Rear Brake Caliper Service

The rear caliper was working when we received the bike however it looked worse for wear and a rebuild kit is too cheap to say no to a rebuild.

The Caliper itsself uses two pistons with a bleed nipple for eash side. This is a great design and works well however when it comes to servicing its a bit of a nightmare. The Bleed nipples are very delicate and both of them snapped on our caliper.

The pistons are also very large so a piston pulling kit for normal bikes cant be used and an alternative car tool needs to be used to remove the pistons.

Its is always good prectice to pump the pistons out with the mastercylinder still connected. Of course I forgot this and unbolted all of the hydraulic cables a year ago blissfully unaware.

So after snapping the two nipples I quickly bought another caliper that had two free moving nipples offline. I then connected the mastercylinder and reblead the system on the bench. Using this set up I pumped the pistons out as far as they would go. For the bleeding I used a syringe that I bought off of ebay for £3 to suck the fluid through the system. This worked very well in conjunction with the conventional master cylinder pumping it through.

A jubilee clip was clamped around the pistons and they were levered out after the caliper had been split open. There was a bit of surface corrosion and the rubber seal very completely gone.

 The corrosion behind the dust seal mainly, causes the pinching on the piston and makes for a stiff and poor performing brake.

 I use this bent piece of steel and a scribe to break up the corrosion along with WD40 GT80 or just brake cleaner to help blow it away and clean it up,

 Corrosion  behind the dust seal is very prominant. Not so much in the hydraulic seal.
This can be overcome by introducing another dust seal that clips onto the front edge of the piston and is more like a gator beacuse it extends with the pistons positve displacement. This is very common in cars to improve the working life of the brakes.

 Before.

 After.

A dremmel can be used its effectively a dentist drill meets actual drill. The attachments can be very thin and fit into these groves perfectly. However They are delicate and damage can easily be done to both the tool or the caliper.

 I use rubber grease when fitting any new rubber seal, it helps hold off corrosion and helps the movement of the piston.

 New dust seal get the rubber grease treatment too.

 The piston was sprayed and cleaned with a rag to get any old deposits off, then its slides straight in. note, if the piston doesnt slide in with just one finger then pull it out and clean out the seal groves again it means the seals are still pinching.

This is how I get by without a bench wire wheel for now.

 

Simple piece of cardboard makes a great bolt holder. 

The hydraulic seal inbetween the two halves of the caliper were also replaced plus the corrosion was scraped off using a straight edge.

 The caliper bolts were cleaned and sprayed just to help its aesthetics, then the nipples were copper greased up and fitted along with their new rubber caps, which were also rubber greased up.

 Suns out guns out.

I cleaned up the caliper mount and bolts.
Its now ready to be fitted and blead.

The next job will be the welding of the exhaust and the subframe, the newly powdercoated swinging arm and new tyres wont be near the bike until all the welding/grinding is finished off.

Until next time!