Do you ever need to shim back a torque converter on a 727?

Don Frelier

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My friend had to rebuild his transmission due to a piece of converter blocking the cooler line and overheating it badly.
He's a very good mechanic lots of experience.
He bought a new high stall converter from Hughes, rebuilt the transmission and installed it.
Drove it just a few miles and it started leaking badly out of the front seal.
Took it apart checked everything the seal looked good, installed another new seal and it leaked almost immediately.
He told me that Hughes says to shim the converter back if there is more than 5/16" from fully seated to the flex plate.
We've both never shimmed a Chrysler converter.
Anyone with more experience care to comment or offer suggestions.
Thanks.

Another question:
Do you think it's possible that he could just shim it back, not pull it, and have the leak stop?
 

1967coronet

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Don i have not needed to shim a converter,
I will share a front seal leak story.
Different trans, turbo 350.
Front seal leaked pretty bad.
Pulled trans, replaced the seal and did not make it out of the shop.
Big leak again.
My brother spotted the problem, it was the case, at some time it had been ran loose.
Dowel pin holes were oblong as well as the bolt holes. We ended up swapping cases.
 

69 GeeTeeX

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I had to do it with a custom built PTC 9.5” converter and an 8 bolt B&M flex plate. This was a new 505ci street build using a new Eagle stroker crankshaft. This was all new parts but the tolerances didn’t stack up correctly. I used grade 8 washers that were .125” (1/8”) thick to correct the problem.

Some folks say not to do this but it was the only way to make this particular setup work. And PTC that built the converter said it wasn’t a problem because it wasn’t much. Personally I don’t think I would go any thicker than .125”.

I should add the issue I had was with the converter hub bottomed out in the crankshaft leaving a gap between the flex plate and converter lugs. Washers moved the converter hub away from crankshaft to solve the problem.

This is my personal experience.
 

Don Frelier

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From the sound of it he'd be going back more like 3/8".
Not sure I didn't see it.
 

zyzzyx

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There are numerous videos on YouTube about this topic. Not enough end play and you
wear parts. Too much, and you wobble and leak. Shimming with washers is fine.
 

rbkt65

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i do all the trans for our race cars. all of a sudden we started having front seal leaks when we started with stroker motors. i almost gave up on doing them anymore when we found out that a lot of stroker motors have too long a crank snout at the conv end. look very closely at the front pump seal and you will see heat evidence where the snoot has been riding. solution given to us by the trans guy that moved from california to texas( he is the guy that puts 904 stuff in the 727's for the hemi dart and cuda guys), get a mid plate, draw around it and cut the excess and use as a spacer. we did and no more seal leaks. worked for us now every time. spacer is approx .090.
 

65wgn440

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Yep, my trans guy reminds me to check gap every time I pick up a trans. All makes. He blames it on the reman convertors these days.
 

RemCharger

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While probably not the problem.. I chased a front seal problem, after about 4 r+rs, including new pump bushings etc.. it was a hairline Crack at the hub weld on the converter.
 

steve340

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Shimming is common but not 3/8 of an inch - as stated before around 0.125" I would not be concerned.
Anything larger than that I would be.
 

dvw

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Not only have I shimmed converter to flex plate. I've had to shim the trans to block at times as well. Make sure the converter pulls up into the crank until it hits the flex plate (and a lot of times they won't). If it doesn't either see what's holding it back. If the distance is minimal you can shim the converter to flex plate. As far as a leak. If the seal is good. The bushing is good. And it's not spitting out the vent. My bet is there is a pinhole in the neck weld.
Doug
 

Don Frelier

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Not only have I shimmed converter to flex plate. I've had to shim the trans to block at times as well. Make sure the converter pulls up into the crank until it hits the flex plate (and a lot of times they won't). If it doesn't either see what's holding it back. If the distance is minimal you can shim the converter to flex plate. As far as a leak. If the seal is good. The bushing is good. And it's not spitting out the vent. My bet is there is a pinhole in the neck weld.
Doug
By neck weld you mean on the converter?
 

RemCharger

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By neck weld you mean on the converter?
That weld right there.:thumbsup:
20220526_150857.jpg
 

Geoff 2

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If the gap is excessive, I would looking at a bent/warped flex plate. Flexed once too often....
 

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