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.

[Dave_Darling]

So, do you know you can't lock up the brakes in your 914, or does it just feel that way after driving cars with power-assisted brakes for several years? I know that going back and forth is an interesting change for me, and it seems like I really have to stand on the middle pedal in the 914...

Is your floor board flexing when you push the pedal hard? It's not that uncommon, especially given the way our cars rust, and the fact that brake fluid leaks eat paint. There are master cylinder braces out there to help with this phenomenon.

Are your pads decent ones? Are they made to last a very very very long time? Ones that are may not offer terrific stopping power. Could the pads be glazed, perhaps? A little careful sanding on the pad face and/or the rotor face can help deal with that, if that is the case.

--DD

[87m491]

First, thanks for all the thoughts so far. As I mentioned all my brake work was done 7 years ago with absolutely zero miles on it until last week. That was likely my first of many mistakes! I didn't even realize that the rotors were new until I reviewed my receipts! Calipers are slightly used PMB rebuilts I acquired, also with zero miles on this car. I have no receipts for pads so I may have swapped them from my existing front calipers, mistake # 2. (I believe my rear calipers/pads were untouched from car purchase and fine when last driven)

That said, in my ~15 miles of mostly in town driving, The cars braking was abysmal, and I couldn't panic stop the car from any speed with near maximum pedal effort.
i.e., lock anything up. orders of magnitude worse than my other non PB car, 1987 911.

I apologize as I haven't been able to dig in yet, hopefully this weekend. Given I also redid the interior, I will start by making sure the pedal and linkages are free and clear. I'll remove pads and check for proper caliper operation all around.

As the rotors only have 15 miles on them I will swap in a pair of partially used, highly recommended Porterfields R4-S, that I acquired. The ensuing discussion on bedding these in is very interesting, but even if prebedded per se., I don't imagine using other folks, and my, usual, bedding process after the fact could hurt anything.

The glazing discussion is interesting. After 40 years of driving I thought I knew what that meant but the internet has many theories. That said, if I did reuse my existing pads, they were fine when last driven and awful now, so 'm guessing it is something else but everything is on the table.

I'll report back as I go through the system.

Thx for the help.

So, do you know you can't lock up the brakes in your 914, or does it just feel that way after driving cars with power-assisted brakes for several years? I know that going back and forth is an interesting change for me, and it seems like I really have to stand on the middle pedal in the 914...

Is your floor board flexing when you push the pedal hard? It's not that uncommon, especially given the way our cars rust, and the fact that brake fluid leaks eat paint. There are master cylinder braces out there to help with this phenomenon.

Are your pads decent ones? Are they made to last a very very very long time? Ones that are may not offer terrific stopping power. Could the pads be glazed, perhaps? A little careful sanding on the pad face and/or the rotor face can help deal with that, if that is the case.

--DD