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Jim let's step back and talk about brake hydraulics. There is no such thing as one MC kicking in first and no such thing as one MC dominating. When the brakes are pressed, even if one pushrod were to hit it's MC first, there will be no pressure built in that MC. The balance shaft will just cock somewhat. Pressure will only start to build when both pushrods are in contact w/ the MC pistons. The length of the pushrods, MC to balance bar, is adjustable so that at max pedal pressure the balance shaft is roughly perpendicular to the pushrods. The reason this is needed is that w/ varying MC sizes, as well as varying caliper sizes, the MCs typically do not travel the same amount. So the pushrod lengths can be adjusted so that at rest, the balance shaft may not be perpendicular to the pushrods, but when pedal pressure is applied and the MCs move, the balance shaft will move toward being perpendicular.
Wilwood balance 3 by craig stuard, on Flickr
In the pic the green arrows point to the thread on the ends of the balance shaft. The amount of thread showing tells you which MC will get the most pressure from the pedal. More thread = more pressure.
Balance bar 2 by craig stuard, on Flickr
This shows what is inside the top of the pedal. The bearing is locked into position on the shaft by a jam nut on each side. The brass clevises are threaded. So, as the shaft is turned, it moves left or right through the clevises, and pulls the bearing with it. The bearing is free to slide within the top of the pedal. So the pedal pressure is applied more to the MC that the bearing has moved closer to. Since we can't see inside the pedal, we use the amount of threads exposed on the ends of the shaft to indicate where the bearing is.
There is a caution that needs to be checked. Think of the balance shaft in the pedal but not connected to any MCs. There is a limit to how much angle the shaft can be moved to before it binds against the inside bore of the pedal. We need to make sure this limit is not exceeded when the brakes are pushed. This is also why there is a spec for the amount of clearance needed at the red arrows in the first picture. This is also why many people bleed one front and one rear caliper at a time. Because if MC #1 has all the air removed it will only move so far. If MC #2 has a lot of air, when the pedal is pushed, MC #1 stops moving while the other keeps going UNTIL the angle binds the shaft and now both MCs stop. But the one w/ the excess air usually has not gone to it's full travel so all the air will not be pushed out of it.
Wilwood balance 3 by craig stuard, on Flickr
In the pic the green arrows point to the thread on the ends of the balance shaft. The amount of thread showing tells you which MC will get the most pressure from the pedal. More thread = more pressure.
Balance bar 2 by craig stuard, on Flickr
This shows what is inside the top of the pedal. The bearing is locked into position on the shaft by a jam nut on each side. The brass clevises are threaded. So, as the shaft is turned, it moves left or right through the clevises, and pulls the bearing with it. The bearing is free to slide within the top of the pedal. So the pedal pressure is applied more to the MC that the bearing has moved closer to. Since we can't see inside the pedal, we use the amount of threads exposed on the ends of the shaft to indicate where the bearing is.
There is a caution that needs to be checked. Think of the balance shaft in the pedal but not connected to any MCs. There is a limit to how much angle the shaft can be moved to before it binds against the inside bore of the pedal. We need to make sure this limit is not exceeded when the brakes are pushed. This is also why there is a spec for the amount of clearance needed at the red arrows in the first picture. This is also why many people bleed one front and one rear caliper at a time. Because if MC #1 has all the air removed it will only move so far. If MC #2 has a lot of air, when the pedal is pushed, MC #1 stops moving while the other keeps going UNTIL the angle binds the shaft and now both MCs stop. But the one w/ the excess air usually has not gone to it's full travel so all the air will not be pushed out of it.