The New Project: Part Deux!

[HemiOrangeTA]

Awesome stuff; very enjoyable to follow. Thanks for the details and pictures/video!!

[njsteve]

I have been hunting down some parts to try to assemble a correct unitized distributor for the car. I recently got one 1973 1112203 off of ebay, a 1974 1112810 from a trade for an old holley carb I wasn't using, and got a rebuilt 1973 1112203 from an auto parts store. I do still need an actual 1972 1112133 in case anyone has a useable core out there.

These contraptions were a standard option on the 455HO Formula and optional on the Trans Am. They were somewhat notorious for glitches, being the first self-contained transistorized ignition developed by Pontiac. In evolutionary terms, if the the later HEI distributor was a modern human, then the Unitized Distributor was a Neanderthal.

The big problem was that the parts were unique and never produced by the aftermarket. The distributor cap, the rotor, the coil, and most of all, the wire set were unique and insanely expensive even back in 1972. The ignition module was housed in the base with wires that connected to the coil pack. The wire set was a molded one piece octopus that required complete replacement as a unit if you burned or broke a single wire. It sold new from the dealer, for several hundred dollars back when a regular points ignition wire set was around $20. So when something happened, the entire distributor was usually tossed and a newer HEI was installed in its place for 1/4 the price.

Here's one assembled:



Here's the three I have now

[njsteve]

The cap is more of a fixture for holding the wire "octopus" and has no internal termainals for the spark plug leads. It has a spring that sits on the top coil terminal and a spring loaded carbon button that is inserted into the center of the bottom of the cap. (the cap on the eft is cracked and missing the carbon button).





The coil pack sits on top of the wire "octopus" and two long screws go through the coil pack, then the wire set and cap and into the distributor base.

[njsteve]

And here is the notorious wire set. The eight spark plug wires are permanently molded into the center ring. If there was a problem with one wire...you had a problem with the whole set and had to replace it as a unit. Big $$$



Here is a chopped up center ring.



There is a way to split the center seam of the molded rubber ring with a razor and insert a regular wire set into the terminals. I will be trying that just to see if it will work. Others have done this with good results in the past.

[njsteve]

Using the original 1972 service manual, I went through the diagnosis and testing procedures with an ohm-meter as described in the manual. All three distributors, modules and coils packs tested out fine. The common problem with these distributors was overheating the coil pack and melting the windings until it shorted out. If the coil windings were going, then the module was overworked and failed as well. This usually all happened without warning.

I have a pile of original repair work orders from London Motor Products, the dealer that sold the car new. There are multiple work orders for replacing the distributor or coil pack or some other no-start condition.

[njsteve]

Here's the internal module:

[njsteve]

Performed an autopsy on the chopped up spark plug octopus (calimari?)

I initially tried using a hot knife but then just switched to a razor blade. I sliced the seam and then used a combination of Angry Old Man Strength and the razor to peel the top section away. It looks like the factory assembled these units with some type of weatherstrip adhesive/rubber cement. Definitely some tough stuff.



After slicing and fileting the top off, here is what appeared:



It is a pretty simple design. The wires have a terminal end with a tip that resembles a Chevy bowtie. The Bowtie inserts through the eight rectangular slots and is preset into the correct position around the circle.



Here is a close up of the "Bowtie". It can rotate 360 degrees to any position. There are two styles, 6 of the end-mounted tips and 2 of the side mounted tips. Each wire is stenciled with the number of the cylinder it goes to: 1,3,5, and 7 on one side and 2,4,6 and 8 on the other, preset in the 1-8-4-3-6-5-7-2 firing order.



And here is the base with all 8 wires withdrawn. Looks like a reasonably easy swap of the terminal ends onto another set of wires and then reseal the top with a suitable adhesive.



I will update once the replacement donor wires arrive.