There is no more popular basis for oval track race cars than the 1978-87 GM "Metric Chassis". The ready availability lead many tracks to base their rules around them as a cost saving measure whether for Modifieds, Street Stocks, Hobby Stocks, SportMods, or other classes. GM engineers never would have imagined how these pedestrian passenger vehicles would end up ruling the circle tracks of America 40 years later.

The 1978 General Motors A-body (later called G-body) intermediate platform used mostly metric nuts and bolts, which is why everyone calls it the "Metric Chassis" now. The most common were the 1978-83 Chevy Malibu, 1977-87 El Camino, and 1977-88 Monte Carlo, but every division had them. Pontiac made the Grand Prix, Grand Am, Le Mans, and Bonneville. Oldsmobile had the Cutlass in various forms. Buick sold the Century, Regal, and Grand National. Even GMC had their version of the El Camino car/truck hybrid called the Caballero.

From the factory, these cars and trucks all used the same front brake caliper, often called D154, and Wilwood has several upgrade options available. With the right brake pads these can be used on street cars as well.

Improved GM Metric Iron Replacement

Wilwood D154 GM Metric Chassis Caliper

Wilwood has made calipers similar to the OEM part, but with significant advantages, for years. Recently part number 120-16101, in cast iron with a 2.5" piston, was approved by the International Motor Contest Association (IMCA) for use on the metric chassis in all classes. This new Wilwood caliper is considered a stock replacement. IMCA sanctions races in 36 of the 50 states, and also in Canada, so what they decide carries a lot of weight with short track rule making bodies.

Despite being considered "stock" Wilwood engineered these calipers to be better. Unlike the many cheap replacement calipers available, the Wilwood caliper starts with a proprietary casting, not a copy of the original or worse, a reconditioned part. The pistons feature special high temperature seals, with a square section for better pedal feel and "knock-back" resistance. All sliding surfaces, and the slide pin bores, are machined to exacting tolerances for minimal friction. Engineering and manufacturing their own casting has allowed Wilwood to make this caliper reversible as well, mounting on the left or right just by swapping the bleed screw and brake line.

Engineering drawing of Metric Iron D154 Caliper

Wilwood offers the cast iron version of the D154 caliper in three piston sizes, all using the same pad shape. If you race in a class not following the full IMCA rule book, but still requiring a stock type cast iron caliper, there are 2.00" and 2.75" piston sizes available. For a given size master cylinder bore, the larger the caliper bore the more clamping force you get when you step on the brakes.

(Note: While these are OEM replacements, you must use the Wilwood hardened slide pins, sold separately. Order Wilwood part number 230-0619.)

Aluminum D154-R Race Calipers

Wilwood D154-R race caliper for GM Metric Chassis

If you are racing a GM "Metric Chassis" with less restrictive rules, Wilwood has a forged aluminum caliper upgrade, that improves on the stock design. The Wilwood D154-R caliper starts with a specially forged billet which aligns the metal grain structure for a stronger part. The aluminum construction makes these calipers weigh several pounds less than any cast iron replacement; just 3.3lbs for the 2.5" piston version. 

This unique caliper design has less deflection than any competitor's caliper. Less deflection means higher volumetric efficiency, for better feel and consistent bite, lap after lap. As an added bonus, aluminum dissipates heat faster, so less is absorbed by the brake fluid.

Wilwood D154-R engineering drawing

Like the Wilwood stock replacement, the forged aluminum D154-R is also reversible, for use on passenger or driver side. The brake inlet port is directly behind the piston, so as not to interfere with the slide pins, with a bleed screw on either end.

High Performance D154 Brake Pads

Wilwood D154 Brake Pad engineering drawing

Wilwood also sells nine different brake pad compounds that fit any and all GM "Metric" D154 calipers. Depending on what sort of racing you are doing, choose the ProMatrix, PolyMatrix, or SmartPad with the best initial bite and fade resistance for your style of driving.


The Wilwood ProMatrix is a dual-sport, street focused compound. It is a quiet, long wearing pad, and produces only a low to moderate amount of dust. Initial bite is aggressive, but overall friction is moderate. This compound is rated for moderate temperatures. Order Wilwood part number 150-D0154K.

PolyMatrix A, B, E, and Q

The PolyMatrix family of brake compounds comes in quite a few different varieties.

PolyMatrix A has the highest friction response when cold and maintains high friction at all temperatures. It was formulated as a severe duty pad for oval track, road course, and other forms of racing in need of immediate high torque response. They offer long wear even under high heat use. Order Wilwood part number 15A-6219K.

PolyMatrix B is the traditional favorite of asphalt Late Model and Modified racers, and popular with hard braking dirt drivers. This compound beds easily, and has a less aggressive initial bite, but grips harder as it gets hotter. They offer very predicable engagement with a slowly rising torque curve. Order Wilwood part number 15B-3998K.

PolyMatrix E is popular with all types of dirt racing thanks to its nearly flat torque curve, even as it gets hot. This compound lacks an aggressive initial bite, making it much better suited for low traction surfaces. Even under extreme temperature, these pads still give good consistent friction, not falling by much even at 1000 degrees. Order Wilwood part number 15E-6103K.

PolyMatrix Q is specifically formulated to be quiet in use, that is what the "Q" stands for. This is not a compound used for racing, except Sprint cars and others with aluminum rotors. Its ceramic based formula does work well in street cars though. Order Wilwood part number 15Q-6831K.

SmartPad BP-10, 20, 30, and 40

SmartPad BP-10 is a high performance street compound, with more friction, less wear, and less dust than most replacement pads. In oval truck, it is usually used in dirt racing with light to moderate brake usage. They have a smooth engagement and flat torque curve. Order Wilwood part number 150-8936K.

SmartPad BP-20 offers extreme temperature braking abilities but still has a good initial bite and friction when cold. These pads are use on dirt for medium and heavy braking, and asphalt for sportsman and Hobby Stock cars. As these pads get hot, they offer more friction, and still work well at over 1000 degrees. Order Wilwood part number 150-9442K.

SmartPad BP-30 is a race only pad for heavy braking on dirt, and intermediate needs on asphalt. They bed in quickly and wear a long time, but get better as they get hot. Order Wilwood part number 150-14778K.

SmartPad BP-40 is for  severe duty oval, road course, and off-road series that require an aggressive response and durability in the highest temperature ranges. If you have a problem with brake fade, this is the extreme heat pad you need. Order Wilwood part number 150-12250K.

Visit the Wilwood Racing website for oval track, drag  racing, road course, and off-road competition parts and information.

Wilwood Racing Website

Dirt track racers go into a corner three wide


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