Still trying to nail down head bolt info
 

Attached pics show cast bracket that holds a/c compressor on 66 GTO and also a page from the 66 Pontiac A/C manual showing how this bracket is retained by two head bolts. Bolt A goes in the rear hole of the bracket. Bolt B goes in the front hole of the bracket. I don’t have the correct bolts for this bracket. In order to obtain them I need to know the length of each bolt, measured from the bottom of the hex head to the end of the bolt. Can somebody provide these dimensions?

The parts book lists a head bolt specific to A/C applications. P/N 538946 1/2-13X 4 5/8 inches. Description is Bolt, head comp. mtg. bracket and oil level tube. The other bolt must be a standard head bolt but I dont know the length.

Still trying to nail down head bolts info
 

That’s great info. Thanks for your help. Maybe somebody else can give me the length of the other bolt.

There must be the same length on both bolts.

In my book it says 5-5/8" not 4-5/8".

You may be correct. 4-5/8 is the same length as other head bolts and I thought it would take a longer bolt by the looks of the bracket. My 7-73 MPC clearly shows that part number twice with both instances showing 4-5/8 inch length but I wonder if it is a misprint in the MPC. Does your MPC show that same number with the longer length, and what is the revision date on your MPC. A newer version of the MPC may have corrected an earlier misprint.

From 1967 Pontiac Chassis Parts Catalog:

Bolt A #538946, 3/8" - 24 x 1/2" - 13 x 5 5/8"

Bolt B #518031, 1/2" - 13 x 4 5/8"

HTH

Roger that. I will update my MPC with the correct information.

The bolts must be the same length since the head of the bolt sits on the same height from the block.

Still trying to nail down
 

One last update on this. I dug up the two different style bolts that retain the a/c bracket. Each one is 4 5/8 long. Did some more measuring and came up with the dimensions shown on the attached diagram reflecting this 4 5/8 length. It looks like a 5 5/8 length bolt would bottom out on either hole in the block, so I used 4 5/8 to attach my a/c bracket. Not sure why parts manual would specify 5 5/8.