Sinter Model 023 Hayes Dominion A4

Hayes Dominion A4 is the American brand's high-end four-piston MTB caliper, designed for downhill and aggressive enduro with the lever feel and modulation that pulled Hayes from the budget tier back into pro-mechanic conversation when it launched. The Sinter Model 023 is the organic-compound pad built for the Dominion A4 specifically.

What's in the kit

One caliper's worth of pads (2 pads, left and right) for the Hayes Dominion A4 pocket. The kit ships with the spring, pin, and bedding-in instructions. Order two kits if you're replacing front and rear pads on the same service.

Fits

Hayes Dominion A4 pad shape:

• Hayes Dominion A4 (the four-piston flagship MTB caliper)

The Dominion A4's pad pocket is unique to that caliper family in the current Hayes catalog. If your Hayes is the two-piston Dominion or an older Hayes brake from the Stroker era, this isn't the right pad; the A4 specifically takes the Model 023.

Compound and feel

The Dominion A4 caliper was praised at launch for the lever feel and modulation it brought into a price tier that conventional wisdom said couldn't deliver them. Sinter's organic ceramic-loaded compound is the right pad to preserve what the rider chose the brake for: the resin matrix bites cleanly off the Hayes lever, modulates linearly across the lever travel, and runs quiet on the Centerline-pattern rotors most Dominion A4 customers run. The kevlar, ceramic, clay, and carbon fibers in the matrix hold their bite through the sustained-pressure descending pattern enduro and gravity-light riders ask the brake for.

Specs

• Compound: organic (ceramic-loaded, resin-bound)
• Backing plate: steel
• Pad shape: Hayes Dominion A4
• Pads per package: 2 (one caliper)
• Includes spring and pin

Includes: 2 pads (left and right), spring, pin, bedding-in instructions.

Slovenian friction materials, distributed by Euro Toolworks

Sinter has been making friction materials in Ljubljana since 1969, and developed the first disc brake pads in the former Yugoslavia in 1972. The plant supplies organic-compound pads at scale to motorcycle OEMs alongside the bicycle aftermarket. Unior has been forging hand tools in Zreče since 1919, and is the official technical partner of multiple World Tour and downhill teams. Both brands route through Euro Toolworks in North America. The Hayes Dominion A4 is a four-piston caliper whose installed base in the US market is growing as the brake's reputation has spread; the Model 023 is the Sinter catalog's pad coverage for that build.

Pro tip from our mechanics

The Dominion A4's piston design retracts more thoroughly than many four-piston calipers, which means a fresh pad install requires less aggressive piston-spreading than the equivalent SRAM Code or Magura MT5/MT7 install. Use a piston-spreader lightly to confirm even retraction, and the Sinter pads slide in cleanly without the typical four-piston pad-rub-on-install complaint.

For the broader compound primer and fitment grid, see How to choose Sinter brake pads →.

FAQ

Which brakes does the Sinter Model 023 fit? This pad is made for Hayes Dominion A4 calipers. Even within one brand the pad shapes can differ, so the safe step is to remove a worn pad and match the backing plate, mounting tab, and retaining-pin hole to this one, or read any model number stamped on the back. That physical match is more reliable than the caliper name alone. If you are not certain your caliper takes this shape, send us a clear photo of the old pad and we'll confirm it for you.

Are these sintered or organic pads? They are organic. Despite the Sinter name, Sinter only makes organic brake pads, not sintered-metal ones. Organic compounds run cooler at the caliper, give more lever feel and modulation, and tend to be quieter with less rotor wear and vibration than a sintered pad. The Black s550 uses ceramic particles in an organic compound, but it is still organic, not semi-metallic.

Do I need to bed in new pads? Yes. Fresh pads and rotors need a bedding-in process to transfer an even layer of pad material onto the rotor and reach full power. Find a quiet stretch, bring the bike up to a moderate speed, then brake firmly down to walking pace without locking the wheel, and repeat that ten to twenty times. Expect bite and power to keep improving over the first few rides.

Why won't the new pads fit back into the caliper? As the old pads wore down, the caliper pistons crept outward to keep contact with the rotor, so there isn't enough room for thicker new pads. Before fitting the 023s, push the pistons all the way back into the caliper with a clean plastic tire lever or a dedicated piston-press tool. Reset both sides evenly, then slide the new pads in and reseat the wheel.