5/16 torque converter bolts

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Garys72Duster

Garys72Duster

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View attachment 1715782764 View attachment 1715782764 View attachment 1715782764 Bought a 72 Demon complete, less engine, set up for racing. Came with a 727 tranny, and a hi stall 10 inch Torque converter. But it has the small 5/16 bolts that attach the flex plate to the torque converter. I think I'll re tap the threads for 3/8 bolts, as I have some already. The flex plate is the smaller street hemi type, with a diameter of 10" I've never seen a performance T converter with the 5/16 bolts, except on a stock 383. Has anyone used the 5/16 bolts on a 512 stroker motor? I just don't think they are strong enough. Any ideas?

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The big bolts were/are 7/16, and on a smaller bolt circle than the 5/16. You'd best make sure your flex plate and converter match.
If they do, I see no reason that you couldn't redrill your flexplate and drill/tap your converter, assuming you can drill and tap it without drilling into the converter.
 
I've lined up the flex plate and converter, both 10" across for opposing bolts. The flex plate bolt holes are a diameter of 3/8. Small Bolt on left fits the T Converter . One on right fits the flex plate. So should I re tap the converter to accept the larger 3/8-16 bolt?
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Garys72Duster said:
View attachment 1715782776 View attachment 1715782764 View attachment 1715782764 View attachment 1715782764 Bought a 72 Demon complete, less engine, set up for racing. Came with a 727 tranny, and a hi stall 10 inch Torque converter. But it has the small 5/16 bolts that attach the flex plate to the torque converter. I think I'll re tap the threads for 3/8 bolts, as I have some already. The flex plate is the smaller street hemi type, with a diameter of 10" I've never seen a performance T converter with the 5/16 bolts, except on a stock 383. Has anyone used the 5/16 bolts on a 512 stroker motor? I just don't think they are strong enough. Any ideas?

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The treads holes are so shallow I dont know how you drill and tap them without getting into the converter housing.
If the mounting blocks are welded on you may be able to cut them off and replace them?
Food for thought
 
The 5/16 pattern is 11+", and the holes are .337, for a .312 bolt.
The 7/16 pattern is 10", and the holes are .450 for a .437 bolt.
I would not use the 3/8 bolts you have , for two reasons . They are coarse thread, fine thread holds torque better and is stronger, and the heads on your bolts are thicker than normal converter bolts, and may hit the back of the block.
If your converter body is small enough that you can drill through and tap, have at it. If you will hit the converter body if you drill too deep.... I would probably get the best quality big head grade eight 5/16 converter bolts I could find, read ARP, some blue locktite, and fly it.
I was a machinist, I would have drilled and tap for a 7/16 fine thread like the factory did. That would be my preferred fix.
 
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Bolted the flex plate to the converter, and it all fits great. This is the first converter I've seen with the 5/16 bolts on the 10 inch pattern. I also looked at the larger 11 inch plate, and this one is definitely the 10". Guess I'll use what it came with, 5/16 bolts, get the strongest ones I can find, and loctite them.
 
The bolts are pretty small but we lift full dress big blocks with 4 5/16" studs and a lift plate.

lift plate.jpg
 
shear strength is amazing on a good grade 8 or better bolt. Run it. This bolt (X3) held a DC10 engine on a wing! It broke.....
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512Stroker said:
Are you sure the car had a BBM in it?
That looks like the setup that is on my 340.
Different 727 trans SBM vs BBM not the same.
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This is definitively a 727 for a big block. Plus the plate fits the converter, and the crankshaft. I'll check to see if the converter fits into the tranny splines ok.
 
A late converter will fit small block or big block 727. (Essentially) the only significance difference is the engine bolt pattern. Exception would be the prior to 66
727 that used a smaller input.
Later small and big 727 converters interchange.
 
Garys72Duster said:
View attachment 1715782776 View attachment 1715782764 View attachment 1715782764 View attachment 1715782764 Bought a 72 Demon complete, less engine, set up for racing. Came with a 727 tranny, and a hi stall 10 inch Torque converter. But it has the small 5/16 bolts that attach the flex plate to the torque converter. I think I'll re tap the threads for 3/8 bolts, as I have some already. The flex plate is the smaller street hemi type, with a diameter of 10" I've never seen a performance T converter with the 5/16 bolts, except on a stock 383. Has anyone used the 5/16 bolts on a 512 stroker motor? I just don't think they are strong enough. Any ideas?

View attachment 1715782760
Click to expand...

I questioned that when I bought my hughs convertor , them and summitt said they`d take all you can give them . Have had no problems on my 505 !
they are ARP tho.
 
Have decided to run the one I have in this 727- B T Flite. Most guys around here are saying the 727-A and the 727-B converters are interchangeable. Looks like the flex plate is the difference. The 727-A probably uses the 5/16 bolts.
 
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