Yes I found the answer I think
it must be the wrong converter. Taking trans engine matrimony apart and then fitting the converter on the flexplate, can get the 4 studs in place doesn't completely inserts in the pilot hole. The converter pilot is just about 1/8 inch too long.
Checking info on various websites came to that conclusion.
the pilot hole seems 2 stages first and biggest stage is 1.848 in diameter, second stage is 1.240 about.
The converter pilot is 1.375 in diameter of the stage that should fit in the 1.240 part.
Came to the conclusion is that the deeper stage pilot hole of 1.240 is not used but the first 1.848 is the important one so the converter pilot is just too long.
Which means the wrong converter type.
wonder if I could cut of 1/8 of an inch of the converter pilot.
Not thinking of widening the hole in the crankshaft pilot because it cause imbalance, maybe the same for the converter balance if I cut a piece off.

information website:
http://www.gopnh.com/Transmissions.c...mission=%20FMX

regards,
Ron

Ron, when I marry an engine to an automatic trans, I always build the flex plate to the crank, then I offer the torque converter and trans to the flex plate.

That's how the factory does it, too. After a couple wiggles, the four torque converter studs should slip right into the flex plate. Then the bell housing is tightened, and finally, the four converter nuts are installed. Rotating the starter gear to tighten the four nuts, seats the whole thing nicely.

There is really no such thing as a C10 or C9, they are just slang terms. Ford built C4's, C6's, then AOD's, etc.

You must find the right combination of flex plate, starter motor, and bell housing. The bell housing will determine which flex plate and torque converter will fit. Some engines use a 'sandwhich plate' between the engine and trans (like my 351W and AOD).

I have never run into your problem, where the torque converter pilot was too large for the crankshaft hole. I once had a converter that bloated so much, I could see imprints of the five crank bolts in the converter. Make sure there is no pilot bushing or bearing in the crankshaft (for a manual trans).

Good luck, Ron. - Dave

Thanks Dave,

yes remember my old thread from 2009:


the gearbox casting number being C9ZP was standing for C9(FMX 1969) z= mustang and P= automatic.
by checking the right torque converter for it could not figure it out because my 'FMX' has 31 splines and there seems to be no FMX transmission and torque converter for it with 31 splines.
FMX has only 20 splines.
But my gearbox does have 31 splines so it must somehow be an overhauled gearbox with the 'wrong' casting code, the middle section being from a FMX.
But if I look for torque converters and the measurements then I came to the conclusion that it must be the C6 and not mentioned is the FMX name by those. all the measurements on the input drive shaft are correct for the C6, also the bell housing is correct.
The flex plate looks correct but no marking on it about a casting number.
The crank pilot hole looks like 2 stages but probably not used as 2 stages. the mane stage being 1.848 is correct for the C6 converter and also that converter has the shorter pilot.

I can probably answer my own question if I can shorten my pilot shaft on the converter I have now if the pilot shaft does not fit correctly, being smaller that the converter might be out of balance and vibrate. the pilot shaft with the correct fit makes sure that the (balanced) converter is exactly center, the studs just rotates the converter.
So if the converter is out of balance because of the wrong pilot shaft, the studs will just break.

Have to start looking for another torque converter.

The way I (tried to)installed it was exactly as you said, first the flexplate on the crank, the converter on the gearbox in the bell housing and line them up and 'marry' them. I did seem to go well with the exception of tightening the last 1/8 inch or so.
If I would have tried to put the converter on the flexplate before on the engine when the engine was out of the care I could have noticed it before but I didn't, I was so sure I had the right converter but I failed to do that.

regards,
ron

But you are right, there are no such thing as a c9 or c10, found that a casting number of C9 is very likely to be a FMX but doing the search couldn't find a FMX with a spline count of more than 29. info on the C6 type matching with a 352(390) and 31 splines was an easy match and gave the answers.

Anyway, trying to do anything perfect but failed to mount the trans on the engine before putting it in the car, just for trying out. paid for that dearly now with 2 extra days figuring it out.

I will 'marry' the trans with the engine now anyway but without the converter (who needs a converter anyway, lol) no just so I can continue, won't be ready to drive anyway until next summer. Have 2 or 3 weeks more work days on the car before I have to store it for the winter.
I can put the converter always in later. In this case I can make the rest of the car ready and hopefully start and run the engine without running the transmission.
My goal is before the winter storage to run the engine, make the brakes ready, normal and parking brake.
Also I got/ordered the wrong spark plug wires, had them on(ford racing red wires 9mm) from Summit, only to find out that they did not fit the distributor cap(original cap) because the distri. boots were HEI. considering either cutting them off and mount some boots that I can by locally or ordering new ones, the right ones this time.

regards,
Ron

hard to imagine, weather temperature still about 74F, leaves are already changing color and in another 4 or 5 weeks the first snow will fall.
I just heard that there will be likely another container from CA to Europe so I can do some more shopping and have the stuff and a correct converter maybe here by next spring, anybody has a converter laying around that they don't need?