351w mated to an AOD trans Which flexplate to use?

Jan 3, 2007
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You'll find lots of conflicting answers to this question posted on line.

I had been trying to answer this for days now without the answer. Then I discovered it. I have a 351w engine from an 85 Ford van and an 85 or so AOD transmission. I purchased the trans from a swap meet, so I really had no idea what it was from, only that it was an AOD. I installed the combo in my 1957 T-Bird because the parts suppliers said it was the right one, only to have the front pump self destruct. Why? Because I put in a ATP Z-110 flex plate. Later, after a lengthy search on the internet, I discovered this flex plate was for only a C6 or e4od.

Anyway, my search for the correct flexplate went on for 4 days. Finally, I settled on a Pioneer FRA-205 because all the web postings said it would work. Wrong. The torque bolt circle was wrong and it would not go on the torque converter without forcing it. This flex plate, which by the way doesn't have its bolt circle listed anywhere has an 11 3/8 (11.375in) bolt circle. My converter is 11 7/16 (11.4375). Now considering that I had another AOD sitting in the shop with the same converter in it, I assumed that all the AOD converters were the same. WRONG!!!!! Some converters have an 11 3/8 bolt circle which match the FRA-205 flex plate. So, I had the wrong converter. Make sure your converter has the right bolt circle.

1985 F-150 and Crown Vics with an AOD trans have torque converters with an 11 3/8 bolt circle which matches the Pioneer FRA-205 flex plate that will fit the 351w engine and have the proper spacing for the trans front pump. These cars came from the factory with a 351w and an aod trans. So that's the solution that has been so difficult to discover. All the AOD converters are NOT the same. I have not seen this information posted anywhere. Now you know.
Jim
 
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moonraker

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Jun 3, 2008
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Konakovo Russia
Great post, I wish I knew all of that 5 years ago :)
I ended up with using FRA-205 for my combo. I have Lentechauto AOD with their torque converter that has a correct bolt circle for that flexplate, so I was lucky there.
 
Jan 3, 2007
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Okay, this is my final update on installing an AOD on an early 70s 351w. This has been a really bumpy ride and I have the final answer to the question of which flex plate to use on your 351w with an AOD trans.
I called many tranny shops around the country, some more well known than others and a bunch of torque converter rebuilders looking for answers. Many of the sources had conflicting responses, but I finally decided on a course of action, installed it and it works.

First, I was wrong about different bolt circles on AOD converters. Apparently, they are all 11.4375 inches. There are web sites that list them as 11.375, but when you get it, that's not the case. They are all 11.4375. Some advertisers list them as 11.5 inches. No, they rounded it out and when asked specifically of those who want to take the time to measure exactly, that 11.5 turns out to be 11.4375.

Why is this important? Because almost without exception every flex plate I purchased, and I have a pile of them, measures 11.375 inches. Close, but no cigar. If you try to use one of these smaller bolt circle flex plates on the larger bolt circle torque converter, the flex plate gets hung up on the shoulder of the bolts in the torque converter and won't fully seat on the converter face. Moonraker noted that he used an FRA-205 on his AOD. He was half right. If you try this, you will have the problem mentioned above and the nuts that hold the flex plate to the converter will have to deform the holes in the flex plate to get the plate to seat on the converter. Not only that, the plate is tighter than crap going on the converter bolts. I know, I tried.

Okay, so what works? First of all, you need a flex plate. A Pioneer brand FRA-205 will work. This plate is nearly identical to the F200 plate that I used and the trans shops I spoke to claimed this would work. A couple of them even sell F200 flex plates for this application. But they don't fit properly. There is one other plate that is similar, but if you stick with these two, you'll be okay.

So, first measure the bolt circle of your converter to confirm that it measures exactly 11.4375. That's 11 7/16 inch on a tape measure. Make sure you're not bending the tape measure in an arc or the measurement will be inaccurate. Once you've confirmed this, take your FRA-205 or F200 flex plate and stick it in a vice holding onto the toothed outer ring. You will need to file 1/32 of an inch off of the outer edge of the converter mounting hole. This is so that the shoulder of the converter bolt doesn't hang up on the flex plate. You can use a dial caliper when you're carefully filing and when the length of the hole measures .46875 inches, you're done. You've successfully filed 1/32 of an inch off of a 7/16 hole making it slightly oblong shaped. This is easiest if you use a 7/16 inch round file and it cuts fast. Do this for each of the 4 mounting holes. Now your flex plate will fit correctly on the torque converter.

After bolting the trans onto the engine, being careful to line up the bolts with the holes when drawing up the trans to the engine, you will notice that the torque converter bolts with the converter still fully back into the trans were allowed movement in the flex plate holes showing no signs of binding. The converter will slide forward effortlessly towards the flex plate and bottom fully on the plate. The converter will pull forward .108 inches once the nuts on the converter are tightened. Plenty of room for the front pump to operate properly. Converter bolt shoulders will clear the filed, enlarged holes. Everything looks good. Tomorrow I'll fire it up and drive it around.

This has been a long process of discovery. Use the information and don't spend weeks like me trying to figure it out.

One other bit of information I discovered. My engine is a mid 70s casting, a D2 to be exact. This engine has a 2 piece crank seal. Later 351s of the late 80s or early 90s have a 2 piece seal. The cranks have different part numbers. There is a flex plate ATP 110 that will fit perfectly on your AOD converter. It will also wipe out your front pump in your AOD if you have a 70s 351w engine. My guess is the crank is shorter for the one piece seal cranks and so required a flex plate with a larger offset.

Why I can't find a flex plate that will fit the AOD torque converter bolt circle for use on a 70s 351w and fit without modification is anyone's guess. I never did find one.
 
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Jan 3, 2007
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A typo. Late 80's early 90s 351w have a 1 piece seal.

I have included 2 photos. The first shows how an FRA205 flex plate fits onto an AOD converter. Notice that the converter bolt is not centered in the flex plate hole. The second photo shows what the bolt on the converter looks like. Notice the shoulder at the base of the bolt. This is why you have to file 1/32 off of the outside of the mounting hole in the flex plate. The plate is hanging up on the bolt shoulder. If you do not file the flex plate hole, the plate will not fully seat on the converter unless you really crank on the nuts and manage to deform the flex plate holes enough to force your way over the bolt shoulders. I hope this clears things up.
P1050916 (Large).JPG
 

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