Vacuum Relay Valve Mount

[Tom R.]

Trying to determine how to reinstall the relay valve assemblies for the headlights. Based upon the AIM UPC 12, sheet A13, I was missing mounting bracket #3966703. The drawing shows the relays mounted to this bracket and the bracket mounted to the underneath side of the front cross reinforcement assembly. The purpose of the bracket was to move the relays forward to clear the horns. I could not find this bracket, didn't remember it, but was able to find a used one. So, after I installed my horns, I attached both relays to the bracket and attempted to mount the bracket according to the AIM. This is where my issues came to light. The bracket (with original part number stamped same as shown in the AIM) has a different mounting hole pattern than my reinforcing bar underneath. No way, no how to make the two work together as my reinforcing bar has four holes whereas the bracket has three. In other words, I do not have the three weld nuts and pattern as shown in the AIM to receive the bracket (I have four holes). At first, I thought maybe someone had replaced the reinforcing member with a different year. However, after reviewing my pre-disassembly photos, I find there was no bracket present at all and the relays were mounted without it. This all will be clearer after viewing the attached photos. The photos also show the horns were originally mounted differently than shown in the AIM with the right one using an extending bar to lower it. So, after all of that, I'm asking for anyone with knowledge/opinion as to how to proceed. As in, was the original configuration shown in my photos, correct even though different than the AIM? Or, had the reinforcing bar been replaced? If so, can anyone identify it by it's four hole pattern so that I can get the matching year bracket to mount my relays? A lot to ask I realize.

[Mike E.]

Re: Vacuum Relay Valve Mount

Tom,
Which year are you working on? I'm assuming 1970, because 71 and 72 had single horns. I can't get a picture of my 70 until later today, but I know it doesn't have the extension for the one horn. Hopefully someone else will chime in.
Mike

[Tom R.]

Re: Vacuum Relay Valve Mount

Mine is a 70 and I was assuming someone would tell me that about the horn extension. So that leaves me to determine what year the reinforcing bar is in order to match the four mounting holes I think.

[Terry M.]

Re: Vacuum Relay Valve Mount

Not only does the year of the car matter, but as in this case often the build date of the car will also matter.

One must understand that the AIM(s) [there are multiple versions of the AIM for each year 1970 to 1972] represent a slice in time. That slice may or may not represent your car. In this case I believe it should be clear that the AIM you have does not represent that slice of time when your car was built.

We could, and at some point probably should, get into delineating the differing versions of the AIMs for each of the years, but this post and on this board is not that time. IMO

[Bob I.]

Re: Vacuum Relay Valve Mount

My June built 1970, the horns bolt to the Reinforcement Bar as shown in the AIM. Your bracket, I don't see all seven holes in the photo.
Bob

[Tom R.]

Re: Vacuum Relay Valve Mount

Point taken. Mine is a July built 70.

[Bill L.]

Re: Vacuum Relay Valve Mount

Hi Tom,

My 70 was built 1st week in June. I will see if I can get some pics tonight. The plate mounts exactly as shown in the AIM with hex head screws. I know both horns on my 70 have the same length bracket unlike the long bracket on your one horn. In addition to the bolt, the horns have an alignment hole that the bracket fits in to. The brackets should have a small tab each that fit in the alignment hole. They mount either side of center. There is also one hole on the header that is a ground and there is at least one other hole on the header where a harness clip attaches near the center.

Bill

[Bill L.]

Re: Vacuum Relay Valve Mount

Hi Tom,

My 70 was built 1st week in June. I will see if I can get some pics tonight. The plate mounts exactly as shown in the AIM with hex head screws. I know both horns on my 70 have the same length bracket unlike the long bracket on your one horn. In addition to the bolt, the horns have an alignment hole that the bracket fits in to. The brackets should have a small tab each that fit in the alignment hole. They mount either side of center. There is also one hole on the header that is a ground and there is at least one other hole on the header where a harness clip attaches near the center.

Bill

[Tom R.]

Re: Vacuum Relay Valve Mount

To answer Bob Imhoff's from earlier - yes, my bracket 3966703 has all seven holes. Two are below the limit of the photo attached.

And only my left horn has the receiving/aligning hole on the reinforcing header. The right does not but I drilled and added to keep that horn in place. Now I just have to hope somebody can identify my replacement header by it's four hole pattern from the picture.

[Bill L.]

Re: Vacuum Relay Valve Mount

To answer Bob Imhoff's from earlier - yes, my bracket 3966703 has all seven holes. Two are below the limit of the photo attached.

And only my left horn has the receiving/aligning hole on the reinforcing header. The right does not but I drilled and added to keep that horn in place. Now I just have to hope somebody can identify my replacement header by it's four hole pattern from the picture.

Tough to get a picture with the center grill in place. The pic will show how the valves are installed opposite on the plate. The three holes to attach to vette are on the engine side. Sorry I could not get a better pic.


BillHL Vaccuum valves.jpg

[Siegfried K.]

Re: Vacuum Relay Valve Mount

I am restoring a 1970 late March LS5 coupe car, same issue. After much investigation, I have determined that the front of the car was hit and repaired at one point in it's past. The replacement reinforcement bars only have the 4 holes offset more to the passenger side I have found, and not the 3 holes in a triangular patten in the center for the relay offset mount plate, also no extra holes for a passenger side horn. The 1971 and on cars only had one horn, thus the deletion of all the other holes and the offset relay mounting plate. As far as I have found, no 1970 reinforcement bars were available, that is why we have this issue now. Drill 3 mounting holes and use thread inserts, once plate is mounted no one will ever know. As well, additional holes will have to be drilled on the passenger side of bar to accept the other horn in the correct position.

[Tom R.]

Re: Vacuum Relay Valve Mount

Thank you for that very comprehensive answer. I did exactly what you suggested - drilled and tapped the three holes necessary for the relay bracket as well as the right side horn alignment tab. All are now installed as they should be and if not for the four out of place holes in the replacement header bar, no one will know.