What flexplate with my 351w and 4r70w?

[SSDDBRONCO]

Hey all!

From my research in the past, I came to the conclusion that I can use the flexplate off my 302 with the 351 that I am swapping into my bronco since it's the same 28oz balance and teeth pattern. Is that correct or am I wrong? If I wrong what flexplate did you use for your 4r70w and 351?

You may have seen my post on Facebook Early Bronco group. But the reason I am asking this question is because I installed the 4r70w with the 351 and when I was going to tighten the bolts on the torque converter I was not able to turn the engine. Then one guy commented that he had a similar problem and used a different flexplate so Im just trying to figure out if my flexplate is the problem?

Thanks for the help!

Just to add for more info I was running a C4 before the 4r70w.

 

[DirtDonk]

Interesting to hear the results. Same question came up recently in another discussion.
Seems like a 351 out of a later model truck, or a bronco, would at least be similar. Same 28 ounce in balance, and the same 160 for tooth size.
But even then, I don’t think Ford used the same offset (maybe not even the same bolt pattern! ) for all of their overdrive transmissions.
So I’m very curious what the answer is.

 

[Broncobowsher]

Correct, original (pre-1982 balance change) 302 flexplate that is already on the Bronco will work with any year 351. If it has the right convertor bolt pattern. If you have an original Bronco flexplate with the 10.5" bolt circle, that one won't work. Has to be the 11.4" convertor bolt circle.

164 tooth, 28.8 oz-in balance factor, C4/AOD application (not C6 or E4OD). Typical parts store shopping is for a 1984 crown vic with a 351 and AOD. Shop car, not truck.

 

[JKH67302]

You can use your old C4 flexplate. I did same swap, but behind a 28 oz 302, assuming you have the same tooth count. I reused my flexplate. You can also search for a vehicle with a 351 and AOD, I believe the early 80s Crown Vic had that combo. Either way it was the same part numbers as the C4/302 28oz combo flexplate. I don't believe any of the 90s F150s ran AODEs behind 351s, but I could be wrong. You will also notice that aftermarket race flex plates often list them as fitting C4, AOD, AODE and 4r70w.

What flexplate did you use? When I did my swap I researched this topic a lot. Some had mistakenly used a flexplate from either a c6 or maybe E4OD? I can't remember which one, but those flexplates fit but they have different offsets. This offset might cause a bind and likely ruin the pump in the transmission as well.

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[SSDDBRONCO]

Correct, original (pre-1982 balance change) 302 flexplate that is already on the Bronco will work with any year 351. If it has the right convertor bolt pattern. If you have an original Bronco flexplate with the 10.5" bolt circle, that one won't work. Has to be the 11.4" convertor bolt circle.

164 tooth, 28.8 oz-in balance factor, C4/AOD application (not C6 or E4OD). Typical parts store shopping is for a 1984 crown vic with a 351 and AOD. Shop car, not truck.

You can use your old C4 flexplate. I did same swap, but behind a 28 oz 302, assuming you have the same tooth count. I reused my flexplate. You can also search for a vehicle with a 351 and AOD, I believe the early 80s Crown Vic had that combo. Either way it was the same part numbers as the C4/302 28oz combo flexplate. I don't believe any of the 90s F150s ran AODEs behind 351s, but I could be wrong. You will also notice that aftermarket race flex plates often list them as fitting C4, AOD, AODE and 4r70w.

What flexplate did you use? When I did my swap I researched this topic a lot. Some had mistakenly used a flexplate from either a c6 or maybe E4OD? I can't remember which one, but those flexplates fit but they have different offsets. This offset might cause a bind and likely ruin the pump in the transmission as well.

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Ok Im sure I have the 11.4" converter bolt pattern because I am using a FM69 torque converter and with a quick search it said 11.375" so pretty sure 11.4" is just rounded up?

Does the C6/E40D have the same converter bolt pattern?

@JKH67302 I have no history on the flexplate. It's was already installed on my Bronco and I just used the same one when I went from my c4 to 4r70w.

 

[JKH67302]

I misunderstood, that flexplate should work. Was the torque converter seated all the way into the pump when you installed it?

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[SSDDBRONCO]

I misunderstood, that flexplate should work. Was the torque converter seated all the way into the pump when you installed it?

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When I installed it I guess I didn't seat it all the way which is why I wasnt able to turn the engine to tighten the converter bolts. I took it back down and kept trying to seat it and always got the same measurements. So I decided to to get a rubber mallet and hit that hump part on the converter and it went in about a 1/4 in. So now Im thinking it's seated but then Im also thinking that when i tighten all the nuts it will just bring the converter close to the flexplate again? Not sure what to think about this lol

 

[DirtDonk]

The converter is supposed to float slightly between the flex plate, and the transmission.
So when you turn the engine to line up the studs with the holes in the flexplate, you can pull the TC forward to insert them.

There are plenty of things to worry about when mounting an automatic transmission to an engine. But pulling the torque converter towards the flex plate is not one of them.
It has to be pulled forward to the flex plate in order to torque the nuts, right?
However, if you are pulling it forward by hand, and it is hitting something else before the studs are fully inserted, then you have a flex plate offset issue to deal with.

 

[SSDDBRONCO]

The converter is supposed to float slightly between the flex plate, and the transmission.
So when you turn the engine to line up the studs with the holes in the flexplate, you can pull the TC forward to insert them.

There are plenty of things to worry about when mounting an automatic transmission to an engine. But pulling the torque converter towards the flex plate is not one of them.
It has to be pulled forward to the flex plate in order to torque the nuts, right?
However, if you are pulling it forward by hand, and it is hitting something else before the studs are fully inserted, then you have a flex plate offset issue to deal with.

It’s not hitting anything. There was clearance between the flexplate and engine plate. I was able to tighten one nut and then was going to tighten the other ones but couldn’t because the engine wouldn’t turn over meaning that the flexplate and torque converter were too tight together?

 

[Broncobowsher]

Ok Im sure I have the 11.4" converter bolt pattern because I am using a FM69 torque converter and with a quick search it said 11.375" so pretty sure 11.4" is just rounded up?

Does the C6/E40D have the same converter bolt pattern?

@JKH67302 I have no history on the flexplate. It's was already installed on my Bronco and I just used the same one when I went from my c4 to 4r70w.

Yes, that is just rounding.

The C6/E4OD has the right everything except offset. The convertor will be bottomed out in the transmission and the thrust bearing will be loaded on the crankshaft. It will all fit, start, run, drive. But with everything running bottomed out, just don't expect it to last.

 

[SSDDBRONCO]

Yes, that is just rounding.

The C6/E4OD has the right everything except offset. The convertor will be bottomed out in the transmission and the thrust bearing will be loaded on the crankshaft. It will all fit, start, run, drive. But with everything running bottomed out, just don't expect it to last.

Ok Im just going to order a flexplate from a 1984 crown vic with a 351 and AOD and compare it with the flexplate I have. Hopefully that'll give me some answers.

Looks like this is the one I need: Pioneer FRA-205

https://www.oreillyauto.com/detail/...5/v/a/5440/automotive-car-1984-ford-ltd?pos=0

 

[DirtDonk]

Could the transmission being in the park cause this? Unsecured the transmission is not supposed to turn with the engine. Isn’t that how it works?
Even if not, try neutral anyway.

 

[SSDDBRONCO]

Could the transmission being in the park cause this? Unsecured the transmission is not supposed to turn with the engine. Isn’t that how it works?
Even if not, try neutral anyway.

This was actually my first thought so I put the trans and the tc both in neutral but same result. After talking with someone they said that the engine should still be able to turn freely as the converter is not locked when the vehicle is in park.

 

[Broncobowsher]

It’s not hitting anything. There was clearance between the flexplate and engine plate. I was able to tighten one nut and then was going to tighten the other ones but couldn’t because the engine wouldn’t turn over meaning that the flexplate and torque converter were too tight together?

That's usually the torque convertor isn't seated all the way in the transmission. Don't force it, you can break stuff. Either the transmission or engine back out and work the troque convertor further into the transmission. There are multiple steps as the input shaft splines seat, the stator splines seat, and the flats of the pump engine the snout of the torque convertor. I forget the exact numbers but the face of the torque convertor needs to be about an inch in from mating surface of the bellhousing.

 

[SSDDBRONCO]

That's usually the torque convertor isn't seated all the way in the transmission. Don't force it, you can break stuff. Either the transmission or engine back out and work the troque convertor further into the transmission. There are multiple steps as the input shaft splines seat, the stator splines seat, and the flats of the pump engine the snout of the torque convertor. I forget the exact numbers but the face of the torque convertor needs to be about an inch in from mating surface of the bellhousing.

Ok good to know. I'll work on it Sunday and hopefully report back with good news.

Thank you all for your help.

 

[Broncobowsher]

If someone has actual specs, correct me...
With the correct flexplate the back of the block plate to the mating surface of the flexplate is just under 1". Something like .940 or .900"
The convertor fully installed is about an inch
The wrong (C6/E4OD) flexplate is just over 1" from the block plate to the flexplate mounting surface.

When installing the first nut on the torque convertor there should be a visible draw up of the convertor into the flexplate. Should not be a tight fit without hardware.

 

[rocknhorse76]

73-77 Ford Bronco 28 oz Flexplate for C4/AOD Automatic Transmission

Enhance your Bronco's transmission with a 28 oz Flexplate from TOMS OFFROAD. Perfect for C4/AOD models. Shop now!

tomsoffroad.com

This one worked for my 4R70W swap. Also, you might consider the FM69C converter. Same stall but a bit heavier duty.

 

[SSDDBRONCO]

That's usually the torque convertor isn't seated all the way in the transmission. Don't force it, you can break stuff. Either the transmission or engine back out and work the troque convertor further into the transmission. There are multiple steps as the input shaft splines seat, the stator splines seat, and the flats of the pump engine the snout of the torque convertor. I forget the exact numbers but the face of the torque convertor needs to be about an inch in from mating surface of the bellhousing.

Ok so I’m working on the trans and need some clarification. When you say “the face of the converter” are you talking about the hump? If it’s the hump it’s not flush with the bell housing. It’s sticking out about almost half an inch.

 

[ba123]

The ENTIRE converter goes behind the edge of the bellhousing. The flexplate sticks out of the engine and fits inside the bell housing.

Here, maybe this pic helps?


I think the converter might move slightly when you tighten, but I believe it is a totally minimal amount. The bolts on the torque converter will come through the bolt holes on the flexplate before the engine and tranny are mounted together. That’s one of the pain in the ass things about mating the two together. You’ve got to get it perfectly. I try to line them up before mating and also use the spot on the flexplate that has the hole so you can kinda feel and maybe move it a little if you’re lucky. You can also rotate the engine slightly to get the bolt holes to meet.

Once you can see them come through, you should be able to rotate the engine freely and not sure about not in park, but I usually have mine in park when I do this. Really not sure it matters though, just might be harder to turn not in park.