Flexplate help

Discussion in 'Ranchero Tech Help' started by 74Chero, Jan 13, 2019.

  1. 74Chero

    74Chero In Third Gear

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    Do anyone here know the part number to the right flexplate I can use for my 351w and FMX? I trashed my transmission and had to rebuild because the flexplate I used that came with the 351w was for a c6 and was wrong. Now I'm in search of the right flexplate to use so I can get it back together. Thanks
     
  2. handy_andy_cv64

    handy_andy_cv64 In Maximum Overdrive SILVER MEMBER

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    What was different about a flexplate supposedly for a C6 that wouldn't work with an FMX? My understanding is that each engine's flexplate is made to work with each of the Cruise-o-Matics. Are you sure the flexplate hadn't been installed backward or had a bend in it, something like that? Even though the 351W I used in Babe came from a Grand Marquis with a C4, if I had decided to keep the FMX Babe had, it should've mated right up with no problems. Also, you have a '74, did it come with a 351C originally? Because the only other thing that could've been wrong is if the pilot on the torque converter for the 351C is different for a 351W (but I admit, I could be wrong).
     
  3. 74Chero

    74Chero In Third Gear

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    The depth of the flexplate. When transmission is mated the torque converter is already against the flexplate with no room to come forward . I know it's wrong because last install it destroyed the front pump and yes the converter was seated all the way. I did measurements between the 2 engines. The 351m with its flexplate and the 351w and flexplate and the 351w is about a 1/4 different. I used the c6 flexplate that's on my 351w with my FMX because I was told on here it would work and it cost me almost $1k because of the wrong flexplate. I've been researching a bit and supposedly the c6 flexplate is different and cannot be used with c4 and fmx or aid. The current flexplate on the 351w is a FRA-202
     
  4. pmrphil

    pmrphil In Overdrive GOLD MEMBER

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    I just checked the Pioneer book - 351W w/FMX is supposed to use a FRA-205 flexplate, can also be used w/C-4, but NOT C-6.
     
  5. 74Chero

    74Chero In Third Gear

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    Thanks for the info. Will a 302 flexplate interchange with a 351w ? I might have the flexplate I need laying around that came off a 302 with a c4
     
  6. burninbush

    burninbush In Maximum Overdrive

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    Check the balance issue ... 28 vs 50 vs ??
     
  7. pmrphil

    pmrphil In Overdrive GOLD MEMBER

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    A 302 (or 289) will interchange, 1980 is the break point. After that, the 5.0 went to 50 oz. in. imbalance.
     
  8. colnago

    colnago In Fourth Gear

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    Do you know what makes the C-6 different? Not that I have any desire, but I thought I could replace my C-4 with a C-6 fairly easily.

    Joseph
     
  9. 74Chero

    74Chero In Third Gear

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    That's great so the 302 one I have It should work then? I couldn't find any part numbers on it but I know for Sure it came off a 1972 302 with a c4 transmission because I still have the 302 and transmission .
     
  10. Basstrix

    Basstrix In Maximum Overdrive BRONZE MEMBER

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    One thing I know is that the c6 has 2 different size pilot hubs for the torque converter. I'd have to do some research with regard to TC setback.
     
    colnago likes this.
  11. 74Chero

    74Chero In Third Gear

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    That's not my problem though because the converter sits flush against the flexplate and the studs go all the way through. The flexplate is definitely not the right one.
     
  12. cbolt

    cbolt In Overdrive SILVER MEMBER

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    I have a brand new 302/289 flexplate if anyone needs one. My car is a 3 speed manual so it is fairly useless to me.
     
  13. handy_andy_cv64

    handy_andy_cv64 In Maximum Overdrive SILVER MEMBER

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    The converter sits flush with no room to move back and forth? Is your separator plate installed? Something isn't right if there's no room to move the torque converter back and forth; the other thing that would do that is not having the converter fully seated into the pump gerotors, causing the pump to get 'stacked,' which happens when you tighten the bellhousing to the engine without verifying proper converter-to-pump engagement. What damage was caused to the trans? I have dealt with another shop doing this to a truck C6 to a 460; you should've seen how much aluminum was dug from the bellhousing bolt holes, as they used a rattle gun to push the engine and trans together.
     
    Last edited: Jan 14, 2019
  14. 74Chero

    74Chero In Third Gear

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    Yes separator is installed. Ok with the c6 flexplate I was still able to mate the transmission without force but since the c6 flexplate didn't give the converter room to come forward like it's supposed to it put enough pressure against the pump gear to bind against the back of the pump housing to grind against it and lock it up and brake it . When the engine was running
     
  15. Hillbilly

    Hillbilly In Maximum Overdrive

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    Got a dumb question. Are you positive that the converter had the correct snout to match the index hole in the back of the crank ? With the flexplate bolted to the crank, if you could install the converter onto the flexplate and tighten the four nuts down without bending the flexplate the depth the converter went into the trans. front pump should have been good. ????
     
  16. handy_andy_cv64

    handy_andy_cv64 In Maximum Overdrive SILVER MEMBER

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    See, that's why I'm thinking the pump got stacked. The converter could've slid forward just enough to disengage from the gerotors during handling. Then, just unknowingly turning the converter could've misaligned it. I don't 100% know, but it's starting to sound like the flexplate was not the exact problem.
     
  17. Hillbilly

    Hillbilly In Maximum Overdrive

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    Just about bet you are right too.
     
  18. handy_andy_cv64

    handy_andy_cv64 In Maximum Overdrive SILVER MEMBER

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    Sickening to think of, though.
     
  19. 74Chero

    74Chero In Third Gear

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    Can anyone here tell by looking at this if this is a 28 or 50 oz flexplate?
     

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  20. handy_andy_cv64

    handy_andy_cv64 In Maximum Overdrive SILVER MEMBER

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    I think the first one is the 50 oz., owing to the large weight attached. I could be wrong, though.
     

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