Problem with torque converter threads

[billtroth]

I am pushing hard to get the car ready for Beaver Springs and the good news is I got the motor back into the Galaxie yesterday.  The bad news is I am having a problem with the torque converter.

The issue is the tabs are drilled and tapped for a 3/8-24 bolt on the converter I had rebuilt for the new C4 trans. The threads were originally tapped with a 7/16-20 bolt. 

The quick fix would be to just get a set of 3/8-24 bolts but I contacted ARP and learned that the 7/16-20 bolts that were in the converter I had rebuilt are very common.  They are ARP part #200-2902.  They are described on the package as "Chevy & Ford Flex plate bolt kit".   The ARP rep. told me the only flexplate bolts they sell that have a 3/8-24 thread is their part number 206-2802 and they don't sell many of them.  They are almost twice the price of the 7/16-20 bolts, $30.31 versus $19.48 for the 7/16-20.  They are longer and I am not sure they will have the correct head flange to work with my flex plate.  I have ordered a set and I should have them tomorrow to compare to the 7/16-20 bolts.  I will have to check to make sure the small flange under the bolt head that mates to the ATI flexplate is a match.  If they match would the smaller diameter be sufficient for the torque.


The shop that did the rebuild advised to re-drill and tap the 3/8-24 holes to 7/16-24.  Although it will solve the mounting problem, I am concerned that the problem occured in the first place. Do you guys remember what threads are on your converters?  Is anyone running a converter with a 3/8-24 bolt  I am very leery about risking my motor and the new $3,000 transmission unless I can be sure the converter is a match.

[blykins]

ARP is confused.  They are thinking you're referring to the bolts that attach the flexplate to the crankshaft.  They are indeed 7/16-20 and the part number you gave is for those bolts. 

So the hole in your flexplate that corresponds to the torque converter tab is a 7/16" hole and your torque converter tab is drilled/tapped for a 3/8" bolt?

[thatdarncat]

I have a few C6 race convertors, and they all use the 7/16-20 thread. Although now I use the same ARP bolts you are using, years ago ( before ARP was so common ) I used the bolts Ford used to attach the flexplate to the crank as they were the same thread and with the large head. I don't know if any manufacturer used a 3/8-24 bolt for that purpose? Also some convertors come with a separate stud to use, might be something to consider? I guess the question for the engineers on the page is if the extra strength of the larger size is needed for a race application?   

[billtroth]

Yes the hole in my flexplate that corresponds to the torque converter tab is a 7/16" hole and your torque converter tab is drilled/tapped for a 3/8" bolt.  This is the same converter I have run for years.  I just wanted them to redo the stall and put in a new sprag.  They are claiming they did not change the cover but I do not know now else the holles could be different .  They have offered to drill and retap the holes.  I checked with Joel Rabe and he thinks they did use a new cover.  Joel thought it would be OK to redrill and tap the holes to 7/16". 

Its still a big PITA to have to pull the converter out drive 40 miles to the converter shop to drop it off  and pick it up.  Lesson learned.

[Falcon67]

I use common Grade 8 bolts to mount my converter, never used any "converter bolts" from ARP.  Also FWIW, none of the converters I use have tapped tabs - all are thru bolt types.  Having a tapped tab is certainly convenient. 

[gt350hr]

  My C4 converters ( and all factory Ford converters) have 3/8ths -24 studs on them. With four attaching points , they will not fail.

[Falcon67]

That's usual - my bad, I was thinking of the PG 9" converter I use in the dragster.  It uses through bolts.  I'm pretty sure the 10" Freakshow 4600 stall C4 unit in the Mustang uses 7/16 studs.

[TomP]

Are we all confused? I think a Chevy used three short 7/16" bolts, but normal cars use four 3/8" studs welded right into the convertor , and for those you use nuts to attach them to the flexplate.

You sure yours uses bolts ? The flexplate holes are normally for 3/8'

[thatdarncat]

Are we all confused? I think a Chevy used three short 7/16" bolts, but normal cars use four 3/8" studs welded right into the convertor , and for those you use nuts to attach them to the flexplate.

You sure yours uses bolts ? The flexplate holes are normally for 3/8'

Tom is right that stock Ford FE torque converters ( and probably some aftermarket ones ) use 3/8" studs welded on the converter, the aftermarket race torque converters I own use 7/16" threaded holes on the tabs or plate on the converter that attach it to the Flexplate. By Bill's description, that's what I think he has.

Tom can be forgiven, I'm guessing his cars have a clutch, and he's not one of us misguided fluid coupling folks 

Here's a picture of one of my converters to show what we're talking about.

[Falcon67]

Are we all confused? I think a Chevy used three short 7/16" bolts, but normal cars use four 3/8" studs welded right into the convertor , and for those you use nuts to attach them to the flexplate.

You sure yours uses bolts ? The flexplate holes are normally for 3/8'

8" or 9" converters are not big enough to have studs that will fit in 10 1/2" bolt spaced flex plate holes.  Most flex plates come with the 3/8 holes, you have to drill them out for larger fasteners.  And yes, a PG converter uses 3 mounts instead of 4.  I'm using a multi-pattern SFI  rated flex plate so the provisions are already there for the smaller PG converter mounts. 

More fun with a PowerGlide - the PG snout requires an adapter to mate to a Ford crank.  And then you have to account for the 1/4" thick mid plate.  The adapter mates the converter snout and includes enough meat to cover for the mid plate, then the converter lugs need 1/4" thick spacers to make up the difference in the mounting to the flex plate.  After all that, you need to allow for .125 worth of converter clearance (pull out) from the pump.  Gets pretty busy back there LOL.

[cjshaker]

I've always found this simplified diagram to help me understand these automated power loss units...

[Bolted to Floor]

Tell us how you really feel Doug!! Thanks for the laugh.

[gdaddy01]

thank you doug

[TomP]

These fluid coupling deals confuse me. Doug's picture sure clears it up.