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Worthwhile in emphasis, that of any disc brake system that's giving poor results, one way or another, its all but 100% related to that seal function bring compromised, that's across all system whatever the scale of components. The hydraulic piston caliper is brutally simple, only the moving piston and its accompanying seal ultimately affect operation. That's aside from leaking etc. Most, after reasonable time, will get the seal's movement compromised through that operation. These original Honda type have effectively nil weatherproof mitigation with piston boot or other external seal arrangement, and so are vulnerable to the effects of localised atmosphere in way of moisture etc.Stainless piston will resolve the corrosion of the original plated piston, but it can't do anything for galvanic corrosion of the piston seal groove in aluminium material of caliper. That risk remains there given any electrolytic activity potential. Honda's original 750 manual specifies silicone grease around that area behind the pad, that being extremely repellent to any water ingress etc. The seal land needs very close detail in cleaning it and removing any of the accumulated aluminium corrosion from the taper space where the seal moves to in normal operation. They have a different lever feel, release characteristics and very low pad to disc friction when thoroughly cleaned and assembled. A compromised example usually exhibiting reduced travel from home position of lever (less pad rollback) and harder/more difficult effort to use the brake, the rotor surface usually taking on a more polished surface appearance is another sign or pad continuous dragging. I haven't tried one in these caliper, but a Phenolic resin piston may hold advantage in conductivity to ultimately reduce galvanic potential in these system.
Interesting about the suspected fluid leak, most of my experience is on disc brakes on cars.I have put new seal rings in calipers after using 1000 grit wet & dry to remove corrosion from the steel caliper walls with no leak when built up. I've assumed the pressure seals any minor imperfections.I have always thought that when you release the pressure from the master cylinder that it's high spots on the disc that push the brake pad and hence the piston back. It appears that on these old bikes it's the piston seal that does the final pull back if I am understanding it correctly.
Quote from: K2-K6 on April 29, 2026, 08:07:24 AMWorthwhile in emphasis, that of any disc brake system that's giving poor results, one way or another, its all but 100% related to that seal function bring compromised, that's across all system whatever the scale of components. The hydraulic piston caliper is brutally simple, only the moving piston and its accompanying seal ultimately affect operation. That's aside from leaking etc. Most, after reasonable time, will get the seal's movement compromised through that operation. These original Honda type have effectively nil weatherproof mitigation with piston boot or other external seal arrangement, and so are vulnerable to the effects of localised atmosphere in way of moisture etc.Stainless piston will resolve the corrosion of the original plated piston, but it can't do anything for galvanic corrosion of the piston seal groove in aluminium material of caliper. That risk remains there given any electrolytic activity potential. Honda's original 750 manual specifies silicone grease around that area behind the pad, that being extremely repellent to any water ingress etc. The seal land needs very close detail in cleaning it and removing any of the accumulated aluminium corrosion from the taper space where the seal moves to in normal operation. They have a different lever feel, release characteristics and very low pad to disc friction when thoroughly cleaned and assembled. A compromised example usually exhibiting reduced travel from home position of lever (less pad rollback) and harder/more difficult effort to use the brake, the rotor surface usually taking on a more polished surface appearance is another sign or pad continuous dragging. I haven't tried one in these caliper, but a Phenolic resin piston may hold advantage in conductivity to ultimately reduce galvanic potential in these system.Good post and very informative.But are we not veering off topic a little?The original post being " Front brake squealing".
If you have the brakes bleed and the moving pad housing in your hand, just rest your finger on the piston and squeeze the lever a small fraction, you should feel the piston move out and then retract a fraction when you release.RegardsDave
Quote from: Skoti on April 29, 2026, 08:17:44 AMQuote from: K2-K6 on April 29, 2026, 08:07:24 AMWorthwhile in emphasis, that of any disc brake system that's giving poor results, one way or another, its all but 100% related to that seal function bring compromised, that's across all system whatever the scale of components. The hydraulic piston caliper is brutally simple, only the moving piston and its accompanying seal ultimately affect operation. That's aside from leaking etc. Most, after reasonable time, will get the seal's movement compromised through that operation. These original Honda type have effectively nil weatherproof mitigation with piston boot or other external seal arrangement, and so are vulnerable to the effects of localised atmosphere in way of moisture etc.Stainless piston will resolve the corrosion of the original plated piston, but it can't do anything for galvanic corrosion of the piston seal groove in aluminium material of caliper. That risk remains there given any electrolytic activity potential. Honda's original 750 manual specifies silicone grease around that area behind the pad, that being extremely repellent to any water ingress etc. The seal land needs very close detail in cleaning it and removing any of the accumulated aluminium corrosion from the taper space where the seal moves to in normal operation. They have a different lever feel, release characteristics and very low pad to disc friction when thoroughly cleaned and assembled. A compromised example usually exhibiting reduced travel from home position of lever (less pad rollback) and harder/more difficult effort to use the brake, the rotor surface usually taking on a more polished surface appearance is another sign or pad continuous dragging. I haven't tried one in these caliper, but a Phenolic resin piston may hold advantage in conductivity to ultimately reduce galvanic potential in these system.Good post and very informative.But are we not veering off topic a little?The original post being " Front brake squealing".As noted above , I think this is absolutely core to the topic and adds to discussion in understanding cause etc for these caliper system. It is a Forum, after all. My intention is to put my experience/view that can add or draw contrary view from others on site with relevant experiences too. This to further the appreciation of technical aspects and help in looking after these design. I'd credit the site contributors with the intelligence to skip posts that they have no interest in, but of course its anyone's prerogative to prove that incorrect Important for me is that the effects of non performance are completely rooted in how the piston and seal perform in the first place. Degradation of that interaction causes many subtle issue which often draw a lot of phaffing (out in general internet-land) as to coping or mitigation of that, like trying different pad materials etc, when putting foundation of how a caliper operates right primarily, will most likely not deliver those problems in the first place.
