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Tech Talk with Master Power Brakes

Rear Brake Caliper Adjustment

Posted by toby on May 21, 2015 9:34:47 AM

Adjusting rear brake caliperOne of the most common calipers used in the aftermarket today in many companies disc brake conversion kits are the exact same General Motors based calipers we use in ours. It is a very good caliper that will work for many different applications.

There is a drawback though. Many people in the classic car/hot rod don’t use the emergency brake. I can say this from previous guilt on this subject. In fact, some people don’t even have the emergency brake hooked up. You might ask “If you don’t need it and therefore don’t use it, why is that a drawback or a problem?”

When the pads wear and material is removed, the pads then become further away from the rotor surface. The calipers use a “one-way clutch” or “sprag” inside the caliper piston.  When the parking brake is applied, the sprag will recognize when there is 0.030” or more clearance between the friction material and the surface contact area on the brake pad.  When the distance is 0.030”, the sprag turns inside the piston adjusting it outward and keeping the rear brakes properly adjusted.

So yes, it is important to use your emergency brake. It also equally as important to have the calipers adjusted correctly to begin with. To adjust initially, the piston is adjusted outward by turning the nut on the lever or by cranking the lever. This ratchets the caliper piston outward just like using the emergency brake would do. This moves the piston outward taking up that distance between the rotor and the pads. With the pads closer to the rotor, additional fluid volume isn’t required to move the pads further and then possibly run out of volume and never properly squeeze the rotor.

http://www.mpbrakes.com/techtalk/wp-content/uploads/re-adjusting-rear-caliper.jpgWhat would happen if you don’t adjust the calipers to begin with or you don’t use the emergency brakes? Usually one of two scenarios will exist:

Scenario #1 – You will start to lose service in the brakes because the caliper piston is traveling more to reach the brake rotors.  If this happens, the brake pedal will feel very soft.

Scenario #2 – The sprag can seize inside the piston and possibly stop working.

Using the emergency brake can be very difficult to remember. Most of us have the park it and walk away mentality. The best thing you can do for your brakes with this type of rear caliper is to get into the habit of using the emergency brake. Not necessarily every time you park...but more than I bet you use it now.

Topics: brakes, classic cars, How To Series, parking brake, rear brake caliper adjustment, Vintage Cars

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