#1  
Old 06-16-2022, 04:51 AM
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Dailydriver Dailydriver is offline
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Default Searching for correct flexplate

I am looking for a new flexplate (old one's missing teeth)
I have a 1966 LeMans but a 66 389 GTO engine installed. Trans is a TH400.

Looking a the dimesnions this plate should be the right fit:

https://www.summitracing.com/parts/pqx-1845501

https://store.prw-usa.com/1845501-po...nce-166-teeth/

What confuses me is that it says "67-79" - can anybody explain that? Did something change on the crankshaft between 66 and 67? Why wouldn't that plate fit on a '66?
I can hardly find anything on crank bolt patterns on Pontiac crankshafts so I assume that pattern never changed?

The dimensions I measured on my engine are:
crank register: 2.75''
crank bolt pattern: 3.79''
converter pattern: 10.75''
166 teeth

Thanks!
TJ


Last edited by Dailydriver; 06-16-2022 at 05:07 AM. Reason: Typo
  #2  
Old 06-16-2022, 07:40 AM
66sprint6 66sprint6 is offline
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I see on Rock Auto that it's the same part number for both '66 and '67 cars.

  #3  
Old 06-16-2022, 09:34 AM
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Dailydriver Dailydriver is offline
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Great idea! I assume it should be a fit.
Thanks
TJ


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  #4  
Old 06-16-2022, 03:17 PM
gtospieg gtospieg is offline
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I have flex plates from 66 OHC6 and 67 326 as well as 65 389...all appear to be the same.

  #5  
Old 06-16-2022, 04:05 PM
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Sirrotica Sirrotica is offline
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Differences in factory (65 and later) Pontiac flexplates were they were not all drilled for the dual fit bolt pattern, I.E. T400, T350, and T300. Some were only drilled for the T400. If you wanted to, you could drill the needed corresponding holes for the smaller convertor on the single pattern flexplate. I assume aftermarket parts have both convertor patterns. I've always had enough old factory ones that I never needed to buy an aftermarket one.

Then in 1975 they went from 2.75 register size to 2.5 (center hole in the flywheel). The 6 bolt pattern on the crank has been the same from 55-81.

In 77 the 301 debuted, and used an externally balanced flexplate. In 1980 Pontiac made the 265 V8 which was only a 2 year run, it also was externally balanced, and cannot be interchanged on 326 through 455 engines (internally balanced) and the internally balanced flexplates.

Those facts are known to me from working extensively on Pontiacs for over 50 years, and to my best knowledge are correct information. Hopefully this answers the OPs questions.

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  #6  
Old 06-18-2022, 08:52 PM
Goatracer1 Goatracer1 is offline
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You are correct on the single and dual pattern flex plates. I was going to mention it but you beat me to it.

  #7  
Old 07-12-2022, 04:54 PM
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Dailydriver Dailydriver is offline
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Thanks all for your help and giving me the confidence in that fleplate.
Finally got it and it fits perfectly!

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