Disc brake caliper overhaul


Brake calipers. Warning: do not tackle brake repairs unless you are a competent mechanic
Commander brakes are the same as Yamaha XJ 900 and therefore, unlike the Interpol, F1 and Classic, the brakes seize up at the first sign of salty roads. The only cure for this is a strip down and rebuild of the calipers. Done properly this job will cost no more than time, plus a pint or so of brake fluid and some brake grease. The following text explains what I do (and why I do it!) . Unless the caliper is in an awkward position , remove the pads before taking the caliper off the bike, otherwise you have nothing to pull against while removing pad pins etc.
Having removed the pads use the relevant brake lever to pump out the pistons a little way, watching the pistons as you go. If only one piston moves, stop the free one from moving by jamming a pad (or anything) between the piston and disc, be careful not to damage the disc. Hydraulic pressure is such that even a seized piston will move out, continue until the piston is close to the disc.
Now is the time to remove the caliper from the bike, if you are working on a double disc set-up, while you still have hydraulic pressure available bring the other side caliper to this stage. Once one piston drops out , obviously fluid pressure can no longer help you , so choose which piston you want to pop out carefully! If you got it right, the other 3 pistons will be very nearly out anyway.
Remove the two bolts holding the two halves of the caliper together , if it is not possible to remove all the pistons by hand then protect the pistons working surface with a cloth and turn the piston with slip joint pliers .
Inspect the surface of the pistons, in most cases these are fine and just need cleaning.
Remove the seals from the caliper castings. I immediately place the seals in lukewarm soapy water and give them a good wash to remove all traces of brake fluid. This may help to stop the seals expanding, at least it gives you a chance to inspect them carefully.
The main reason for brakes binding is a coating of aluminium oxide in the groove where the seal runs , every trace of this must be removed carefully with a pointed scriber or , more slowly with wire wool .
The original seals are usually OK to re use.
While the castings are bare try to remove the bleed nipples, if they are also seized, warm the casting until they come out, only dafties break bleed nipples off!
An absolute must is to reassemble with a brake grease (favourites are Girling or Castrol) do not use ordinary grease, it will damage the seals.
Proper cleaning of the seal grooves and plenty of grease will mean that on reassembly, the pistons can be pushed in with one finger. If they are at all tight, you didn’t clean the grooves properly.
Difficulty can sometimes occur during bleeding a double disc system, if you have trouble, try filling a spotlessly clean oil can with brake fluid and connecting it to the bleed nipple with some plastic bleed pipe and back feed the system.
You may be surprised at my suggestion of re using all the parts, personal experience has shown that only calipers that are leaking need new seals.
The difference in pad wear and fuel consumption can be quite dramatic.
Graham Wilshaw (Startright )


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