For some time I have been plagued with a mysterious miss haunting my TBird.  All is good for a month or two, then out of the blue the engine develops a miss.  I clean the distributor cap, check the plugs, timing and wires and it goes away.  Last week it returned with a vengeance.  It was popping out the exhaust and running rough.  This time I believe I have found the culprit.

My car has it's original three speed manual transmission with overdrive and a 4.11 gear.  I have a 12 volt Pertronics unit in a 1957 distributor.  Overdrive transmissions use a kick down switch under the accelerator pedal.  This switch has a wire running to the coil that sends a momentary ground signal to the ignition to aid in dropping the transmission out of overdrive.   I believe the old kick down switch in my car was sending false signals to my ignition system causing the miss.

I never use the kick down switch.  I downshift manually if I need to pass. I disconnected the wire from the kick down switch to the distributor and went though the engine again.   I checked the valve lash and it was perfect.  I installed new plugs, distributor cap and rotor and retimed the engine. There was an immediate difference in the way my engine sounds and feels.  I believe the bad kickdown switch was causing a lot of other problems which may have become worse with the Pertronix unit.



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My experience with the Pertronix and the overdrive resulted in my cooking on two Pertronix units.
I dont think they handle that momentary short to ground in a good way.
Went back to points and all has been good.

Obviously your experience was different

Oldmics

I was lucky that the O/D circuit didn't fry my Pertronix unit. It definitely had a negative effect on the ignition system in my car. With the wire removed, the engine even sounds different.


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I have Pertronix in my 56 crown for probably 10 years and it also has a three speed overdrive.I have used the kickdown many times and never had a problem with the Pertronix.   Carl

I believe my problem is with the kick down switch itself. The O/D circuit goes through this switch.  I believe it's either sending errant signals or messing up the coil in some way.   I'm running a Pertronix Coil as well.  The kick down switch in my car is most likely original and it's a mess.  I have had intermittent O/D issues ever since I have had this car.  I always trace the problem to the kick down switch and it starts working on it's own.   I should change out the switch, but I never use it so it remains.   It's not an easy thing to change.   Maybe the next owner will replace it?  I'm happy with it disconnected.


71% of original size (was 710x19) - Click to enlarge