Flex Plate?

Well,  it appears that I have busted the center out of my flex plate.  I am looking to buy a beefier/stronger Flex plate to replace it.  But I am getting confused.  I searched Jegs and Summit, both have SFI rated flex plates, but some are for internal balanced engines, and some are for external balanced engines,  most are 164 tooth, but have seen a couple that said they were 184 tooth.  Can someone please help me out as to what flex plate I should buy?

Thanks,
Carl


1984 F250 XLT Supercab,  7.5L/460, Automatic, 4X4.

I'm sure Gary will jump in with all of the correct info, but...

If you have the stock 84 engine and crank, it is externally balanced. You need to by an imbalanced/weighted flexplate. I have a 460 in an 84 Bronco with internal balance and my flywheel is 180 teeth. That's a manual, though, so don't use that as the basis.

Hi Carl

The 460 went to external balance in 1979 (D9TE cast into the block by the starter)
I have never seen anything but a 164 tooth flywheel between a 460 and a C6.
The one you want should cross to D9TZ-6375-A

From what I've seen on various engine building shows, look by the crank pulley... supposedly if it's externally balanced, there's a big balance weight there that fits on the crank snout. At least on the 460's they were tearing down.

Most aftermarket cranks are internally balanced... so if your engine isn't stock, it could be internally balanced despite the engine's factory build date.

The crank throws of an internal balance crank won't fit inside a D9TE block.
So no Bullnose ever came with a front sump internal balance engine.(that has the dipstick in the timing cover)

Yes. If you don't know what year the engine is you can tell if there is a cylindrical spacer behind the harmonic balancer or a tomahawk (hatchet) style external weight.

The most sure way is to look for that casting number right behind the starter motor.

From what I know about this truck it is bone stock.  I haven’t had a chance to check the casting number or the crank snout.  But will do that first thing in the morning.  I would really like to go back with something other than factory original.  According to carfax this truck only had 44,000 miles.  Can’t figure out why the flexplate would fail. I don’t drive mine like it was stolen,  and the truck doesn’t give any indications that is was abused previously.

That really is odd that a flexplate would tear the center out in 44k miles.
Hopefully you will find the cause when you take it apart.

I don't see any issue using an SFI flexplate.
Specification 21.9 mandates they can withstand ~13,000 rpm for an hour.
But that still doesn't mean they are any better balanced for your truck engine turning 4,000.

the only reason i can imagine for the center to fail is alignment. causing over working of the metal flexing out of phase. look for leaking at the rear main seal while it is exposed. a c6 is full hydrostatic. it does not have a locking torque converter and the torque converter is more likely to fail than the flex plate. what does this sound like when the engine is running? is it just not moving or is it grinding?

Well,  I went and bought a digital inspection camera.  It is still hard to see, but I am pretty sure the center of the flexplate busted out.  Here are a few pics that I took of the image on the screen of the inspection camera.

on the plus side. you may not need to remove the four torque converter nuts while under the truck.

Yes sir,  wish I had a shop and a lift and was about 20 years younger.   I know how to perform the work, just can’t do it anymore laying in the dirt.  This 110 degree heat isn’t helping things any.  Quickest I can get it into a shop to be repaired is June 24th.

110? where are you?

35 miles east and south of Abilene, Texas.  Close to and old ghost town called Admiral, Texas.

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwis2ZTTva74AhVGnWoFHcXCAdkQFnoECAQQAQ&url=http%3A%2F%2Fwww.texasescapes.com%2FTexasTowns%2FAdmiral-Texas.htm&usg=AOvVaw1msV3Do4GnMOeaGA1kII59

It was 112 Sunday!

population 0. it don't get much smaller than that

Well,  got Bubba back just a little bit ago.  Here is a picture of the flexplate.  They didn’t find anything else wrong.  Glad to have him back.

Wow!  That's is total failure.  Hope there was no other damage.  

I have seen a couple of those, not on Fords, one on an Oldsmobile Diesel we owned and one on a 3.0L Plymouth Grand Voyager.

well you dont much more certain than that! glad its back and hopefully you are driving it .

85lebaront2 wrote

I have seen a couple of those, not on Fords, one on an Oldsmobile Diesel we owned and one on a 3.0L Plymouth Grand Voyager.

I've had it happen on small block Chevs. Never on a Ford. When it did happen, I caught it before it completely broke out. It was cracked and flexing, causing vibration.

I did see a Ford that was breaking flex plates, an Explorer 4.0L that a shop had put an aftermarket one in. The OEM one had a reinforcement like some other applications, I think the 302 in our 1970 1/2 Falcon had one.

The aftermarket one, it may have been Dorman, had the same design, except the reinforcement was spot welded to the flex plate. The shop told the woman who owned it that there was something wrong with her truck and they weren't going to replace any more for her.

When I pulled the flex plate out, I found it was fractured across two of the three weld boundaries. I ordered a new Ford one and it came with a reinforcement, but not welded. I went to a friend's transmission shop and had him order me an aftermarket replacement.

Into the laboratory it went along with the last failed one. Weld areas were found to be quite hard and brittle and a microscopic examination confirmed some stress cracking in the weld boundaries as it came out of the box. She never had the Ford one fail, and my transmission shop friend decided he would never use an aftermarket one.

This was a definite case of the OEM part being superior to the "improved" replacement.