Practical Sportsbikes (UK)
Critical components require intensive care – and they don’t come more vital than brake calipers. They need regular maintenance. Leave them unused, encrusted with filth, for too long – and you’ll end up going through these procedures
How to master the troubles and fixes of rebuilding brake calipers. It’s kind of important
Equip yourself to overhaul your brake calipers. A handful of tools and a modicum of knowledge and common sense are all you require. Make the most of systems that, while they may have been superseded in the decades since they were designed and manufactured, are still capable of delivering the goods when they’re working to the best of their ability.
You might also save yourself a pointless ‘upgrade’ to other calipers which will eventually require an overhaul themselves – if they don’t already. Many used calipers are decidedly secondhand even before they find their way onto ebay or the like.
Brakes being as important as they are, there’s no room for ‘near enough’ when it comes to overhaul. Don’t refit anything to the bike if you aren’t 100% sure the part or parts are fit for purpose.
The first visible issue might be pistons that have corroded and pitted on the surface area outside the caliper body. Not really a huge issue until you fit new brake pads and the pistons are pushed back into the caliper, damaging the seals and hanging up on them as they go.
Internally, the hygroscopic (waterabsorbing) nature of brake fluid can promote corrosion inside a caliper. Worst of this is when corrosion forms in the grooves that the seals sit in. As this builds up the seals become tighter around the pistons leading to stiction. All of this conspires together so that eventually the pistons don’t want to move in the caliper bodies at all.
Other issues you might find are seized bleed nipples, and on sliding calipers unlubricated pins hinder proper movement. Don’t apply brute force to any recalcitrant nipple – it will snap and then you’ll be faced with even more aggro. Use a little heat and gentle pressure to get it to move.
Popping the pistons
Far and away the simplest method to get pistons moving is while the calipers are still attached to the bike. Remove the caliper from the fork leg, lift it clear of the brake disc and take the pads out, noting their positions if you’re going to be reusing them. Slowly pump the lever until the pistons start to move out.
On multi-piston calipers, if one is reluctant, prevent the other(s) from popping out by placing an old spanner, piece of stee, or something like that, between them.
If the piston still refuses to move or the caliper is already off the bike, there are a few methods open to you. Gentle warm-air heat and brake piston pliers might work. If the piston is to be replaced and there’s enough of it to get a grip of, swan neck pliers might work. Still no movement? We’ve enjoyed much success with a slide-hammer type piston removal tool. A conventional opposed piston caliper will need to be in two halves for this.
A messy but effective method is to hydraulic the piston out with a grease gun. The nuclear option is to deploy compressed air but please take every precaution to prevent pistons flying out of the calipers. They go off like rockets and there’s a massive risk of damage or injury.
Plenty of brake cleaner in a well-ventilated area is a good start. Engineers picks are handy for removing old piston seals, and then gently loosening corrosion in their grooves. A rotary tool with a soft brush can also be employed here.
Lubricate the new seals prior to fitting with a little brake fluid or some red rubber grease. Fit the new or cleaned up pistons, again with a little lubrication. This bit can be fiddly; don’t use force, they’ll slide in when they’re perfectly in line. Renew the seal(s) between the caliper halves if this is the type of caliper you’re dealing with and you had to split it. A light application of silicon grease on the exposed sliding area of the pistons will keep things move for longer.
If you’re overhauling sliding calipers, clean and grease the pins. Pad retaining pins also benefit from a very light smear of grease. Use copper grease on the threads of screw-in pad pins; renew split pins/r-clips on that type of retaining pin. Renew corroded bleed nipples.