Originally Posted by Voyager
Is that top roll pin rusty? It looks so in the picture, but if it is inside the o-ring seal I wonder how it got rusty? Might water have gotten into this unit?
The cover that goes on that section of the unit is just crimped on with a bead of sealer. I suppose a little moisture could have gotten in there and caused the corrosion on that pin.
I don't believe that water got inside this unit.
Nothing else inside the unit suggest water got in there, and it would be hard to imagine how water might get in given where the unit is located on the motorcycle. Water/moisture in the brake fluid however was a definite possiblity and that was something I was looking for. I've rebuild brake calipers of bikes that were parked in the rain for years that we seized; I know what that looks like.
It was next to impossible to check movement of the pistons in the ABS unit before disassembly and decompressing the springs. There is a hugh amount of pent up spring compression when the unit is assembled. These springs are working against the hydraulic pressure of the brake system when brakes are applied.
Once I had decompressed the springs, the pistons moved freely (i.e. they weren't seized), and the was no evidence of deposits, foreign material, or other junk in any of the passages. It was all nice and clean and new looking. This is why I don't think there was water damage and I don't think the problem was related to the mechanical components of the ABS unit.
The ABS unit functions by first activating the motor which causes the "crankshaft" to turn. (You'll note that the assembly does look a little like a crankshaft or camshaft with bearing journals holding the shaft in place.) There are two clutches on the shaft, one for each brake (note that this unit is off a 2000 which does not have the linked brakes so the front and rear brakes are separate systems.) When the ABS is activated for either brake, the respective clutch is activated which then causes a cam on the shaft to rotate which then pulls a chain which lifts a piston. The lifting of the piston is opposed by the springs. Hydraulic pressure in the system and the pulling of the chain oppose the spring pressure resulting the movement of the piston. When the piston moves, hydraulic pressure in the system decreases. The the more the piston moves, the more pressure drop in the system. Obviously, the piston movement is pulsed, being controlled by electrical pulses to the clutches. I don't know if the duration or intensity (or both) of the electrical pulses is varied by the ABS circuitry, but those pulses are modulated by input from the wheel sensors.
Pic before shaft journals were removed:
After journals were removed: