need flexplate: 1978 351W mated to 85 AOD, where?

351W-GT · May 21, 2005

where can i get a flexplate that will fit a 1978 351W and a 1985 AOD? i am in desparate need of one! my transmission finally started leaking and i realized i have the wrong flexplate (the front pump didnt give out, but it vibrated pretty bad) any places to look? people to ask? companies to email? thanks in advance, i get the transmission back in 4 days.

Daggar · May 22, 2005

http://store.summitracing.com/defau...art=TCI-529610&autoview=sku&Ntk=KeywordSearch

Stang8URMPRT · May 22, 2005

Most, if not all if I rememeber correctly, 351s are 28 oz imbalance. You probably reused your stock 50 oz and this is giving you that vibration.

Daggar · May 22, 2005

There was some overlap it appears, so you have to find out which one you have/need. The 28 oz. is $10 more.

Ourobos · May 22, 2005

They were 28 oz until 1985, then they used 50 oz. You need the 28 oz if it's stock internals. You need the one Daggar listed at Summit.

351W-GT · May 22, 2005

well the one Daggar listed at summit was one for a 50oz imbalance, and im pretty sure i need the 28oz imbalance one. also, all those flexplates were for a C4 transmission, i went through and used the catalog search feature at summit and chose the options (flexplate, 351W) dont know how many teeth it has, i'll count that today but as soon as i chose the 351W engine size the option of "C4 or AOD" in the "transmission" section disappeared and became only "C4". so apparently summit doesnt carry a flexplate for this combination. crap. i gotta find some answers QUICK.

rd · May 22, 2005

There is a good chance that a 78 351w stock c4 flexplate will accept the AOD just fine. I have not installed it yet, but I have an aod flexplate and a bunch of 28 oz old style c4 flexplates, and they all seem to fit the aod converter just fine.

You do need to verify that the diameter, or tooth count, is the right one for the aod. I think all of mine are 164 tooth units. You could put the flexplate on the converter, on the trans, with the block plate, and mock up the starter to see if it indexes correctly.

Daggar · May 22, 2005

Here's the link for the 28oz:

http://store.summitracing.com/partd...art=TCI-529618&autoview=sku&Ntk=KeywordSearch

So long as the diameter is correct, you should be in like flint!
I'm no automatic expert (never had one is a Mustang) but isn't the flywheel diamter the determining factor for what tranny it applies to?

Your tooth count should be 157 by the way (same as our flywheels).

351W-GT · May 22, 2005

the tooth count on the flexplate is 164. i counted it twice. the code stamped onto the front harmonic balancer is "DOOE-C2", and the code stamped onto the block itself is "D9AE-6015-ED 16". i wish i had gotten the engine from the original car, but it came out of a truck, and the guy that put it in the truck installed it with the double hump oil pan already on it, which means it was a car chassis, cause of the oil pan layout (double sump), and the only cars with a factory 351W in the 70's are LTDs and Crown Vics. SO. i currently have what looks to be a 50oz, 164-tooth flywheel that FITS FINE with the engine and trans, but its out of balance. so what i need is a 28oz, 164-tooth flexplate that will fit with the mid-70s 351W and a mid 80s AOD with the lockup converter.

Im sorry for talking in circles, but i've heard the horror stories of people bolting up the wrong flexplate and the front pump of the AOD is destroyed because the flexplate sticks out too far. When this goes in my AOD will have just been rebuilt, and i dont need to have it go out again over something like having the wrong flexplate. should i call summit or jegs on monday and talk it over with one of their techs? or maybe call TCI or B&M directly? i hate autos too, this would be my first, but the car already came with an auto trans, so i didnt feel like laboring over bolting on brackets and running lines and stuff like that. so i stuck with an AOD, i needed an overdrive as i drive the car quite a bit.

Daggar · May 22, 2005

Ok... I'm going to take a stab here and guess that even though your current flexplate is 164 tooth, that you will need the 157 tooth in order to be compatable with the AOD. The 164 tooth is 11.5 inches and is too big. You should still be able to use the same starter, as I belive that the spacing between the teeth is the same on either one (hence the larger tooth count for the larger diameter flexplate).

So the 28 oz. that I provided the link for above should still be your flexplate. It certainly would not hurt anything to give them a call to ensure it.

Good Luck!

351W-GT · May 22, 2005

im sorry, but i dont understand how i could use the same starter if i am going to get a flexplate that is a little smaller. i would think that if my flexplate was too big, then it wouldnt start at all. but it cranks over fine every time. i mean i will call them but i just hope i dont ruin this 750 dollar AOD 5 minutes after installing it. nobody seems to be absolutely certain. i just searched around online and came to the realization that accorind to the code stamped onto my block, the engine could be anything from 79-91! i mean thats crazy that this same code could have come from any of those years. its gotta be a 79 then, cause we (the guys i work with and i) are all certain that the 50oz weight on the flexplate was way too big. when i first installed it over 6 months ago it had some hellacious vibrations, so i put a wheel weight on the opposite side of the flexplate that the counterweight was on, and some of the vibrations went away, heck maybe now its just a 35-40oz flexplate, cause we took the wheel weight off and hacked off a portion of the counterweight on the flexplate and the vibrations went away. and if it WAS a 50oz imbalance engine assembly, then it would have been manufactured AFTER 85 right? alright, im just getting a little nervous cause time is passing me by and once i find the right flexplate i STILL have to order it and have it shipped here. then i have to have my custom exhaust headers made and my 2.5" custom downpipes fabricated and welded up to the old 3" exhaust with a Y-pipe. its a secret, i'll tell you all after the car's running with its new transmission.

Daggar · May 22, 2005

What transmission do (or did) you have installed on it now?

351W-GT · May 22, 2005

i've been using the AOD ever since i've had the car. although i've only owned it for the last 6 months, the previous owner is one of the mechanics i work with and we swapped cars, so i watched him build the thing. the reason the transmission came out was that i was racing one night and after the 3rd pass or so i started smelling ATF and pulled over only to see that i was leaking ATF from the bellhousing, i guess the front seal went out cause thats the only thing up there. i proceeded to pull the trans yesterday (only took me 45 minutes i was proud of myself) and its sitting on the stand right now waiting on tomorrow to come around so it can be hauled to a repair facility to get rebuilt. the 351/AOD has been running fine ever since i've had it, and it ran fine while it leaked too, shifted normally, just smelled bad and im sure it wasnt good for my health all that smoke being in the cabin. but i figured i might as well rebuild it while it was out, since the 351 was gettin rebuilt in the next 6 months anyway. and the guy that put the two together said that the inherent vibrations due to not having the correct flexplate could be what caused the seal to start leaking after it was driven hard. cause if you drove it normally for no longer than 30 minutes it wouldnt leak a drop, as soon as you started driving it for an hour or more it leaked like a sieve. but thats water under the bridge. sorry im rambling. point is that the combo has worked, i just need to be sure that its the 28oz flexplate i need, then i need to find someone that sells one. and be positive that its NOT the one that will destroy my front pump when i drive it. you have been lots of help and i appreciate the information, i have learned alot more about my own flexplate in the last 24 hours than i ever expected to. but i havent come ot any conclusions as to what i should do, i will call B&M, TCI, Hughes, and Summit tomorrow on my lunch break to see if they can shed some light on this predicament.

351W-GT · May 22, 2005

oh and i dont mean to say that i no longer need help on this forum, but i've gotta come up with this information QUICK, and if they know they answer then they can also give me part numbers and i can order the part on the spot.

Daggar · May 22, 2005

Well it seems we're getting more of the story in small doses as we go along. LOL

If the size of the flexplate has not caused you any fitment issues then at least you know that that portion of the assembly is good. Stick with what you know and move on. You said you have/had a 50 oz imbalanced flywheel in there and it caused you vibration problems. At some pint you modified that imbalance by cutting a portion of the wight out. Did you have the flywheel balance checked at any time after that? Who's to say that the remaining weight was in the correct counter balance position? If you're sure that the motor you're dealing with doesn't work wll with a 50 oz imbalance then that really only leaves you one option. I guess what I'm saying is: I'm not sure what the problem is here. Install a 28 imblance flywheel and be happy. You say you already know the 50 oz is incorrect, so what's left?

351W-GT · May 23, 2005

right, well the problem is i dont have a clue what flexplate is in there, like is it a flexplate for a 351W/C4? 351W/C6? i dont really know, so i dont know what to order. and while i feel that the 28oz should be perfect, im not absolutely sure, and quite a bit is at stake here, i guess i will order one for a C4 and check the spacing between the converter and the flexplate before i bolt it up, if they are already flush before i pull the converter forward by bolting it up then i know somethings wrong, right?

Rick 91GT · May 23, 2005

Performance Automatic makes the model you need as well. I just installed on ina customers car, 408ci monster, Freddy Brown AOD...28oz.

Ourobos · May 23, 2005

The main thing you should concern yourself with is getting a flexplate that has the correct torque converter bolt pattern for your drain plug in the converter. They come in 45 degree angles and a side by side hole setup. My first post was ass-backwards, pre-1984 351w engines were 28 oz imbalance. I know, I run a 50 oz on my 1984 351w, they changed to that around 1982. SO you need a 164t 28oz flexplate, with the correct torque converter bolt pattern. And the C4 is the same as the AOD.. See the bolt pattern on the second summit link daggar put up? Thats the 45 degree torque converter pattern.. The outter holes (big ones) are half way between the small (coverter studs) ones. That's the plate you need, depending on your converter.

95GTAODE · May 23, 2005

I noticed a little mis-information kicking around. The AOD flexplate is a 164 tooth. The manual (SROD,T5) flywheel is 157 tooth. So if you have a 28 oz, 164 tooth flexplate, you should be fine.

Incidentally, starters will work with either 164 oe 157 tooth flywheels/flexplates. The only thing you need a specific starter for is an old toploader with a 164 tooth flexplate.

351W-GT · May 23, 2005

the converter bolt pattern is 11.5". so the C4 flexplate DOES work with the AOD? well thats good news. im getting a new converter anyway so i guess as long as it all lines up i should be ok. thanks for all your help, i GUESS this is the answer i've been waiting for, i will go ahead and check out the performance automatic site (if they have one) and see the price on that unit.

need flexplate: 1978 351W mated to 85 AOD, where?

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