J 56 bracket bolts

[John S.]

Can any one give me the size and grade of the bolts for the cast iron brake bracket's. I tried to find them in my parts book and could not find them. thanks john

[Joe L.]

Re: J 56 bracket bolts

John------

The bolt size depends upon the year Corvette. 1965-67 used 7/16"-20 bolts whereas 1968-75 use 1/2"-20 bolts. All bolts were GM-300M (SAE grade .

The long bolts were 3-1/8" long; the short bolts were 2-7/8" long. Bolt length is not absolutely critical here and the bolts can be a little longer than original without creating any problems. In fact, sometimes they need to be a little longer than original in case shimming needs to be performed. Very often, when these supports are installed it will cause distortion of the brake caliper and unsatisfactory brake performance.

[William O.]

Re: J 56 bracket bolts

I have a few of the 3 1/8 with the correct finish if you need them.

[William O.]

Re: J 56 bracket bolts

Hey Joe: Is there a head marking to look for on the J-56 bolts?
Regards,

Bill

[Joe L.]

Re: J 56 bracket bolts

Bill----

For the 68-75 1/2" bolts, I believe that "M" was ONE of the headmarks. There may or may not have been others.

[William O.]

Re: J 56 bracket bolts

My bolts have the following: " I M" at 12 oclock with three hash mark at two,six and 10.

[Joe L.]

Re: J 56 bracket bolts

William------

Are these 7/16-20 bolts or 1/2-20 and are they in a GM package with a part number on it? I've never seen a GM-280M (SAE grade 5) bolt used for a front steering arm-to-front spindle attachment for the 68-82 1/2"-20 bolts. I don't know, for sure, what was used for 65-67 but it would surprise me if anything less than GM-300M (SAE grade 8 ) for this application.

[William O.]

Re: J 56 bracket bolts

7/16" 20 beat-up box with no markings, the finish is some what oily black phosphate.

Regards,

[Joe L.]

Re: J 56 bracket bolts

Bill-----

The finish sounds right. However, with no markings on the box as to part number, what leads you to believe that they are bolts for the front steering arm-to-spindle with HD brakes? As I say, the GM 280M material grade (3 lines) would surprise me for that application.

As far as I can tell, GM never catalogued a specific bolt for this specific application. They did for the later 1/2" size bolts, but not for the earlier 7/16" bolts. I can't say, for sure, that they did not, but I can nowhere find any reference to it.

These bolts are kind of "mystery bolts", anyway. I've never been able to find any torque specs for these bolts published anywhere. No edition of the Chevrolet or Corvette Factory Service manual that I've checked has the specs. Of course, it's not in the AIM since these bolts were components of the assembly delivered to St. Louis. And, as I say, I can't find any reference to these 65-67 bolts in parts references. It's almost like GM wanted to "forget about these things". Surprising, too, as these are very critical bolts.

One thing, though: the heads of these bolts are not visible when installed on the car. So, for a situation like this, perhaps an ARP high strength, black oxide bolt would be the way to go. The black oxide protruding threads, the only part visible, would appear just like an original bolt.

[William O.]

Re: J 56 bracket bolts

As always you are a wealth of correct information.

Thanks again.

Bill

[Joe L.]

Re: J 56 bracket bolts

Bill-----

Are the boxes that the bolts are in GM-labeled boxes? If so, is there any information on the box that's even a little legible that I might be able to use to ID them. Even a partial group number or partial part number might be useful.

[William O.]

Re: J 56 bracket bolts

Looked closly at the box, there is not any GM logo or ID.

Thanks again for you input.

I may have located grade 8 bolts that are black phosphate coating I will post if they still manufature the bolts.

Best regards.