So if i understand you correctly, you are suggesting that the less worn inner pad is somehow sticking/binding where it sits in the caliper such that when the piston applies force to it, it is not being pushed into contact (much) with the rotor, and is providing the leverage for the piston to pull in the pad on the outer side?
I agree it’s still a mystery.
Not to me. But without a whiteboard and a dry erase marker I’ve apparently failed to explain it articulately. Sorry about that.
I really appreciate your explanation and i am following what your saying. I do understand fluid dynamics but i think it is the mechanical aspect that is confusing insightful and myself. The way i understand the function of a single piston floating caliper is that the hydraulic pressure causes the piston to extend and when the piston meets resistance (i.e. the pad contacting the rotor) the continued pressure through the piston causes the caliper to slide and thus pressure is applied to the other pad and then the other side of the rotor. It’s not uncommon for people to see more wear on the piston side pad because the piston applies pressure to it first. So, by this understanding, for the pressure from the piston to slide the caliper so that the outer pad contacts the rotor, the piston must meet some resistance from the piston side. Thats usually the pad, but if that pad is not showing expected wear, we are wondering why the caliper is engaging on the non piston side without resulting in normal wear to the piston side pad. Caveat, i may be totally wrong in the way i understand the mechanical function!
Your understanding is correct, but you’re describing a caliper that’s working properly. The caliper in question is not, preventing the pressure of the piston from causing the pressures on both sides to equalize. The reason the caliper is not causing the pressure on the nonwearing pad to be equal to the pressure of the properly wearing pad is because the caliper is not floating properly.
It’s analogous to a C-clamp. If you close a C-clamp onto a piece of wood, the pressure will be equal on both sides. If, however, you clamp the C-clamp into a bench vise and the piece of wood to the bench and then close it, only the side of the C-clamp that moves with the threaded part will press on the wood. Only if the body of the C-clamp is free to float will it equalize its pressure on both sides of the wood. In the case of the malfunctioning caliper, it’s as if the body of the C-clamp (the body of the caliper) is not free to move.
The reason the caliper is not causing the pressure on the nonwearing pad to be equal to the pressure of the properly wearing pad is because the caliper is not floating properly.
So, we posit that the outer pad is wearing properly and the inner pad is wearing at half the proper rate. Exactly how does a caliper that is “not floating properly” cause the correct amount of pressure on the outer pad and deficient pressure on the inner pad?
Forget it. I give up. Just change the caliper. Or not. I really don’t care anymore.
Perhaps this might help (or not).
During normal operation, the inboard pad is pressed against the rotor by the caliper piston(s). The caliper slides to distribute that force more or less equally to the outboard, passive pad. Upon pressure release, the piston ring seal helps to retract the piston/pad. Minor variations (wobble) in the rotor distribute the resulting gap more evenly between the sides, if the caliper can float easily.
If the caliper slides stick, there is more residual pressure continuously applied to the outboard pad since it cannot move away from the rotor. The inboard pad still does, since the piston seal is still retracting the piston slightly and allowing the inboard pad to back off. If the outboard or passive pad is constantly in some contact with the rotor, it will be continuously wearing down versus the inboard pad which only sees stress on application of the brake.
Hydraulic force is more powerful than the rotor wobble so each brake application moves the caliper over to account for outboard wear but it never returns to “center”.
This is simple to verify. Just pull the caliper off, inspect the sliders and end the speculation…