Flex plate bolt patterns

[bcfishon]

So I threw on one of the many GM flex plates I have laying around and when I went to bolt up the torque converter the bolt pattern was slightly off. I was unaware that the patterns were different for different trannys,we are putting in a 700r and I'm guessing I have a old school t350 plate,can someone please confirm.

[kwmech]

Did you spin the converter 60 degrees. There are 2 patterns on the plate for the converters

[bcfishon]

Originally Posted by kwmech

Did you spin the converter 60 degrees. There are 2 patterns on the plate for the converters

I did,I think I need a plate from a 86 or later

[Accelo]

Torque Converter Application Pattern (inches)
PG/TH350 small 10.75
TH350, 700R4 and LT-style 4L60E have a 10.75" diameter bolt pattern.
TH400 large 11.50
LS- early style 4L60E have a 281mm or 11.066" diameter bolt pattern.
LS – late 4L60E have 300 mm
(4L80E) 11.5” same as the TH400.

Many of the dual pattern flex plats have the 350 10.75 and 400 11.5 patterns.
Not all flex plates have the dual patterns.
A 1982 and up flex plate should work. No THM350 were made after 1981 so you should be safe getting one for a truck.

[bry593]

Also, be sure you get the correct ring gear tooth count. There are two different counts.

And lastly, make sure your flexplate is weighted correctly for the type of balance your engine requires.

Geez, who knew flexplates were so complicated?

[MARKDTN]

There are flexplates for 2-pc rear seals and for 1-pc seals. They are not interchangeable. But my '83 K-20 had a 2-pc seal 350 and a 700R4 so that would work for an application.