Caroma Dual-Flush Button Replacement (Part #772135)

In humid environments, the springs inside the dual-flush buttons for Caroma toilets can rust, causing the buttons to stick in the down position. This model is a replacement of the entire push-button assembly that can be used in place of the original buttons.

Parts Needed

To assemble this, you'll need two compression springs that are 35 - 40mm long (free length), and no more than 9.22mm in diameter. Compressed length needs to be 20mm or shorter. To have a reasonable resistance, you're going to want a spring that provides roughly 0.3 N/mm to 0.6 N/mm. Resistances outside this range will probably work, but may be too soft or too stiff for regular use.

See https://www.amazon.com/dp/B005S4I8K2/ and https://www.amazon.com/dp/B076LTYY69/ for examples of suitable springs.
 

Printing

If your slicer supports variable layer depths, you can print the vast majority of this part at 0.3mm. However, since the crown portion that is visible is curved, you're going to want to adjust layers to be as high a resolution as possible for just that part of the print.

For reference, when I take this approach, I can print the frame and both buttons in exactly 6 hours using a Prusa MK3s.

You will want to print the frame upright, and the buttons lying down on the plate. All parts need supports to print properly.

These print and work just fine in PLA (which is what I used for my prototyping), although I would recommend the use of PETG for longevity, since PLA can become weak in consistently wet environments.

Assembly

Once printed, insert the springs into the round holes at the bottom of the frame, then line the buttons up and push them in. You'll have to push really quite hard to get them to insert all the way. Once they reach the bottom, they should snap into place and move freely.

Be careful: once inserted, the buttons are extremely difficult to remove without destroying the buttons and/or the frame. In particular, make sure you are inserting the correct button on the correct side of the frame: they will fit in backwards, but look really bad.

Installation

Once assembled, flip the toilet lid over and remove the screw that secures the old button assembly. Slide the replacement in place, and use the same screw to secure the new buttons.

The flush assembly inside Caroma toilet tanks has a couple of screws that can be used to adjust the height of the surface that the buttons push on. You may need to adjust them up or down slightly to match the new assembly.