Brake caliper re­build

How to res­cue those seized brake calipers by fit­ting new seals and pis­tons.

Classics Monthly - - Contents -


In some cases, a stick­ing pis­ton in­side a brake caliper can be freed off by spray­ing pen­e­trat­ing fluid down in­side the dust cover and around the walls of the pis­ton. This can only be done with the caliper re­moved, but you won’t need to de­tach the flexi-hose. You may have to care­fully press the brake pedal to push the pis­ton out a lit­tle, but not too much.


Once the pis­ton has been lu­bri­cated with pen­e­trat­ing fluid, it will need to be pushed back in again to help the pen­e­trat­ing fluid work and to see if the pis­ton has be­come eas­ier to move (check the brake fluid level in the reser­voir be­fore do­ing this). Use a G-clamp to force the pis­ton in. You may need a flat piece of metal to spread the load across the end of the pis­ton.


Some pis­tons can­not be pushed in, but have to be wound in in­stead. A brake caliper wind­back tool should be used here, al­though some peo­ple have used long nosed pli­ers, but there is a risk of slip­ping and stab­bing your hand. Once the pis­ton has been re­tracted, care­fully press the brake pedal to see if it moves out – but not too much as it may pop out en­tirely.


The pis­tons in the rear calipers on the Mazda MX-5 and some Volvos have a stop fit­ted in the back to help with hand­brake ad­just­ment. If this is wound in too far, then you may think the pis­ton has seized and you won’t be able to re­fit the caliper, es­pe­cially with new discs and pads fit­ted. In­stead, wind the stop out for more clear­ance.

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