Author Topic: 6 bolt Torque Converter  (Read 425 times)

Offline JohnnyPopper

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6 bolt Torque Converter
« on: July 12, 2019, 12:58:46 PM »
Hey Guys,

I bought a '88 C-30 and am replacing the th400. Got a used one (warrantied) from a yard I do a lot of business with, the tech pointed out that the T/C has 6 bolts.

Never seen one before, the original has 3.

Does anyone know the significance of why there are 6?

It came out of a '89 step van.

We opened up the pan and it was clean as a whistle.

Thanks for any guidance you can offer!

Offline Stewart G Griffin

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Re: 6 bolt Torque Converter
« Reply #1 on: July 13, 2019, 04:07:05 PM »
i've been seeing a few of these lately, because i have to do research on my own torque converter issues.....

i think 6-lugs are more heavier dutier/diesels.


What engine is in your c-30?

Offline zieg85

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Re: 6 bolt Torque Converter
« Reply #2 on: July 13, 2019, 04:17:41 PM »
3 are SAE threads, 3 are Metric.  Choose which set of 3 you need
1985 C30 Custom Deluxe Ext. cab 5.7L TH400 3.21 
1985 C20 Scottsdale 7.4L 4 speed 3.21
1986 C10 under construction
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Offline JohnnyPopper

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Re: 6 bolt Torque Converter
« Reply #3 on: July 14, 2019, 09:05:38 PM »
Wow, that's all the difference? You mean my new T/C isn't special after all?  :'(

When wrenching to get this pig out, I ran into bolts Sets, i.e. rear mount bolts,  that were clearly metric, the rest being SAE.

The T/C bolts were/are 15mm.

The only thing I could figure was that the BIG 3 were so $ conscious of cost per vehicle that they went with lower cost hardware where ever they could.

Please feel free to disabuse me if there is another reason!

Offline JohnnyPopper

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Re: 6 bolt Torque Converter
« Reply #4 on: July 18, 2019, 03:04:03 PM »
Carl (Zeig) all the threads are the same. Now what?

Offline zieg85

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Re: 6 bolt Torque Converter
« Reply #5 on: July 18, 2019, 03:33:59 PM »
Choose the 3 that line up with your flex plate
1985 C30 Custom Deluxe Ext. cab 5.7L TH400 3.21 
1985 C20 Scottsdale 7.4L 4 speed 3.21
1986 C10 under construction
https://www.facebook.com/groups/248658382003506/

Offline Irish_Alley

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Re: 6 bolt Torque Converter
« Reply #6 on: July 18, 2019, 04:40:25 PM »
i know on my motor swap the flex plate on the motor there was only 3 holes for the th400. someone modified it to fit the 700r4 (made the holes closer to the edge). when i mounted it up to the 4l80e i had to bring the holes back in
If you canít tell yourself the truth, who can you tell it to?~Irish_Alley

When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes

Offline JohnnyPopper

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Re: 6 bolt Torque Converter
« Reply #7 on: July 18, 2019, 05:06:11 PM »
There are 6 points on the flexplate. Used all 6.

So there is no indication that this is a heavier duty T/C?

Came out of a delivery van.

Offline zieg85

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Re: 6 bolt Torque Converter
« Reply #8 on: July 18, 2019, 05:17:27 PM »
There are 6 points on the flexplate. Used all 6.

So there is no indication that this is a heavier duty T/C?

Came out of a delivery van.

OK.  I learned something today.  I have 2 TH400's and the flexplate in my 85 has 6 holes.  I will have to check and see if mine is the same way.  I am missing a speedometer drive gear before I put the new transmission back in...
1985 C30 Custom Deluxe Ext. cab 5.7L TH400 3.21 
1985 C20 Scottsdale 7.4L 4 speed 3.21
1986 C10 under construction
https://www.facebook.com/groups/248658382003506/

Offline Irish_Alley

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Re: 6 bolt Torque Converter
« Reply #9 on: July 18, 2019, 10:24:53 PM »
i didnt know about the differences till after i bolted the cummins in place and no bolt holes lined up. PIA to pull it back out and modify the flexplate to work with the 4l80e
If you canít tell yourself the truth, who can you tell it to?~Irish_Alley

When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes

Offline Stewart G Griffin

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Re: 6 bolt Torque Converter
« Reply #10 on: July 27, 2019, 05:37:13 AM »
There are 6 points on the flexplate. Used all 6.

So there is no indication that this is a heavier duty T/C?

Came out of a delivery van.

Yes, based  on my research it is heavier duty and/or installed  behind diesels.   C-40,50 trucks, motorhomes etc.

2) if you look at the  custom aftermarket converters that are put behind engines making 800+HP, they are 6 lugs.

 That's all i know for now.
« Last Edit: July 27, 2019, 05:43:24 AM by Stewart G Griffin »

Offline JohnnyPopper

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Re: 6 bolt Torque Converter
« Reply #11 on: July 27, 2019, 08:27:36 PM »
Wow Stuart, quite impressed! Thanks!

I admit I know very little about T/C's but wonder if this has a different 'stall' RPM?

I know that it can vary by design and application.

Hopefully this one isn't with a high RPM, however it is a C-30 with H/D rears suspension.

Any other Heavy Weight care to add to our knowledge base? TIA!