17mm vs 19mm Brake Master Cylinder, again! Options

[87m491]

With the prospect of incoming rotten tomatoes forefront, I wade in here looking for a little BTDT.
Background, just got the 74, 2.0 back on the road after a 7 year hiatus. Over the years,, I did fuel system, brake system (19mm master(ATE) /calipers (PMB rebuilt fronts, stock rears) /rotors/hoses) engine mechanicals and cosmetics.

I haven't driven the car during that time and I only had about 150 miles on it before it came off the road and memory ain't what it used to be.

I did the 19mm MC many years back because it was way less expensive than the 17 and the forum feedback seemed fine. I also have a mid 80's Carrera (with turbo brakes) against which many folks relate the 19mm MC pedal feel. I like a firm pedal and the 911 is pretty easily modulated, heavy but responsive.

Fast forward to this past week and some short shakedown runs. The 914 pedal is "right there" and noticeably firmer than the 911. But while being firmer, the braking is far from commensurate with pedal input. Yes, the 911 pedal is firm, but with the right effort, the car will slow/stop NOW. Been on the track with it no problem. On the 'teener, I feel like I am about to bend/break the pedal and the car seems to barely slow. No way I can lock up these brakes at any road speed, nor do I feel I could lose momentum in a hurried stop situation, even at in town speeds.

I'm wondering if I have missed something or is this type of pedal feel/action is "typical" of the swap? Shamefully, I honestly can't recall if I did pads, but the rotors are spotless and look like they're getting good pad contact but would love any pad advice as well.

[davep]

That is way too much free play. I think spec is 1-2 mm; just enough that it is not touching.

[87m491]

A quick adjustment of the push rod to ~1mm spec and as I suspected, all that did was bring the pedal "hitting a wall" a few mms closer to the driver! For all intents and purposes it seems as if the MC is frozen which I guess is possible given the length of time of non use but it was also full of fluid as the brakes were fully bled after install.

And if trully the case, amazing I had what little braking I did have.

Next item will be removal of MC and bench inspect/test.

That is way too much free play. I think spec is 1-2 mm; just enough that it is not touching.

[87m491]

Finally got into the hydraulics to see if the MC was frozen up. Seems as pliable as the day I installed it. I removed and inspected, then bench bled and reinstalled. Several times actually as getting the pedal cluster and push rod fit is a bit of a PITA with only one person. Quick try and the brake pedal total travel was still only about an inch and like pressing into a brick wall!

I decided time to check to see if the front pistons are seized from sitting. Took quite a bit to get the front wheels off as I had the wheels powder coated years back then installed and sat. Turns out he powder coater had not taped off the hub bores so they easily went on with a torque wrench, not so easy off.

So the front calipers came with brand new pads which I had installed as a unit. So there was no way to tell if the pistons were moving. I pulled the pads and inserted some used ones I had that were about 1/2 worn. I installed those on both fronts and pressure bled all calipers and all ports. With a number of pedal pushes the pistons sat the pads right snug to the rotors.

The MC works and the front calipers are fine. Took the car for a ride and while pedal travel is now "normal", braking is still underwhelming, car will not lock up but pedal pumping indicates there is still some air in there and the rears are dragging noticeably need to be readjusted for proper clearance.

The original problem seems solved, though not sure why, now seems down to a better more thorough bleed and rear adjustments.

A quick adjustment of the push rod to ~1mm spec and as I suspected, all that did was bring the pedal "hitting a wall" a few mms closer to the driver! For all intents and purposes it seems as if the MC is frozen which I guess is possible given the length of time of non use but it was also full of fluid as the brakes were fully bled after install.

And if trully the case, amazing I had what little braking I did have.

Next item will be removal of MC and bench inspect/test.

That is way too much free play. I think spec is 1-2 mm; just enough that it is not touching.