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.

[914Sixer]

Typical response with 19mm master cylinder. Go over to Classic Section and do some reading. Goes in to detail.

[mepstein]

Make sure you bed the pads to the rotors. Do it again if you’re not sure it’s right. PMB/Eric has a video on his website explaining how to bed pads.

[flipb]

I've got the 19mm and I can definitely lock them up without feeling like I'm going to break anything. Sounds to me like you need to go through the whole system and see if something's off.

[87m491]

Very good idea. I sourced some of the very popular Porterfields for the front. Sounds like time to get them in.
PS the link to their bedding article has been seemingly removed.

Make sure you bed the pads to the rotors. Do it again if you’re not sure it’s right. PMB/Eric has a video on his website explaining how to bed pads.

[87m491]

Thanks been all through that but didn't run across any "the car doesn't really stop" scenarios.

Typical response with 19mm master cylinder. Go over to Classic Section and do some reading. Goes in to detail.

[Shivers]

I had a stock system with a 19mm. I submarined my passenger right into the footwell, and had to let up pressure to keep it from locking up. We lived. I’d have to agree with looking elsewhere.

[mepstein]

Very good idea. I sourced some of the very popular Porterfields for the front. Sounds like time to get them in.
PS the link to their bedding article has been seemingly removed.

Make sure you bed the pads to the rotors. Do it again if you’re not sure it’s right. PMB/Eric has a video on his website explaining how to bed pads.

Check youtube but basically 50-60 mph hard braking to 5-10 mph. Never come to a complete stop. Done until the brakes are nice and hot. 6-10 times and then drive for a while at moderate speeds while using the brakes as little as possible so they cool down.
I don’t remember how many stops are suggested but enough that they get HOT.

[MM1]

Re: Porterfield R4-S brake pad OFFICIAL break-in procedure.

I recently installed Porterfield R4-S pads on my 914 V-8 (along with a new 19mm master cylinder). Please note it has the BMW 320 caliper conversion on the front. Yes, the 19mm master feels good to me (subjective preference) and the brakes improve with nearly every stop as I am nowhere near the 100 mile (apparently correct "no-hard-brake") break-in procedure. For reference, the very old and leaky 19mm master cylinder would easily lock up the BMW 320 front calipers with only a bit more than moderate-to-firm pressure.

My research showed that a "standard" break-in procedure is incorrect.

As hearsay from the "interwebs" is useless, I just contacted Porterfied directly after reading this thread. I requested the official break-in procedure for R4-S pads. Below is the text from said .pdf as well as a screen shot of the .pdf Porterfield just sent me:

" Porterfield Bedding procedures recommendations

Street pads (R4-S) are pre-bedded. Just install and drive normally and they will bed themselves in within
about 100 miles. Please avoid the 60+-0 absolute stops upon first installation to see how well they stop.
(Obviously if it is required for safety do so.) This can lead to glazing of the parts. Please allow the 100 or
so miles to pass before being more aggressive with them."

The text above is included so you can copy and paste it to all of your friends (since you don't have the time to call Porterfield), who have already glazed their "parts" with the "standard" break-in procedure. (IMG:style_emoticons/default/blink.gif)

[mepstein]

How do you bed in the rotor if that’s new as well?

[87m491]

Sweet! That'll up my 20 mile per year, the last 7 years, average! Honey, the Mr Porterfield says I have to drive the car, awesome!

Re: Porterfield R4-S brake pad OFFICIAL break-in procedure.

I recently installed Porterfield R4-S pads on my 914 V-8 (along with a new 19mm master cylinder). Please note it has the BMW 320 caliper conversion on the front. Yes, the 19mm master feels good to me (subjective preference) and the brakes improve with nearly every stop as I am nowhere near the 100 mile (apparently correct "no-hard-brake") break-in procedure. For reference, the very old and leaky 19mm master cylinder would easily lock up the BMW 320 front calipers with only a bit more than moderate-to-firm pressure.

My research showed that a "standard" break-in procedure is incorrect.

As hearsay from the "interwebs" is useless, I just contacted Porterfied directly after reading this thread. I requested the official break-in procedure for R4-S pads. Below is the text from said .pdf as well as a screen shot of the .pdf Porterfield just sent me:

" Porterfield Bedding procedures recommendations

Street pads (R4-S) are pre-bedded. Just install and drive normally and they will bed themselves in within
about 100 miles. Please avoid the 60+-0 absolute stops upon first installation to see how well they stop.
(Obviously if it is required for safety do so.) This can lead to glazing of the parts. Please allow the 100 or
so miles to pass before being more aggressive with them."

The text above is included so you can copy and paste it to all of your friends (since you don't have the time to call Porterfield), who have already glazed their "parts" with the "standard" break-in procedure. (IMG:style_emoticons/default/blink.gif)

[SirAndy]

Thanks been all through that but didn't run across any "the car doesn't really stop" scenarios.

Typical response with 19mm master cylinder. Go over to Classic Section and do some reading. Goes in to detail.

Not being able to stop is *not* typical for a 19mm MC. Something ain't right ...
(IMG:style_emoticons/default/popcorn[1].gif)

[76-914]

@Eric_Shea Shea it or don't say it!

[Eric_Shea]

We always bed Porterfields. We're their second largest retailer. And I've spoken with Porterfield about the pre-bed pad scenario. I asked how they pre-bed them and they simply state it's not needed. Basically, the friction numbers come in at a lower temperature. We don't necessarily agree that an "un-bedded pad" is "pre-bedded" but... therein lies what some call "heresay". It never hurts to bed your pads as there are other benefits that come along with it.

Bedding the pads seasons the rotors. Fact.
Bedding the pads breaks in the new caliper seals. Fact. and,
Bedding the pads decreases the stopping times... even on "pre-un-bedded" Porterfields.

We've never, ever glazed a pad. That's our "real world experience" not from the interwebs.

[bkrantz]

To get good braking response I needed to bed my R4-S pads in two separate sessions, with some really hard and hot repeated braking. Along the way I also experienced some slight pulling (to the right) when the car almost stopped. Eventually, the braking improved and the car stopped straight.

I also found that my master cylinder was moving (tilting down) under hard pedal pressure. When I made a brace, the braking response finally got "good".

[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

[914sgofast2]

What kind of brake pads are you running? If they are racing brake pads (i.e., Porterfield brand), they won't have any stopping power until you have heated them up a lot; that is why "racing" brake pads are a big mistake on street cars. If they are normal street brake pads, then I would suspect that the rubber brake hoses have perished and collapsed inside and are preventing the brake fluid from exerting full pressure on the calipers. Second thing to question is the life left in the 19mm master brake cylinder's seals. If they have just been sitting for 7 years, they have probably gone hard/bad, as will the seals in the calipers. Brake systems are like our bodies; if you sit around for 7 years without any exercise, don't expect to be able to go out and run (or walk) a 10K marathon. Everything needs regular exercise!

[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

[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/SS 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.

[87m491]

Data point please for those w 19mm MC. What is your pedal travel? I dug into the pedals tonight sure I would find an obstruction but I did not.

The pedal has about 1 inch free play, and moves less than an inch when it meets resistance. Is this usual for the set up? The brake pedal "lug" on the base of the pedal that limits return pedal travel moves about 1/2 from rest to max travel.

The pedal effort is the same from resistance start to max travel. I hope to get into the calipers this weekend to see if any fluid is really moving through the system as I am not sensing any "give" through the pedal.