Tank Fit

American Standard

Cadet and Champion: three sealing systems under one brand

American Standard has sold millions of toilets and changed its flush valve more than once. Older Cadets seal with a 2-inch flapper, newer Cadet 3 and Champion 4 models use a 3-inch valve, and the Champion family moves a lot of water through a wide-opening valve with its own seal profile. The model name on the tank is not enough — measure the opening.

Step one: measure the flush valve opening

Take the tank lid off, hold the flush, and look at the hole the flapper covers. Measure straight across the opening the flapper seals against — the drain, not the flapper itself, which is always bigger:

  • About 2 inches: older Cadet, Colony, and many builder-grade American Standard models. A standard 2-inch flapper applies; see the flapper measuring guide for the mounting-style check.
  • About 3 inches: Cadet 3 and many Champion-family tanks. Needs a 3-inch flapper — and here the details start to matter, because the hinge and seal profile differ from a generic 3-inch part.
  • A wide piston/tower, no conventional flapper: some Champion models use a flush valve where a canister or piston lifts instead of a hinged flapper. If there is no floppy rubber disc in your tank, stop shopping the flapper aisle entirely.

Cadet: the forgiving case

Conventional Cadet tanks are close to the industry-generic geometry. On a 2-inch Cadet in good condition, a quality universal flapper usually seals and times correctly. On 3-inch Cadet 3 tanks, American Standard's own flapper (sold under the brand's parts program) is shaped to drop and seal on its specific seat; a generic 3-inch flapper can fit the posts and still weep on the dye test. If you have already replaced a flapper on a Cadet 3 once and it still runs, that is probably why — read the seat-damage section on flapper size before buying a third flapper.

Champion: buy the brand's part

The Champion line moves its full tank volume quickly through a wide valve, and the seal is matched to that flow. The honest field experience: generic "fits Champion" flappers are the part most likely to produce a weak or short flush that homeowners then blame on the toilet. American Standard's parts documentation, keyed to the model number inside the tank, lists the exact flapper or seal — buy that part number. The fill valve, by contrast, is usually a standard bottom-entry replacement; measure floor-to-overflow and use the fill valve chooser.

American Standard OEM flapper / seal (by model number)OEM Cadet 3 / Champion flapper or canister sealtypically $8–$20
Fits
Champion and Cadet 3 tanks, and any American Standard where a universal flapper already failed the dye test. The model number inside the tank lid or on the back wall of the tank maps to a specific part in American Standard's parts catalog — that part preserves the flush volume the EPA WaterSense listing (on labeled models) was certified at.
Does not fit
Using it as a first guess on a 2-inch Cadet, where a good universal is fine and cheaper. And never on a non–American Standard tank — brand-specific seals do not cross over.
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Korky 2-inch universal (e.g. 54BP class)Quality universal 2-inch flappertypically $6–$12
Fits
Older 2-inch Cadet, Colony, and similar American Standard tanks with a clean, smooth seat. Adjustable-float versions let you tune flush time to keep a 1.28 gpf tank honest.
Does not fit
Champion and Cadet 3 tanks — wrong geometry, see above. Any tank where the seat is nicked or scaled; fix the seat first or no flapper will hold.
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Does-not-fit notes worth writing down

  • Champion flapper ≠ Cadet flapper ≠ generic 3-inch. All three can hang on the same posts. Only one seals. Measure and match the part number.
  • Some Champion tanks use a canister-style valve. If your tank has a cylinder that lifts straight up, you need that model's canister seal, not any flapper — the same trap as Kohler's Class Five.
  • Pressure-assist American Standard models (the ones with a whoosh and a vessel inside the tank) take no standard tank parts at all. See the pressure-assist section on 400a-does-not-fit.

Find the model number first

It is stamped inside the tank, above the waterline, often starting with a four-digit series number. American Standard's parts diagrams are keyed to it. Thirty seconds with a flashlight beats two trips back to the store.

What usually actually fails

In rough order on these tanks: a hardened flapper or seal (five to eight years, faster in chloraminated water), a fill valve at end of life, and the flush handle or trip arm on Cadets with side levers. The flush valve body itself rarely cracks. If a correct new flapper does not stop the leak, the seat surface is the next suspect.

Next, in the tank