These all new cast, not rebuilt iron calipers are bolt-on replacements for the popular 1978 and later D154 type GM metric calipers that are widely used in "spec" racing categories and low cost disc brake conversions. The availabliltiy of good used or rebuilt OE calipers is on the decline and there are limited options for piston sizes in stock calipers. Wilwood Iron GM Metric Calipers combine new part qualilty with modern machining precision. There are two piston size options to assist builders with properly building static bias into a car. Previously, builders using the metrc calipers generally had to mount the same size calipers on all four wheels. This drastically limited the tuning options and often created front to rear bias ratios that were not conducive to good handling and stability under hard braking. Some builders, and other brake suppliers, chose to offer re-machined OE calipers to provide a bias tuning option. Unfortunately, re-machining a used casting that was never designed for the larger bore size can create real compromises in strength, reliability, and performance. To address these needs, Wilwood has tooled two separate new castings that are fitted with either 2. 75" or 2. 00" stainless steel pistons and high temperature bore seals. Each casting is designed specific for it's intended bore size, and simply not over machined to accept different pistons. The calipers are strong and precise, without unnecessary added weight from oversized castings. The stainless steel pistons resist corrosion in all environments while helping to slow the heat transfer from the pads. The high temperature seals provide long service life when used in hard braking applications and maintain their resilience to provide postive piston retraction on release. In addtition to the optional piston sizes, two models are available wtih slide pin vibration dampers installed to help reduce rattle and other harsh noise. All Wilwood GM Metric calipers use the standard D154 type brake pads. The complete range of Wilwood high performance and racing pad compounds is available to match response, friction, and temperature range to any application.Pit Stop USA offers Wilwood Iron GM Metric Caliper - 2.75" Piston 120-8924 at low everyday prices. Be sure to check out all of our products from Wilwood Engineering including Wilwood Engineering GM Metric Iron.