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HELP - flexplate Issues - SOLVED... Kinda

reddog64

reddog64

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OK...

78 K5
I pulled a small block 350 and TH350 out....

First came the motor..
When i pulled it i noticed it appeared to be a 86+ block as the heads had the bolts in the middle...

I removed the flexplate from it, and put it on the new PRE-1986 motor...
Made sure the correct side went to the motor...

Bolted it to the stock 78 TH350 tranny... didnt put the flex plate bolts in as the tranny was coming out in 2 weeks...
At this point I could EASILY turn the tourque converter in teh TH350 and the flexplate with vice grips...
BOTH turned freely...

So 2 weeks ago I dropped the TH350/203 and put the freshly rebuilt TH400 and a freshly rebuilt tourque converter in. Bolted it up, annded the brace, crossmember etc...

So, This week, i put the dana 60 in and decided to do a bunch of small stuff... 1 step being bolt the flexplate to the tourque converter in the TH400...

THE GOT DANG THING WONT F IN G MOVE...

It's like the flexplate and tourque converter are too close...

Now I know when i put the TQ Conv in i seated it all the way, and it turned freely.
I also know the motor turned freely...

It's like teh flexplate and Trq converter are too close...

Or the flexplate should have been a PRE 86...

Am I smoking something or do i need ot back the transmission back a foot and put a pree 85 flex plate on...

Now i pulled this Th400 out of an 84 K30 truck... I know the thing was bolted to a 350 small block... I know the Tourque converter spun freely...

Please advise...

And partsamerica.com shows 2 different parts...
1986 and newer - FRA159
1985 and older - FRA100
 
Last edited:
I have both on the garage floor right now , and they are absolutely not interchangeable ( wrong bolt pattern on each crank end ) . The heads are so there ya go .

I could see you bolting the flexplate on backwards though , OR not getting the converter seated in the front pump properly so it clicks and seats far enough in ..

According to my witness marks on both my styles of flexplates , the side towards motor has the indents where the converter bolts go , the side towards converter gets the slightly raised pads .
 
So rightnow the flexplate is put on the motor with the raised part where the bolts go facing the converter... the indented part is towards the motor so it is on correct...

I'm guessing it most of tipped forward and unseated itself...
Cause it should freely spin, and have an 8th inch play between the two...

Looking at your two are they the same thickness.. meaning the ring gear is centered...

This flexplate bolted up to a TH350 so it has to be the right one... it has 6 holes in it.... so does my tourque converter...
 
reddog64 said:
I guess what I'm asking is are the pre 86 and post 86 the same, minus the bolt pattern for the tourque converter???
Click to expand...

No , different patterns to bolt to crank .

Your old motor is pre-86 , your new motor is pre-86 .

Someone just put TBI heads on the other motor at some point <------- Really :D
 
idiots... now why would they do that... i think your right...

I it sounds like the TQ Conv slid forward....

this blows...

So this flexplate, having at one time bolted to a TH350.... shold bolt to a TH400...
I need to move the tranny back and see if the Tourque converter isnt seated...
 
yeah... guess it wasnt seated all the way...

a 130 dollar mistake...

Couldda sworn it was seated though... (obviously I was wrong)

Those little tabs belong on the shaft of the pump.... not on the board next to the pump...
 
yeah...

I couldda sworn it was...
But it wasnt...

oh well i wanted to put that stupid th400/205 in again anyways...
Just needed a reason to pull it and paint it... LOL
 
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