Rear Brake Rebuild

Bike is a 2002 non ABS ST1100. Toward end of season in 2013 rear brake became relatively ineffective. Pulled pads and cleaned these + the rotor. Pistons not stuck, but seemed to require a lot of effort to push in. Fluid level in the master cylinder was fine. This cleanup helped marginally, but really did not solve the problem.

Going to do my bi-annual coolant flush, brake & clutch fluid change and will be changing my rear wheel dampers for the first time so ordering parts soon. Plan to pull the rear caliper, clean and replace seals (SEAL SET, PISTON, #06431-MA3-405, $4.32 x 2). I assume I should get the 2 banjo bolt washers as well, or can these be reused?

Based on a review of the brake forum this should do the trick, but anything else I should be looking for as well?

Check for blockage in the brake line also.

ReSTored said:

Pistons not stuck, but seemed to require a lot of effort to push in.

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Which is the first sign that an overhaul is due...

Plan to pull the rear caliper, clean and replace seals (SEAL SET, PISTON, #06431-MA3-405, $4.32 x 2). I assume I should get the 2 banjo bolt washers as well...

Click to expand...

I always get new 'banjo washers' (actually aluminium gaskets), their cheap and you're on the safe side (2x P/N 90545-300-000 washer, oil bolt)
But depending on their state of corrosion you might also need new pistons (2x P/N 45107-ML4-006, piston) I'd first clean them for a closer visual, but anything that cannot be removed with a light abrasive like chrome-polish is IMHO beyond repairability and requires replacement... watch out for dark spots, which could be pitting-corrosion...
Also useful is some dental pick to clean the grooves for the rings (I'd clipped and bend a piece of cloth-hanger wire)
And brake assembly paste, a slight smear on them rings and pistons prior installation eases the job a lot and preserve the outer ring and outer piston surface for quite some time...
And since you've that thing out on the bench anyway, you might consider to also clean & lube (ceramic paste) them 'float pins' inside the rubber boots, enabling proper lateral movement/alignment of the calliper.

So, did the rebuild and everything appeared to be OK, but on reassembly I find that rear brake is better, but still not 100% back to where it should be. I can't lock the rear brake (not an objective, but this is an indicator as to how hard the brakes can be applied) which to me means the caliper is not working correctly. When I reassembled, one piston was looser than the other one, which I think means there is still an issue with the one that was stuck.

So, next step for me would be to disassemble and clean the seal grooves and the piston itself and see if this helps.

Any comments or advice?

I did a "rebuild" of the rear brake on my former bike (Honda CX 650E). I stuck with Honda parts...I did clean the brake piston groves using a dental pic and some other items (I can't remember) and purchased new Honda seals. I found it very tight when all assembled. My issue was dealing with a piston seal that was so tight the brake wouldn't release as I believed it should have. It worked much better than before...put on the newest pads...and yes, you could easily lock up the back wheel. Again, I just felt the new seals were just too large for the piston and cylinder. +1 on the recommendation to check for blockage throughout the entire brake line...starting from your reservoirs!

ReSTored said:

So, did the rebuild and everything appeared to be OK, but on reassembly I find that rear brake is better, but still not 100% back to where it should be. I can't lock the rear brake (not an objective, but this is an indicator as to how hard the brakes can be applied) which to me means the caliper is not working correctly.

Click to expand...

Do you have a firm pressure point on the pedal, or is it sacking down like 45? when pressing it down?
Might be you still have air in the system, might be that your rear master cylinder is also in need of an overhaul-kit...

Replaced the brake fluid on my '00 just two weeks ago, bike on main-stand, spin the rear wheel, one finger on the brake pedal, after <20mm movement on the tip of the pedal, I hear the "bang!" of the rear wheel stopping... release the pedal, spin the wheel again (calliper releases instantly), another push of a finger "bang!", wheel stopped...

And my mech showed me a nasty, efficient way of bleeding brakes with his air-powered vacuum bleeder:
- blow off all dust from the exposed parts of the calliper pistons with a gentle stream of your air nozzle (if you find them significantly dirtied up, remove any grid with some pipe-cleaners)
- push calliper pistons in all the way
- pump pistons back out by pedal/lever
- open reservoir cover, suck out all old fluid (especially any crud at the bottom)
- top off with new fluid
- start drawing out old fluid at the calliper bleeder bold while continiously topping off the reservoir (nicely done with 2 people though)
- once only new, clear fluid shows in the transparent vinyl hose of the vacuum bleeder, stop all activities, close bleeder and:
- again push calliper pistons in all the way and pump back out three times
- restart your vacuum-bleeder, and again draw fluid out the calliper while topping off reservoir
- once this is done (100% clear, new fluid, no bubbles), close bleeder bold, and again push them calliper pistons fully in
- now top off the reservoir to the MAX line (in the view-glass or at the side of plastic vessel)
- wipe all dew/condensate off the diaphragm underneath the cover, once clean place it back on carefully
- Now do NOT forget to pump your brakes back up with pedal/lever BEFORE leaving the bike-lift/garage! (Normally you do a functional test anyway: unload the wheel, spin it and grab the pedal/lever to check proper function and pressure point... but still...)