GM 350 flexplate and tranny question

[DaveB]

I tried to put on the flexplate I picked up for the 350 SBC that I'm putting in the commando project but it didn't fit. The flexplate that I have came off of an 89 Blazer with a TBI 350. The motor I am using is a nearly new GM crate 350 that was in my brother's carbureted 78 Blazer. The flexplate mounting pattern and the center hole on the crate motor is quite a bit bigger than the TBI 350 pattern and flexplate center hole. A flexplate for an older non TBI 350 should match up but will I have issues hooking it to a torque converter from a 700R4 ? Or do I just need to find a flexplate from a carbureted 350 which had a 700R4 ?

I have two trannies to choose from in the garage a TH400 and a 700R4. I know the TH400 is stronger but I like the idea of overdrive, shorter length, and a lower first gear for crawling that the 700R4 gives me. Any thoughts ?

 

[4554x4]

The tbi motor will have a one piece rear main seal that installs from the rear of the engine over the end of the crank where the flexplate bolt to.

The carb motor has a two piece rear main seal that goes under the rear main cap.

What you need is a flexplate for the carb motor regardless of what trans it had.

As far as the trans, if you are going to drive on the street go with the 700r4 for the overdrive. If it is a trail rig only, or mostly, use the 400.

 

[DaveB]

Thanks for the info, I'll have to find a flexplate from an older rig. The jeep will need to do both road and trail so it looks like the 700r4 is the way to go. Anyone want to trade a good TBI flexplate for an older one ?

 

[Tacoma]

Let me take a look, I've got a stack of GM flexplates, I'm sure a couple of them are pre-TBI.