While transferring/replacing parts from my old engine to the new one, I noticed my current flexplate has got more than a few teeth chipped, so naturally I figured I’d replace it while I have everything apart. I ordered a new one for a '68 302 from MustangsUnlimited, and it is at least an inch or so larger in diameter than the flexplate I am replacing.
The old engine is supposedly a 1978 302. The trans is a C4, and is original to the car (only the engine was replaced due to valve problems, and that god awful 1978 block was put in instead of another 1968 block), so I had assumed that the flexplates between the two years would be the same, since the 1968 transmission is mated to the 1978 engine.
Does all of this mean I pretty much need to find a 1978 flexplate? I’m assuming the larger diameter one will not mate with the starter correctly, but then again, I’ve assumed before and look where it got me…
Thanks for reading.
On the originals there were 157 and 164 tooth flex plates. I am pretty sure that the 302’s got the 164 tooth one, and the 289’s got the 157 tooth version.
So the mystery deepens.
My current flexplate (from origins unknown at this point): 141 teeth with a diameter of just a hair under 12 inches.
The one I ordered from MustangsUnlimited for a 1968 302: 157 teeth with a diameter of 13.25 inches
I can’t seem to find much info on a 141 tooth flexplate, other than it might have been used in the Mustang II, and that somewhere on a random forum somebody had a larger 14.5 inch diameter 141 tooth plate that came from a '78 Granada.
Most of what I’m seeing shows that the C4 trans supported three different flexplates, depending on the size of the bellhousing:
- the 164 tooth flexplate that was used in heavy-duty trucks and full sized Ford cars (but requires a larger bellhousing)
- the 157 tooth flexplate that was used in compact to intermediate sized Fords
- the 148 tooth flexplate that was rarely used and only on Mustang IIs
Not sure how my transmission supports this random 141 tooth variety, unless it happens to have the same diameter as the rarely used 148 tooth flexplate. My trans bellhousing measures 15.5 inches from top to bottom (outside diameter). Will this bellhousing support the 157 tooth flexplate, and if so, will it mesh up with the starter even though it’s a larger diameter plate?
I’m at a complete loss as this point, and feel like my eyes are about to bleed from reading about Ford 302 flexplates all day.
I am sure you would need to know the bellhousing part number in order to identify an appropriate FW. You must take it off the trans in order to find the part number. This will give you a better idea of the year of the bell housing. The part number is cast in the face where it mounts to the trans. Thanks Ford for hiding this so well. 
I strongly suspect now that the motor came from a 1978 Mustang II, and that the current transmission is the matching C4 to that engine, not the original transmission from the car, but I won’t be sure until I find the codes on the transmission itself. In the meantime, I managed to find a new 141 tooth flexplate that should fit no problem, and that way I can keep my existing transmission/bellhousing, since they don’t have any issues that I know of.