Caliper Rebuild Kits for Subaru Impreza GD

Caliper rebuild kits renew the seals and dust boots that keep a brake caliper’s pistons sealed, clean and free to move. Alongside full rebuild kits come dust boot kits, caliper stud kits and titanium backing plate kits.

Each piston runs in a square-section seal set in a groove in the bore. As pressure builds, the seal grips the piston and twists slightly; when the pedal is released it springs back and pulls the piston with it. That small rollback lets the pad back off the disc.

Heat cycles slowly harden the seal, so rollback shrinks, the pads drag and the disc runs hotter. The dust boot keeps grit and water off the piston; once it splits, the piston corrodes and the seal starts to weep or stick. Track use speeds all of this up.

Match the kit to the caliper on the car.

• Piston sizes: kits are listed by piston diameter, from single sizes such as 36 or 40 mm to staggered sets such as 28/32, 40/44 or 30/34/38 mm.
• Axle and quantity: front and rear calipers usually differ, so most kits name the axle. Kits come as a set for one caliper or for two.
• Boots only: a dust boot kit suits a caliper whose seals are sound but whose boots have split or hardened.
• Material: most seal and boot kits are listed as silicone, which stays flexible at higher temperatures than the EPDM rubber in standard brakes.
• Titanium backing plates: thin plates fitted between pad and pistons, sold as a set for two calipers. Being a poor conductor of heat, titanium acts as a barrier between the hot pad and the hydraulics.
• Caliper studs: stud kits put studs and nuts where bolts were, sparing the threads in the mounting when a caliper comes off often.

Rebuild one caliper at a time so parts cannot be mixed. Ease the pistons out with gentle air pressure, a wooden block in their path and fingers well clear. Clean the bores and seal grooves with brake cleaner, never with petrol or mineral oil, which swell brake rubber.

Replace any pitted or scored piston, as a new seal cannot seal against a damaged surface. Fit seals wet with clean brake fluid or the assembly lubricant the kit calls for, and seat each boot fully. Leave two-piece calipers in one piece unless the maker allows splitting them, as the bridge bolts and transfer seal need their own procedure. Bleed with fresh fluid, then check that every piston returns freely before driving.