Introduction: How to Rebuild a Brake Caliper (WITHOUT Removing It From You Car!)

About: I'm Chris, a thirty-something British bloke with a ton of passions: sailing, travelling, DIY, adventure, climbing... I love making YouTube videos about these passions. Check out my videos on my website or YouT…

Brake calipers are located in a very dirty area of your car and are subjected to years of abuse at the hands of road dirt, water and salt (and as a result of your 'sporty' driving technique!).

Eventually the piston can corrode and the brake caliper will seize (aka 'freeze') and when you release the brake the brake fails to release. If this happens you may hear 'squeeling', smell overheating of the brake components and the entire wheel may get very hot.

My 1999 Ford Focus has lived its life in the wet and windy North West of England. The fact that this 18 year old car still drives like a dream despite this (and despite the fact I bought it years ago for only $800 and despite my sporty driving technique...) is nothing short of a miracle! However, one of the brake calipers did seize recently so I had to fix it - hence this Instructable.

Often the whole brake caliper assembly is replaced when this happens but that is a real shame: They are very simple things, and for about 20 USD you can buy a brake caliper repair kit (which can include a brand new piston) and with an hour or so of work, your caliper will be as good as new!

If you're in a hurry to get your car back on the road, like I was, then you don't even need to remove the brake caliper from your car: you can refurbish it with the brake line still attached.

(Yes, there will be people who say "don't clamp your brake line" but I have worked with hydraulics for many years and see no problem with this. I have never seen an actual case of a brake line being damaged by clamping - I have only ever hear anecdotal stories and warnings. If you take your car to a garage, most of them will clamp the brake line and you will never even know they did it...)

If you have decent internet access then the video above shows you the whole process. If you prefer to read the Instructableubblyabubblyubblyabubble steps instead, then please feel free to do so.

Tools / materials required to complete this job:

  • Jack
  • Axle stands
  • Drip tray
  • Socket set
  • Screwdrivers
  • Hex key set (aka allen keys)
  • Brake caliper repair kit for your caliper
  • Brake fluid

Step 1: Jack Up the Car, Support on Axle Stands and Remove the Wheel

Crack the wheel nuts, then jack up the car and support on axle stands. This needs to be done safely, but we won't cover the procedure for this here, other than to say never work under a car supported only on a jack!

Remove the wheel to gain access to the brake caliper. Feel free to sit on the wheel whilst you do the rest of the job. :-)

Step 2: Remove the Caliper

This is easy - you just have to remove the upper and lower caliper mounting bolts. Once the caliper has been removed from its mounted position, you can easily remove the brake pads.

Step 3: Pump Out the Piston Using Brake Pressure

There are all kinds of weird and wonderful ways to remove pistons from calipers, some involving compressed air which can result in the piston shooting out like a shotgun slug... I like simplicity, so I prefer to just pump the brake and the piston will pump itself out thanks to hydraulic pressure.

Ask a friend, or preferably a beautiful assistant, to pump the brake for you until the piston gently pops out with a curiously satisfying gush of brake fluid.

Step 4: Remove the Old Seals and Clean Up the Caliper

Once the piston has been removed, you can -dum dum dum- clamp the brake line (you can use a special brake line clamping tool for this, or if you don't have one, a set of mole grips with some cardboard in the jaws will work just fine).

Once you've done this, remove the outer gaitor seal and the square profile seal on the inside (cylinder) section of the caliper.

The square profile seal is a very simple, but very clever, part of the caliper. On a correctly functioning brake caliper, when brake pressure is applied and the piston is pushed outwards towards the brake disk (squeezing the disk in between the pads) the square profile seal deforms. When the brake is released the square profile seal returns to its original shape and this is what draws the piston back inside the cylinder, releasing the brake.

The seals can easily be removed with the help of a small flat-blade screwdriver - just be careful not to score any of the parts, so you don't cause any leaks in the future.

Clean up the inside of the caliper and all the seal mating surfaces, ready for the next step.

Step 5: Fit the New Piston & Seals

Get your cheap, but perfectly formed, brake caliper repair kit and grease up the seals using the appropriate (red) grease - which you should get in the brake caliper repair kit.

Fit the new square profile seal inside the caliper.

Take the new gaitor seal and apply some red grease to the mating surface of the seal where it will meet the piston. Fit the gaitor to the brand new shiny piston so that it engages into the grooved section on the piston. Done it? Groovy!

Now open the bleed point on the caliper (so you aren't pushing against an airlock) and push the new piston squarely back into the cylinder. Once you've done that, you can finish fitting the gaitor, which engages onto a chamfered edge on the caliper.

Top tip: start at the most difficult, out of reach part of the gaitor, this way the tightest final part of the seal will be easily accessible whilst you engage it onto the caliper.

Step 6: Replace Any Extra Parts, Refit the Caliper & Bleed the Brakes

The $20 brake caliper repair kit that I bought had new rubber grommets and dust caps for the caliper mounting bolts. If yours does too, then pop out the old grommets with a screwdriver and insert the new ones after lubricating them with the grease supplied in the kit.

Once this is done you can refit the brake pads and caliper back into their original position. (You don't have to replace the pads if they still have plenty of life left in them.)

Remove the -dum dum dum- clamp from the brake line and bleed the brakes by having your beautiful assistant repeatedly depress the pedal whilst you open and close the bleed point on the top of the caliper.

Step 7: Finish the Job Then Bask in Your Glory

Refit the wheel, drop the car off the axle stands, torque up all the wheel nuts, top up the brake fluid and test the brakes again. If they are spongy at all then bleed them again.

Now, enjoy a cup of tea before taking your pride and joy on a test drive, or finish your test drive and then have a celebratory beer (or case of beers, using the money that you saved by not throwing a perfectly good caliper in the bin!).

Well done for fixing your car. Your grandfather is / would be proud of you!

Check out the other videos on my YouTube channel for more randomness.


Chris :-)