wrote:
Dave Benoff wrote:

I have a set of Magura Marta disc brakes and had the oddest
experience that I figured I'd share...

The symptom was after installing new pads, the grip strength of the
rear caliper was insufficient to lock up the rear wheel. Lever
travel and feel was normal, the only difference was braking force.

Long story short, after endless futzing with pads, rotors, and
bedding- in techniques, the problem was ultimately fixed with a
bleed. I figure that pressing in the pistons before installing the
pads must have allowed some air intrusion.

What's odd to me is that when I've had air bubbles in the brake
lines in the past, pumping the lever would enable me to get
sufficient power. This makes sense to me. With enough pressure,
the air will compress enough to transmit braking force. That wasn't
the case this time.

Its not at all clear to me how a bleed could fix the issue I was
experiencing, but it did.

That's what makes me wonder what you fixed. Air in the system causes
sponge that should have been obvious, but as you say "Lever travel and
feel was normal". With air in the system, the hand lever would have
run out of travel when gripped forcefully.

er, that depends on the /amount/ of air in the system jobst.


Are you sure about the
hand lever response? Air in the brake fluid compresses
asymptotically, never becoming solid,

but neither does the fluid...


and by that time brake lever
travel is gone. Pumping the lever does not get rid of sponge.

on open systems it can.

1. the master cylinder has a return circuit through which air can
permanently bleed if that's where the air is located.

2. elsewhere in the system, temporary dissolution under higher pressure
can render fluid compressible. when the air re-evolves back to bubble
form, sponginess returns. hence the "pump up" effect.

your lack of knowledge in this stuff is remarkable. tell me, is your
stanford degree actually in /engineering/ jobst? like /mechanical/
engineering? it seems most bizarre that an accredited mechanical
engineering degree holder is so underinformed on basic principles.