Does anyone know what will happen if you put a 727 Torqueflite together and leave out the (lower big) accumulator spring?

A rather firm upshift.

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Part of Tyrde-Browne Racing

That depends. If it was left out on purpose and the accumulator was blocked (with a spacer or socket) then you'll have harder upshifts. If the spring was left out accidentally and the accumulator wasn't blocked, you'll have generally harder but somewhat inconsistent upshifts.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I think it may have been left out by accident - could that explain lots of dark grey debris, ~1/8" magnetic slivers, and <1/16" nonmagnetic fragments after only 5K miles following a rebuild? It seemed to shift perfectly the last time I drove it and for the whole 5K miles until the 2nd-to-last drive, but on that one drive it suddenly seemed to empty the torque converter at random intervals (making the fluid appear >> high in N and being unable to move), then suddenly appear to work fine again (and fluid level appeared normal in N and all gears seemed OK).

I removed the valve body, but can't find the spring, so I suspect that might have something to do with the problem.

Definitely not. You've got other problems. Sounds like major ones.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I took the debris and valve body to the expert who built the trans, and he couldn't find anything wrong inside. He noted it has a shift kit in it, and the kit (probably) said to leave out the spring and agreed with you that that couldn't be the cause of the debris and oddball problems.

He gave me a hi-flow filter and new gasket and suggested I see what happens, as my only alternative is to pull the trans. He suggested against Lucas trans additive or anything like that.

We'll see what happens. Thanks again for your help.

Don't get Dan started on Lucas "products".......

-Mike

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I am the Guardian, I hate helos, everything leaks.......

Here's what an unknown brand of "transmission fix-it" did in 2 weeks to a customer's trans <a href="http://s686.photobucket.com/albums/vv224/bigslant6fan/?action=view&current=P5270098.jpg" target="_blank"><img src="http://i686.photobucket.com/albums/vv224/bigslant6fan/P5270098.jpg" border="0" alt="Photobucket"></a>

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V8?? We don't need no stink'n V8!!