Brake Failure, Brake Failure Options

[Rod911964]

914 Brake failure!
Took my 914 1.8 on a 2300 mile rally this past autumn. 914 did great except the brakes went spongy. So I bled the brakes thinking the was air in the lines. Actually bled them 3x.
On the way home I had to pump the brakes to get any braking action, ugh!
Got home and put the 914 on the lift and started the diagnostic process. Upon the 1st round of inspections… no leaks, reservoir maintains fluid level, no indication of caliper hang up.
Took the master cylinder off and disassembled, scoped the bores and found annular rust in the bores. So I figure I’m getting fluid bypass to not hold fluid pressure. Probably the root cause.
Then I take the pads out to measure both the rotors and pads to spec. All looks good except for the front left pads. Uneven/slanted wear! (See pics). If I hold the friction surfaces parallel it would mean pistons are cocked. Doesn’t make sense. Or the rotor surface is not parallel.
So what causes this situation?
Thanks in advance.
Rob

[Dave_Darling]

A couple of things to try to get a hard pedal near the top of the movement range:

- Set the venting clearance in the rear brakes. Use half the spec from the manual on each side.
- Fabricate a brace that keeps the whole master cylinder from moving when you press on the pedal. The floorboard where the MC mounts can flex under hard pressure, and that feels like a soft pedal and moves the actuation point further down.

If you're really ambitious, you can try reducing the rear venting clearance a little bit, or reducing the free play on the pedal's pushrod, but those can cause problems with (e.g.) the brakes not releasing fully when warmed up or similar. I don't really recommend that, though.

--DD