FMX Transmission Stutter

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Joined
Jul 26, 2022
Messages
22
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Location
York, SC
My Car
1971 Mach 1 - 351c 2v - FMX transmission
Hi all,
I have a 71 Mach 1 with a 351c and an FMX transmission.
I recently installed a Pertronix Ignitor and a new Pertronix coil. At the same time I installed a phenolic carb spacer. This made my cranking much better. But it also advanced my timing and was idling too fast. I read where installing the Pertronix unit could cause that, so I backed the timing down to 12 degrees and set the idle about 800 RPM. The car ran good and seemed happy with that.
But when I went to drive it, the transmission would hardly engage. It was sluggish and “stuttering”. If I pushed the accelerator and revved it up some it seemed to catch.
My question is; could me backing the idle down be causing too low of vacuum to the transmission? I might have thought it was a vacuum leak, but it was perfectly fine until I backed the timing and idle down.
I am a little puzzled. Does anybody have any thoughts?
I should also say the transmission was rebuilt 12 months ago and has a new vacuum modulator.
 
Last edited:
Agee with Spike above, check the vacuum with a gauge. Also, by any chance have you checked your trans fluid level, if it is too low, it will feel like you have to rev the engine up to really get moving.

Good luck
Tom
 
Agee with Spike above, check the vacuum with a gauge. Also, by any chance have you checked your trans fluid level, if it is too low, it will feel like you have to rev the engine up to really get moving.

Good luck
Tom
I’ve checked it and it shows full. But now that you make me think of it, I wonder if it’s the right dip stick. It bottoms out and doesn’t completely sit down on the tube at the top. Perhaps I’m getting a bad reading? The stick seems it
May be too long. Thanks for reminding me of that.
 

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