Welcome aboard..
Now let me justify my answer. I'm a 73 year old old retired Parts Man since 1967. I've actually ''NEVER REBUILT A TRANS in My Life.'' but my Parts Store was the main place to buy kits. The shops used to build all kind of trans ... I sold ATP Kits back in my day. that's me! in a nut shell!
Now 1st off, what's wrong with your 727.
or .. What are you needing to fix..
What kind of use will your new 727 Trans be expected to return to you..
These old 727's are just about the best trans made / years ago.
SO Most likely you don't need a $400.00 kit that seems very expensive to me . But we have not seen what wrong inside your case yet.
.... My kits back in my days would have cost maybe $45.00 .. Yes every thing has gone up 50 times.
But we know you need ... all the Gaskets... All the Rubber Lip ring seals. & All the Fluid Seals ''Front & Rear, SHIFT SHAFT items like those.
& YES replace all the FIBER & the STEAL Clutches. & The Bronze bushings .
& OF Course your get a new Filter .& Make sure it's correct.. Ask your local trans Man , I'm sure he'll be thrilled to give you free advise.
He may even want to through you out of his shop . Sorry to many mechanics are God's Gift to the Automotive World .
But some will help.
Someone else can either add to my post. Or even disagree with me. FINE..
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.......Now normally . YOU'LL have a bushing that's gone bad & let you loose fluid , Causing you to need new forward clutches or . Only the rear clutches . Back in my early day .. GUYS might even get a 2nd or 3rd core trans ..& just remove the best parts & put them all back ing the best case & ONLY BUY GASKET & FRONT & REAR SEAL from me . & Other than their labor they'd fix the tran for about $50.00.. & Sell the truck.