transmission trouble after swap to 351w - Ford Mustang Forum
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post #1 of 7 (permalink) Old 01-20-2019 Thread Starter
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transmission trouble after swap to 351w

Replaced 302 w c4 transmission to a 351w.

Using the old C4 transmission

Got new flexplate (pioneer fra203) that was for the c4 which was proper diameter and teeth.

Followed a video regarding seating the torque convertor and seemed to be set properly.
Got engine in relatively easily and the torque converter seemed to attach easily. All were loctited and torque set for convertor and flexplate.


Ran fine but did note a faint occ squeal or scrape for a couple seconds when put into gear (forward or reverse). Now note after we ran it a few times some difficulty engaging the transmission though no noises or difficulty moving the shifter (doesn't drop into gear). It will eventually engage. We drove it slowly for mile than applied moderate acceleration which yielded a terrible noise from trans of a grinding squeal that is from convertor after listening to some videos.

I removed transmission and it appears that the flexplate is scraping the transmission spacer on the block. All bolts seemed fine. When I took the engine out originally this spacer was somewhat bent so i flattened it and reused. Prob not good idea... I also noted the new flexplate that i used was about 3/16 inch thicker then the old one the transmission worked with. O/w everything looks ok to my untrained eye..

so now what?

I am waiting on a new spacer.
How do I tell if trans was damaged other than putting it back in?
Is the fact that the new flxplate is thinner a problem? If so which should I use?

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post #2 of 7 (permalink) Old 01-21-2019
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probably fine or take it and have it gone through.

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post #3 of 7 (permalink) Old 01-21-2019
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I ruined a torque converter once by bolting it up improperly. It made a raspy scraping sound when I tried to turn the engine over (and when I started it!). I, too, thought it was rubbing the separator plate, but it was not. If you can't find any scratches on the plate, and your flexplate seems to be fine, your bellhousing is fine, make sure you check out your converter.

Aside from the bellhousing itself breaking, which will be loud and obvious when it cracks, you might notice some damage to the pump if you get it as spectacularly wrong as I did. Just check for hairline fractures around where the input shaft of the transmission is. They will show right up, with a dab of transmission fluid, if things are clean.

When mating the engine and transmission, if you've got everything seated right, it goes together *easy*. No fuss. If it's not perfect, don't try to get that last 1/4" with the bolts, because I promise you, it's not "right". I found out the hard way, as many others have. =)

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post #4 of 7 (permalink) Old 01-21-2019
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When mating the engine and transmission, if you've got everything seated right, it goes together *easy*. No fuss. If it's not perfect, don't try to get that last 1/4" with the bolts, because I promise you, it's not "right". I found out the hard way, as many others have. =)
I can attest to this as I forced the last 1/4" on my transmission setup and paid the price with an instant cracked bellhousing.....here is the sad thing, it happened not once, but twice.
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post #5 of 7 (permalink) Old 01-21-2019
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Quote:
Originally Posted by Grimbrand View Post
I ruined a torque converter once by bolting it up improperly. It made a raspy scraping sound when I tried to turn the engine over (and when I started it!). I, too, thought it was rubbing the separator plate, but it was not. If you can't find any scratches on the plate, and your flexplate seems to be fine, your bellhousing is fine, make sure you check out your converter.

Aside from the bellhousing itself breaking, which will be loud and obvious when it cracks, you might notice some damage to the pump if you get it as spectacularly wrong as I did. Just check for hairline fractures around where the input shaft of the transmission is. They will show right up, with a dab of transmission fluid, if things are clean.

When mating the engine and transmission, if you've got everything seated right, it goes together *easy*. No fuss. If it's not perfect, don't try to get that last 1/4" with the bolts, because I promise you, it's not "right". I found out the hard way, as many others have. =)
EXTREMELY important point, unless one enjoys re-doing with $$$ and time. I found if room allows it, (sometimes tilt engine backwards to clear junk above with trans, use two threaded studs, long enough to have unthreaded shank, maybe 3 inches long. Bolts can be used; cut the heads off, file smooth. Use them in two places best near top of bell, but not too close together, slide trans forward with bolts holding it up in front, jack under pan, seam between eng/trans nice and even get to the dowels, which should have been cleaned and greased, holes in bell as well, that baby should slide home using your hands.
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post #6 of 7 (permalink) Old 01-28-2019
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I see no problem reusing that spacer plate. I've used worse. As long as it can flatten out nicely between engine and bellhousing it should be (and have been) OK. That means no kinks in it.
I see where the the converter studs have scraped it though, which should NOT have happened. Since I don't think it's possible to bolt the flexplate on backwards and the part number seems to be the correct one, the only other reason I can think of for it doing that is because at some point it STILL was not all the way in the transmission.

Final check for those is when the transmission is fully bolted to the engine, slightly less than half the converter stud is protruding through the flexplate bolt holes. When you tighten up the first converter nut then and only then is the converter drawn up flush to the flexplate. If you put the transmission on and then say "Oh look, the converter studs are all the way through the holes already" then you've messed up. Usually savable at that point by taking the transmission back off and seating or reseating the converter some more. But if the engine was started like that, you broke it. Usually major destruction of the pump gears int he transmission, though it sounds like you may just have cracked something.

I would do nothing at this point except disassemble the transmission pump. It's possible I'm completely wrong about what's happened but at least I'd KNOW if the pump survived or not. Just saying what I would do.
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post #7 of 7 (permalink) Old 01-30-2019
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samckay, lay the new flexplate next to the old flexplate and meausre the distance to the flat surface its laying on from the edge the converter is mounted to. if its more on the new flexplate its s probably pushing the converter in too much and bending stuff. 1) are yo sure you are putting the plate on correctly in the engine side trans side orientation?
2) is the spacer being installed directly under the flexplate bolts sandwiching the flexplate? 3) are you sure its the right flexplate? The engine block shield is usually not bent but wither stamped a certain way or simply flat. The 3/16 thicker flexplate is probably your culprit?
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