace, base engine w A/C

Hi Joe:

I agree that if the pullies used for A/C were larger, the required belt length would be longer. As best as I can tell, the alternator pulley was the same part number (3909815) for both A/C and non-A/C, but the crank pulley and the water pump pulley were different part numbers.

It appears that one reason the A/C pullies were different part numbers was that the base configuration parts were single groove, but the A/C parts were double groove. From the resources I have available I can not tell what the diameters of the different parts were, but if you have an available reference that shows diameters, following are the part numbers from the 1967 AIM:

Crank pulley, base configuration: 3755820
Crank pulley, 327 A/C configuration: 3850838

Water pump pulley, base configuration: 3905995
Water pump pulley, 327 A/C configuration: 3890419

Eventually I can probably measure the pullies on my car and compare them to someone else's base car, but if you have the diameter info available I would love to know what the books say.