'66 upper A-arm to frame bolts; GM 3888248

[Michael H.]

Re: '66 upper A-arm to frame bolts; GM 3888248

The bolts that held the upper A-arms to the frame on my '66, which I believe to be original to the car, should be GM # 3888248. My bolts are 7/16-20 x 2.125" long. Thanks,

Gary

Gary,

If your original bolts are 2 1/8", I think they are the 3719947 bolts used for early production 66. The same 3719947 was used for 63 through early 66.

For later 66, the 3888248 was used. The 3888248 is/was 2 1/4" long.

I THINK the 3888248 replaced the 3719947 in production about the same time that the nut was also changed from a "high nut" and lock washer to a lock nut without lock washer.

Both bolts were 7/16-20.

I agree, none of these were zincad. I have new/NOS 3888248's, purchased decades ago, and they are black.

[Joe L.]

Re: '66 upper A-arm to frame bolts; GM 3888248

All-----


During the 60's and 70's it was very unusual for ANY GM high strength fastener (i.e GM 300M) to be finished in anything but phosphate or natural. There may have been a few that were finished in zinc or cadmium but, offhand, I can't think of any.

[Gary B.]

'66 upper A-arm to frame bolts

Michael,

On my car, both of my presumed original upper A-arms were attached to the frame with identical bolts, lock washers and (heavy) nuts. The bolts are definitely 2 1/8" long, not 2 1/4, so they must be the early bolt, albeit on a late car (July 20 build date).

Gary

[John D.]

Re: GM 3888248 vs 382909

John,

Sounds like another nail in the zinc/cad finish coffin.

Does the GM drawing for 382909 also specify the same decarburization class C spec?

Gary

Gary

yes it does

john

[Ronald L.]

Re: '66 upper A-arm to frame bolts; GM 3888248

Gary,
and for those that have those prints or access to them, if a part came into GM spec'd with nothing but the metal, that is what you got, coming in the door.

But that was not the end of the story, there were many parts that GM heat treated inside and then sent to the assembly plant. As a metallurgist back then we did tons of that and was a great job in the winter, one sweat box in the summer.

This part would have been 'cooked' in a carburization furnace and then oil quenched. It would have been dark gray to blackish if the part was on the top or the side of the bin and oily.

Sounds like someone has the original print - can you post it?