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I'm trying to determine if the 2 coil wires from the engine bay wiring harness should pass through the hole on the back of the shielding ala midyear big block shielding. Should there also be a rubber grommet in the hole?
The JG makes no mention of the correct configuration.
Thanks, Chris
1969 Riverside Gold Coupe, L71, 14,000 miles. Top Flight, 2 Star Bowtie.
Yes, for your application the wires from the ignition harness pass through a hole in the rear of the distributor ignition shield. There should be a "cutout" hole in the upper rear of your shield. A black rubber grommet, slit for insertion of the wires, should slide down into this "cutout" and fit into the semi-circualr radius at the bottom of it.
I beg to differ Joe. My observations are that even late 1969 (both large and small block) do not use the grommet and the wires to the coil pass under the distributor shielding. I have never seen a 1970 (again, either engine) with the grommet and wires through the hole.
That's news to me. I thought that 1970's, at least early if not all, used basically the same 3 piece distributor shield as 68 and 69. The 68 rear shield of this assembly was GM #3934835. This shield had the cut-out that I described on the laft side. The 1969, and I thought 1970, rear shield was GM #3973610. This shield also had the cut-out in the same place. Was the cutout unused in 1970? My very late 69 has the wires going through the grommet which is installed in the cutout.
Chris, Terry, Joe,
70 #11756 has 3 piece shielding. 70 #14803 has 1 piece shielding. #11756 had a rubber grommet but who knows if it was original to the car.
Joe, Yes the three piece distributor shield is the same for the early part of 1970 production - say maybe into/through February. Then we begin to see a two piece shield in which the two halves of the box are spot welded together - no screws on the passenger side, for the brief remainder of the use of the box type shielding. The spot welded assembly is a real PITA to work around. Worse than the three piece, which is plenty bad enough. It is off the topic of this thread, but I do have some notes that indicate the spot welds show up on some 1969 Mark IV installations in the October/November 1969 time frame.
Neither of these designs used the grommet, and the wires to the coil pass under the box. The hole (or slot if you will) is still in the box part, as is the semi-circle cut out in the rear edge of the top. The opening is just not used.
We might need to define what my terminology is with respect to "late" 1969 in my original post on this subject. I was thinking in terms of anything produced after September 1969 not having the grommet. If one were able to do a survey on this subject it might be important to include information on engine size as well as conventional or TI ignition, as any of these may have influenced the installation details. Sadly, in the mid-1980s when we did the beginning research for the then new early C3 judging manuals, the grommet was one of the features we did not record. I am basing my comments on my observations from judging.
It surprises me, in a way, that the grommet was not used in 1970. Also, although the pre-70 AIM sheets for U69 show the grommet as being used only for "427" applications, that surprises me, too. The coil wires are exactly the same for small blocks or big blocks. I can tell you, for sure, that my September, 1969 built small block had the grommet and the wires passed through the grommet. Absolutely no question about that, at all.
It would seem to me that, especially with the 3 piece shield, if the wires were routed under the shield and then, necessarily, up to the coil top terminals, then the wires would be almost assuredly chafed or even cut by the lower edge of the shield. That seems very "un-factory-like" to me. I'm not saying that it didn't happen, but it seems very odd.
Joe,
I am aware of the AIM indicating use of the grommet on BB only, but I have seen its use on both applications often enough to discount that notation. September is within my comfort zone too.
The length of the wires is no problem going under the shield, in fact it makes removal of the shield moderately easier. Next time I get the car and camera together I'll snap a photo for you. I suppose there is always a chance that this is more complex than we are considering. Could the later wires be longer - maybe they changed the wire harnesses on us?
Very interesting. For what it's worth, my 454, standard ignition car is VIN 531, with a body build date of Jan 9, 1970.
It's a pretty original car and I'm considering it for a Bowtie. The coil and distributor were replaced at some point, although I rebuilt and reinstalled the original distributor.
There is no grommet, and the coil wires do run under the shielding. Noting Joe's point about chaffing wires, one of mine is slightly chaffed from rubbing the lower edge of the sheilding.
The wires seem to have a natural curl to them, like they have always been in this configuration. I would think that if they were routed through the shielding hole at one time, there would be more bends in the wire, etc.
Chris
1969 Riverside Gold Coupe, L71, 14,000 miles. Top Flight, 2 Star Bowtie.
My car is a July 20 build and has the three-piece shielding. No grommet in the hole. The wires pass under the shielding to the distributor. Last year on a trip to CT from PA, the white wire going to the distributor chafed through and shut down the engine. A little bit of white electrical tape around the wire and on the lower part of the shielding allowed me to complete the trip.
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