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C4 swap...shim?

zbronc

Jr. Member
Joined
Feb 29, 2004
Messages
98
I am swapping in a c4 and i've noticed that the c4/d20 setup that i got from a donor Bronco has a 4" diam. disc/shim piece that apparently was bolted on with the flexplate bolts between the flexplate and torque conv? This piece hasn't been used on my 3 spd trannys. I notice the holes are precisely placed and it will only fit one way.
What is this piece, what does it do and do i need it?
 

PaulS

Jr. Member
Joined
Dec 6, 2007
Messages
96
Loc.
Greater Seattle area
That small piece is meant to spread the torque at the bolt holes so the drive plate (flex plate) doesn't crack at the bolt holes. The flex plate goes against the crank then the torque plate then the bolts. Look to see if it is cupped - if it is then the center should be cupped out away from the crank so that when it is tightened down it will spread the load better.
 

Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
34,821
That small piece is meant to spread the torque at the bolt holes so the drive plate (flex plate) doesn't crack at the bolt holes. The flex plate goes against the crank then the torque plate then the bolts. Look to see if it is cupped - if it is then the center should be cupped out away from the crank so that when it is tightened down it will spread the load better.

That's it. Not always used. My replacment flexplate stated not to use it and the ARP bolts stated do not put anything between the heads and the flexplate. But the flexplat I took off had one. I keep it together with the original flexplate in the spare parts bin.
 

Itsa67

Sr. Member
Joined
Jan 26, 2006
Messages
446
Yep, my 65 Stang has one of those weird plates...only time I had seen or heard of one of those till now.
 
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zbronc

zbronc

Jr. Member
Joined
Feb 29, 2004
Messages
98
Broncobowsher...what kind/brand of flexplate did you use? I just ordered a racing flexplate...i believe it was 3/16th thick and rated to 12500rpms. I may have to leave mine out also.
Thanks for all the info guys.
 

BwoncoHowie

C-4 Wizard
Joined
Nov 11, 2002
Messages
3,571
Broncobowsher...what kind/brand of flexplate did you use? I just ordered a racing flexplate...i believe it was 3/16th thick and rated to 12500rpms. I may have to leave mine out also.
Thanks for all the info guys.
You may not need the reinforcing plate with the heavy gauge flexplate. Sometimes if the flywheel bolt heads stick up too high, they will bite into the converter shell.

:) Use a torque wrench when installing the flexplate. :)
 

Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
34,821
Broncobowsher...what kind/brand of flexplate did you use? I just ordered a racing flexplate...i believe it was 3/16th thick and rated to 12500rpms. I may have to leave mine out also.
Thanks for all the info guys.

I do not know what I used. One of them may be a B&M. The other, I can't remember.
 
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